The Open Toolkit Manual

OpenTK%20Manual

OpenTK%20Manual

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The Open Toolkit Manual
The manual is not complete. You can find (and add) experimental pages here. Also,
check the available translations.
Welcome and thanks for using the Open Toolkit library!
This manual will guide you through the necessary steps to develop a project with
OpenTK. You will learn how to setup a new project, how to successfully use the tools
provided by OpenTK and, finally, how to distribute your project to your end-users.
You will also find information on writing performing code and maintaining cross-
platform compatibility.
This manual is written in a way that allows skipping from section to section as
needed, so feel free to do that; or you can read it sequentially from start to end, if you
prefer. Keep in mind that you may add a comment at any point - we always try to
improve the manual and high-quality feedback will help not only you but future
OpenTK users, too. You can also browse the OpenTK API reference.
It is our hope that the time invested reading this book will be paid back in full. So let's
get started!
Table of Contents
Table of Contents
Chapter 0: Learn OpenTK in 15'
Chapter 1: Installation
o Linux
o Windows
o Troubleshooting
Chapter 2: Introduction to OpenTK
o The DisplayDevice class
o The GameWindow class
o The NativeWindow class
o Building a Windows.Forms + GLControl based application
o Avoiding pitfalls in the managed world
Chapter 3: OpenTK.Math
o Half-Type
Chapter 4: OpenTK.Graphics (OpenGL and ES)
o The GraphicsContext class
Using an external OpenGL context with OpenTK
o Textures
Loading a texture from disk
2D Texture differences
S3 Texture Compression
o Frame Buffer Objects (FBO)
o Geometry
1. The Vertex
2. Geometric Primitive Types
3.a Vertex Buffer Objects
3.b Attribute Offsets and Strides
3.c Vertex Arrays
4. Vertex Array Objects
5. Drawing
5.b Drawing Optimizations
6. OpenTK's procedural objects
o OpenGL rendering pipeline
o Fragment Operations
01. Pixel Ownership Test
02. Scissor Test
03. Multisample Fragment Operations (WIP)
04. Stencil Test
05. Depth Test
06. Occlusion Query
Conditional Render
07. Blending
08. sRGB Conversion
09. Dithering
10. Logical Operations
o How to save an OpenGL rendering to disk
o How to render text using OpenGL
Chapter 5: OpenTK.Audio (OpenAL)
o 1. Devices, Buffers and X-Ram
o 2. Sources and EFX
o 3. Context and Listener
Chapter 6: OpenTK.Compute (OpenCL)
Chapter 7: OpenTK.Input
Chapter 8: Advanced Topics
o Vertex Cache Optimizations
o Garbage Collection Performance
o GC & OpenGL (work in progress)
Chapter 9: Hacking OpenTK
o Project Structure
o OpenTK Structure
o Wrapper Design
Appendix 1: Frequently asked questions
Appendix 2: Function Reference
Appendix 3: The project database
o Creating a project
o Creating a project release
Appendix 4: Links
o Models and Textures
o OpenGL Books and Tutorials
o Programming links
o Tools & Utilities
o Tutorials
Appendix 5: Translations
Chapter 0: Learn OpenTK in 15'
So, you have downloaded the latest version of OpenTK - what now?
This is a short tutorial that will help you get started with OpenTK in 3 simple steps.
[Step 1: Installation]
Open the zip you downloaded and extract it to a folder of your choosing. I usually
create a 'Projects' folder on my desktop or in my documents but any folder will do.
[Step 2: Use OpenTK]
Open the folder you just extracted. Inside, you will find three solutions: OpenTK.sln,
Generator.sln and QuickStart.sln. The first two contain the OpenTK source code - no
need to worry about them right now. The QuickStart solution is what we are
interested in.
Double-click QuickStart.sln. This will launch your .Net IDE (don't have a .Net IDE?
Check out MonoDevelop or Visual Studio Express).
Take a few moments to take in the contents of the QuickStart project:
Game.cs: this contains the code for the game. Scroll to the bottom: the Main()
method is where everything begins.
References: click on the '+' sign to view the project references. The 'OpenTK'
reference is the only one you need in order to use OpenTK.
Now, press F5 to run the project. A window with a colored triangle will show up - not
very interesting, is it? Press escape to close it.
[Step 3: Play]
Now it's time to start playing with the code. This is a great way to learn OpenGL and
OpenTK at the same time.
Every OpenTK game will contain 4 basic methods:
1. OnLoad: this is the place to load resources from disk, like images or music.
2. OnUpdateFrame: this is a suitable place to handle input, update object
positions, run physics or AI calculations.
3. OnRenderFrame: this contains the code that renders your graphics. It typically
begins with a call to GL.Clear() and ends with a call to SwapBuffers.
4. OnResize: this method is called automatically whenever your game window
changes size. Fullscreen applications will typically call it only once.
Windowed applications may call it more often. In most circumstances, you
can simply copy & paste the code from Game.cs.
Why don't you try modifying a few things? Here are a few suggestions:
1. Change the colors of the triangle or the window background (OnLoad and
OnRenderFrame methods).
2. Make the triangle change colors when you press a key (OnUpdateFrame and
OnRenderFrame methods).
3. Make the triangle move across the screen. Use the arrow keys or the mouse to
control its position (OnUpdateFrame and OnRenderFrame methods).
4. Use a for-loop to render many triangles arranged on a plane (OnRenderFrame
method).
5. Rotate the camera so that the plane above acts as ground (OnRenderFrame
method).
6. Use the keyboard and mouse to walk on the ground. Make sure you can't fall
through it! (OnUpdateFrame and OnRenderFrame methods).
Some things you might find useful: Vector2, Vector3, Vector4 and Matrix4 classes
for camera manipulations. Mouse and Keyboard properties for interaction with the
mouse and keyboard, respectively. Joysticks property for interaction with joystick
devices.
Don't be afraid to try things and see the results. OpenTK lends itself to explorative
programming - even if something breaks, the library will help you pinpoint the cause
of the error.
[Step: next]
There's a lot of functionality that is not visible at first glance: audio, advanced opengl,
display devices, support for GUIs through GLControl... Then there's the subject of
proper engine and game design, which could cover a whole book by itself.
Hopefully, you'll have gained a feel of the library by now and you'll be able to
accomplish more complex tasks. You might wish to consult the complete
documentation for the more advanced aspects of OpenTK and, of course, don't
hesitate to post at the forums if you hit any roadblocks!
Chapter 1: Installation
[Prerequisites]
OpenTK is a managed library that targets the .Net 2.0 framework. To use it, you will
need either the .Net or Mono runtime, plus device drivers for OpenGL (graphics),
OpenAL (audio) and OpenCL (compute), depending on the parts of OpenTK you
wish to use.
Most operating systems come with a version of the .Net runtime preinstalled, which
means OpenTK is typically usable out of the box. In a few cases, you might need to
install manually a version of .Net runtime (Windows) or the Mono runtime
(Linux/Mac OS X/Windows). Any version equal to or newer than .Net 2.0 / Mono 2.0
will work fine. Earlier versions of Mono may also work, but are no longer supported.
Earlier versions of .Net will not work.
Additionally, most recent operating systems come with OpenGL drivers preinstalled.
For OpenAL and OpenCL drivers, you should refer to the website of your hardware
vendors. [todo: add links to common hardware vendors]
Last, but not least, you will need to download the latest OpenTK release.
[Installation]
OpenTK releases are simple compressed archives. Simply extract the archive contents
to a location on your disk and add OpenTK.dll as a reference to your project. You can
find OpenTK.dll under the Binaries/OpenTK folder of the OpenTK archive.
Additionally, you should add OpenTK.dll.config to your project and instruct your IDE
to copy this file to the output directory. This is necessary for your project to function
under Linux and Mac OS X.
The following pages contain specific instructions for using or building OpenTK on
different platforms.
Linux
Installing Mono
If you are using a recent Linux distribution, all prerequisites for OpenTK projects
should be readily available: the Mono runtime and the Mono compilers. Execute
"mono --version" and "gmcs --version" and check if the output looks like this:
$ mono --version
Mono JIT compiler version 1.2.6 (tarball)
Copyright (C) 2002-2007 Novell, Inc and Contributors. www.mono-
project.com
TLS: __thread
GC: Included Boehm (with typed GC)
SIGSEGV: altstack
Notifications: epoll
Architecture: amd64
Disabled: none
$ gmcs --version
Mono C# compiler version 1.2.6.0
If one or both of these commands fail, you'll have to install Mono. Mono packages
should be readily available through your package manager:
# Ubuntu and other .deb-based distributions
sudo apt-get install mono mono-gmcs
# or
su -c "apt-get install mono mono-gmcs"
# Fedora Core and .rpm-based distributions
su -c "yum install mono mono-gmcs"
If no Mono packages are available, or they are outdated (mono --version returns
something less than 1.2.6), you should build Mono from source. There is a message in
the support forum describing the process of building mono from source here.
Alternatively, you can find use one of the Mono binary packages on the Mono
download page.
Using a binary release
Download the latest opentk-x.y.z-mono.tar.gz release from Sourceforge and untar it:
tar -xvf opentk-0.3.13-mono.tar.gz
A new opentk-x.y.z will be created with four subfolders: "Documentation",
"Examples", "Libraries" and "QuickStart". Try running the examples contained in the
second folder to make sure everything works alright:
cd opentk-0.3.13/Examples
mono Examples.exe
A new window will hopefully show up, listing all available examples. If not, check
the troubleshooting section below.
The "Libraries" folder contains the main OpenTK assembly (OpenTK.dll) and the
OpenTK.dll.config file - these are all you need to run OpenTK projects. If you are
using MonoDevelop, check the "QuickStart" folder for a ready-to-use project. Last,
don't forget to take a look at the release notes contained in the "Documentation"
folder.
Troubleshooting
The following error has been reported on Fedora Core 8, when running Examples.exe:
Unhandled Exception: System.TypeInitializationException: An exception
was thrown by the type initializer for System.Windows.Forms.Form --->
System.Reflection.TargetInvocationException: Exception has been
thrown by the target of an invocation. --->
System.TypeInitializationException: An exception was thrown by the
type initializer for System.Drawing.GDIPlus --->
System.DllNotFoundException: gdiplus.dll
at (wrapper managed-to-native)
System.Drawing.GDIPlus:GdiplusStartup
(ulong&,System.Drawing.GdiplusStartupInput&,System.Drawing.GdiplusSta
rtupOutput&)
at System.Drawing.GDIPlus..cctor () [0x00000] --- End of inner
exception stack trace ---
This is caused by a missing entry in "/etc/mono/config". To correct this issue, open
the aforementioned file (you must be root!), and add this line: <dllmap
dll="gdiplus.dll" target="/usr/lib/libgdiplus.so.0" />. Now,
Examples.exe should work.
Building OpenTK from source
OpenTK's build system currently uses NAnt, so you'll need to install that:
# Ubuntu
sudo apt-get install nant
# Debian
su -c "apt-get install nant"
# Fedora
su -c "yum install nant"
Once that is out of the way, untar the source release and cd to the Build folder:
unzip opentk-0.3.13.zip
cd opentk-0.3.13/Build
mono Build.exe mono
Wait a few seconds for the compilation to end, and check the "Binaries" folder that
just appeared in the base OpenTK directory. To build the debug version, append
"debug" so that the last command looks like:
mono Build.exe mono debug
[Add an appendix that describes how to build Mono from source, in case there is no
package available]
Windows
OpenTK does not come with any installer or setup. Instead, you download the
OpenTK binaries and add a reference to "OpenTK.dll" in your Visual
Studio/SharpDevelop/MonoDevelop project. (Unzip the binaries first!)
OpenTK demo
To run all of the OpenTK builtin examples, the following software is required:
1. .NET2.0 or Mono 1.2.6
2. OpenAL 2.0.3
This is also the software required for an end-user running an OpenTK application.
Note that OpenAL is not strictly required if the application does not use any sound.
OpenTK development
If you want to start developing applications using OpenTK, first make sure the items
under "OpenTK demo" are installed, then download a compiler/IDE for .NET/mono.
Here are some popular choices:
1. SharpDevelop
2. MonoDevelop (bundled in the mono installer)
3. Visual Studio Express
Setting up an OpenTK application in Visual Studio Express
It is a good idea to add "OpenTK.dll.config" to your project, and make sure the "Copy
To Output Folder" (not "compile"!) is set to "Copy Always". The application will run
without this on Windows, but not on Linux or Mac OS X.
Last, but not least, make sure the "Copy Local" property is set to true for the OpenTK
reference, to simplify the distribution of your application.
Setting up an OpenTK application in SharpDevelop
Include the "OpenTK.dll.config" in your project, if you want it to run under Linux
Mac OS X.
Visual explanation:
Troubleshooting
Most problems with running OpenTK-based Applications are related to the target
platform missing the proper drivers.
OpenTK requires these components installed:
Either Mono or .Net (not both).
An OpenGL driver for your graphics card.
The OpenAL driver for your Operating System.
Below are links for your convenience. Note: Many of those sites require Javascript
enabled to function.
Mono
Novell (Linux, Mac & Windows) http://www.go-mono.com/mono-
downloads/download.html
.Net
Microsoft (Windows)
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=...
OpenAL
Note: It doesn't matter what brand your soundcard is, just chose the proper Operating
System.
Creative Labs (Mac & Windows) http://www.openal.org/downloads.html
Direct link to download page for Windows:
http://connect.creativelabs.com/developer/Wiki/OpenAL%20Installer%20for%...
Strangesoft (Linux) http://kcat.strangesoft.net/openal.html
OpenGL
ATi (Linux, Mac & Windows) http://ati.amd.com/support/driver.html
NVIDIA (Linux & Windows) http://www.nvidia.com/Download/index.aspx?lang=en-
us
Intel (Windows) http://downloadcenter.intel.com/
Intel (Linux) http://intellinuxgraphics.org/download.html
Mesa 3D (software rendering)
http://sourceforge.net/project/showfiles.php?group_id=3
If you have a laptop with an Nvidia card, you can obtain updated drivers through:
http://www.laptopvideo2go.com
Last edit of the links: March 2008
Tags for searches:
help problem error outdated trouble crash fail failure exception abort opengl openal
driver ati intel nvidia
Chapter 2: Introduction to OpenTK
First of all, what is OpenTK?
Simply put, the Open Toolkit is a free project that allows you to use OpenGL,
OpenGL|ES, OpenCL and OpenAL APIs from managed languages.
OpenTK started life as an experimental fork of the Tao framework before during the
summer of 2006. It's original intention was to provide a cleaner wrapper than
Tao.OpenGL, but it quickly grew in focus: right now, it provides access to various
Khronos and Creative APIs and handles the necessary initialization logic for each
API. As such, the Open Toolkit is most similar to projects like Tao, SlimDX, SDL or
GLFW.
Unlike similar libraries, OpenTK attempts provide a consistent interface that utilizes
the superior managed runtime. Instead of untyped pointers, OpenTK provides
generics. Instead of plain constants, OpenTK uses strongly-typed enumerations.
Instead of plain function lists, OpenTK separates functions per extension category. A
common math library is integrated and directly usable by each API.
Features:
Written in cross-platform C# and usable by all managed languages (F#, Boo,
VB.Net, C++/CLI).
Consistent, strongly-typed bindings, suitable for RAD development.
Usable stand-alone or integrated with Windows.Forms, GTK#, WPF.
Cross-platform binaries that are portable on .Net and Mono without
recompilation.
Wide platform support: Windows, Linux, Mac OS X, with iPhone port in
progress.
The Open Toolkit is suitable for games, scientific visualizations and all kinds of
software that requires advanced graphics, audio or compute capabilities. It's license
makes it suitable for both free and commercial applications.
The DisplayDevice class
There are three main types of display devices: monitors, projectors and TV screens.
OpenTK exposes all of them through the same interface: OpenTK.DisplayDevice.
You can use OpenTK.DisplayDevice to query available display devices, discover and
modify their properties.
Example 1: discover available devices
using OpenTK;
foreach (DisplayDevice device in DisplayDevice.AvailableDisplays)
{
Console.WriteLine(device.IsPrimary);
Console.WriteLine(device.Bounds);
Console.WriteLine(device.RefreshRate);
Console.WriteLine(device.BitsPerPixel);
foreach(DisplayResolution res in device.AvailableResolutions)
{
Console.WriteLine(res);
}
}
Example 2: set the resolution of the first device to 800x600x32@60Hz:
using OpenTK;
devices[0].ChangeResolution(800, 600, 32,60);
Example 3: set the resolution of the second device to 800x600x32 using the preferred
refresh rate:
using OpenTK;
devices[1].ChangeResolution(800, 600, 32, -1);
Example 4: restore all devices to their default settings
using OpenTK;
foreach (DisplayDevice device in DisplayDevice.AvailableDevices)
{
device.RestoreResolution();
}
OpenTK will try to match your custom resolution to the closest supported resolution.
If a specific bit depth or refresh rate is not supported, the current bit depth or refresh
rate will be used. If no custom resolution matches the specified parameters, the
current DisplayResolution will be used. You can specify a negative number or zero
to indicate that a specific parameter is of no interest: for example, specifying a refresh
rate of 0 will result in the default refresh rate being used.
Note that it is your responsibility to call RestoreResolution() prior to exiting your
application. Failing to call this method will result in undefined behavior.
[Todo: add information about hotplugging support]
The GameWindow class
[Describe the functionality of the GameWindow class]
The NativeWindow class
[Describe the functionality of the NativeWindow class]
Building a Windows.Forms +
GLControl based application
Note 1: This tutorial is somewhat dated. For example, no "garbage" is seen
anymore in the design view of Visual Studio. And the default color is beige, not
black. Apart from those (minor) issues, this tutorial will get you started using
OpenTK+Windows.Forms.
Note 2: If you have some spare time and want to contribute to the OpenTK
project, please update the below page (by clicking the "Edit" link above when
logged in) to reflect the current state of OpenTK.
This tutorial assumes familiarity with Windows.Forms application development in
Visual Studio 2005/C#, and at least basic knowledge of OpenGL. It also assumes a
top-to-bottom readthrough; it is a guide and not a reference.
To begin with, it is quite a different approach one has to take when designing a
game/application using the GLControl in a Windows.Form compared to using the
GameWindow. GLControl is more low-level than GameWindow so you'll have to pull the
strings on for example time measurements by yourself. In GameWindow, you get more
for free!
Just as in the GameWindow case, GLControl uses the default OpenGL driver of the
system, so with the right drivers installed it will be hardware accelerated. However,
with large windows it will be slower than the corresponding fullscreen GameWindow,
because of how the underlying windowing system works [someone with more
detailed knowledge than me may want to elaborate on this..].
If you come from a "main-loop-background" (C/SDL/Allegro etc.) when it comes to
coding games, you'll have to rethink that fundamentally. You'll have to change into a
mindset of "what event should I hook into, and what events should I trigger, and
when?" instead.
Why use Windows.Forms+GLControl instead of GameWindow?
The first thing you'll have to decide is:
"Do I really need the added complexity of Windows.Forms + embedded GLControl
compared to a windowed GameWindow?"
Here are some reasons why you would like to add that complexity:
1. You want to build a GUI-rich/RAD kind of application using the
Windows.Forms controls. Eg. level editors or model viewers/editors may be in
this category while a windowed game leans more towards a GameWindow kind
of application.
2. You want to have an embedded OpenGL rendering panel inside an already
existing Windows.Forms application.
3. You want to be able to do drag-and-drop into the rendering panel, for example
dropping a model file into a model viewer.
Assuming you've got at least one of those reasons to build a
Windows.Forms+GLControl based application, here's the steps, gotchas and whys for
you.
Adding the GLControl to your Windows.Form
(I am assuming you are using Visual Studio 2005 Express Edition. Your mileage may
vary if using VS2008 or Monodevelop -- I don't know the details for them -- but the
follow sections should be the same no matter how you add the GLControl)
To begin with, create a Form on which you will place your GLControl. Right click in
some empty space of the Toolbox, pick "Choose Items..." and browse for OpenTK.dll.
Make sure you can find the "GLControl" listed in the ".NET Framework
Components", as in the image below.
Then you can add the GLControl to your form as any .NET control. A GLControl
named glControl1 will be added to your Form.
The first thing you'll notice is the "junk graphics" inside glControl1. Under the
hood, GLControl uses a so called GLContext to do the actual GL-rendering and so
on, and this context is only created in runtime, not in design time. So no worries.
Order of creation
The fact that glControl1's GLContext is created in runtime is important to remember
however, since you cannot access or change glControl1's properties reliably until the
GLContext has been created. The same is true for any GL.* commands (or Glu for
that matter!). The conceptual order is this:
1. First the Windows.Form constructor runs. Don't touch glControl/GL
2. Then the Load event of the form is triggered. Don't touch glControl/GL
3. Then the Load event of the GLControl is triggered. OK to touch
glControl/GL
4. After the Load event handler has run, any event handler may touch
glControl/GL.
So one approach to address this problem is having a bool loaded=false; member
variable in your Form, which is set to true in the Load event handler of the
GLControl:
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;
public partial class Form1 : Form
{
bool loaded = false;
public Form1()
{
InitializeComponent();
}
private void glControl1_Load(object sender, EventArgs e)
{
loaded = true;
}
}
Note: the GLControl.Load event is never fired -- please use the Form.Load event
instead until this issue of OpenTK is fixed.
Then in any event handler where you are going to access glControl1/GL you can put
a guard first of all:
private void glControl1_Resize(object sender, EventArgs e)
{
if (!loaded)
return;
}
A popular way of adding a Load event handler to a Form is via the Properties window
of Visual Studio, something like this:
1. Click anywhere on the GLControl in the Designer
2. Make sure glControl1 is listed in the Properties window
3. Click the "Events" button to list all events of glControl1
4. Double-click the empty cell right of the Load event to create and hook an
event handler for the Load event
Hello World!
The absolutely minimal code you can add at this stage to see something is adding an
event handler to the Paint event of glControl1 and filling it with this:
private void glControl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded) // Play nice
return;
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
glControl1.SwapBuffers();
}
Yes! A black viewport. Notice that the GLControl provides a color- and a depth
buffer, which we have to clear using GL.Clear(). [TODO: how to control which
buffers and formats the GLControl has? Possible at all?]
Next thing would be setting the clear color. An appropriate place to do GL
initialization is in the form's Load event handler:
private void glControl1_Load(object sender, EventArgs e)
{
loaded = true;
GL.ClearColor(Color.SkyBlue); // Yey! .NET Colors can be used
directly!
}
Viewport initialization
Next thing we want to do is draw a single yellow triangle.
First we need to be good OpenGL citizen and setup an orthographic projection matrix
using GL.Ortho(). We need to call GL.Viewport() also.
For now we'll add this in the Load event handler by the other initialization code --
ignoring the fact that we may want to allow the user to resize the window/GLControl.
We'll look into window resizing later.
I put the viewport initialization in a separate method to make it a little more readable.
private void glControl1_Load(object sender, EventArgs e)
{
loaded = true;
GL.ClearColor(Color.SkyBlue);
SetupViewport();
}
private void SetupViewport()
{
int w = glControl1.Width;
int h = glControl1.Height;
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Ortho(0, w, 0, h, -1, 1); // Bottom-left corner pixel has
coordinate (0, 0)
GL.Viewport(0, 0, w, h); // Use all of the glControl painting
area
}
And between Clear() and SwapBuffers() our yellow triangle:
private void glControl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded)
return;
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
GL.Color3(Color.Yellow);
GL.Begin(BeginMode.Triangles);
GL.Vertex2(10, 20);
GL.Vertex2(100, 20);
GL.Vertex2(100, 50);
GL.End();
glControl1.SwapBuffers();
}
Voila!
Keyboard input
Next thing we want to do is animate the triangle via user interaction. Every time
Space is pressed, we want the triangle to move one pixel right.
The two general approaches to keyboard input in a GLControl scenario is using
Windows.Forms key events and using the OpenTK KeyboardDevice. Since the rest of
our program resides in the Windows.Forms world (our window might be a very small
part of a large GUI) we'll play nice and use Windows.Forms key events in this guide.
We'll have an int x=0; variable that we'll increment in a KeyDown event handler.
Adding it to the glControl1 and not the Form, means the glControl has to be
focused, ie. clicked by the user for key events to be sent to our handler.
int x = 0;
private void glControl1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Space)
x++;
}
We add GL.Translate() to our Paint event handler:
private void glControl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded)
return;
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
GL.Translate(x, 0, 0); // position triangle according to our x
variable
...
}
.. and we run our program. But wait! Nothing happens when we push Space! The
reason is, glControl1 is not painted all the time; the operating systems window
manager (Windows/X/OSX) makes sure as few Paint events as possible happens.
Only on resize, obscured window and a couple of more situations do Paint events
actually get triggered.
What we would like to do is have a way of telling the window manager "This control
needs to be repainted since the data it relies on has changed". We want to notify the
window manager that our glControl1 should be repainted. Easy, Invalidate() to the
resque:
private void glControl1_KeyDown(object sender, KeyEventArgs e)
{
if (!loaded)
return;
if (e.KeyCode == Keys.Space)
{
x++;
glControl1.Invalidate();
}
}
Focus behaviour
If you're anything like me you're wondering a little how this focusing behaves; let's
find out!
A simple way is painting the triangle yellow when glControl1 is focused and blue
when it is not. Right:
private void glControl1_Paint(object sender, PaintEventArgs e)
{
...
if (glControl1.Focused) // Simple enough :)
GL.Color3(Color.Yellow);
else
GL.Color3(Color.Blue);
GL.Begin(BeginMode.Triangles);
...
}
So now anytime the triangle is yellow, Space should work alright, and when it's blue
any keyboard input will be ignored.
Freedom at last: resizing the window
We will now turn our attention to a sore teeth: window resizing.
Anytime a Windows.Forms control is resized, it's Resize event is triggered. That is
true for glControl1 too. That's one piece in the puzzle.
The other piece to find is "What do we need to update when a GLControl is resized?"
and the answer is "The viewport and the projection matrix".
Well it seems our SetupViewport() will come in handy once more! Add an event
handler to the Resize event of glControl1 and fill it in:
private void glControl1_Resize(object sender, EventArgs e)
{
SetupViewport();
}
There is still one problem though: if you shrink the window using eg. the bottom-right
resize grip of the window, no repaint will trigger automatically. That's because the
window manager makes assumptions about where the (0, 0) pixel of a control resides,
namely in the top-left corner of the control. (Try resizing using the top-left grip
instead - the triangle is repainted continously!). Our general fix to alleviate this
problem is instructing the window manager that we really want the repaint to occur
upon any resize event:
private void glControl1_Resize(object sender, EventArgs e)
{
SetupViewport();
glControl1.Invalidate();
}
I want my main loop: driving animation using Application.Idle
So, what if we wanted our triangle to rotate continously? This would be childs play in
a main loop scenario: just increment a rotation variable in the main loop, before we
render the triangle.
But we don't have any loop. We only have events!
To mend for this lack of continuity we have to force Windows.Forms to do it our way.
We want an event triggered every now and then, fast enough to get that realtime
interactive feeling.
Now there are several ways to achieve this. One is adding a Timer control to our
form, changing rotation in the timers Tick event handler. Another is adding a wild
Thread to the soup. The first is a little too high-level and slow while the second is
really low-level and a bit harder to get right.
We will take a third path and use a Windows.Forms event designed just for the
purpose of being executed "when nothing else is going on": meet the
Application.Idle event.
This event is special in a number of ways as you may have guessed already. It is not
associated with any Form or other control, but with the program as a whole. You
cannot hook into it from the GUI Designer; you'll have to add it manually -- for
example in the Load event:
private void glControl1_Load(object sender, EventArgs e)
{
loaded = true;
GL.ClearColor(Color.SkyBlue);
SetupViewport();
Application.Idle += new EventHandler(Application_Idle); //
press TAB twice after +=
}
void Application_Idle(object sender, EventArgs e)
{
}
One good thing about the Idle event is that the corresponding event handlers are
executed on the Windows.Forms thread. That is good since it means we can access all
GUI controls without having to worry about threading issues, a pain we would have to
deal with if we cooked our own thread.
So we simply increment our rotation variable in the Idle event handler and
Invalidate() glControl1 -- business as usual.
float rotation = 0;
void Application_Idle(object sender, EventArgs e)
{
// no guard needed -- we hooked into the event in Load handler
while (glControl1.IsIdle)
{
rotation += 1;
Render();
}
}
Let's update our rendering code while we're at it:
private void Render()
{
...
if (glControl1.Focused)
GL.Color3(Color.Yellow);
else
GL.Color3(Color.Blue);
GL.Rotate(rotation, Vector3.UnitZ); // OpenTK has this nice
Vector3 class!
GL.Begin(BeginMode.Triangles);
...
}
private void glControl1_Paint(object sender, PaintEventArgs e)
{
Render();
}
Happy wonders! Look:
The triangle rotates slower when the window is big! How come?
(This might not be true if you have a super-fast-computer with a super-fast-graphics-
card; but you want your game to run on your neighbours computer too, don't you?)
The reason is that windowed 3d rendering just is a lot slower than full-screen
rendering, in general.
But you can reduce the damage by using a technique called frame-rate independent
animation. The idea is simple: increment the rotation variable not with 1 but with
an amount that depends on the current rendering speed (if the speed is slow,
increment rotation with a larger amount than if the speed is high).
But you need to be able to measure the current rendering speed or, equivalently, how
long time it takes to render a frame.
Since .NET2.0 there is a class available to do high-precision time measurements
called Stopwatch. Here's how to use it:
Stopwatch sw = new Stopwatch();
sw.Start();
MyAdvancedAlgorithm();
sw.Stop();
double milliseconds = sw.Elapsed.TotalMilliseconds;
(don't try with DateTime.Now -- it has a granularity of 10 or more milliseconds,
which is in the same size as typical frame rendering -- worthless..)
Now, if we could measure the time it takes to perform the glControl painting, we
would be close to making some kind of frame-rate-independent animation. But there
is an even more elegant way: let's measure all time that is not Application.Idle
time! Then we'll be sure it is not just the painting that is measured, but everything that
has been going on since our last Idle run:
Stopwatch sw = new Stopwatch(); // available to all event
handlers
private void glControl1_Load(object sender, EventArgs e)
{
...
sw.Start(); // start at application boot
}
float rotation = 0;
void Application_Idle(object sender, EventArgs e)
{
// no guard needed -- we hooked into the event in Load handler
sw.Stop(); // we've measured everything since last Idle run
double milliseconds = sw.Elapsed.TotalMilliseconds;
sw.Reset(); // reset stopwatch
sw.Start(); // restart stopwatch
// increase rotation by an amount proportional to the
// total time since last Idle run
float deltaRotation = (float)milliseconds / 20.0f;
rotation += deltaRotation;
glControl1.Invalidate();
}
Cool! The triangle spins with the same speed regardless of window size.
I want an FPS counter!
Yeah me too. It's quite simple now that we've got a Stopwatch.
The idea is just counting the Idle runs, and every second or so, update a Label control
with the counter! But we'll have to know when a second has passed, so we need an
accumulator variable adding all time slices together.
Quite a lot of logic started to add up in the Idle event handler, so I split it up a little:
void Application_Idle(object sender, EventArgs e)
{
double milliseconds = ComputeTimeSlice();
Accumulate(milliseconds);
Animate(milliseconds);
}
private double ComputeTimeSlice()
{
sw.Stop();
double timeslice = sw.Elapsed.TotalMilliseconds;
sw.Reset();
sw.Start();
return timeslice;
}
float rotation = 0;
private void Animate(double milliseconds)
{
float deltaRotation = (float)milliseconds / 20.0f;
rotation += deltaRotation;
glControl1.Invalidate();
}
double accumulator = 0;
int idleCounter = 0;
private void Accumulate(double milliseconds)
{
idleCounter++;
accumulator += milliseconds;
if (accumulator > 1000)
{
label1.Text = idleCounter.ToString();
accumulator -= 1000;
idleCounter = 0; // don't forget to reset the counter!
}
}
Our FPS counter in all its glory:
Can't you put the complete source code somewhere?
Sure, here it is:
using System;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;
using System.Diagnostics;
namespace GLControlApp
{
public partial class Form1 : Form
{
bool loaded = false;
public Form1()
{
InitializeComponent();
}
Stopwatch sw = new Stopwatch(); // available to all event
handlers
private void glControl1_Load(object sender, EventArgs e)
{
loaded = true;
GL.ClearColor(Color.SkyBlue); // Yey! .NET Colors can be used
directly!
SetupViewport();
Application.Idle += new EventHandler(Application_Idle); //
press TAB twice after +=
sw.Start(); // start at application boot
}
void Application_Idle(object sender, EventArgs e)
{
double milliseconds = ComputeTimeSlice();
Accumulate(milliseconds);
Animate(milliseconds);
}
float rotation = 0;
private void Animate(double milliseconds)
{
float deltaRotation = (float)milliseconds / 20.0f;
rotation += deltaRotation;
glControl1.Invalidate();
}
double accumulator = 0;
int idleCounter = 0;
private void Accumulate(double milliseconds)
{
idleCounter++;
accumulator += milliseconds;
if (accumulator > 1000)
{
label1.Text = idleCounter.ToString();
accumulator -= 1000;
idleCounter = 0; // don't forget to reset the counter!
}
}
private double ComputeTimeSlice()
{
sw.Stop();
double timeslice = sw.Elapsed.TotalMilliseconds;
sw.Reset();
sw.Start();
return timeslice;
}
private void SetupViewport()
{
int w = glControl1.Width;
int h = glControl1.Height;
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Ortho(0, w, 0, h, -1, 1); // Bottom-left corner pixel has
coordinate (0, 0)
GL.Viewport(0, 0, w, h); // Use all of the glControl painting
area
}
private void glControl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded)
return;
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
GL.Translate(x, 0, 0);
if (glControl1.Focused)
GL.Color3(Color.Yellow);
else
GL.Color3(Color.Blue);
GL.Rotate(rotation, Vector3.UnitZ); // OpenTK has this nice
Vector3 class!
GL.Begin(BeginMode.Triangles);
GL.Vertex2(10, 20);
GL.Vertex2(100, 20);
GL.Vertex2(100, 50);
GL.End();
glControl1.SwapBuffers();
}
int x = 0;
private void glControl1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Space)
{
x++;
glControl1.Invalidate();
}
}
private void glControl1_Resize(object sender, EventArgs e)
{
SetupViewport();
glControl1.Invalidate();
}
}
}
Next step: What about multiple GLControls at once?
Yeah it is possible. It is even simple!
All you have to do is "make the appropriate GLControl current".
Let's say you have one GLControl named glCtrl1 and one named glCtrl2. And you
have added handlers to the Paint event of both. This is what you do in the event
handler of glCtrl1 (of course you do something similar in the event handler of
glCtrl2!):
private void glCtrl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded)
return;
glCtrl1.MakeCurrent(); // Ohh.. It's that simple?
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
...
}
The same is true for any code calling a GL.* or Glu.* method!
Although each GLControl has its own GraphicsContext, OpenTK will share OpenGL
resources by default. This means, any context can use textures, display lists, etc.
created on any other context. You can disable this behavior via the
GraphicsContext.ShareContexts property.
Avoiding pitfalls in the managed world
This text is intended for someone with a C/OpenGL background.
Even though OpenTK automatically translates GL/AL calls from C# to C, some
things work slightly differently in the managed world, when compared to plain C.
This page describes a few rules you need to keep in mind:
Rules of thumb
1. Use server storage rather than client storage.
A few legacy OpenGL functions use pointers to memory managed by the user.
The most popular example is Vertex Arrays, with the GL.***Pointer family of
functions.
This approach cannot be used in a Garbage Collected environment (as .NET),
as the garbage collector (GC) may move the contents of the buffer in memory.
It is strongly recommended that you replace legacy Vertex Arrays with Vertex
Buffer Objects, which do not suffer from this problem.
Unlike OpenGL 2.1, OpenGL 3.0 will not contain any functions with client
storage.
2. Try to minimize the number of OpenGL calls per frame.
This is true for any programming environment utilizing OpenGL, but a little
more important in the OpenTK case; while the OpenGL/OpenAL bindings are
quite optimized, the transition from managed into unmanaged code incurs a
small, but measurable, overhead.
To minimize the impact of this overhead, try to minimize the number of
OpenGL/OpenAL calls. A good rule of thumb is to make no more than 300-
500 OpenGL calls per frame, which can be achieved by avoiding Immediate
Mode, in favour of Display Lists and VBO's.
3. For optimal math routine performance, use the ref and out overloads.
This is because Vector3, Matrix4 etc. are structures, not classes. Classes are
passed by reference by default in C#.
4. Vector3 v1 = Vector3.UnitX;
5. Vector3 v2 = Vector3.UnitZ;
6. Vector3 v3 = Vector3.Zero;
7. v3 = v1 + v2; // requires three copies;
slow.
Vector3.Add(ref v1, ref v2, out v3); // nothing is copied;
fast!
The same holds true when calling OpenGL functions:
GL.Vertex3(ref v1.X); // pass a pointer to v1; fast!
GL.Vertex3(v1); // copy the whole v1 structure; slower!
Measuring performance
1. GameWindow provides built-in frames-per-second counters [Someone with
confidence in the details please fill in here] However, GLControl does not.
2. A simple and convenient way to measure the performance of your code, is via
the .NET 2.0 / Mono 1.2.4 Stopwatch class. Use it like this:
3. Stopwatch sw = new Stopwatch();
4. sw.Start();
5. // Your code goes here.
6. sw.Stop();
double ms = sw.Elapsed.TotalMilliseconds;
Note: Avoid using DateTime.Now or other DateTime-based method on any
periods shorter than a couple of seconds, since its granularity is 10 ms or
worse. (rumour has it, it may even go backwards on occasion!) Using
DateTime to measure very long operations (several seconds) is OK.
7. If you are on Windows, you can download Fraps to measure how many frames
per second are rendered in your application. For linux (and Windows), you can
use the commercial tool gDEBugger [anyone: any similar tools for Mac? Any
free tool for Linux?]
References:
http://www.gamedev.net/community/forums/topic.asp?topic_id=484756&whichp...
Chapter 3: OpenTK.Math
To help you write cleaner code, OpenTK defines commonly used vectors, quaternions
and matrices to extend the standard scalar types. They are generally nicer to handle
than the arrays which the C API expects.
For example: OpenTK allows you to set the parameters of GL.Color() in various
ways, the color cyan is used in this case.
GL.Color( 0.0f, 1.0f, 1.0f );
Vector3 MyColor = new Vector3( 0.0f, 1.0f, 1.0f );
GL.Color( MyColor );
// requires the System.Drawing library
GL.Color( Color.Cyan );
Function overloads like this can be found all over OpenTK.Graphics and
OpenTK.Audio, where applicable.
Overview
Everything listed below is type-safe, code using these types will work across all
supported platforms.
Vectors
Half-precision Floating-point
o Half - new scalar type with 16 Bits of precision. More information can
be found here.
o Vector2h - 2-component vector of the type Half.
o Vector3h - 3-component vector of the type Half.
o Vector4h - 4-component vector of the type Half.
Single-precision Floating-point
o Single - standard scalar type with 32 Bits of precision.
o Vector2 - 2-component vector of the type Single.
o Vector3 - 3-component vector of the type Single.
o Vector4 - 4-component vector of the type Single.
Double-precision Floating-point
o Double - standard scalar type with 64 Bits of precision.
o Vector2d - 2-component vector of the type Double.
o Vector3d - 3-component vector of the type Double.
o Vector4d - 4-component vector of the type Double.
Quaternion
Quaternion - single-precision floating-point Quaternion using 4 components.
Quaterniond - double-precision floating-point Quaternion using 4
components.
Row-Major Matrices
Matrix3d - 3x3 double-precision Matrix.
Matrix4 - 4x4 single-precision Matrix.
Matrix4d - 4x4 double-precision Matrix.
These are all value types (struct), not reference types. The implications of this can be
read here.
Casts
For symmetry with established types, all OpenTK.Math types can be cast and allow
serialization.
Vector2d TexCoord = new Vector2d( 0.2, 0.5 );
Vector2h HalfTexCoord = (Vector2h)TexCoord;
Vector3h Normal = (Vector3h)Vector3.UnitX;
Instance and Static Methods
The exact methods for each struct would be too numberous to list here, the function
reference and inline documentation serve that purpose. It might not be obvious that
some functionality is only available for instances of the structs, while others are static.
Vector3 Normal = Vector3.UnitX;
Normal.Normalize();
Vector4 TransformedVector = Vector4.Transform( Vector4.UnitX,
Matrix4.Identity );
Half-Type
The new half-precision floating-point type in OpenTK.Math is specifically designed
for computer graphics. It is commonly used to reduce the memory footprint of
floating-point textures, which can become huge at high resolutions. It is also useful
for Vertex attributes, because it can help your vertex struct to stay within the 16 or 32
Byte boundary, which processors like.
Internally the 16 Bit are represented similar to IEEE floating-point numbers:
1 Sign Bit.
5 Exponent Bits.
10 Mantissa Bits. This is sometimes called the Significand, but called
Mantissa in all OpenTK documentation.
It is important to understand that this type is a pure container to transfer data to or
from the GPU, it does not support arithmetic operations. So if you want to use Half
for Texture Coordinates or Normals, you have to perform any calculations with it in
single- or double-precision first and then cast the final result to half-precision.
When using the Half type you should be aware of it's poor precision:
Casting Math.PI to Half will result in 3.1406...
Numbers above 2048 and below -2048 will be rounded to the closest
representable number.
The further away the value of the floating-point number gets from 1.0, the
worse the Epsilon gets. Try to stay within [0.0 .. 1.0] range for best accuracy.
Chapter 4: OpenTK.Graphics (OpenGL
and ES)
In order to use OpenGL functions, your System requires appropriate drivers for
hardware acceleration.
The OpenGL Programming Guide is a book written by Silicon Graphics engineers
and will introduce the reader into graphics programming. It is highly recommended
you take a look at this resource to learn about the essential concepts in OpenGL.
These pages are more focused about OpenTK specific changes to the C API, and how
to use OpenTK.Utility classes to assist with some common tasks.
Todo: Missing Pages
window-related, etc. (brings the reader to the level of a Quickstart Template)
GLSL related changes.
OpenTK.Utility related
The GraphicsContext class
[Introduction]
The OpenTK.Graphics.GraphicsContext is a cross-platform wrapper around an
OpenGL context. The context routes your OpenGL commands to the hardware driver
for execution - which means you cannot use any OpenGL commands without a valid
GraphicsContext.
[Constructors]
OpenTK creates a GraphicsContext automatically as part of the GameWindow and
GLControl classes:
You can specify the desired GraphicsMode of the context using the mode
parameter. Use GraphicsMode.Default to set a default, compatible mode or
specify the color, depth, stencil and anti-aliasing level manually.
You can specify the OpenGL version you wish to use through the major and
minor parameters. As per the OpenGL specs, the context will use the highest
version that is compatible with the version you specified. The default values
are 1 and 0 respectively, resulting in a 2.1 context.
You can request an embedded (ES) context by specifying
GraphicsContextFlags.Embedded to the flags parameter. The default value
will construct a desktop (regular OpenGL) context.
If you are creating the context manually, you must specify a valid
IWindowInfo instance to the window parameter (see below). This is the default
window the GraphicsContext will draw on and can be modified later using
the MakeCurrent method.
Examples:
// Creates a 1.0-compatible GraphicsContext with GraphicsMode.Default
GameWindow window = new GameWindow();
// Creates a 3.0-compatible GraphicsContext with 32bpp color, 24bpp
depth
// 8bpp stencil and 4x anti-aliasing.
GLControl control = new GLControl(new GraphicsMode(32, 24, 8, 4), 3,
0);
Sometimes, you might wish to create a second context for your application. A typical
use case is for background loading of resources. This is very simple to achieve:
// The new context must be created on a new thread
// (see remarks section, below)
// We need to create a new window for the new context.
// Note 1: new windows remain invisible unless you call
// INativeWindow.Visible = true or IGameWindow.Run()
// Note 2: invisible windows fail the pixel ownership test.
// This means that the contents of the front buffer are
undefined, i.e.
// you cannot use an invisible window for offscreen
rendering.
// You will need to use a framebuffer object, instead.
// Note 3: context sharing will fail if the main context is in use.
// Note 4: this code can be used as-is in a GLControl or GameWindow.
EventWaitHandle context_ready = new EventWaitHandle(false,
EventResetMode.AutoReset);
Context.MakeCurrent(null);
Thread thread = new Thread(() =>
{
INativeWindow window = new NativeWindow();
IGraphicsContext context = new
GraphicsContext(GraphicsMode.Default, window.WindowInfo);
context.MakeCurrent(window.WindowInfo);
while (window.Exists)
{
window.ProcessEvents();
// Perform your processing here
Thread.Sleep(1); // Limit CPU usage, if necessary
}
});
thread.IsBackground = true;
thread.Start();
context_ready.WaitOne();
MakeCurrent();
If necessary, you can also instantiate a GraphicsContext manually. For this, you will
need to provide an amount of platform-specific information, as indicated below:
using OpenTK.Graphics;
using OpenTK.Platform;
using Config = OpenTK.Configuration;
using Utilities = OpenTK.Platform.Utilities;
// Create an IWindowInfo for the window we wish to render on.
// handle - a Win32, X11 or Carbon window handle
// display - the X11 display connection
// screen - the X11 screen id
// root - the X11 root window
// visual - the desired X11 visual for the window
IWindowInfo wi = null;
if (Config.RunningOnWindows)
wi = Utilities.CreateWindowsWindowInfo(handle);
else if (Config.RunningOnX11)
wi = Utilities.CreateX11WindowInfo(display, screen, handle, root,
visual);
else if (Config.RunningOnMacOS)
wi = Utilities.CreateMacOSCarbonWindowInfo(handle, false, false);
// Construct a new IGraphicsContext using the IWindowInfo from above.
IGraphicsContext context = new GraphicsContext(GraphicsMode.Default,
wi);
Finally, it is possible to instantiate a 'dummy' GraphicsContext for any OpenGL
context created outside of OpenTK. This allows you to use OpenTK.Graphics with
windows created through SDL or other libraries:
// The 'external' context has to be current on the calling thread:
GraphicsContext context = GraphicsContext.CreateDummyContext();
A common use-case is integration of OpenGL 3.x through OpenTK.Graphics into an
existing application.
[Remarks]
A single GraphicsContext may be current on a single thread at a time. All OpenGL
commands are routed to the context which is current on the calling thread - issuing
OpenGL commands from a thread without a current context may result in a
GraphicsContextMissingException. This is a safeguard placed by OpenTK: under
normal circumstances, you'd get an abrupt and unexplained crash.
[Methods]
MakeCurrent
You can use the MakeCurrent() instance method to make a context current
on the calling thread. If a context is already current on this thread, it will be
replaced and made non-current. A single context may be current on a single
thread at any moment - trying to make it current on two or more threads will
result in an error. You can make a context non-current by calling
MakeCurrent(null) on the correct thread.
To retrieve the current context use the GraphicsContext.CurrentContext
static property.
If you wish to use OpenGL on multiple threads, you can either:
o create one OpenGL context for each thread, or
o use MakeCurrent() to make move a single context between threads.
Both alternatives can be quite complicated to implement correctly. For this
reason, it is usually advisable to restrict all OpenGL commands to a single
thread, typically your main application thread, and use asynchronous method
calls to invoke OpenGL from different threads. The GLControl provides the
GLControl.BeginInvoke() method to simplify asynchronous method calls
from secondary threads to the main System.Windows.Forms.Application
thread. The GameWindow does not provide a similar API.
To use multiple contexts on a single thread, call MakeCurrent to select the
correct context prior to any OpenGL commands. For example, if you have two
GLControls on a single form, you must call MakeCurrent() on the correct
GLControl for each Load, Resize or Paint event.
GLControl.MakeCurrent() and GameWindow.MakeCurrent() are instance
methods that simplify the handling of contexts.
SwapBuffers
OpenTK creates double-buffered contexts by default. Single-buffered
contexts are considered deprecated, since they do not work correctly with
compositors found on modern operating systems.
A double-buffered context offers two color buffers: a "back" buffer, where all
rendering takes place, and a "front" buffer which is displayed to the user. The
SwapBuffers() method "swaps" the front and back buffers and displays the
result of the rendering commands to the user. The contents of the new back
buffer are undefined after the call to SwapBuffers().
The typical rendering process looks similar to this:
// Clear the back buffer.
GL.Clear(ClearBufferMask.ColorBufferBit |
ClearBufferMask.DepthBufferBit);
// Issue rendering commands, like GL.DrawElements
// Display the final rendering to the user
GraphicsContext.CurrentContext.SwapBuffers();
Note that caching the current context will be more efficient than retrieving it
through GraphicsContext.CurrentContext. For this reason, both
GameWindow and GLControl use a cached GraphicsContext for efficiency.
[Stereoscopic rendering]
You can create a GraphicsContext that supports stereoscopic rendering (also
known as "quad-buffer stereo"), by setting the stereo parameter to true in the
context constructor. GameWindow and GLControl also offer this parameter in their
constructors.
Contexts that support quad-buffer stereo distinguish the back and front buffers
between "left" and "right" buffer. In other words, the context contains four distinct
color buffers (hence the name): back-left, back-right, front-left and front-right. Check
out the stereoscopic rendering page for more information ([Todo: add article and
link]).
Please note that quad-buffer stereo is typically not supported on consumer video
cards. You will need a workstation-class video card, like Ati's FireGL/FirePro or
Nvidia's Quadro series, to enable stereo rendering. Trying to enable stereo rendering
on consumer video cards will typically result in a context without stereo capabilities.
[Accessing internal information]
GraphicsContext hides an amount of low-level, implementation-specific information
behind the IGraphicsContextInternal interface. This information includes the raw
context handle, the platform-specific IGraphicsContext implementation and
methods to initialize OpenGL entry points (GetAddress() and LoadAll()).
To access this information, cast your GraphicsContext to
IGraphicsContextInternal:
IntPtr raw_context_handle = (my_context as
IGraphicsContextInternal).Context.Handle;
IntPtr function_address = (my_context as
IGraphicsContextInternal).GetAddress("glGenFramebufferEXT");
Using an external OpenGL context with
OpenTK
Starting with version 0.9.1, OpenTK requires the existence of an OpenGL context
prior to the initialization of the OpenGL subsystem. In other words, you cannot use
any OpenGL methods prior to the creation of a GraphicsContext.
If you create the OpenGL context through an external library (for example SDL or
GTK#), you will need to inform OpenTK of the context's existence using the
GraphicsContext.CreateDummyContext() static method. This method will return a
new GraphicsContext instance for the context that is current on the calling thread.
Optionally, you can pass the handle (IntPtr) of a specific external context to
CreateDummyContext; in this case, the external context need not be current on the
calling thread.
You will typically call this method as soon as the external context is created. For
example, using Tao.Glfw:
Tao.Glfw.glfwOpenWindow(640, 480, 8, 8, 8, 8, 16, 0,
Tao.Glfw.GLFW_WINDOW);
OpenTK.Graphics.GraphicsContext.CreateDummyContext();
// You may now use OpenTK.Graphics methods normally.
Please note that it is an error to call CreateDummyContext() multiple times for the
same external context.
Textures
The following pages will describe the concepts of OpenGL Textures, Frame Buffer
Objects and Pixel Buffer Objects. These concepts apply equally to OpenGL and
OpenGL|ES - differences between the two will be noted in the text or in the example
source code.
Loading a texture from disk
Before going into technical details about textures in the graphics pipeline, it is useful
to know how to actually load a texture into OpenGL.
A simple way to achieve this is to use the System.Drawing.Bitmap class (MSDN
documentation). This class can decode BMP, GIF, EXIG, JPG, PNG and TIFF images
into system memory, so the only thing we have to do is send the decoded data to
OpenGL. Here is how:
using System.Drawing;
using System.Drawing.Imaging;
using OpenTK.Graphics.OpenGL;
int LoadTexture(string filename)
{
if (String.IsNullOrEmpty(filename))
throw new ArgumentException(filename);
int id = GL.GenTexture();
GL.BindTexture(TextureTarget.Texture2D, id);
Bitmap bmp = new Bitmap(filename);
Bitmap bmp_data = bitmap.LockBits(new Rectangle(0, 0, bmp.Width,
bmp.Height), ImageLockMode.ReadOnly,
System.Drawing.Imaging.PixelFormat.Format32bppArgb);
GL.TexImage2D(TextureTarget.Texture2D, 0,
PixelInternalFormat.Rgba, bmp_data.Width, bmp_data.Height, 0,
OpenTK.Graphics.OpenGL.PixelFormat.Bgra,
PixelType.UnsignedByte, bmp_data.Scan0);
bmp.UnlockBits(bmp_data);
// We haven't uploaded mipmaps, so disable mipmapping (otherwise
the texture will not appear).
// On newer video cards, we can use GL.GenerateMipmaps() or
GL.Ext.GenerateMipmaps() to create
// mipmaps automatically. In that case, use
TextureMinFilter.LinearMipmapLinear to enable them.
GL.TexParameter(TextureTarget.Texture2D,
TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
GL.TexParameter(TextureTarget.Texture2D,
TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
return id;
}
Now you can bind this texture id to a sampler (with GL.Uniform1) and use it in your
shaders. If you are not using shaders, you should enable texturing (with GL.Enable)
and bind the texture (GL.BindTexture) prior to rendering.
2D Texture differences
The most commonly used textures are 2-dimensional. There exist 3 kinds of 2D
textures:
1. Texture2D
Power of two sized (POTS) E.g: 1024²
These are supported on all OpenGL 1.2 drivers.
o MipMaps are allowed.
o All filter modes are allowed.
o Texture Coordinates are addressed parametrically: [0.0f ... 1.0f]x[0.0f
... 1.0f]
o All wrap modes are allowed.
o Borders are supported. (Exception: S3TC Texture Compression does
not allow borders)
2. Texture2D
Non power of two sized (NPOTS) E.g: 640*480.
GL.SupportsExtension( "ARB_texture_non_power_of_two" ) must
evaluate to true.
o MipMaps are allowed.
o All filter modes are allowed.
o Texture Coordinates are addressed parametrically: [0.0f ... 1.0f]x[0.0f
... 1.0f]
o All wrap modes are allowed.
o Borders are supported. (Exception: S3TC Texture Compression does
not allow borders)
3. TextureRectangle
Arbitrary size. E.g: 640*480.
GL.SupportsExtension( "ARB_texture_rectangle" ) must evaluate to
true.
o MipMaps are not allowed.
o Only Nearest and Linear filter modes are allowed. (default is Linear)
o Texture Coordinates are addressed non-parametrically:
[0..width]x[0..height]
o Only Clamp and ClampToEdge wrap modes are allowed. (default is
ClampToEdge)
o Borders are not supported.
Note that 1 and 2 both use the same tokens. The only difference between them is the
size.
S3 Texture Compression
Introduction
A widely available Texture Compression comes from S3, mostly due to Microsoft
licensing it and including it into DirectX. It was added into the file format DDS
(DirectDraw Surface), which is basically a copy of the Texture in Video Memory.
Every graphics accelerator compatible with DirectX 7 or higher supports this Texture
Compression.
The DXT Formats
What the S3 Texture Compression (abbreviation: S3TC. The Formats are named
DXTn, where ( 1 <= n <= 5 ) ) does is encode the whole Image into Blocks of 4x4
Texel, instead of storing every single Texel of the Image. Thus the ideal compressed
Texture dimension is a multiple of 4, like 640x480 or a power of 2, which can be
nicely fit into these Blocks. This is the ideal and not a restriction, the specification
allows any non-power-of-two dimension, but will internally use a 4x4 Block for a
Texture with the size of 2x1 (the other Texels in the Block are undefined).
This results into an 1:6 compression for DXT1 and 1:4 compression for DXT3/5,
which translates into smaller disk size, load times and also render times.
DXT1, 8 Bytes per Block, Accuracy: R5G6B5 or R5G5B5A1
DXT3, 16 Bytes per Block, Accuracy: R5G6B5A8
DXT5, 16 Bytes per Block, Accuracy: R5G6B5A8
The formats DXT2 and DXT4 do exist, but they include pre-multiplied Alpha which
is problematic when blending with images with explicit Alpha (RGBA, DXT3/5, etc).
That's why those formats have barely been used, and are partially not supported by
hardware and export/import tools. Avoiding DXT2/4 is strongly recommended, as
they offer no beneficial functionality over established formats.
Compressed vs. Uncompressed
You probably guessed it already, there is a catch involved when reliably shrinking an
image to 25% of it's uncompressed size: A lossy compression technique. This quality
loss involved, which can be altered by tweaking the Filter options when compressing
the image, is different to the one used in JPG compression. Although both formats -
.dds and .jpg - are designed to compress an Image, the S3TC format was developed
with graphics hardware in mind.
A bilinear Texture lookup usually reads 2x2 Texels from the Texture and interpolates
those 4 Texels to get the final Color. Since a Block consists of 4x4 Texels, there is a
good chance that all 4 Texels - which must be examined for the bilinear lookup - are
in the same Block. This means that the worst case scenario involves reading 4 Blocks,
but usually only 1-2 Blocks are used to achieve the bilinear lookup. When using
uncompressed Textures, every bilinear lookup requires reading 4 Texels.
If you do the maths now you will notice that the compressed image actually needs 16
Bytes for 1 Block of RGBA Color, but the uncompressed 4 Texels of RGBA need 16
Bytes too. And yes, if you would only draw a single Pixel on the screen all this would
not bring any noticable performance gains, actually it would be slower if multiple
Blocks must be read to do the lookup.
However in OpenGL you typically draw more than a single Pixel, at least a Triangle.
When the Triangle is rasterized, alot of Pixels will be very close to each other, which
means their 2x2 lookup is very likely in the same 4x4 Block used by the last lookup,
or a close neighbour. Graphic cards usually support this locality by using a small
amount of memory in the chip for a dedicated Texture Cache. If a Cache hit is made,
the cost for reading the Texels is very low, compared to reading from Video Memory.
That's why S3TC does decrease render times: the earlier mentioned 16 Bytes of a
DXTn Block contain 16 Texels (1 Byte per Texel), while 16 Bytes of uncompressed
Texture only contain 4 Texels (4 Bytes per Texel). Alot more data is stored in the 16
Bytes of DXTn, and alot of lookups will be able to use the fast Texture Cache. The
game Quake 3 Arena's Framerate increases by ~20% when using compressed
Textures, compared to using uncompressed Textures.
Restrictions
Although you might be convinced now that Texture Compression is something worth
looking into, do handle it with care. After all, it's a lossy compression Technique
which introduces compression Artifacts into the Texture. For Textures that are close
to the Viewer this will be noticed, that's why 2D Elements which are drawn very close
to the near Plane - like the Mouse Cursor, Fonts or User Interface Elements like the
Health display - are usually done with uncompressed Textures, which do not suffer
from Artifacts.
As a rule of thumb, do not use Texture Compression where 1 Texel in the Texture
will map to 1 Pixel on the Screen.
Using OpenTK.Utilities .dds loader
At the time of writing, the .dds loader included with OpenTK can handle compressed
2D Textures and compressed Cube Maps. Keep in mind that the loader expects a valid
OpenGL Context to be present. It will only read the file from disk and upload all
MipMap levels to OpenGL. It will NOT set minification/magnification filter or
wrapping mode, because it cannot guess how you intent to use it.
void LoadFromDisk( string filename, bool flip, out int texturehandle, out
TextureTarget dimension)
Input Parameter: filename
A string used to locate the DDS file on the harddisk, note that escape-sequences like
"\n" are NOT stripped from the string.
Input Parameter: flip
The DDS format is designed to be used with DirectX, and that defines
GL.TexCoord2(0.0, 0.0) at top-left, while OpenGL uses bottom-left. If you wish to
use the default OpenGL Texture Matrix, the Image must be flipped before loading it
as Texture into OpenGL.
Output Parameter: texturehandle
If there occured any error while loading, the loader will return "0" in this parameter. If
>0 it's a valid Texture that can be used with GL.BindTexture.
Output Parameter: dimension
This parameter is used to identify what was loaded, currently it can return "Invalid",
"Texture2D" or "TextureCube".
Example Usage
TextureTarget ImageTextureTarget;
int ImageTextureHandle;
ImageDDS.LoadFromDisk( @"YourTexture.dds", true, out
ImageTextureHandle, out ImageTextureTarget );
if ( ImageTextureHandle == 0 || ImageTextureTarget ==
TextureTarget.Invalid )
// loading failed
// load succeeded, Texture can be used.
GL.BindTexture( ImageTextureTarget, ImageTextureHandle );
GL.TexParameter( ImageTextureTarget,
TextureParameterName.TextureMagFilter, (int) TextureMagFilter.Linear
);
int[] MipMapCount = new int[1];
GL.GetTexParameter( ImageTextureTarget,
GetTextureParameter.TextureMaxLevel, out MipMapCount[0] );
if ( MipMapCount == 0 ) // if no MipMaps are present, use linear
Filter
GL.TexParameter( ImageTextureTarget,
TextureParameterName.TextureMinFilter, (int) TextureMinFilter.Linear
);
else // MipMaps are present, use trilinear Filter
GL.TexParameter( ImageTextureTarget,
TextureParameterName.TextureMinFilter, (int)
TextureMinFilter.LinearMipmapLinear );
Remember that you must first GL.Enable the states Texture2D or TextureCube,
before using the Texture in drawing.
Useful links:
ATi Compressonator:
http://ati.amd.com/developer/compressonator.html
nVidia's Photoshop Plugin:
http://developer.nvidia.com/object/photoshop_dds_plugins.html
nVidia's GPU-accelerated Texture Tools:
http://developer.nvidia.com/object/texture_tools.html
Detailed comparison of uncompressed vs. compressed Images:
http://www.digit-life.com/articles/reviews3tcfxt1/
OpenGL Extension Specification:
http://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt
Microsoft's .dds file format specification (was used to build the OpenTK .dds loader)
http://msdn.microsoft.com/archive/default.asp?url=/archive/en-us/dx81_c/...
DXT Compression using CUDA
http://developer.download.nvidia.com/compute/cuda/sdk/website/projects/d...
Real-Time YCoCg-DXT Compression
http://news.developer.nvidia.com/2007/10/real-time-ycocg.html
Last Update of the Links: January 2008
Frame Buffer Objects (FBO)
Every OpenGL application has at least one framebuffer. You can think about it as a
digital copy of what you see on your screen. But this also implies a restriction, you
can only see 1 framebuffer at a time on-screen, but it might be desireable to have
multiple off-screen framebuffers at your disposal. That's where Frame Buffer Object
(FBO) comes into play.
Typical usage for FBO is High Dynamic Range Rendering, Shadow Mapping and
other Render-To-Texture effects. Assuming the buzzwords tell you nothing, here's a
quick example scenario. We have a Texture2D of a sign that has some wooden texture
and reads "Blacksmith". However you intend to localize that sign, so the german
version of your game reads "Schmiede" or the spanish version "herrería". What are
the options? Manually create a new Texture for every sign in the game with a paint
program? No. All you need is the wooden texture of the sign, without any letters. The
texture can be used as target for Render-To-Texture, and OpenTK.Fonts provides you
a way to write any text you like ontop of that texture.
The traditional approach to achieve that was rendering into the visible framebuffer,
read the information back with GL.ReadPixels() or GL.CopyTexSubImage(), then
clear the screen and proceed with rendering as usual. With FBO the copy can be
avoided, since it allows to render directly into a texture.
Framebuffer Layout
A framebuffer consists of at least one of these buffers:
A depth buffer, with or without stencil mask. Typical depth buffer formats are
16, 24, 32 Bit integer or 32 Bit floating point. Stencil buffers can only be 8
Bits in size, a good mixed depth and stencil format is depth 24 Bit with stencil
8 Bit.
Color buffer(s) have 1-4 components, namely Red, Green, Blue and Alpha.
Typical color buffer formats are RGBA8 (8 Bit per component, total 32 Bit) or
RGBA16f (16 Bit floating point per component, total 64 Bit). This list is far
from complete, there exist dozens of formats with different amount of
components and precision per component.
Please note that there is no requirement to use both. It's perfectly valid to create a
FBO which has only a color attachment but no depth attachment. Or the other way
around.
When you use more than one buffer, some restrictions apply: All attachments to the
FBO must have the same width and height. All color buffers must use the same
format. For example, you cannot attach a RGBA8 and a RGBA16f Texture to the
same FBO, even if they have the same width and height. OpenGL 3.0 does relax this
restriction, by allowing attachments of different sizes to be attached. But only the
smallest area covered by all attachments can be written to. The Extension
EXTX_mixed_framebuffer_formats allows attaching different formats to the
framebuffer, however this is reported to be very slow so far.
Renderbuffers
FBO allows 2 different types of targets to be attached to it. The already known
textures 1D, 2D, Rectangle, 3D or Cube map, and a new type: the renderbuffer. They
are not restricted to depth or stencil like the name might suggest, they can be used for
color formats aswell.
Renderbuffer
Pro:
May support formats which are not available as texture.
Allows multisampling through Extensions.
Con:
Does not allow MipMaps, filter or wrapping mode to be specified.
Cannot be bound as sampler for shaders.
Restricted to be a 2-dimensional image.
Texture2D
Pro:
Allows MipMaps, filter and wrapping modes, just like every other texture.
Can be bound as sampler to a shader.
Con:
Might be slower than a renderbuffer, depending on hardware.
As a rule of thumb, do not use a renderbuffer if you plan to use the FBO attachments
as textures at some later stage. The copy from renderbuffer into a texture will perform
worse than rendering directly to the texture.
Let's take the wooden "Blacksmith" sign example from earlier again. The required
end result must be a Texture2D, which can be bound when drawing the geometry of
the sign. To give an overview about the options, here are some brief summaries how
to accomplish obtaining the desired Texture2D:
1. Using a visible framebuffer.
The wooden texture is drawn into the framebuffer. Text is drawn. The final
Texture is copied into a Texture2D. The screen must be cleared when done.
2. Using a renderbuffer.
The renderbuffer must be attached and the FBO bound. The wooden texture is
drawn. Text is drawn. The final Texture is copied into a Texture2D. Either the
renderbuffer is redundant now, or the screen must be cleared.
3. Using a Texture2D.
The texture must be attached and the FBO bound. Only Text is drawn. Done.
Example Setup
To give a concrete example how all this theory looks in practice: let's create a color
texture, a depth renderbuffer and a FBO, then attach the texture and renderbuffer to
the FBO. I'm assuming you read the VBO tutorial before this, so I'm not going
through the purpose of handles, GL.Gen*, GL.Bind* and GL.Delete* functions again.
Note that this is a C API and the same rule of binding 0 to disable or detach
something is valid here too. E.g. GL.Ext.BindFramebuffer(
FramebufferTarget.FramebufferExt, 0 ); will disable the last bound FBO and return
rendering back to the visible window-system provided framebuffer.
const int FboWidth = 512;
const int FboHeight = 512;
uint FboHandle;
uint ColorTexture;
uint DepthRenderbuffer;
// Create Color Texture
GL.GenTextures( 1, out ColorTexture );
GL.BindTexture( TextureTarget.Texture2D, ColorTexture );
GL.TexParameter( TextureTarget.Texture2D,
TextureParameterName.TextureMinFilter, (int) TextureMinFilter.Nearest
);
GL.TexParameter( TextureTarget.Texture2D,
TextureParameterName.TextureMagFilter, (int) TextureMagFilter.Nearest
);
GL.TexParameter( TextureTarget.Texture2D,
TextureParameterName.TextureWrapS, (int) TextureWrapMode.Clamp );
GL.TexParameter( TextureTarget.Texture2D,
TextureParameterName.TextureWrapT, (int) TextureWrapMode.Clamp );
GL.TexImage2D( TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba8,
FboWidth, FboHeight, 0, PixelFormat.Rgba, PixelType.UnsignedByte,
IntPtr.Zero );
// test for GL Error here (might be unsupported format)
GL.BindTexture( TextureTarget.Texture2D, 0 ); // prevent feedback,
reading and writing to the same image is a bad idea
// Create Depth Renderbuffer
GL.Ext.GenRenderbuffers( 1, out DepthRenderbuffer );
GL.Ext.BindRenderbuffer( RenderbufferTarget.RenderbufferExt,
DepthRenderbuffer );
GL.Ext.RenderbufferStorage(RenderbufferTarget.RenderbufferExt,
(RenderbufferStorage)All.DepthComponent32, FboWidth, FboHeight);
// test for GL Error here (might be unsupported format)
// Create a FBO and attach the textures
GL.Ext.GenFramebuffers( 1, out FboHandle );
GL.Ext.BindFramebuffer( FramebufferTarget.FramebufferExt, FboHandle
);
GL.Ext.FramebufferTexture2D( FramebufferTarget.FramebufferExt,
FramebufferAttachment.ColorAttachment0Ext, TextureTarget.Texture2D,
ColorTexture, 0 );
GL.Ext.FramebufferRenderbuffer( FramebufferTarget.FramebufferExt,
FramebufferAttachment.DepthAttachmentExt,
RenderbufferTarget.RenderbufferExt, DepthRenderbuffer );
// now GL.Ext.CheckFramebufferStatus(
FramebufferTarget.FramebufferExt ) can be called, check the end of
this page for a snippet.
// since there's only 1 Color buffer attached this is not explicitly
required
GL.DrawBuffer(
(DrawBufferMode)FramebufferAttachment.ColorAttachment0Ext );
GL.PushAttrib( AttribMask.ViewportBit ); // stores GL.Viewport()
parameters
GL.Viewport( 0, 0, FboWidth, FboHeight );
// render whatever your heart desires, when done ...
GL.PopAttrib( ); // restores GL.Viewport() parameters
GL.Ext.BindFramebuffer( FramebufferTarget.FramebufferExt, 0 ); //
return to visible framebuffer
GL.DrawBuffer( DrawBufferMode.Back );
At this point you may bind the ColorTexture as source for drawing into the visible
framebuffer, but be aware that it is still attached as target to the created FBO. That is
only a problem if the FBO is bound again and the texture is used at the same time for
being a FBO attachment target and the source of a texturing operation. This will cause
feedback effects and is most likely not what you intended.
You may detach the ColorTexture from the FBO - the texture contents itself is not
affected - by calling GL.Ext.FramebufferTexture2D() and attach a different target
than ColorTexture to the ColorAttachment0 slot, for example simply 0. However the
FBO would then be incomplete due to the missing color attachment, the best course of
action is to detach the DepthRenderbuffer too and delete the renderbuffer and the
FBO. Do not repeatedly attach and detach the same Texture if you want to update it
every frame - just keep it attached to the FBO and make sure no feedback situation
arises.
It is valid to attach the same texture or renderbuffer to multiple FBO at the same time.
Example: you can avoid copies and save memory by attaching the same depth buffer
to the FBOs, instead of creating multiple depth buffers and copy between them.
Special care has to be taken about 2 states that are always affected by FBOs:
GL.Viewport() and GL.DrawBuffer(s). When switching from the visible framebuffer
to a FBO, you should always set a proper viewport and drawbuffer. Switching
framebuffer targets is such an expensive operation that the cost of the 2 extra calls to
set up drawbuffers and viewport can be ignored. In the example setup above, the
Viewport was stored and restored using GL.PushAttrib() and GL.PopAttrib(), but you
may ofcourse specify it manually using GL.Viewport().
GL.DrawBuffer(s)
A FBO supports multiple color buffer attachments, if they have the same dimension
and the same format. It is allowed to attach multiple color buffers - but only draw to
one of them - by using the GL.DrawBuffer() command. Selecting multiple color
buffers to write to is done with the GL.DrawBuffers() command, which expects an
array like this:
DrawBuffersEnum[] bufs = new DrawBuffersEnum[2] {
(DrawBuffersEnum)FramebufferAttachment.ColorAttachment0Ext,
(DrawBuffersEnum)FramebufferAttachment.ColorAttachment1Ext }; //
fugly, will be addressed in 0.9.2
GL.DrawBuffers( bufs.Length, bufs );
This code declares the color attachments 0 and 1 as buffers that can be written to. In
practice this makes only sense if you're writing shaders with GLSL. (Look up
"gl_FragData" for further info)
The exact number how many attachments are supported by the hardware must be
queried through GL.GetInteger( GetPName.MaxColorAttachmentsExt, ... ) and the
number of allowed Drawbuffers at the same time through GL.GetInteger(
GetPName.MaxDrawBuffers, ... )
To select which buffer is affected by GL.ReadPixels() or GL.CopyTex*() calls, use
GL.ReadBuffer().
Remarks
For the sake of simplicity, the window-system provided framebuffer was called
"visible framebuffer". In reality this is only true if you requested a single-buffer
context from OpenGL, but the more likely case is that you requested a double-
buffered context. When using double buffers, the 'back' buffer is the one used for
drawing and never visible on screen, the 'front' buffer is the one that is visible on
screen. The two buffers are swapped with each other when you call
this.SwapBuffers(), to avoid that slow computers show unfinished images on
screen. FBO are not designed to be double buffered, because they are off-screen at all
times.
The wooden "Blacksmith" sign example has some hidden complexities that are
ignored for the sake of simplicity, such as that you may not want to print with
standard fonts on the sign, that words in different languages can have different length
or that it might be desireable to add an additional mask when writing the text to
simulate the paint peeling off the sign.
This page does not cover all commands exposed by FBO. For a more detailed
description you'll have to dig through the official specification.
These Extensions were merged into ARB_framebuffer_objects with OpenGL 3.0:
EXT_framebuffer_multisample allows the creation of renderbuffers with n samples
per image.
EXT_framebuffer_blit allows to bind 2 FBO at the same time. One for reading and
one for writing. Without this Extension the active framebuffer is used for both:
reading and writing.
Snippet how to interpret the possible results from GL.CheckFramebufferStatus
private bool CheckFboStatus( )
{
switch ( GL.Ext.CheckFramebufferStatus(
FramebufferTarget.FramebufferExt ) )
{
case FramebufferErrorCode.FramebufferCompleteExt:
{
Trace.WriteLine( "FBO: The framebuffer is
complete and valid for rendering." );
return true;
}
case
FramebufferErrorCode.FramebufferIncompleteAttachmentExt:
{
Trace.WriteLine( "FBO: One or more attachment
points are not framebuffer attachment complete. This could mean
there’s no texture attached or the format isn’t renderable. For color
textures this means the base format must be RGB or RGBA and for depth
textures it must be a DEPTH_COMPONENT format. Other causes of this
error are that the width or height is zero or the z-offset is out of
range in case of render to volume." );
break;
}
case
FramebufferErrorCode.FramebufferIncompleteMissingAttachmentExt:
{
Trace.WriteLine( "FBO: There are no attachments."
);
break;
}
/* case
FramebufferErrorCode.GL_FRAMEBUFFER_INCOMPLETE_DUPLICATE_ATTACHMENT_E
XT:
{
Trace.WriteLine("FBO: An object has been
attached to more than one attachment point.");
break;
}*/
case
FramebufferErrorCode.FramebufferIncompleteDimensionsExt:
{
Trace.WriteLine( "FBO: Attachments are of
different size. All attachments must have the same width and height."
);
break;
}
case
FramebufferErrorCode.FramebufferIncompleteFormatsExt:
{
Trace.WriteLine( "FBO: The color attachments have
different format. All color attachments must have the same format."
);
break;
}
case
FramebufferErrorCode.FramebufferIncompleteDrawBufferExt:
{
Trace.WriteLine( "FBO: An attachment point
referenced by GL.DrawBuffers() doesn’t have an attachment." );
break;
}
case
FramebufferErrorCode.FramebufferIncompleteReadBufferExt:
{
Trace.WriteLine( "FBO: The attachment point
referenced by GL.ReadBuffers() doesn’t have an attachment." );
break;
}
case FramebufferErrorCode.FramebufferUnsupportedExt:
{
Trace.WriteLine( "FBO: This particular FBO
configuration is not supported by the implementation." );
break;
}
default:
{
Trace.WriteLine( "FBO: Status unknown. (yes, this
is really bad.)" );
break;
}
}
return false;
}
Geometry
These pages of the book discuss how to define, reference and draw geometric Objects
using OpenGL.
Focus is on storing the Geometry directly in Vertex Buffer Objects (VBO), for using
Immediate Mode please refer to the red book.
1. The Vertex
A Vertex (pl. Vertices) specifies a number of Attributes associated with a single Point
in space. In the fixed-function environment a Vertex commonly includes Position,
Normal, Color and/or Texture Coordinates. The only Attribute that is not optional an
must be specified is the Vertex's Position, usually consisting of 3 float.
In Shader Program driven rendering it is also possible to specify custom Vertex
Attributes which are previously unknown to OpenGL, such as Radius or Bone Index
and Weight for Skeletal Animation. For the sake of simplicity we'll re-create one of
the Vertex formats OpenGL already knows, namely
InterleavedArrayFormat.T2fN3fV3f. This format contains 2 float for Texture
Coordinates, 3 float for the Normal direction and 3 float to specify the Position.
Thanks to the included Math-Library in OpenTK, we're allowed to specify an
arbitrary Vertex struct for our requirements, which is much more elegant to handle
than a float[] array.
[StructLayout(LayoutKind.Sequential)]
struct Vertex
{ // mimic InterleavedArrayFormat.T2fN3fV3f
public Vector2 TexCoord;
public Vector3 Normal;
public Vector3 Position;
}
This leads to a Vertex consisting of 8 float, or 32 byte. We can now declare an
Array of Vertices to describe multiple Points and allow easy indexing/referencing
them.
Vertex[] Vertices;
The Vertex-Array Vertices can now be created and filled with data. Addressing
elements is as convenient as in the following example:
Vertices = new Vertex[ n ]; // -1 < i < n (Remember that arrays
start at Index 0 and end at Index n-1.)
// examples how to assign values to the Vector's components:
Vertices[ i ].Position = new Vector3( 2f, -3f, .4f ); // create a new
Vector and copy it to Position.
Vertices[ i ].Normal = Vector3.UnitX; // this will copy Vector3.UnitX
into the Normal Vector.
Vertices[ i ].TexCoord.X = 0.5f; // the Vectors are structs, so the
new keyword is not required.
Vertices[ i ].TexCoord.Y = 1f;
// Ofcourse this also works the other way around, using the Vectors
as the source.
Vector2 UV = Vertices[ i ].TexCoord;
An Index is simply a byte, ushort or uint, referencing an element in the Vertices
Array. So if we decide to draw a single Vertex 100 times at the same spot, instead of
storing 100 times the same Vertex in Vertices, we can reference it 100 times from the
Indices Array:
uint[] Indices;
Basically the Indices Array is used to describe the primitives and the Vertex Array is
used to declare the corner points.
We can also use collections to store our Vertices, but it's recommended you stick with
a simple Array to make sure your Indices are valid at all times.
Now the Vertices and Indices Arrays can be used to describe the edges of any
Geometric Pritimitve Type.
Once the Arrays are filled with data it can be drawn in Immediate Mode, as Vertex
Array or sent into a Vertex Buffer Object.
2. Geometric Primitive Types
OpenGL requires you to specify the Geometric Primitive Type of the Vertices you
wish to draw. This is usually expected when you begin drawing in either Immediate
Mode (GL.Begin), GL.DrawArrays or GL.DrawElements.
Fig. 1: In the above graphic all valid Geometric Primitive Types are shown, their
winding is Clockwise (irrelevant for Points and Lines).
This is important, because drawing a set of Vertices as Triangles, which are internally
set up to be used with Quads, will result only in garbage being displayed.
Examine Figure 1, you will see that v3 in a Quad is used to finish the shape, while
Triangles uses v3 to start the next shape. The next drawn Triangle will be v3, v4, v5
which isn't something that belongs to any surface, if the Vertices were originally
intended to be drawn as Quads.
However Points and Lines are an Exception here. You can draw every other
Geometric Primitive Type as Points, in order to visualize the Vertices of the Object.
Some more possibilities are:
QuadStrip, TriangleStrip and LineStrip can be interchanged, if the source data
isn't a LineStrip.
Quads can be drawn as Lines with the restriction that there are no lines
between v1, v2 and v3, v0.
Polygon can be drawn as LineLoop
TriangleFan can be drawn as Polygon or LineLoop
The smallest common denominator for all filled surfaces (i.e. no Points or Lines) is
the Triangle. This Geometric Primitive Type has the special attribute of always being
planar and is currently the best way to describe a 3D Object to GPU hardware.
While OpenGL allows to draw Quads or Polygons aswell, it is quite easy to run into
lighting problems if the surface is not perfectly planar. Internally, OpenGL breaks
Quads and Polygons into Triangles, in order to rasterize them.
1. Points
Specifies 1 Point per Vertex v, thus this is usually only used with
GL.DrawArrays().
n Points = Vertex * (1n);
2. Lines
Two Vertices form a Line.
n Lines = Vertex * (2n);
3. LineStrip
The first Vertex issued begins the LineStrip, every consecutive issued Vertex
marks a joint in the Line.
n Line Segments in the Strip = Vertex * (1+1n)
4. LineLoop
Same as LineStrip, but the very first and last issued Vertex are automatically
connected by an extra Line segment.
n Line Segments in the Loop = Vertex * (1n);
5. Polygon
Note that the first and the last Vertex will be connected automatically, just like
LineLoop.
Polygon with n Edges = Vertex * (1n);
Note: This primitive type should really be avoided whenever possible,
basically the Polygon will be split to Triangles in the end anyways. Like
Quads, polygons must be planar or be displayed incorrectly. Another Problem
is that there is only 1 single Polygon in a begin-end block, which leads to
multiple draw calls when drawing a mesh, or using the Extensions
GL.MultiDrawElements or GL.MultiDrawArrays.
6. Quads
Quads are especially useful to work in 2D with bitmap Images, since those are
typically rectangular aswell. Care has to be taken that the surface is planar,
otherwise the split into Triangles will become visible.
n Quads = Vertex * (4n);
7. QuadStrip
Like the Triangle-strip, the QuadStrip is a more compact representation of a
sequence of connected Quads.
n Quads in Quadstrip = Vertex * (2+2n);
8. Triangles
This way to represent a mesh offers the most control over how the Triangles
are sorted, a Triangle always consists of 3 Vertex.
n Triangles = Vertex * (3n);
Note: It might look like an inefficient brute force approach at first, but it has
it's advantages over TriangleStrip. Most of all, since you are not required to
supply Triangles in sequenced strips, it is possible to arrange Triangles in a
way that makes good use of the Vertex Caches. If the Triangle you currently
want to draw shares an edge with one of the Triangles that have been recently
drawn, you get 2 Vertices, that are stored in the Vertex Cache, almost for free.
This is basically the same what stripification does, but you are not restricted to
a certain Direction and forced to insert degenerated Triangles.
9. TriangleStrip
The idea behind this way of drawing is that if you want to represent a solid
and closed Object, most neighbour Triangles will share 2 Vertices (an edge).
You start by defining the initial Triangle (3 Vertices) and after that every new
Triangle will only require a single new Vertex for a new Triangle.
n Triangles in Strip = Vertex * (2+1n);
Note: While this primitive type is very useful for storing huge meshes (2+1n
Vertices per strip as opposed to 3n for BeginMode.Triangles), the big
disadvantage of TriangleStrip is that there is no command to tell OpenGL that
you wish to start a new strip while inside the glBegin/glEnd block. Ofcourse
you can glEnd(); and start a new strip, but that costs API calls. A workaround
to avoid exiting the begin/end block is to create 2 or more degenerate
Triangles (you can imagine them as Lines) at the end of a strip and then start
the next one, but this also comes at the cost of processing Triangles that will
inevitably be culled and aren't visible. Especially when optimizing an Object
to be in a Vertex Cache friendly layout, it is essential to start new strips in
order to reuse Vertices from previous draws.
10. TriangleFan
A fan is defined by a center Vertex, which will be reused for all Triangles in
the Fan, followed by border Vertices. It is very useful to represent convex n-
gons consisting of more than 4 vertices and disc shapes, like the caps of a
cylinder.
When looking at the graphic, Triangle- and Quad-strips might look quite appealing
due to their low memory usage. They are beneficial for certain tasks, but Triangles are
the best primitive type to represent an arbitrary mesh, because it's not restricting
locality and allows further optimizations. It's just not realistic that you can have all
your 3D Objects in Quads and OpenGL will split them internally into Triangles
anyway. 3 ushort per Triangle isn't much memory, and still allows to index 64k
unique Vertex in a mesh, the number of Triangles can be much higher. Don't hardwire
BeginMode.Triangles into your programs though, for example Quads are very
commonly used in orthographic drawing of UI Elements such as Buttons, Text or
Sprites.
Should TriangleStrip get an core/ARB command to start a new strip within the
begin/end block (only nVidia driver has such an Extension to restart the primitive)
this might change, but currently the smaller data structure of the strip does not make
up for the performance gains a Triangle List gets from Vertex Cache optimization.
Ofcourse you can experiment with the GL.MultiDraw Extension mentioned above,
but using it will break using other Extensions such as DirectX 10 instancing.
3.a Vertex Buffer Objects
Introduction
The advantage of VBO (Vertex Buffer Objects) is that we can tell OpenGL to store
information used for drawing - like Position, Colors, Texture Coordinates and
Normals - directly in the Video-card's Memory, rather than storing it in System
Memory and pass it to the graphics Hardware every time we wish to draw it. While
this has been already doable with Display Lists before, VBO has the advantage that
we're able to retrieve a Pointer to the data in Video Memory and read/write directly to
it, if necessary. This can be a huge performance boost for dynamic meshes and is for
years the best overall solution for storing - both, static and dynamic - Meshes.
Creation
Handling VBOs is very similar to handling Texture objects, we can generate&delete
handles, bind them or fill them with data. For this tutorial we will need 2 objects, one
VBO containing all Vertex information (Texture, Normal and Position in this example
case) and an IBO (Index Buffer Object) referencing Vertices from the VBO to form
Triangles. This has the advantage that, when we have uploaded the data to the
VBO/IBO later on, we can draw the whole mesh with a single GL.DrawElements call.
First we acquire two Objects to use:
uint[] VBOid = new uint[ 2 ];
GL.GenBuffers( 2, out VBOid );
Although it is unlikely, OpenGL could complain that it ran out of memory or that the
extension is not supported, it should be checked with GL.GetError. If everything went
smooth we have 2 objects to work with available now.
Delete
The OpenGL driver should clean up all our mess when it deletes the render context,
it's always a good idea to clean up on your own where you can. We remove the
objects we reserved at the buffer creation by calling:
GL.DeleteBuffers( 2, ref VBOid );
Binding
To select which object you currently want to work with, simply bind the handle to
either BufferTarget.ArrayBuffer or BufferTarget.ElementArrayBuffer. The first is
used to store position, uv, normals, etc. (named VBO) and the later is pointing at
those vertices to define geometry (named IBO).
GL.BindBuffer( BufferTarget.ArrayBuffer, VBOid[ 0 ] );
GL.BindBuffer( BufferTarget.ElementArrayBuffer, VBOid[ 1 ] );
It is not required to bind a buffer to both targets, for example you could store only the
vertices in the VBO and keep the indices in system memory. Also, the two objects are
not tied together in any way, for example you could build different triangle lists for
BufferTarget.ElementArrayBuffer to implement LOD on the same set of vertices,
simply by binding the desired element array.
Theres two important things to keep in mind though:
1) While working with VBOs, GL.EnableClientState(EnableCap.VertexArray); must
be enabled. if using Normals, GL.EnableClientState(EnableCap.NormalArray), just
like classic Vertex Arrays.
2) All Vertex Array related commands will be used on the currently bound objects
until you explicitly bind zero '0' to disable hardware VBO.
GL.BindBuffer( BufferTarget.ArrayBuffer, 0 );
GL.BindBuffer( BufferTarget.ElementArrayBuffer, 0 );
Passing Data
There are several ways to fill the object's data, we will focus on using GL.BufferData
and directly writing to video memory. The third option would be GL.BufferSubData
which is quite straightforward to use once you are familiar with GL.BufferData.
1. GL.BufferData
We will start by preparing the IBO, it would not make a difference if we set up
the VBO first, we simply start with the shorter one.
We make sure the correct object is bound (it is not required to do this, if the
buffer is already bound. Just here to clarify on which object we currently work
on)
GL.BindBuffer( BufferTarget.ElementArrayBuffer, VBOid[ 1 ] );
In the example application ushort has been used for Indices, because 16 Bits
[0..65535] are more available Vertices than used by most real-time rendered
meshes, however the mesh could index way more Vertices using a type like
uint. Using ushort, OpenGL will store this data as 2 Bytes per index, saving
memory compared to a 4 Bytes UInt32 per index.
The function GL.BufferData's first parameter is the target we want to use, the
second is the amount of memory (in bytes) we need allocated to hold all our
data. The third parameter is pointing at the data we wish to send to the
graphics card, this can be IntPtr.Zero and you may send the data at a later
stage with GL.MapBuffer (more about this later). The last parameter is an
optimization hint for the driver, it will place your data in the best suited place
for your purposes.
GL.BufferData( BufferTarget.ElementArrayBuffer, (IntPtr) (
Indices.Length * sizeof( ushort ) ), Indices,
BufferUsageHint.StaticDraw );
That's all, OpenGL now has a copy of Indices available and we could dispose
the array, assuming we have the Index Count of the array stored in a variable
for the draw call later on.
Now that we've stored the indices in an IBO, the Vertices are next. Again, we
make sure the binding is correct, give a pointer to the Vertex count, and finally
the usage hint.
GL.BindBuffer( BufferTarget.ArrayBuffer, VBOid[ 0 ] );
GL.BufferData( BufferTarget.ArrayBuffer, (IntPtr) (
Vertices.Length * 8 * sizeof( float ) ), Vertices,
BufferUsageHint.StaticDraw );
There's a table at the bottom of this page, explaining the options in the enum
BufferUsageHint in more detail.
2. GL.MapBuffer / GL.UnmapBuffer
While the first described technique to pass data into the objects required a
copy of the data in system memory, this alternative will give us a pointer to
the video memory reserved by the object. This is useful for dynamic models
that have no copy in client memory that could be used by GL.BufferData,
since you wish to rebuild it every single frame (e.g. fully procedural objects,
particle system).
First we make sure that we got the desired object bound and reserve memory,
the pointer towards the Indices is actually IntPtr.Zero, because we only need
an empty buffer.
GL.BindBuffer( BufferTarget.ElementArrayBuffer, VBOid[ 0 ] );
GL.BufferData( BufferTarget.ElementArrayBuffer, (IntPtr) (
Indices.Length * sizeof( ushort ) ), IntPtr.Zero,
BufferUsageHint.StaticDraw );
Note that you should change BufferUsageHint.StaticDraw properly according
to what you intend to do with the Data, there's a table at the bottom of this
page. Now we're able to request a pointer to the video memory.
IntPtr VideoMemoryIntPtr =
GL.MapBuffer(BufferTarget.ElementArrayBuffer,
BufferAccess.WriteOnly);
Valid access flags for the pointer are BufferAccess.ReadOnly,
BufferAccess.WriteOnly or BufferAccess.ReadWrite, which help the driver
understand what you're going to do with the data. Note that the data's object is
locked until we unmap it, so we want to keep the timespan over which we use
the pointer as short as possible. We may now write some data into the buffer,
once we're done we must release the lock.
unsafe
{
fixed ( ushort* SystemMemory = &Indices[0] )
{
ushort* VideoMemory = (ushort*)
VideoMemoryIntPtr.ToPointer();
for ( int i = 0; i < Indices.Length; i++ )
VideoMemory[ i ] = SystemMemory[ i ]; // simulate what
GL.BufferData would do
}
}
GL.UnmapBuffer( BufferTarget.ElementArrayBuffer );
The pointer is now invalid and may not be stored for future use, if we wish to
modify the object again, we have to call GL.MapBuffer again.
Further reading
Visit this link in order to tell OpenGL about the composition of your Vertex data, and
this link for drawing the data.
Optimization:
One hint from the nVidia whitepaper was regarding the situation, if we want to update
all data in the buffer object by using GL.MapBuffer and not retrieve any of the old
data. Although this is a bad idea, because mapping the buffer is a more expensive
operation than just calling GL.BufferData, it might be necessary in cases where you
have no copy of the data in system memory, but build it on the fly. The solution to
making this somewhat efficient is first calling GL.BufferData with a IntPtr.Zero
again, which tells the driver that the old data isn't valid anymore. Calling
GL.MapBuffer will return a new pointer to a valid memory location of the requested
size to write to, while the old data will be cleaned up once it's not used in any draw
operations anymore.
Also note that either reading from a VBO or wrapping it into a Display List is very
slow and should both be avoided.
Table 1:
BufferUsageHint.Static... Assumed to be a 1-to-n update-to-draw. Means the data is
specified once (during initialization).
BufferUsageHint.Dynamic... Assumed to be a n-to-n update-to-draw. Means the data
is drawn multiple times before it changes.
BufferUsageHint.Stream... Assumed to be a 1-to-1 update-to-draw. Means the data is
very volatile and will change every frame.
...Draw Means the buffer will be used to sending data to GPU. video memory
(Static|StreamDraw) or AGP (DynamicDraw)
...Read Means the data must be easy to access, will most likely be system or AGP
memory.
...Copy Means we are about to do some ..Read and ..Draw operations.
3.b Attribute Offsets and Strides
Setting Strides and Offsets for Vertex Arrays and VBO
There are 2 ways to tell OpenGL in which layout the Vertices are stored:
1. GL.InterleavedArrays()
What GL.InterleavedArrays does is enable/disable the required client states for
OpenGL to interpret our passed data, the first parameter tells that we have 2
floats for Texture Coordinates (T2f), 3 floats for Normal (N3F) and 3 floats
for position (V3F). The second parameter is the stride that will be jumped to
find the second, third, etc. set of texcoord/normal/position values. Since our
Vertices are tighly packed, no stride (zero) is correct. The last parameter
should point at Indices, but we already sent them to the VBO in video
memory, no need to point at them again:
GL.InterleavedArrays( InterleavedArrayFormat.T2fN3fV3f, 0, null
);
This command has the advantage that it's very obvious to the OpenGL driver
what layout of data we have supplied, and it may be possible for the driver to
optimize the memory. Remember that GL.InterleavedArrays will change
states, if you manually disable EnableCap.VertexArray,
EnableCap.NormalArray, EnableCap.TextureCoordArray or changing
GL.VertexPointer, GL.NormalPointer or GL.TexCoordPointer (after calling
GL.InterleavedArrays and before calling GL.DrawElements) make sure to
enable them again or you won't see anything.
2. Setting the offsets/strides manually
For the Vertex format InterleavedArrayFormat.T2fN3fV3f, the correct pointer
setup is:
3. GL.TexCoordPointer( 2, TexCoordPointerType.Float, 8 * sizeof(
float ), (IntPtr) ( 0 ) );
4. GL.NormalPointer( NormalPointerType.Float, 8 * sizeof( float ),
(IntPtr) ( 2 * sizeof( float ) ) );
GL.VertexPointer( 3, VertexPointerType.Float, 8 * sizeof( float
), (IntPtr) ( 5 * sizeof( float ) ) );
1. The first parameter is the number of components to describe that
attribute. For GL.NormalPointer this is always 3 components, but is
variable for Texture coordinates and Position (and Color).
2. The second parameter is the type of the components.
3. The third parameter is the number of bytes of the Vertex struct. This
stride is used to define at which offset the next Vertex begins.
4. The last parameter indicates the byte offset of the first appearance of
the attribute, this makes perfect sense if you recall the layout of our
Vertex struct.
Byte 0-7 are used for the Texture Coordinates, Byte 8-19 for the
Normal and Byte 20-31 for the Vertex Position.
3.c Vertex Arrays
Although it's really not recommended using them (besides for compiling to a Display
List), Vertex Arrays can be safely used like this:
pseudocode:
float[] Positions;
float[] Normals;
unsafe
{
fixed (float* PositionsPointer = Positions)
fixed (float* NormalsPointer = Normals)
{
GL.NormalPointer(..., NormalsPointer);
GL.VertexPointer(..., PositionsPointer);
GL.DrawArrays(...);
GL.Finish(); // Force OpenGL to finsh drawing while the
arrays are still pinned.
}
}
You must use the unsafe float* overloads for this to work, not the object overloads
(which pin internally)
The important bit is that the pin between GL.*Pointer and GL.Draw* may not be
released. For arrays smaller than 85000 Bytes it is also important to call GL.Finish in
order for the CPU to wait until the GPU is done reading all pinned data. You might
get away without the GL.Finish command for a very short VA or ones larger than
85000 Bytes, but once the pin is released the Garbage Collector is allowed to move or
cleanup your array. This leads to difficult to trace access violations with medium
sized VA (without waiting for OpenGL to finish processing it) and will randomly
occur at frames where the GC kicks in.
GL.Finish will obviously kill performance, since you have a blocking statement
executed, which forces CPU and GPU to work in sync and not taking advantage of
parallel processing. That's why it's recommended to use Display Lists or Vertex
Buffer Objects instead.
Please visit this discussion in the forum for more information.
4. Vertex Array Objects
Vertex Array Objects (abbreviation: VAO) are storing vertex attribute setup and VBO
related state. This allows to reduce the number of OpenGL calls when drawing from
VBOs, because all attribute declaration and pointer setup only needs to be done once
(ideally at initialization time) and is afterwards stored in the VAO for later re-use.
But before a VAO can be bound, a handle must be generated:
void GL.GenVertexArrays( uint[] );
void GL.DeleteVertexArrays( uint[] );
bool GL.IsVertexArray( uint );
Binding a VAO is as simple as
void GL.BindVertexArray( uint );
The currently bound VAO records state set by the following commands:
GL.EnableVertexAttribArray()
GL.DisableVertexAttribArray()
GL.VertexAttribPointer()
GL.VertexAttribIPointer()
Indirectly it also saves the state set by GL.BindBuffer() at the point of time when
GL.VertexAttribPointer() was called. A more technical description can be found at
the OpenGL Wiki.
5. Drawing
In order to tell OpenGL to draw primitives for us, there's basically two ways to go:
1. Immediate Mode, as in specifying every single Vertex manually.
2. Vertex Buffers (or Vertex Arrays), drawing a whole Mesh with a single Command.
In order for all GL.Draw*-Functions to output geometric Primitives,
EnableCap.VertexArray must be enabled first.
1. Immediate Mode
Hereby every single Vertex we wish to draw has to be issued manually.
2. // GL.DrawArrays behaviour
3. GL.Begin( BeginMode.Points );
4. for ( uint i = 0; i < Vertices.Length; i++ )
5. {
6. GL.TexCoord2( Vertices[ i ].TexCoord );
7. GL.Normal3( Vertices[ i ].Normal );
8. GL.Vertex3( Vertices[ i ].Position );
9. }
10. GL.End( );
11.
12. // GL.DrawElements behaviour
13. GL.Begin( BeginMode.Points );
14. for ( uint i = 0; i < Indices.Length; i++ )
15. {
16. GL.TexCoord2( Vertices[ Indices[ i ] ].TexCoord );
17. GL.Normal3( Vertices[ Indices[ i ] ].Normal );
18. GL.Vertex3( Vertices[ Indices[ i ] ].Position );
19. }
GL.End( );
20. GL.DrawArrays( BeginMode, int First, int Length )
This Command is used together with Vertex Arrays or Vertex Buffer Objects,
see setting Attribute Pointers. This line will automatically draw all Vertex
contained in Vertices in order of appearance in the Array.
GL.DrawArrays( BeginMode.Points, 0, Vertices.Length );
21. GL.DrawElements( BeginMode, int Length, DrawElementsType, object )
Like DrawArrays this Command is used together with Vertex Arrays or VBO.
It uses an unsigned Array (byte, ushort, uint) to Index the Vertex Array.
This is particularly useful for 3D Models where the Triangles describing the
surface share Edges and Vertices.
GL.DrawElements( BeginMode.TriangleStrip, Indices.Length,
DrawElementsType.UnsignedInt, Indices );
22. GL.DrawRangeElements( BeginMode, int Start, int End, int Count,
DrawElementsType, object )
This function behaves largely like GL.DrawElements, with the change that
you may specify a starting index rather than starting at 0.
Start and End are the smallest and largest Array-Index into Indices. Count is
the number of Elements to render.
23. // behaviour equal to GL.DrawElements
GL.DrawRangeElements( BeginMode.TriangleStrip, 0,
Indices.Length-1, Indices.Length, DrawElementsType.UnsignedInt,
Indices );
24. GL.DrawArraysInstanced( BeginMode, int First, int Length, int
primcount )
This function is only available on DX10 hardware and basically behaves like
this:
25. for (int gl_InstanceID=0; gl_InstanceID < primcount;
gl_InstanceID++ )
GL.DrawArrays( BeginMode, First, Length );
gl_InstanceID is a uniform variable available to the Vertex Shader, which (in
conjunction with GL.UniformMatrix) can be used to assign each Instance
drawn it's own unique Orientation Matrix.
26. GL.DrawElementsInstanced( BeginMode, int Length,
DrawElementsType, object, int primcount )
This function is only available on DX10 hardware and internally unrolls into:
27. for (int gl_InstanceID=0; gl_InstanceID < primcount;
gl_InstanceID++ )
GL.DrawElements( BeginMode, Length, DrawElementsType, Object
);
gl_InstanceID is a uniform variable available to the Vertex Shader, which (in
conjunction with GL.UniformMatrix) can be used to assign each Instance
drawn it's own unique orientation Matrix.
Extension References
http://www.opengl.org/registry/specs/EXT/draw_range_elements.txt
http://www.opengl.org/registry/specs/EXT/draw_instanced.txt
http://www.opengl.org/registry/specs/EXT/multi_draw_arrays.txt
5.b Drawing Optimizations
This page is just giving a starting point for optimizations, the links below provide
more in-depth information.
Make sure there are no OpenGL errors. Any error usually kills the framerate.
Enable backface culling with GL.Enable(EnableCap.CullFace) rather than
relying only on the Z-Buffer.
If you're drawing a scene that covers the whole screen each frame, only clear
depth buffer but not the color buffer.
Organize drawing in a way that requires as few state changes as possible.
Don't enable states that are not needed.
Use GL.Hint(...) wherever applicable.
Avoid Immediate Mode or Vertex Arrays in favor of Display Lists or Vertex
Buffer Objects.
Use GL.DrawRangeElements instead of GL.DrawElements for a slight
performance gain.
Take advantage of S3TC Texture compression and Vertex Cache optimizing
algorithms.
Links:
http://www.mesa3d.org/brianp/sig97/perfopt.htm
http://ati.amd.com/developer/SDK/AMD_SDK_Samples_May2007/Documentations/.
..
http://developer.nvidia.com/object/gpu_programming_guide.html
http://www.opengl.org/pipeline/article/vol003_8/
http://developer.apple.com/graphicsimaging/opengl/
Last edit of Links: March 2008
6. OpenTK's procedural objects
Placeholder
http://www.opentk.com/node/649
OpenGL rendering pipeline
Rendering works by projecting 3-dimensional objects to a 2-dimensional plane, so
they can be displayed on a screen. In modern OpenGL the 3D objects are read from
Vertex Buffer Objects (VBO) and the resulting image is written to a framebuffer. This
page will cover the pipeline operations involved between input and output.
Some of the steps involved are fully programmable (namely: Vertex, Geometry and
Fragment Shader) while the rest is hardwired. However even the hardwired logic can
be manipulated by setting OpenGL's state machine's toggles, which are shown in the
diagram and described in detail in the OpenGL specification.
In order to begin drawing, A Vertex and Fragment Shader are required and OpenGL
must know about the 3D object, which is done by using VBO (and optionally VAO).
The Vertex Shader is responsible for transforming each Vertex from Object
Coordinates into Clip Coordinates.
The primitive assembly will use the resulting Clip Coordinates to create geometric
primitives, which are then divided by the vertex' w-component (perspective divide)
and clipped against the [-1.0..+1.0] range of normalized device-coordinate space
(NDC).
As a final step, the viewport application will offset&scale the normalized device-
coordinates to window coordinates.
The resulting transformed geometric primitive types can now be rasterized into
fragments. Each fragment receives interpolated vertex shader data from the primitive
it belongs to, which is at least position and depth. The fragment shader's output must
be either gl_FragColor, gl_FragData[] or set by GL.BindFragDataLocation(). This
output is called a "fragment", which is a candidate to become a pixel in the
framebuffer. Before this can happen, the fragment muss pass a series of tests called
the Fragment Operations.
There is one noteworthy special case found in some modern hardware. The
functionality is called "Early-Z" or "HyperZ". After rasterization of the primitive, the
resulting Z is used to discard fragments even before the fragment shader is executed.
This functionality is not exposed to OpenGL and works behind the scenes. In the
diagram to the left, it would belong between the Triangle, Line or Point rasterization,
and the fragment shader.
Also note: This diagram targets the OpenGL 3.2 pipeline, but contains a few
commands which belong to the ARB_compatibility extension and may be
unavailable.
Fragment Operations
A Fragment is a candidate to become a pixel in the framebuffer. For every fragment,
OpenGL applies a series of tests in order to eliminate the fragment early to avoid
updating the framebuffer.
Most of these tests can be toggled through GL.Enable/Disable, the pages below cover
this in more detail. However the most in-depth description of the functionality can
only be found in the official OpenGL specification.
The tests are executed from top to bottom, if a fragment did not pass an early test,
later tests are ignored. I.e. If the fragment does not pass the Scissor Test, there would
be no point in determining whether Depth Test passes or not.
01. Pixel Ownership Test
Citation with minor modifications. Cannot explain it better.
"GL 3.1 spec" wrote:
This test is used to determine if the pixel at the current location in the framebuffer is
currently owned by the GL context. If it is not, the window system decides the fate the
incoming fragment. Possible results are that the fragment is discarded or that some
subset of the subsequent per-fragment operations are applied to the fragment. This test
allows the window system to control the GL’s behavior, for instance, when a GL
window is obscured.
If the draw framebuffer is a framebuffer object, the pixel ownership test always
passes, since the pixels of framebuffer objects are owned by the GL, not the window
system. If the draw framebuffer is the default framebuffer, the window system
controls pixel ownership.
02. Scissor Test
The Scissor Test is used to limit drawing to a rectangular region of the viewport.
When enabled, only fragments inside the rectangle are passed to later pipeline stages.
The ScissorTest can be enabled or disabled using EnableCap.ScissorTest
GL.Enable( EnableCap.ScissorTest );
GL.Disable( EnableCap.ScissorTest ); // default
Only a single command is related to the ScissorTest, GL.Scissor( x, y, width, height ).
By default the parameters are set to cover the whole window.
X and Y are used to specify the lower-left corner of the rectangle.
Width is used to specify the horizontal extension of the rectangle.
Height is used to specify the vertical extension of the rectangle.
State Queries
To determine whether ScissorTest is enabled or disabled, use Result =
GL.IsEnabled( EnableCap.ScissorTest );
The values set by GL.Scissor() can be queried by GL.GetInteger(
GetPName.ScissorBox, ... ); // returns an array
03. Multisample Fragment Operations
(WIP)
Multisampling is designed to counter the effects of aliasing at the edges of a
primitive, when it is rasterized into fragments. Multisampling can be also applied to
transparent textures, like wire fences, blades of grass or the leaves of trees. In this
case, it is called 'alpha-to-coverage' and replaces the legacy alpha test.
A multisample buffer contains multiple samples per pixel, with each sample having
it's own color, depth and stencil values. The term 'coverage' refers to a bitmask that is
used to determine which of these samples will be updated: a coverage value of 1
indicates that the relevant sample will be updated; a value of 0 indicates it will be left
untouched.
However, when EnableCap.SampleAlphaToCoverage is used, the coverage is
obtained by interpreting the alpha as a percentage: an alpha of 0.0 means that no
samples are covered, while a value of 1.0 indicates that all samples are covered. For
example, a multisample buffer with 4 samples per pixel and an Alpha value of 0.5
indicates that half of the samples are covered (their coverage bit is 1) and two are not
covered (coverage bit is 0).
"figure out whether this is true" wrote:
The coverage bitmask of incoming fragments can be set in a Fragment Shader with
the variable gl_Coverage.
http://www.humus.name/index.php?page=Comments&ID=230
To enable alpha-to-coverage, enable multisampling
(GL.Enable(EnableCap.Multisample)) and make sure that
GL.GetInteger(GetPName.SampleBuffers, out buffers) is 1. If
EnableCap.Multisample is disabled but GetPName.SampleBuffers is 1, alpha-to-
coverage will be disabled.
There are three OpenGL states related to alpha-to-coverage, they are controlled by
GL.Enable() and GL.Disable()
EnableCap.SampleAlphaToCoverage
For each sample at the current pixel, the Alpha value is read and used to
generate a temporary coverage bitmask which is then combined through a
bitwise AND with the fragment's coverage bitmask. Only samples who's bit is
set to 1 after the bitwise AND are updated.
EnableCap.SampleCoverage
Using GL.SampleCoverage( value, invert ) the temporary coverage
bitmask is generated by the value parameter - and if the invert parameter is
true it is bitwise inverted - before the bitwise AND with the fragment's
coverage bitmask.
EnableCap.AlphaToOne
Each Alpha value is replaced by 1.0.
GL.SampleCoverage
The values set by the command GL.SampleCoverage( value, invert ) are only
used when EnableCap.SampleCoverage is enabled.
value is a single-precision float used to specify the Alpha value used to create
the coverage bitmask.
invert is a boolean toggle to control whether the bitmask is bitwise inverted
before the AND operation.
State Queries
The states of EnableCap.Multisample, EnableCap.SampleAlphaToCoverage,
EnableCap.SampleCoverage and EnableCap.AlphaToOne can be queried with
Result = GL.IsEnabled( cap )
The value set by GL.SampleCoverage() can be queried with GL.GetFloat(
GetPName.SampleCoverageValue, ... )
The boolean set by GL.SampleCoverage() can be queried with GL.GetBoolean(
GetPName.SampleCoverageInvert, ... )
04. Stencil Test
The Stencil buffer's primary use is to apply a mask to the framebuffer. Simply put,
you can think of it as a cardboard stencil where you cut out holes, so you may use a
can of spraypaint to paint shapes. The paint will only pass the holes you had cut out
and be blocked otherwise by the cardboard. OpenGL's Stencil testing allows you to
layer several of these masks over each other.
A more OpenGL related example: In any vehicle simulation the interior of the cockpit
is usually masked by a stencil buffer, because it does not have to be redrawn every
frame. That way alot of fragments of the outside landscape can be skipped, as they
would not contribute to the final image anyway.
In order to use the Stencil buffer, the window-system provided framebuffer - or the
Stencil attachment of a FBO - must explicitly contain a logical stencil buffer. If there
is no stencil buffer, the fragment is always passed to the next pipeline stage.
For the purpose of clarity in this article, the Stencil Buffer is assumed to be 8 Bit large
and able to represent the values 0..255
StencilTest functionality is enabled and disabled with EnableCap.StencilTest
GL.Enable( EnableCap.StencilTest );
GL.Disable( EnableCap.StencilTest ); // default
The value used by GL.Clear() commands can be set through:
GL.ClearStencil( int ); // 0 is the default, Range [0..255]
If StencilTest is enabled, writing can be limited by a bitfield through a bitwise AND.
GL.StencilMask( bitmask ); // By default all bits are set to 1.
Note: The command GL.StencilMaskSeparate() behaves exactly like
GL.StencilMask() but allows separate comparison functions for front- and back-
facing polygons.
GL.StencilFunc()
The command GL.StencilFunc( func, ref, mask ) is used to specify the conditions
under which the StencilTest succeeds or fails. It sets the comparison function,
reference value and mask for the Stencil Test.
ref is an integer value to compare against. By default this value is 0, range [0 ..
255]
mask is a bitfield which will be used in a bitwise AND. Only the bits which
are set to 1 are considered. By default all bits are set to 1.
func of the test can have the following values, the default is
StencilFunction.Always.
o StencilFunction.Always - Test will always succeed.
o StencilFunction.Never - Test will never succeed.
o StencilFunction.Less - Test will succeed if ( ref & mask ) < ( pixel &
mask )
o StencilFunction.Lequal - Test will succeed if ( ref & mask ) <= ( pixel
& mask )
o StencilFunction.Equal - Test will succeed if ( ref & mask ) == ( pixel
& mask )
o StencilFunction.Notequal - Test will succeed if ( ref & mask ) != (
pixel & mask )
o StencilFunction.Gequal - Test will succeed if ( ref & mask ) >= ( pixel
& mask )
o StencilFunction.Greater - Test will succeed if ( ref & mask ) > ( pixel
& mask )
The word 'pixel' means in this case: The value in the Stencil Buffer at the
current pixel.
Note: The command GL.StencilFuncSeparate() behaves exactly like GL.StencilFunc()
but allows separate comparison functions for front- and back-facing polygons.
GL.StencilOp()
Depending on the result determined by GL.StencilFunc(), the command
GL.StencilOp( fail, zfail, zpass ) can be used to decide what action should
be taken if the fragment passes the test.
fail - behavior when StencilTest fails, regardless of DepthTest.
zfail - behavior when StencilTest succeeds, but DepthTest fails.
zpass - behavior when both tests succeed, or if StencilTest succeeds and
DepthTest is disabled.
The following values are allowed, the default for all operations is StencilOp.Keep
StencilOp.Zero - set Stencil Buffer to 0.
StencilOp.Keep - Do not modify the Stencil Buffer.
StencilOp.Replace - set Stencil Buffer to ref value as specified by last
GL.StencilFunc() call.
StencilOp.Incr - increment Stencil Buffer by 1. It is clamped at 255.
StencilOp.IncrWrap - increment Stencil Buffer by 1. If the result is greater
than 255, it becomes 0.
StencilOp.Decr - decrement Stencil Buffer by 1. It is clamped at 0.
StencilOp.DecrWrap - decrement Stencil Buffer by 1. If the result is less than
0, it becomes 255.
StencilOp.Invert - Bitwise invert. If the Stencil Buffer currently contains the
bits 00111001, it is set to 11000110.
Note: The command GL.StencilOpSeparate() behaves exactly like GL.StencilOp() but
allows separate comparison functions for front- and back-facing polygons.
State Queries
To determine whether StencilTest is enabled or disabled, use Result =
GL.IsEnabled( EnableCap.StencilTest );
The bits available in the Stencil Buffer can be queried by GL.GetInteger(
GetPName.StencilBits, ... );
The value set by GL.ClearStencil() can be queried by GL.GetInteger(
GetPName.StencilClearValue, ... );
The bitfield set by GL.StencilMask() can be queried by GL.GetInteger(
GetPName.StencilWritemask, ... );
The state of the Stencil comparison function can be queried with GL.GetInteger()
and the following parameters:
GetPName.StencilFunc - GL.StencilFunc's parameter 'func'
GetPName.StencilRef - GL.StencilFunc's parameter 'ref'
GetPName.StencilValueMask - GL.StencilFunc's parameter 'mask'
The state of the Stencil operations can be queried with GL.GetInteger and the
following parameters:
GetPName.StencilFail - GL.StencilOp's parameter 'fail'
GetPName.StencilPassDepthFail - GL.StencilOp's parameter 'zfail'
GetPName.StencilPassDepthPass - GL.StencilOp's parameter 'zpass'
If the GL.Stencil***Separate() functions have been used, the tokens
GetPName.StencilBack*** become available to query the settings for back-facing
polygons. With Intellisense you should not have any problems finding them.
Related Extensions for further reading
http://www.opengl.org/registry/specs/EXT/stencil_clear_tag.txt
http://www.opengl.org/registry/specs/EXT/stencil_wrap.txt (promoted to core in GL
2.0)
http://www.opengl.org/registry/specs/ATI/separate_stencil.txt (promoted to core in
GL 2.0)
http://www.opengl.org/registry/specs/EXT/stencil_two_side.txt (basically the same
functionality as ATI_separate_stencil, not in core though)
05. Depth Test
A commonly used logical buffer in OpenGL is the Depth buffer, often called Z-
Buffer. The name was chosen due to X and Y being used to describe horizontal and
vertical displacement on the screen, so Z is used to measure the distance
perpendicular to the screen.
The general purpose of this buffer is determining whether a fragment is occluded by a
previously drawn pixel. I.e. If the fragment in question is further away from the eye
than an already existing pixel, the fragment cannot be visible and is discarded.
In order to use the Depth buffer, the window-system provided framebuffer - or the
Depth attachment of a FBO - must explicitly contain a logical Depth buffer. If there is
no Depth buffer, the fragment is always passed to the next pipeline stage.
DepthTest functionality is enabled and disabled with EnableCap.DepthTest
GL.Enable( EnableCap.DepthTest );
GL.Disable( EnableCap.DepthTest ); // default
The value used by GL.Clear() commands can be set through:
GL.ClearDepth( double ); // 1.0 is the default, Range: [0.0 .. 1.0]
If DepthTest is enabled, writing to the Depth buffer can be toggled by a boolean flag.
GL.DepthMask( bool ); // true is the default
GL.DepthFunc
The command GL.DepthFunc( func ) is used to specify the comparison method
used whether a fragment is closer to the eye than the existing pixel it is compared to.
Function of the test can have the following values, the default is DepthFunction.Less.
DepthFunction.Always - Test will always succeed.
DepthFunction.Never - Test will never succeed.
DepthFunction.Less - Test will succeed if ( fragment depth < pixel depth )
DepthFunction.Lequal - Test will succeed if ( fragment depth <= pixel depth )
DepthFunction.Equal - Test will succeed if ( fragment depth == pixel depth )
DepthFunction.Notequal - Test will succeed if ( fragment depth != pixel depth
)
DepthFunction.Gequal - Test will succeed if ( fragment depth >= pixel depth )
DepthFunction.Greater - Test will succeed if ( fragment depth > pixel depth )
GL.DepthRange
The command GL.DepthRange( near, far ) is used to define the minimum (near
plane) and maximum (far plane) z-value that is stored in the Depth Buffer. Both
parameters are expected to be of double-precision floating-point and must lie within
the range [0.0 .. 1.0].
It is allowed to call GL.DepthRange( 1.0, 0.0 ), there is no rule that must satisfy (
near < far ).
For an in-depth explanation how the distribution of z-values in the Depth buffer
works, please read Depth buffer - The gritty details.
State Queries
To determine whether DepthTest is enabled or disabled, use Result =
GL.IsEnabled( EnableCap.DepthTest );
The bits available in the Stencil Buffer can be queried by GL.GetInteger(
GetPName.DepthBits, ... );
The value set by GL.ClearDepth() can be queried by GL.GetFloat(
GetPName.DepthClearValue, ... );
The boolean set by GL.DepthMask() can be queried by GL.GetBoolean(
GetPName.DepthWritemask, ... );
The Depth comparison function can be queried with GL.GetInteger(
GetPName.DepthFunc, ... );
The Depth range can be queried with GL.GetFloat( GetPName.DepthRange, ...
); // returns an array
06. Occlusion Query
Occlusion queries count the number of fragments (or samples) that pass the depth test,
which is useful to determine visibility of objects.
If an object is drawn but 0 fragments passed the depth test, it is fully occluded by
another object. In practice this means that a simplification of an object is drawn using
an occlusion query (for example: A bounding box can be the occlusion substitute for a
truck) and only if fragments of the simple object pass the depth test, the complex
object is drawn. Please read Conditional Render for a convenient solution.
Note that the simplified object does not actually have to become visible, one can set
GL.ColorMask and GL.DepthMask to false for the purpose of the occlusion query.
The only GL.Enable/Disable state associated with it is the DepthTest. If DepthTest is
disabled all fragments will automatically pass it and the occlusion test becomes
pointless.
Occlusion Query handles are generated and deleted similar to other OpenGL handles:
uint MyOcclusionQuery;
GL.GenQueries( 1, out MyOcculsionQuery );
GL.DeleteQueries( 1, ref MyOcculsionQuery );
The draw commands which contribute to the count must be enclosed with
GL.BeginQuery() and GL.EndQuery().
GL.BeginQuery( QueryTarget.SamplesPassed, MyOcculsionQuery );
// draw...
GL.EndQuery( QueryTarget.SamplesPassed );
It is very important to understand that this process is running asynchronous, by the
time the CPU is querying the result of the count the GPU might not be done counting
yet. OpenGL provides additional query commands to determine whether the occlusion
query result is available, but before it is confirmed to be available any query of the
count is not reliable. The following code will get a reliable result.
uint ResultReady=0;
while ( ResultReady == 0 )
{
GL.GetQueryObject( MyOcculsionQuery,
GetQueryObjectParam.QueryResultAvailable, out ResultReady );
}
uint MyOcclusionQueryResult=0;
GL.GetQueryObject( MyOcculsionQuery, GetQueryObjectParam.QueryResult,
out MyOcclusionQueryResult );
// MyOcclusionQueryResult is now reliable.
However this is not very efficient to use because the CPU will spin in a loop until the
GPU is done counting.
A better approach is to do the occlusion queries in the first frame and do not wait for a
result. Instead continue drawing as normal and wait for the next frame, before you
check the results of the query. In other words frame n executes the query and frame n
+ 1 reads back the results.
This approach hides the latency inherent in occlusion queries and improves
performance, at the cost of slight visual glitches (an object may become visible one
frame later than it should). You can read a very detailed description of this technique
on Chapter 29 of GPU Gems 1, which also covers other caveats of occlusion queries.
Conditional Render
The Extension NV_conditional_render adds a major improvement to occlusion
queries: it allows a simple if ( SamplesPassed > 0 ) conditional to decide
whether an object should be drawn based on the result of an occlusion query.
This is probably best shown by a simple example, in the given scene there are 3
objects:
A huge cylinder which acts as occluder. Think of it as a pillar in the center of
the "room".
A small cube which acts as ocludee. Think of it as a box that is anywhere in
the "room" but not intersecting the pillar.
A small sphere which sits ontop of the cube. If the cube is fully occluded by
the cylinder, drawing the sphere can be skipped.
Here is some pseudo-code how the implementation looks like.
uint MyOcculsionQuery;
public void OnLoad()
{
GL.GenQueries(1, out MyOcculsionQuery);
// etc...
GL.Enable( EnableCap.DepthTest );
}
public void OnUnload()
{
GL.DeleteQueries(1, ref MyOcculsionQuery);
// etc...
}
public void OnRenderFrame()
{
// The cylinder is drawn unconditionally and used as occluder for
the Cube and Sphere
MyCylinder.Draw();
// Next, the cube is drawn unconditionally, but the samples which
passed the depth test are counted.
GL.BeginQuery( QueryTarget.SamplesPassed, MyOcculsionQuery );
MyCube.Draw();
GL.EndQuery( QueryTarget.SamplesPassed );
// depending on whether any sample passed the depth test, the
sphere is drawn.
GL.NV.BeginConditionalRender( MyOcculsionQuery,
NvConditionalRender.QueryWaitNv );
MySphere.Draw();
GL.NV.EndConditionalRender();
this.SwapBuffers();
}
Although the running program might only show a single object on screen (the
cylinder), the cube is always drawn too. Only drawing of the sphere might be skipped,
depending on the outcome of the occlusion query used for the cube.
Please note that this is not the standard case how to use occlusion query. The most
common way to use them is drawing a simple bounding volume (of a more complex
object) to determine whether samples passed and only draw the complex object itself,
if the bounding volume is not occluded. For example: Drawing a character with
skeletal animation is usually expensive, to determine whether it should be drawn at
all, a cylinder can be drawn using an occlusion query and the character is only drawn
if the cylinder is not occluded.
07. Blending
Without blending, every fragment is either rejected or written to the framebuffer. That
behaviour is desireable for opaque objects, but it does not allow rendering of
translucent objects. The correct order of operation to draw a simple scene containing a
solid table with a transparent glass ontop of it: draw the opaque table first, then enable
blending (also set the desired blend equation and factors) and finally the glass is
drawn.
Blending is an operation to mix the incoming fragment color (SourceColor) with the
color that is currently in the color buffer (DestinationColor). This happens in two
stages for each channel of the color buffer:
1. The factors used in this stage can be controlled with GL.BlendFunc()
The SourceColor is multiplied by the SourceFactor.
The DestinationColor is multiplied by the DestinationFactor.
2. The equation used in this stage can be controlled with
GL.BlendEquation()
The results of the above multiplications are then combined together to obtain
the final result.
In order to use blending, the logical color buffer must have an Alpha channel. If there
is no Alpha channel, or the color buffer uses color-index mode (8 Bit), no blending
can occur and behaviour is the same as if blending was disabled.
Blending functionality for all draw buffers is enabled and disabled with
EnableCap.Blend
GL.Enable( EnableCap.Blend );
GL.Disable( EnableCap.Blend ); // default
To enable or disable only a specific buffer if multiple color buffers are attached to the
FBO, use
GL.Enable( IndexedEnableCap.Blend, index);
GL.Disable( IndexedEnableCap.Blend, index);
Where index is used to specify the draw buffer associated with the symbolic constant
GL_DRAW_BUFFER(index).
GL.BlendEquation
The command GL.BlendEquation( mode ) specifies how the results from stage 1 are
combined with each other. If you wanted to implement this with OpenTK.Math, it
would look like this:
Color4 SourceColor, // incoming fragment
DestinationColor, // framebuffer contents
SourceFactor, DestinationFactor, // specified by
GL.BlendFunc()
FinalColor; // the resulting color
Please note that for fixed-point color buffers both Colors are clamped to [0.0 .. 1.0]
prior to computing the result. Floating-point color buffers are not clamped. Clamping
into this range is left out in this code to improve legibility.
BlendEquationMode.Min: When using this parameter, SourceFactor and
DestinationFactor are ignored.
FinalColor.Red = min( SourceColor.Red, DestinationColor.Red );
FinalColor.Green = min( SourceColor.Green, DestinationColor.Green );
FinalColor.Blue = min( SourceColor.Blue, DestinationColor.Blue );
FinalColor.Alpha = min( SourceColor.Alpha, DestinationColor.Alpha );
BlendEquationMode.Max: When using this parameter, SourceFactor and
DestinationFactor are ignored.
FinalColor.Red = max( SourceColor.Red, DestinationColor.Red );
FinalColor.Green = max( SourceColor.Green, DestinationColor.Green );
FinalColor.Blue = max( SourceColor.Blue, DestinationColor.Blue );
FinalColor.Alpha = max( SourceColor.Alpha, DestinationColor.Alpha );
BlendEquationMode.FuncAdd: This is the default.
FinalColor.Red = SourceColor.Red*SourceFactor.Red +
DestinationColor.Red*DestinationFactor.Red;
FinalColor.Green = SourceColor.Green*SourceFactor.Green +
DestinationColor.Green*DestinationFactor.Green;
FinalColor.Blue = SourceColor.Blue*SourceFactor.Blue +
DestinationColor.Blue*DestinationFactor.Blue;
FinalColor.Alpha = SourceColor.Alpha*SourceFactor.Alpha +
DestinationColor.Alpha*DestinationFactor.Alpha;
BlendEquationMode.FuncSubtract:
FinalColor.Red = SourceColor.Red*SourceFactor.Red -
DestinationColor.Red*DestinationFactor.Red;
FinalColor.Green = SourceColor.Green*SourceFactor.Green -
DestinationColor.Green*DestinationFactor.Green;
FinalColor.Blue = SourceColor.Blue*SourceFactor.Blue -
DestinationColor.Blue*DestinationFactor.Blue;
FinalColor.Alpha = SourceColor.Alpha*SourceFactor.Alpha -
DestinationColor.Alpha*DestinationFactor.Alpha;
BlendEquationMode.FuncReverseSubtract:
FinalColor.Red = DestinationColor.Red*DestinationFactor.Red -
SourceColor.Red*SourceFactor.Red;
FinalColor.Green = DestinationColor.Green*DestinationFactor.Green -
SourceColor.Green*SourceFactor.Green;
FinalColor.Blue = DestinationColor.Blue*DestinationFactor.Blue -
SourceColor.Blue*SourceFactor.Blue;
FinalColor.Alpha = DestinationColor.Alpha*DestinationFactor.Alpha -
SourceColor.Alpha*SourceFactor.Alpha;
If the color buffer is using fixed-point precision, the result in FinalColor is clamped to
[0.0 .. 1.0] before it is passed to the next pipeline stage, no clamping occurs for
floating-point color buffers.
OpenGL 2.0 and later supports separate equations for the RGB components and the
Alpha component respectively. The command GL.BlendEquationSeparate(
modeRGB, modeAlpha ) accepts the same parameters as GL.BlendEquation( mode ).
GL.BlendColor
The command GL.BlendColor( R, G, B, A ) is used to specify a constant color that
can be used by GL.BlendFunc(). For the scope of this page it is used to define the
variable Color4 ConstantColor;.
GL.BlendFunc
The command GL.BlendFunc( src, dest ) is used to select the SourceFactor (src) and
DestinationFactor (dest) in the above equation. By default, SourceFactor is set to
BlendingFactorSrc.One and DestinationFactor is BlendingFactorDest.Zero, which
gives the same result as if blending were disabled.
.Zero: Color4 (0.0, 0.0, 0.0, 0.0)
.One: Color4 (1.0, 1.0, 1.0, 1.0)
.DstColor: Color4 (DestinationColor.Red, DestinationColor.Green,
DestinationColor.Blue, DestinationColor.Alpha)
.SrcColor: Color4 (SourceColor.Red, SourceColor.Green, SourceColor.Blue,
SourceColor.Alpha)
.OneMinusDstColor: Color4 (1.0-DestinationColor.Red, 1.0-
DestinationColor.Green, 1.0-DestinationColor.Blue, 1.0-
DestinationColor.Alpha)
.OneMinusSrcColor: Color4 (1.0-SourceColor.Red, 1.0-SourceColor.Green,
1.0-SourceColor.Blue, 1.0-SourceColor.Alpha)
.SrcAlpha: Color4 (SourceColor.Alpha, SourceColor.Alpha,
SourceColor.Alpha, SourceColor.Alpha)
.OneMinusSrcAlpha: Color4 (1.0-SourceColor.Alpha, 1.0-SourceColor.Alpha,
1.0-SourceColor.Alpha, 1.0-SourceColor.Alpha)
.DstAlpha: Color4 (DestinationColor.Alpha, DestinationColor.Alpha,
DestinationColor.Alpha, DestinationColor.Alpha)
.OneMinusDstAlpha: Color4 (1.0-DestinationColor.Alpha, 1.0-
DestinationColor.Alpha, 1.0-DestinationColor.Alpha, 1.0-
DestinationColor.Alpha)
.SrcAlphaSaturate: f = min( SourceColor.Alpha, 1.0-DestinationColor.Alpha
);
Color4 ( f, f, f, 1.0 )
.ConstantColor: Color4 ( ConstantColor.Red, ConstantColor.Green,
ConstantColor.Blue, ConstantColor.Alpha )
.OneMinusConstantColor: Color4 ( 1.0-ConstantColor.Red, 1.0-
ConstantColor.Green, 1.0-ConstantColor.Blue, 1.0-ConstantColor.Alpha )
.ConstantAlpha: Color4 (ConstantColor.Alpha, ConstantColor.Alpha,
ConstantColor.Alpha, ConstantColor.Alpha)
.OneMinusConstantAlpha: Color4 (1.0-ConstantColor.Alpha, 1.0-
ConstantColor.Alpha, 1.0-ConstantColor.Alpha, 1.0-ConstantColor.Alpha)
OpenTK uses the enums BlendingFactorSrc and BlendingFactorDest to narrow down
your options what is a valid parameter for src and dest. Not all parameters are valid
factors for both, SourceFactor and DestinationFactor. Please refer to the inline
documentation for details.
OpenGL 2.0 and later supports separate factors for RGB and Alpha, for source and
destination respectively. The command GL.BlendFuncSeparate( srcRGB, dstRGB,
srcAlpha, dstAlpha ) accepts the same factors as GL.BlendFunc( src, dest ).
State Queries
To determine whether blending for all draw buffers is enabled or disabled, use Result
= GL.IsEnabled( EnableCap.Blend );
To query blending state of a specific draw buffer: Result =
GL.IsEnabled(IndexedEnableCap.Blend, index);
The selected blend factors can be queried separately for source and destination by
using GL.GetInteger() with
GetPName.BlendSrc - set by GL.BlendFunc()
GetPName.BlendDst - set by GL.BlendFunc()
GetPName.BlendSrcRgb - set by GL.BlendFuncSeparate()
GetPName.BlendSrcAlpha - set by GL.BlendFuncSeparate()
GetPName.BlendDstRgb - set by GL.BlendFuncSeparate()
GetPName.BlendDstAlpha - set by GL.BlendFuncSeparate()
The selected blend equation can be queried by using GL.GetInteger() with
GetPName.BlendEquation - set by GL.BlendEquation()
GetPName.BlendEquationRgb - set by GL.BlendEquationSeparate()
GetPName.BlendEquationAlpha - set by GL.BlendEquationSeparate()
08. sRGB Conversion
This stage of the pipeline is only applied if EnableCap.FramebufferSrgb is enabled
and if the color encoding for the framebuffer attachment is sRGB (as in: not linear).
If those conditions are true, the Red, Green and Blue values after blending are
converted into the non-linear sRGB color space.
If any of those conditions is false, no conversion is applied.
The resulting values for R, G, and B, and the unmodified Alpha form a new RGBA
color value. If the color buffer is fixed-point, each component is clamped to the range
[0.0 .. 1.0] and then converted to a fixed-point value. The resulting four values are
sent to the subsequent dithering operation.
09. Dithering
Dithering is similar to halftoning in newspapers. Only a single color (black) is used in
contrast to the paper (white), but due to using patterns the appearance of many shades
of gray can be represented. In a similar way, OpenGL can dither the fragment from a
high precision color to a lower precision color. I.e. dithering is used to find one or
more representable colors to ensure the image shown on the screen is a best-match
between the capability of the monitor and the computed image.
This is always needed when working with 8 Bit color-index mode, where only 256
unique colors can be represented, but the image to be drawn is actually calculated
with higher precision. Dithering also applies when a RGBA32f color is converted to
display on the screen, which is usually RGBA8. In RGBA mode, dithering is
performed separately for Red, Green, Blue and Alpha.
Dithering is the only state that is enabled by default, the programmer has no control
over how the image is manipulated (the graphics hardware decides which algorithm is
used) besides enabling or disabling dithering with EnableCap.Dither.
GL.Enable( EnableCap.Dither ); // default
GL.Disable( EnableCap.Dither );
State Query
The state of dithering can be queried through Result = GL.IsEnabled(
EnableCap.Dither );
10. Logical Operations
Before a fragment is written to the framebuffer, a logical operation is applied which
uses the incoming fragment values as source (s) and/or those currently stored in the
color buffer as destination (d). After the selected operation is completed, destination is
overwritten. Logical operations are performed independently for each Red, Green,
Blue and Alpha value and if the framebuffer has multiple color attachments, the
logical operation is computed and applied separately for each color buffer.
If Logic Op is enabled, OpenGL behaves as if Blending is disabled regardless whether
it was previously enabled.
In order to apply the Logicial Operation, use EnableCap.ColorLogicOp
GL.Enable( EnableCap.ColorLogicOp );
GL.Disable( EnableCap.ColorLogicOp ); // default
Note: If you use EnableCap.LogicOp or EnableCap.IndexLogicOp, only indexed
color buffers (8 Bit) are affected.
To select the logical operation to be performed, use GL.LogicOp( op ); where op is
by default LogicOp.Copy.
LogicOp.Clear: 0
LogicOp.And: s & d
LogicOp.AndReverse: s & !d
LogicOp.Copy: s
LogicOp.AndInverted: !s & d
LogicOp.Noop: d
LogicOp.Xor: s XOR d
LogicOp.Or: s | d
LogicOp.Nor: !(s | d)
LogicOp.Equiv: !(s XOR d)
LogicOp.Invert: !d
LogicOp.OrReverse: s | !d
LogicOp.CopyInverted: !s
LogicOp.OrInverted: !s | d
LogicOp.Nand: !(s & d)
LogicOp.Set: all 1's
State Queries
The state of LogicOp can be queried with Result = GL.IsEnabled(
EnableCap.LogicOp );
Which operation has been set through GL.LogicOp() can be queried with
GL.GetInteger( GetPName.LogicOpMode, ... )
How to save an OpenGL rendering to
disk
You can use the following code to read back an OpenGL rendering to a
System.Drawing.Bitmap. You can then use the Save() method to save this to disk.
Hints:
Don't forget to call Dispose() on the returned Bitmap once you are done with
it. Otherwise, you will run out of memory rapidly. If you wish to save a video,
rather than a single screenshot, consider modifying this method to reuse the
same Bitmap.
Call GrabScreenshot() from your main rendering thread, i.e. the thread
which contains your GraphicsContext.
Make sure you have bound the correct framebuffer object before calling
GrabScreenshot().
You can improve performance significantly by removing the
bmp.RotateFlip() call and saving the resulting image as a BMP rather than a
PNG file. This is especially important if you wish to record a video - it is the
difference between a real-time recording and a slideshow.
This code can record 720p/30Hz video relatively easily, given suitable
hardware and a little optimization (as outlined above). There are many
programs that can encode a stream of consecutive BMP files into a high
definition video.
using System;
using System.Drawing;
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;
static class GraphicsHelpers
{
// Returns a System.Drawing.Bitmap with the contents of the
current framebuffer
public static Bitmap GrabScreenshot()
{
if (GraphicsContext.CurrentContext == null)
throw new GraphicsContextMissingException();
Bitmap bmp = new Bitmap(this.ClientSize.Width,
this.ClientSize.Height);
System.Drawing.Imaging.BitmapData data =
bmp.LockBits(this.ClientRectangle,
System.Drawing.Imaging.ImageLockMode.WriteOnly,
System.Drawing.Imaging.PixelFormat.Format24bppRgb);
GL.ReadPixels(0, 0, this.ClientSize.Width,
this.ClientSize.Height, PixelFormat.Bgr, PixelType.UnsignedByte,
data.Scan0);
bmp.UnlockBits(data);
bmp.RotateFlip(RotateFlipType.RotateNoneFlipY);
return bmp;
}
}
How to render text using OpenGL
The simplest way to render text with OpenGL is to use System.Drawing. This
approach has three steps:
1. Use Graphics.DrawString() to render text to a Bitmap.
2. Upload the Bitmap to an OpenGL texture.
3. Render the OpenGL texture as a fullscreen quad.
This approach is extremely efficient for text that changes infrequently, because only
step 3 has to be performed every frame. Additionally, dynamic text can be reasonably
efficient as long as care is taken to update only regions that are actually modified.
The downside of this approach is that (a) rendering is constrained by the capabilities
of System.Drawing (i.e. poor support for complex scripts) and (b) it only supports 2d
text. Moreover, care should be taken to recreate the Bitmap and OpenGL texture
whenever the parent window changes size.
Sample code:
using System.Drawing;
using OpenTK.Graphics.OpenGL;
Bitmap text_bmp;
int text_texture;
window.OnLoad += (sender, e) =>
{
// Create Bitmap and OpenGL texture
text_bmp = new Bitmap(ClientSize.Width, ClientSize.Height); //
match window size
text_texture = GL.GenTexture();
GL.BindTexture(text_texture);
GL.TexParameter(TextureTarget.Texture2D,
TextureParameterName.TextureMagFilter, (int)All.Linear);
GL.TexParameter(TextureTarget.Texture2D,
TextureParameterName.TextureMinFilter, (int)All.Linear);
GL.TexImage2D(TextureTarget.Texture2D, 0,
PixelInternalFormat.Rgba, text_bmp.Width, text_bmp.Height, 0,
PixelFormat.Bgra, PixelType.UnsignedByte, IntPtr.Zero); //
just allocate memory, so we can update efficiently using
TexSubImage2D
};
window.Resize += (sender, e) =>
{
// Ensure Bitmap and texture match window size
text_bmp.Dispose();
text_bmp = new Bitmap(ClientSize.Width, ClientSize.Height);
GL.BindTexture(text_texture);
GL.TexSubImage2D(TextureTarget.Texture2D, 0, 0, 0,
text_bmp.Width, text_bmp.Height,
PixelFormat.Bgra, PixelType.UnsignedByte, IntPtr.Zero);
};
// Render text using System.Drawing.
// Do this only when text changes.
using (Graphics gfx = Graphics.FromImage(text_bmp))
{
gfx.Clear(Color.Transparent);
gfx.DrawString(...); // Draw as many strings as you need
}
// Upload the Bitmap to OpenGL.
// Do this only when text changes.
BitmapData data = text_bmp.LockBits(new Rectangle(0, 0,
text_bmp.Width, text_bmp.Height), ImageLockMode.ReadOnly,
System.Drawing.Imaging.PixelFormat.Format32bppArgb);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba,
Width, Height, 0,
PixelFormat.Bgra, PixelType.UnsignedByte, data.Scan0);
text_bmp.UnlockBits(data);
// Finally, render using a quad.
// Do this every frame.
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Ortho(0, Width, Height, 0, -1, 1);
GL.Enable(EnableCap.Texture2D);
GL.Enable(EnableCap.Blend);
GL.BlendFunc(BlendingFactorSrc.One,
BlendingFactorDst.OneMinusSourceAlpha);
GL.Begin(BeginMode.Quads);
GL.TexCoord(0f, 1f); GL.Vertex2(0f, 0f);
GL.TexCoord(1f, 1f); GL.Vertex2(1f, 0f);
GL.TexCoord(1f, 0f); GL.Vertex2(1f, 1f);
GL.TexCoord(0f, 0f); GL.Vertex2(0f, 1f);
GL.End();
This method can be easily generalized to use a more powerful text rendering library,
like Pango#.
Chapter 5: OpenTK.Audio (OpenAL)
The OpenAL 1.1 Crashcourse will give an introduction how to use OpenAL in your
applications.
OpenAL contains the following classes:
AL "Audio Library"
Alc "Audio Library Context"
Alut "Audio Library Utilities"
XRam "Memory Extension"
Efx "Effects Extension"
OpenAL 1.0 Extensions that were included into 1.1: Multi-Channel Buffer playback
Extension, Audio Capture Extension, Enumeration Extension.
It is recommended using these book pages as a starting point, and visit the online
resources from the OpenAL website's documentation page for in-depth information.
Downloading the OpenAL SDK is not required, but will provide you with some .wav
files to toy around with and a few .pdf files not available directly at the OpenAL site.
Regarding compatibility, the "Generic Software" and "Generic Hardware"
implementations of the OpenAL driver support OpenAL 1.1 and a few EFX
Extensions, namely the Reverb Effect and Lowpass Filter. If the used Device cannot
handle EAX natively, the driver will attempt to emulate the missing features.
Note that some functions of the OpenAL API are not imported for safety reasons.
Rather use .Net's Thread.Sleep than Alut.Sleep, and Alut.CreateBuffer* instead of
Alut.LoadMemory*. If this is a Problem, please voice it in the forum.
1. Devices, Buffers and X-Ram
OpenTK.Audio.AudioContext handles Device and Context allocation through Alc.
Instantiating a new AudioContext with a parameterless constructor will initialize the
default Device and Context and makes it current. Calling the instance's Dispose
method will destroy the Device and Context.
Buffers
Buffers in OpenAL are merely the storage for audio data in raw format, a Buffer
Name (often called Handle) must be generated using AL.GenBuffers(). This buffer
can now be filled using AL.BufferData() or using the AudioReader class (which loads
a file from disk). The AudioReader functions implicitly use AL.BufferData() to pass
the raw sound data into OpenAL's internal memory.
X-Ram
The X-Ram Extension allows to manually assign Buffers a storage space, it's use is
optional and not required. To use the Extension, the XRam wrapper must be
instantiated (per used Device), which will take care of most ugly things with
Extensions for you. The instantiated object contains a bool that returns if the
Extension is usable, which should be checked before calling one of the Extension's
Methods.
Example code:
try
{
AudioContext AC = new AudioContext();
} catch( AudioException e)
{ // problem with Device or Context, cannot continue
Application.Exit();
}
XRam = new XRamExtension( ); // must be instantiated per used Device
if X-Ram is desired.
// reserve 2 Handles
uint[] MyBuffers = new uint[2];
AL.GenBuffers( 2, out MyBuffers );
// Load a .wav file from disk
if ( XRam.IsInitialized ) XRam.SetBufferMode( ref MyBuffer[0],
XRamStorage.Hardware ); // optional
AudioReader sound = new AudioReader(filename)
AL.BufferData(MyBuffers[0], sound.ReadToEnd());
if ( AL.GetError() != ALError.NoError )
{
// respond to load error etc.
}
// Create a sinus waveform through parameters, this currently
requires Alut.dll in the application directory
if ( XRam.IsInitialized ) XRam.SetBufferMode( ref MyBuffer[1],
XRamStorage.Hardware ); // optional
MyBuffers[1] = Alut.CreateBufferWaveform(AlutWaveform.Sine, 500f,
42f, 1.5f);
// See next book page how to connect the buffers to sources in order
to play them.
// Cleanup on application shutdown
AL.DeleteBuffers( 2, ref MyBuffers ); // free previously reserved
Handles
AC.Dispose();
A description of the sound data in the Buffer can be queried using AL.GetBuffer().
Now that the Buffer Handle has been assigned a sound, we need to attach it to a
Source for playback.
2. Sources and EFX
Sources
Sources represent the parameters how a Buffer Object is played back. These
parameters include the Source's Position, Velocity, Gain (Volume amplification) and
more. The settings can be set/get by using AL.Source and AL.GetSource functions.
Continuation of the sourcecode from previous page:
uint[] MySources = new uint[2];
AL.GenSources( 2, out MySources ); // gen 2 Source Handles
AL.Source( TestSources[0], ALSourcei.Buffer, (int)MyBuffers[0] ); //
attach the buffer to a source
AL.SourcePlay( MySources[0]); // start playback
AL.Source( MySources[0], ALSourceb.Looping, true ); // source loops
infinitely
AL.Source( MySources[1], ALSourcei.Buffer, (int)MyBuffers[1] );
Vector3 Position = new Vector3( 1f, 2f, 3f );
AL.Source( MySources[1], ALSource3f.Position, ref Position );
AL.Source( MySources[1], ALSourcef.Gain, 0.85f );
AL.SourcePlay( MySources[1] );
Console.ReadLine(); // wait for keystroke before exiting
AL.SourceStop( MySources[0] ); // halt playback
AL.SourceStop( MySources[1] );
AL.DeleteSources( 2, ref MySources ); // free Handles
// now delete Buffer Objects and dispose the AudioContext
EFX
I'm sorry to do this, but if you want to work with EFX there is no other way. All I can
give here is a brief overview that might help you make the decision if EFX is what
you need. You will have to download the OpenAL SDK to get a copy of "Effects
Extension Guide.pdf" from Creative labs, for in-depth information about
programming with DSPs.
My advice is ignoring EFX, unless your game project is in 1st Person 3D.
Environmental effects might look nice as a "selling point" on paper, but do not add
any gameplay value to a Strategy game, or a 2D platform game.
The addition to OpenAL with EFX Extension is the rerouting of output signals.
In vanilla OpenAL you load a Buffer, attach it to a Source and besides the
Source's parameters that's all the influence you have about what ends up in the
mixer.
With EFX you may reroute a source's output through Filters and/or into
Auxiliary Effect Slots. This allows more fine control about how a Source
sounds when played, which is useful to achieve the effect of obstruction,
occlusion or exclusion of a sound due to environment features like walls,
obstacles or doors.
The new OpenAL Objects that come with EFX are "Effect", "Auxiliary Effect Slot"
and "Filter".
An Effect Object stores the type of effect and the values for parameters of that effect.
Types of Effects are for example Echo, Distortion, Chorus, Flanger, etc.
Auxiliary Effect Slots are containers for Effect Objects, whose output goes directly
into the final output mix. The Slots are only used if there is a valid Effect Object
attached to them, binding the reserved Handle 0 to a Slot will detach the previously
bound Effect Object from it.
A Filter can be attached to a source, and either filter the "dry signal" that goes
directly into the output mixer, or filter the "wet signal" that is forwarded to an
Auxiliary Effect Slot.
3. Context and Listener
Like in OpenGL, a Context can be understood as an instance of OpenAL State. You
can create multiple Contexts per Device, but each Context has the restriction of 1
Listener it's own unique Sources. Buffer Objects on the other hand may be shared by
Contexts, which use the same Device.
Note that in contrast to OpenGL, OpenAL does not have an equivalent to
SwapBuffers(). A Sources are automatically played until the end of their attached
Buffer is reached, or until the programmer manually stops the Source playback.
Listener
The Listener represents the position and orientation of the Camera in the environment,
thus there can be only one per Context. The settings can be set/get by using
AL.Source and AL.GetSource functions.
It makes sense to handle it together with your OpenGL camera, to make sure a Source
is properly positioned. This is very similar to OpenGL's Projection Matrix, with the
exception that there is no Frustum culling for audio (you may not see something
behind you, but you can hear it).
A sample Camera, taken from the OpenAL manual:
void PlaceCamera(Vector3 ListenerPosition, float listenerAngle)
{
// prepare some calculations
float Sinus = (float)Math.Sin(listenerAngle);
float Cosinus = (float)Math.Cos(listenerAngle);
Vector3 ListenerTarget = new Vector3(ListenerPosition.X + Sinus,
ListenerPosition.Y, ListenerPosition.Z - Cosinus);
Vector3 ListenerDirection = new Vector3(Sinus, 0, Cosinus);
// update OpenGL - camera position
GL.MatrixMode(MatrixMode.Projection);
GL.LoadIdentity();
GL.Frustum(-0.1333, 0.1333, -0.1, 0.1, 0.2, 50.0);
Glu.LookAt(ListenerPosition, ListenerTarget, Vector3.UnitY);
// update OpenAL - place listener at camera
AL.Listener(ALListener3f.Position, ref ListenerPosition);
AL.Listener(ALListenerfv.Orientation, ref ListenerDirection, ref
Vector3.UnitY);
}
Chapter 6: OpenTK.Compute
(OpenCL)
[Describe the OpenTK.Compute namespace]
Chapter 7: OpenTK.Input
[Discuss the input classes provided by OpenTK]
Chapter 8: Advanced Topics
This chapter discusses advanced topics on the interaction of .Net/Mono, OpenGL and
OpenAL. It builds on the previous two chapters and a good grasp of C#, OpenGL and
OpenAL is assumed.
Vertex Cache Optimizations
Graphic cards usually have 2 Caches designed to help processing Vertices, one of
their favorite tasks.
Pre T&L Cache
This Cache merely stores the untransformed Vertex read from a VBO. Optimizations
regarding this part of the Cache are simply sorting your Vertices in order of
appearance, so the IBO issues Triangles in this order (0,1,2,0,2,3) rather then
(999,17,2044,999,2044,2). This Cache is typically extremely large, being able to hold
~64k Vertices on a Geforce 3 and up.
Post T&L Cache
The more valuable Cache is the one storing the transformed results from the Vertex
Shader, this Cache is typically very small (8 is minimum, 12-24 common) holding
only very few Entries. It will only work with indexed primitives passed to
GL.DrawElements, because GL.DrawArrays cannot make any assumptions which
Vertices are actually identical.
While Pre-T&L Cache optimization only operates on the Vertices, Post T&L
optimization will only operate on Indices (Primitives). Typically the Post T&L is
calculated first, and the Pre T&L sorting step is performed on the optimized Indices
Array.
Links for further reading
http://ati.amd.com/developer/i3d2006/I3D2006-Sander-TOO.pdf
http://www.cs.princeton.edu/gfx/pubs/Sander_2007_%3ETR/index.php
http://www.cs.umd.edu/Honors/reports/Vertex_Reordering_for_Cache_Coheren...
http://home.comcast.net/~tom_forsyth/papers/fast_vert_cache_opt.html
http://ati.amd.com/developer/tootle.html
http://developer.nvidia.com/object/vertex_cache_opt.html (ancient)
http://developer.nvidia.com/object/nvtristrip_library.html
http://www.clootie.ru/delphi/dxtools.html (DirectX based detector)
Useful quotes:
truncated quote from: http://developer.nvidia.com/object/devnews005.html
"When rendering using the hardware transform-and-lighting (TnL) pipeline or vertex-
shaders, the GPU intermittently caches transformed and lit vertices. Storing these
post-transform and lighting (post-TnL) vertices avoids recomputing the same values
whenever a vertex is shared between multiple triangles and thus saves time. The post-
TnL cache increases rendering performance by up to 2x. ...
...The post-TnL cache is a strict First-In-First-Out buffer, and varies in size from
effectively 10 (actual 16) vertices on GeForce 256, GeForce 2, and GeForce 4 MX
chipsets to effectively 18 (actual 24) on GeForce 3 and GeForce 4 Ti chipsets. Non-
indexed draw-calls cannot take advantage of the cache, as it is then impossible for the
GPU to know which vertices are shared. ...
...The mesh needs to be submitted in a single draw-call to optimize batch-size. The
draw-call must be with an indexed primitive-type (see above), either strips or lists --
the performance difference between strips and lists is negligible when taking
advantage of the post-TnL cache."
Last Update of the Links: January 2008
Garbage Collection Performance
The .Net Framework features an aggressive, generational and compacting Garbage
Collector (GC): aggressive because it knows the location and reachability of every
managed object, generational because it distinguishes long-lived objects objects from
temporary ones, and compacting because it moves data in memory to avoid leaving
holes behind. The GC is a great tool in the .Net arsenal, not only because it increases
productivity but also because it provides extremely fast memory allocations
(compared to standard C/C++ malloc/new).
[Describe the unmanaged resource pool, pinning and performance considerations]
GC & OpenGL (work in progress)
As discussed in the previous chapter, GC finalization occurs on the finalizer thread.
This poses some problems on OpenGL resource deallocation, since the context used
to create the resources is not available in the finalizer thread!
Since OpenGL functions cannot be called in finalizers, a different methodology must
be followed. By implementing the disposable pattern, we can use the Dispose()
method to deterministaclly destroy OpenGL resources in the main thread. By
modifying the finalizer logic we can provide a way to flag resources as 'dead', and
destroy them from the main thread. Last, by extending the concept of the OpenGL
context, we can be notified of context destruction, to release all related resources.
The following code describes the implementation of the "OpenGL disposable pattern"
in OpenTK, but it is easy to adapt this code to any managed OpenGL project:
// This code is out-of-date. Please do not use it!
// The OpenGL disposable pattern
class GraphicsResource: IDisposable
{
int resource_handle; // The OpenGL handle to the resource
GraphicsContext context; // The context which owns this
resource
public GraphicsResource()
{
// Obtain the current OpenGL context, and allocate the
resource
context = GraphicsContext.CurrentContext;
if (context == null)
throw new InvalidOperationException(String.Format(
"No OpenGL context available in thread {0}.",
System.Threading.Thread.CurrentThread.ManagedThreadId));
resource_handle = [...];
context.Destroy += ContextDisposed;
}
#region --- Disposable Pattern ---
private void ContextDisposed(IGraphicsContext sender, EventArgs
e)
{
context.Destroy -= ContextDisposed;
// TODO: Shared resources shouldn't be destroyed here.
Dispose();
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
// If the owning context is current then destroy the resource,
// otherwise flag it (so it will be destroyed from the correct
thread)..
// TODO: Is the "manual" flag necessary? Simply checking for the
// owning context should be enough.
private void Dispose(bool manual)
{
if (!disposed)
{
if (!context.IsCurrent || !manual)
{
GC.KeepAlive(this);
context.RegisterForDisposal(this);
}
else
{
// Destroy resource_handle through OpenGL
disposed = true;
}
}
}
~GraphicsResource()
{
Dispose(false);
}
#endregion
}
In OpenTK, each GraphicsContext class maintains a queue of OpenGL resources that
need to be destroyed. Resources are added to this queue through the
RegisterForDisposal() call, and they are destroyed through the DisposeResources()
method. The whole process is deterministic: it is your responsibility to call
DisposeResources at appropriate time intervals (or setup up a timer event to do this
for you).
Resource creation takes a small performance hit due to the call to
GraphicsContext.CurrentContext, while garbage collect-able OpenGL resources
consume slightly more memory (due to the reference to the GraphicsContext). Prefer
calling the Dispose() method to destroy resources instead of relying on the GC, as
finalizable resources are only collected on a generation 1 or 2 GC sweep.
The current implementation in OpenTK does not take shared contexts into account -
this will be taken care of in the near future.
Chapter 9: Hacking OpenTK
This chapter contains instructions for people wishing to modify or extend OpenTK. It
describes the project structure, wrapper design, coding style and various caveats and
hacks employed by OpenTK to achieve wider platform support.
Project Structure
The OpenTK project consists of a number of managed, cross-platform assemblies:
OpenTK: this is the core OpenTK assembly. It provides the Graphics, Audio
and Compute APIs, the math toolkit and the platform abstraction layer.
OpenTK.Compatibility: this assembly provides an upgrade path for
applications compiled against older versions of OpenTK and the Tao
Framework. When a deprecated method is removed from core OpenTK, it is
added to this dll.
OpenTK.GLControl: this assembly provides the GLControl class, which adds
OpenGL support to System.Windows.Forms applications.
OpenTK.Build: this assembly provides the cross-platform build system for
OpenTK. It can be used to generate MSBuild-compatible project files for use
with Visual Studio (version 2005 or higher), Sharpdevelop (version 2.0 or
higher) and MonoDevelop (version 2.0 or higher).
OpenTK.Examples: this assembly provides a number of samples built with
OpenTK. It covers topics related to OpenGL, OpenGL|ES, OpenAL, OpenCL
and general OpenTK usage.
In addition to these assemblies, OpenTK maintains a custom binding generator which
generates the OpenGL, OpenGL|ES and OpenCL bindings. It consists of two
assemblies:
Converter, which converts the OpenGL|ES and OpenCL C headers to XML
files.
Bind, which converts the OpenGL .spec files or the Converter XML files into
C# code.
Finally, OpenTK provides a QuickStart project, which shows how to setup and build
an OpenTK application.
OpenTK Structure
The OpenTK solution provides the following public namespaces:
OpenTK: contains classes to create windows (GameWindow, NativeWindow),
perform 3d math, interact with the monitor (DisplayDevice,
DisplayResolution) as well as query the platform configuration.
OpenTK.Graphics: contains bindings for OpenGL and OpenGL|ES.
OpenTK.Audio: contains bindings for OpenAL.
OpenTK.Compute: contains bindings for OpenCL.
OpenTK.Input: contains classes to interact with input devices (Keyboard,
Mouse, Joystick).
OpenTK.Platform: contains classes to extend OpenTK or interact with the
underlying platform.
The public API of OpenTK is completely cross-platform. All platform-specific code
is contained in internal interfaces under the OpenTK.Platform namespace. In that
sense, most public classes act as façades that forward method calls to the correct
platform-specific implementation.
public class Foo : IFoo
{
IFoo implementation;
public Foo()
{
implementation = OpenTK.Platform.Factory.Default.CreateFoo();
}
#region IFoo Members
public void Bar()
{
implementation.Bar();
}
#endregion
}
This pattern is used in all public OpenTK classes that need platform-specific code to
operate: DisplayDevice, DisplayResolution, GraphicsContext, GraphicsMode,
NativeWindow and the various input classes.
Classes that do not rely on platform-specific code and classes that contain
performance-sensitive code do not use this pattern: the various math classes, the
OpenGL, OpenCL and OpenAL bindings, the AudioContext and AudioCapture
classes all fall into these categories.
Wrapper Design
OpenTK provides .Net wrappers for a various important native APIs: OpenGL,
OpenGL ES, OpenAL and OpenCL (in progress). Unlike similar libraries, OpenTK
places an emphasis in usability and developer efficiency, while staying true to the
nature of the native interface. To that end, it utilizes a number of .Net constructs that
are not available in native C by default:
Strongly-typed enum parameters instead of integer constants.
Generics instead of void pointers.
Namespaces instead of function prefixes ('gl', 'al').
Function overloads instead of function suffices (Vector3 instead of
Vector3f>, Vector3d, ...).
Automatic extension loading.
Inline documentation for functions and parameters, accessible through IDE
tooltips (intellisense).
CLS-compliance, which makes the bindings usable by all .Net languages.
Cross-platform support, which allows the bindings to be used by any platform
supported by .Net or Mono.
The bindings are generated through an automated binding generator, which converts
the official API specifications into C# code. The following pages describe the
generation process in detail.
Official API specifications:
OpenGL: http://www.opengl.org/registry
OpenGL ES: http://www.khronos.org/registry/gles/
OpenAL:
http://connect.creativelabs.com/openal/Downloads/Forms/AllItems.aspx
OpenCL: http://www.khronos.org/registry/cl/
Appendix 1: Frequently asked questions
[General Questions]
1. What is the Open Toolkit exactly?
The Open Toolkit is a C# library that:
1. allows .Net programs to access OpenGL, OpenAL and OpenCL
2. abstracts away the platform-specific code for window creation, input
devices, and
3. provides helper functions (math, fonts, etc)
As such, is roughly analogous to SlimDX, SDL or GLFW.
2. Is OpenTK limited to games?
No! OpenTK can be - and has been - used in scientific visualizations, VR,
modeling/CAD software and other projects.
3. What is the difference between OpenTK and the Tao framework?
The Tao framework tries to follow the unmanaged APIs as closely as possible.
OpenTK, on the other hand, takes advantage of .Net features like function
overloading, strong-typing and generics. Consider the following code snippet:
4. // OpenTK.Graphics code:
5. GL.Begin(BeginMode.Points);
6. GL.Color3(Color.Yellow);
7. GL.Vertex3(Vector3.Up);
GL.End();
// Tao.OpenGl code:
Gl.glBegin(Gl.GL_POINTS);
Gl.glColor3ub(255, 255, 0);
Gl.glVertex3f(0, 1, 0);
Gl.glEnd();
The code is trivial, but it illustrates the difference nicely: OpenTK removes
unecessary cruft ('gl', 'ub', 'f'), uses strongly-typed enums ('BeginMode') and
integrates better with .Net ('Color').
There are other differences not so readily apparent: OpenTK will not allow
you to pass invalid data to OpenGL (wrong tokens or non-valuetype data); it
plays better with intellisense (inline documentation, overloads, strong-types);
it checks for OpenGL errors automatically in debug builds.
All these become more important as a project grows in size.
8. Will my Tao project run on OpenTK?
Starting with version 0.9.9-2, OpenTK is compatible with Tao.OpenGl,
Tao.OpenAl and Tao.Platform.Windows.SimpleOpenGlControl. Simply
replace your Tao.OpenGl, Tao.OpenAl and Tao.Platform.Windows references
with OpenTK and OpenTK.Compatibility and your project will as before,
while gaining advantage of all OpenTK features.
9. OpenGL is not object-oriented. Does OpenTK change that?
No, the Open Toolkit mirrors the raw OpenGL API. This was a conscious
design decision, to avoid introducing artificial limitations. However, users
have contributed object-oriented libraries built on top of OpenTK - check out
the project database.
10. I care about speed. Is OpenTK slow?
No, OpenTK introduces minimal overhead over raw OpenGL. However, do
note that the underlying runtimes (.Net/Mono) introduce some unique
performance considerations - refer to our documentation for more information.
Performance is always a concern, so please report an issue if you believe
something could run faster.
11. Which platforms does OpenTK run on?
OpenTK is primarily tested on Windows, Linux and Mac OS X, but is also
known to work on Solaris and *BSD variants. All features work across
platform without recompilation.
A lighter version is also made available for the iPhone through the
MonoTouch project (recompilation required). There is no official support for
Windows Mobile or Android at this point.
12. Is OpenTK safe to use? How mature is it?
OpenTK is considered safe for general use. It is being used successfully by
both free and commercial projects and the library is under active development,
with regular bugfix and feature releases.
[Windows.Forms & GLControl Questions]
1. How can I make my Form fullscreen?
Use the following code snippet:
2. myForm.TopMost = true;
3. myForm.FormBorderStyle = FormBorderStyle.None;
myForm.WindowState = FormWindowState.Maximized;
4. My GLControl.Load event isn't fired.
Please upgrade to OpenTK 0.9.9-4 or newer.
5. How do I use stencil, antialiasing or OpenGL 3.x with GLControl?
Create a custom control that inherits from GLControl:
6. class CustomGLControl : GLControl
7. {
8. // 32bpp color, 24bpp z-depth, 8bpp stencil and 4x
antialiasing
9. // OpenGL version is major=3, minor=0
10. public CustomGLControl()
11. : base(new GraphicsMode(32, 24, 8, 4), 3, 0,
GraphicsContextFlags.ForwardCompatible)
12. { }
}
[Graphics questions]
1. How can I save a screenshot?
Refer to the "How to save an OpenGL rendering to disk" section in the
documentation.
Appendix 2: Function Reference
You can read the function reference online. A PDF version of this reference is
included with your OpenTK distribution, under the Documentation/ folder.
Appendix 3: The project database
The project database is an index of projects related to the Open Toolkit. Every project
in the database receives a unique project page and gains access to the issue tracker
and the project release service.
All registered users may submit their own projects, subject to the following
restrictions:
1. Your project must use, extend or be somehow related to the Open Toolkit
library.
2. Your project must be released under an OSI approved license.
Closed-source and / or commercial projects will be reviewed by the Open Toolkit
team and approved on a case by case basis.
By submitting a project to the database, you acknowledge that:
1. This is a free service provided to the Open Toolkit community that comes
without any warranty. In case there is any doubt, the OpenT Toolkit team does
not offer you any warranty, express or implied, for the behavior of the project
database, nor fitness of purpose towards any application. Keep backups!
2. The Open Toolkit team maintains the right to remove any project from the
database or terminate the whole database, for whatever reason, without prior
notice.
Creating a project
Only registered users are allowed to create projects. To create a project, click on
Create content -> Project and complete the required information:
1. In the "project categories" section, click "Contributed" and select all relevant
categories.
o You can use the control key to select multiple categories.
o If your project is closed-source or commercial, you must select the
relevant categories.
o Please do not use the "Core" category. It is reserved for the Open
Toolkit.
2. In the "full project name" field, type a descriptive name for your project (e.g.
The Open Toolkit library).
3. In the "full description" field, describe what your project is, what it does and
any other information you deem relevant (e.g. requirements, features).
4. In the "short project name" field, type a compact name for your project.
This will be used in the URL of the project page and the issue tracker (e.g.
project/opentk). Do not use spaces or any other special characters.
5. Upload screenshots for your project. This step is very important, as users tend
to avoid projects without or with low quality screenshots. If your screenshots
display 3d graphics, you can improve their quality by enabling antialiasing
and anisotropic filtering.
6. Don't forget to add a link to the homepage of the project (if any), its source
code repository and license!
Creating a project release
Once you have created a project, you can create a project release by clicking on
Create content -> Project release.
The first step is to select your project from the drop-down list. Click next to proceed
to the actual release page:
1. Choose which OpenTK version your project targets. For example, if your
project uses relies on OpenTK 0.9.5, you should choose 0.9.x here. If your
project targets OpenTK 1.0 (not yet released at the time of writing), you
should choose 1.0.x. This information is important, as it indicates whether
different projects can be used together. Please note that OpenTK is backwards
compatible, which means you should choose the lowest OpenTK version that
can support your project.
2. Fill in the release version. This should match the actual version in your
project properties (you can view this information in Visual Studio by right-
clicking your project, selecting properties and then "assembly information".
Likewise for SharpDevelop and MonoDevelop). You can optionally add an
exta identifier to convey more information (typical identifiers include "beta",
"rc", "final" and "wip").
3. Fill in the "body" textbox with your release notes.
4. Optionally, you can upload your release to opentk.com using the file field.
Please consult with us before uploading releases bigger than 20MB! If
your release is very large, consider using a torrent for distribution.
You can also redirect the downloads to an external resource (e.g. your own
homepage or sourceforge), by using a html redirect. Copy the following code
to a file named [project name]-[release number].html (e.g. opentk-0.9.5.html),
edit the necessary links and upload it through the "file" field:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Redirecting to download.</title>
<meta http-equiv="REFRESH"
content="0;url=http://www.example.com" />
</head>
<body>Redirecting to the <a
href="http://www.example.com">download page</a>.</body>
</html>
Appendix 4: Links
The following pages contain links selated to game development, graphics and audio
programming in general.
Models and Textures
File Formats don't matter. Please do not add commercial 3D model sites, unless they
offer a huge collection of free models aswell.
Textures
http://www.imageafter.com/textures.php
http://www.cgtextures.com/
http://developer.nvidia.com/object/IO_TTVol_01.html
http://www.freefoto.com/browse/33-00-0?ffid=33-00-0
http://www.noctua-graphics.de/english/freetex_e.htm
http://www.grsites.com/textures/
http://www.absolutecross.com/graphics/textures/
http://www.m3corp.com/a/download/3d_textures/pages/index.htm
http://studio.planethalflife.gamespy.com/textures.asp
http://local.wasp.uwa.edu.au/~pbourke/texture_colour/index.html
Models
http://www.highend3d.com/downloads/
Sites that have both
http://telias.free.fr/
http://www.psionic3d.co.uk
Tools
Generates Explosion Sprite sheets http://www.geocities.com/starlinesinc/
Procedural Materials http://www.spiralgraphics.biz/viewer/
Reference Images, Concept Art and the likes
http://www.prideout.net/colors.php
http://www.3d.sk/
http://www.fineart.sk/
Disclaimer: Some links lead directly to download sections of websites in order to be
convenient for the reader. The Copyright and license details vary between the
websites, if you follow one of the links above it is your own responsibility to read and
acknowledge the websites terms of use. The authors of this link collection take no
liability for any misuse or copyright violation by the readers.
OpenGL Books and Tutorials
OpenGL related Books
The 'red book' (start here when in doubt) http://www.glprogramming.com/red/
OpenGL Programming Guide for Mac OS X
http://developer.apple.com/documentation/GraphicsImaging/Conceptual/Open...
Programming with OpenGL: Advanced Rendering
http://www.opengl.org/resources/code/samples/advanced/
GPU Gems 1 http://developer.nvidia.com/object/gpu_gems_home.html
GPU Gems 2 http://developer.nvidia.com/object/gpu_gems_2_home.html
GPU Gems 3 http://http.developer.nvidia.com/GPUGems3/gpugems3_pref01.html
OpenGL related Tutorials
Transforms & Drawing http://www.codecolony.de/
Step by Step, from a Triangle to more complex scenes http://nehe.gamedev.net/
Lots of Extension-related Examples http://www.codesampler.com/oglsrc.htm
Misc. advanced Tutorials http://www.opengl.org/sdk/docs/tutorials/Lighthouse3D/
GLSL related Tutorials
Compilation, Linking & State
http://www.opengl.org/sdk/docs/tutorials/ClockworkCoders/
Material & Lighting http://www.typhoonlabs.com/
Articles, Demos & Research Papers
Old Website, Forum is a goldmine http://www.gamedev.net/
Misc. advanced Demos /w Source http://www.humus.name
Voxel & Raytracing http://www.codermind.com/articles/Technical-articles.html
Programming links
MSDN Library, and especially its .Net subsection is an essential programming
resource.
Rico Mariani's Performance Tidbits provide invaluable information on .Net
optimization techniques.
Gamedev contains game news and articles on game development.
OpenGL SDK is an one stop resource for OpenGL related questions.
OpenGL registry contains specifications for all OpenGL functions. For
advanced developers.
Tools & Utilities
Blender is an excellent 3d modeller and editor.
NShader adds GLSL syntax highlighting to Visual Studio 2008.
glView is an excellent utility that shows the extensions supported on your
platform. Available for Windows and Mac OS platforms.
GLIntercept is a free and open-source OpenGL function call interceptor.
Windows only.
The Tao Framework is a collection of .Net/Mono bindings to libraries like
OpenAL, DevIL, ODE and more.
NBidi is a .Net Implementation of the BIDI algorithm for complex Hebrew
and Arabic RTL scripts.
AgateLib is a cross-platform 2d OpenGL library with an OpenTK driver.
Golem3D is a cross-platform model editor that uses OpenTK.
Tutorials
External tutorials
Lighthouse3D (High quality tutorials on GLSL, shadows, math and more)
NeHe OpenGL tutorials (wide range of topics, from simple to advanced.
Written as annotated code)
Clockwork Coders (GLSL)
Code Colony (Camera, Vertex Arrays)
Appendix 5: Translations
The Open Toolkit manual is available in the following languages:
Deutsch
Ελληνικά
Russian

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