in OpenGL vertex shaders, what is w, and why do I divide by it?

Posted by anon on Stack Overflow See other posts from Stack Overflow or by anon
Published on 2010-03-11T05:29:23Z Indexed on 2010/03/11 5:33 UTC
Read the original article Hit count: 319

Filed under:

opengl

|

vertex-shader

void main(void)
{
  vec4 clipCoord = glModelViewProjectionmatrix * gl_Vertex;
  gl_Position = clipCoord;

  gl_FrontColor = gl_Color;

    vec3 ndc = clipCoord.xyz / clipCoord.w;

So the clipCoord is just doing standard fixed pipeline ransforms. Now, the ndc ... why do I divide by w, and what do I get from this?

© Stack Overflow or respective owner

Related posts about opengl

Unity completely broken after upgrade to 12.10?

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I am facing a very frustrating issue with my computer right now. I successfully upgraded to Ubuntu 12.10 this afternoon, but after the upgrade, the graphical user interface seems completely broken. To be more specific, I can not get the Unity bar to appear on the right. I have tried many things,… >>> More
OpenGL or OpenGL ES

as seen on Game Development - Search for 'Game Development'
What should I learn? OpenGL 4.1 or OpenGL ES 2.0? I will be developing desktop applications using Qt but I may start developing mobile applications in a few months, too. I don't know anything about 3D, 3D math, etc and I'd rather spend 100 bucks in a good book than 1 week digging websites and going… >>> More
OpenGL extension vs OpenGL core

as seen on Programmers - Search for 'Programmers'
I was doubting: I'm writing a cross-platform engine OpenGL C++, I figured out windows forces the developers to access OpenGL features above 1.1 through extensions. Now the thing is, on Linux, I know that I can directly access functions if the version supports it through glext.h and opengl version… >>> More
OpenGL ES 2/3 vs OpenGL 3 (and 4)

as seen on Game Development - Search for 'Game Development'
I have migrated my code from OpenGL ES 2/3 to OpenGL 3 (I added bunch of defines and abstract classes to encapsulate both versions, so I have both in one project and compile only one or another). All I need to change was context initialization and glClearDepth. I dont have any errors. This was kind… >>> More
LWJGL - Eclipse error [on hold]

as seen on Game Development - Search for 'Game Development'
When I try to run my lwjgl project, an error pops . Here is the log file: # A fatal error has been detected by the Java Runtime Environment: # EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x6d8fcc0a, pid=5612, tid=900 # JRE version: 6.0_16-b01 Java VM: Java HotSpot(TM) Client VM (14.2-b01 mixed… >>> More

Related posts about vertex-shader

change the color of a vertex in a vertex shader

as seen on Stack Overflow - Search for 'Stack Overflow'
Is it possible to set the color of a single vertex using a GLSL vertex shader program, in the same way that gl_Position changes the position of a vertex ? >>> More
set the color of a vertex using a GLSL vertex shader

as seen on Stack Overflow - Search for 'Stack Overflow'
Is it possible to set the color of a single vertex (not a face) using a GLSL vertex shader program (using GL_ARB_shading_language_100 extension) ? >>> More
Compute bounding quad of a sphere with vertex shader

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to implement an algorithm from a graphics paper and part of the algorithm is rendering spheres of known radius to a buffer. They say that they render the spheres by computing the location and size in a vertex shader and then doing appropriate shading in a fragment shader. Any guesses… >>> More
My vertex shader doesn't affect texture coords or diffuse info but works for position

as seen on Game Development - Search for 'Game Development'
I am new to 3D and DirectX - in the past I have only used abstractions for 2D drawing. Over the past month I've been studying really hard and I'm trying to modify and adapt some of the shaders as part of my personal 'study project'. Below I have a shader, modified from one of the Microsoft samples… >>> More
In OpenGL vertex shader, gl_Position doesn't get homogenized..

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi everyone, I was expecting gl_Position to automatically get homogenized (divided by w), but it seems not working.. Why do the followings make different results? 1) void main() { vec4 p; ... omitted ... gl_Position = projectionMatrix * p; } 2) ... same as above ... p = projectionMatrix… >>> More