In OpenGL vertex shader, gl_Position doesn't get homogenized..

Posted by KJ on Stack Overflow See other posts from Stack Overflow or by KJ
Published on 2010-04-17T00:55:24Z Indexed on 2010/04/17 1:03 UTC
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opengl

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glsl

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3d

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graphics

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 * p; gl_Position = p / p.w;

I think the two are supposed to generate the same results, but it seems it's not the case. 1 doesn't work while 2 is working as expected.. Could it possibly be a precision problem? Am I missing something? This is driving me almost crazy.. helps needed. Many thanks in advance!

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