source: code/trunk/Tutorial/Media/DeferredShadingMedia/DeferredShading/post/glsl/LightMaterial_vs.glsl @ 44

/******************************************************************************
Copyright (c) W.J. van der Laan

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this software  and associated documentation files (the "Software"), to deal in 
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The above copyright notice and this permission notice shall be included in all copies 
or substantial portions of the Software.

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******************************************************************************/
/** Deferred shading framework
        // W.J. :wumpus: van der Laan 2005 //
        
        Post shader: Light geometry material
*/
varying vec2 texCoord;
varying vec3 projCoord;

uniform float vpWidth;
uniform float vpHeight;
uniform mat4 invProj;

void main()                    
{
   vec4 projPos = gl_ModelViewProjectionMatrix * gl_Vertex;
   projPos = projPos/projPos.w;
   
   // projPos is now in nonhomogeneous 2d space -- this makes sure no perspective interpolation is
   // done that could mess with our concept.
   //gl_Position = projPos;
   vec2 texSize = vec2(vpWidth, vpHeight);
   vec2 tcTemp = vec2(projPos[0], projPos[1])/2.0+0.5;
   tcTemp = (floor(tcTemp * texSize)+0.5)/texSize;
   
   //float3 position = mul(invProj, float4(projCoord, 0, 1))*distance; 
   // Acquire view space position via inverse projection transformation
   // Optimisation for perspective, symmetric view frustrums 
   // These interpolate over the frustrum plane for w=1
   
   projCoord = vec3(projPos[0], projPos[1], 1)*vec3(
                invProj[0][0], // X vector component from X
                invProj[1][1], // Y vector component from Y
                invProj[3][2]  // Z vector component from W
   );
   
   //projCoord = vec3(invProj*vec4(projPos[0], projPos[1], 0, 1));
   
   // Texture coordinate magic, this compensates for jitter
   texCoord = vec2(tcTemp[0], 1.0-tcTemp[1]);   
   gl_Position = vec4((tcTemp-0.5)*2.0, 0.0, 1.0);
}