source: GTP/trunk/App/Demos/Illum/Ogre/Media/materials/programs/GameTools_ReduceCubeMap.hlsl @ 1519

int CUBEMAP_SIZE = 128;
int RATE = 32;
int nFace;

float4 readCubeMap(samplerCUBE cm, float3 coord)                
{
        float4 color = texCUBE( cm, float3(coord.xy, coord.z) );
        return color;
}


struct VS_INPUT {           // vertex shader input
    float4 Position : POSITION;
};

struct VS_OUTPUT {          // vertex shader output, pixel shader input
    float4 hPosition : POSITION;
    float2 Position  : TEXCOORD0;
};

VS_OUTPUT ReduceTextureVS(VS_INPUT IN) {
        VS_OUTPUT OUT;
    OUT.hPosition = IN.Position;
    OUT.Position = IN.Position.xy;
    //OUT.Position.y = 1 - OUT.Position.y;
    return OUT;
}

float4 ReduceTexturePS(VS_OUTPUT IN,
                                                uniform samplerCUBE EnvironmentMapSampler : register(s0) ) : COLOR
{  
        RATE = 32;
        CUBEMAP_SIZE = 128;
    float4 color = 0;
    // color += texCUBE( EnvironmentMapSampler, Tex );
    float3 dir;
  
   for (int i = 0; i < RATE; i++)
     for (int j = 0; j < RATE; j++)
    {
                float2 pos;
                pos.x = IN.Position.x + (2*i + 1)/(float)CUBEMAP_SIZE;
                pos.y = IN.Position.y - (2*j + 1)/(float)CUBEMAP_SIZE;  // y=-u

                // "scrambling"
                if (nFace == 0) dir = float3(1, pos.y, -pos.x);
                if (nFace == 1) dir = float3(-1, pos.y, pos.x);
                if (nFace == 2) dir = float3(pos.x, 1, -pos.y);
                if (nFace == 3) dir = float3(pos.x, -1, pos.y);
                if (nFace == 4) dir = float3(pos.x, pos.y, 1);
                if (nFace == 5) dir = float3(-pos.x, pos.y,-1);

                color += texCUBE( EnvironmentMapSampler, dir);
    }
  /*  
    if (nFace == 0)     dir = float3(1, 0, 0);
        if (nFace == 1) dir = float3(-1, 0, 0);
        if (nFace == 2) dir = float3(0, 1, 0);
        if (nFace == 3) dir = float3(0, -1, 0);
        if (nFace == 4) dir = float3(0, 0, 1);
        if (nFace == 5) dir = float3(0, 0,-1);
                
    return texCUBE(EnvironmentMapSampler, dir);*/
    //return float4(IN.Position.xy,1,1);
        return color / (RATE*RATE);     
        
}