source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/sky_preetham.cg @ 3041

struct vtxin
{
        float4 position: POSITION;
        float3 normal: NORMAL;
        float3 color: COLOR;
        float2 texcoord: TEXCOORD0;
};


// vtx output
struct vtxout
{
        float4 color: COLOR0;  
        float4 position: POSITION; 

        float4 texCoord: TEXCOORD0;    
        float3 normal: TEXCOORD1;
        float4 hdrColor: TEXCOORD2;
};


// fragment input
struct fragin
{
        float4 color: COLOR0;  
        //float4 projPos: WPOS;
        //float4 position: POSITION;

        float4 texCoord: TEXCOORD0;    
        float3 normal: TEXCOORD1;
        float4 hdrColor: TEXCOORD2;
};


struct pixel
{
        float4 col: COLOR0;
        float3 norm: COLOR1;
        float3 pos: COLOR2;
};



//--------------------------------------------------------------------------------------
// Vertex Shaders
//--------------------------------------------------------------------------------------


vtxout default_vs(vtxin IN,
                                  uniform float3 lightDir,
                                  uniform float2 thetaSun,
                                  uniform float3 zenithColor,
                                  uniform float3 aColor,
                                  uniform float3 bColor,
                                  uniform float3 cColor,
                                  uniform float3 dColor,
                                  uniform float3 eColor,
                                  uniform float multiplier)
{
        vtxout OUT;

        OUT.position = mul(glstate.matrix.mvp, IN.position);

        const float dotLN = dot(lightDir, IN.normal);   
        const float cos2gamma = dotLN * dotLN; 

        const float gamma = acos(dotLN);    
        const float theta = dot(float3(.0f, .0f, 1.0f), IN.normal);

    float3 num = (1.0f + aColor * exp(bColor / theta)) * (1.0f + cColor * exp(dColor * gamma) + eColor * cos2gamma);    
        float3 den = (1.0f + aColor * exp(bColor)) * (1.0f + cColor * exp(dColor * thetaSun.x) + eColor * thetaSun.y);   
    float3 xyY = (num / den) * zenithColor;    
    
    float3 XYZ;                                                                                             
                                                                                                            
    XYZ.x = (xyY.x / xyY.y) * xyY.z;                                                                        
        XYZ.y = xyY.z;                                                                                          
        XYZ.z = ((1.0f - xyY.x - xyY.y) / xyY.y) * xyY.z;   
        
    const static float3x3 conv_Mat = 
                float3x3( 3.240479f, -1.537150f, -0.498535f,
                         -0.969256f,  1.875992f,  0.041556f,
                              0.055648f, -0.204043f,  1.057311f);

        float3 hcol = mul(conv_Mat, XYZ);
        OUT.color = float4(hcol, 1.0f);

        OUT.color.rgb *= multiplier;
        /// put out color into different color channel to avoid clamping
        OUT.hdrColor  = OUT.color;

        OUT.normal = IN.normal;

        return OUT;
}


pixel frag_skydome(fragin IN)
{
        pixel pix;

        pix.col = IN.hdrColor;
        pix.col.w = 1e20f;
        pix.norm = IN.normal;
        
        return pix;
}