source: GTP/trunk/App/Demos/Illum/Ogre/Media/materials/programs/GameTools_DepthShadow.hlsl @ 1131

///////depth map
struct VS_OUT
{
        float4 hPosition        : POSITION;
        float4 Position         : TEXCOORD0;    
};

VS_OUT DepthVS(float4 position : POSITION,      
                                uniform float4x4 worldViewProj)
{
  
  VS_OUT OUT;
 
  OUT.hPosition = mul(worldViewProj, position);
  OUT.Position = mul(worldViewProj, position);
  
  return OUT;
}

//for directional light
float4 DepthPS(VS_OUT IN ):COLOR
{
        float4 pos = (IN.Position / IN.Position.w);
        pos = (pos +1.0 ) / 2.0;
        return float4(pos.z, pos.z * pos.z, 1, 1);      
}

///////////////Shadow

struct VS_OUT_SHADOW
{
        float4 hPosition        : POSITION;
        float4 Position         : TEXCOORD0;
        float4 lPosition        : TEXCOORD1;
};

VS_OUT_SHADOW depthShadowVS(float4 position : POSITION, 
                                                        uniform float4x4 worldViewProj,
                                                        uniform float4x4 world,
                                                        uniform float4x4 lightViewProj)
{
  VS_OUT_SHADOW OUT;
  OUT.hPosition = mul(worldViewProj, position);
  float4 wPos = mul(world, position);
  OUT.lPosition = mul(lightViewProj, wPos);  
  OUT.Position = position;  
  return OUT;
}


float4 depthShadowPS(VS_OUT_SHADOW IN,
                                        uniform float4x4 lightViewProj,
                                        uniform sampler2D depthShadowMap : register(s0)
                                        ):COLOR
{       
        float bias = 0.1;
        float4 light = float4(1,1,1,1);
        float4 shadow = float4(0.3,0.3,0.3,1);
        
        float4 pos = (IN.lPosition / IN.lPosition.w);
        pos.xy = (pos.xy +1.0 ) / 2.0;
        pos.y = 1.0 - pos.y;
        float4 storedDepth = tex2D(depthShadowMap, pos.xy);
        
        if(storedDepth.r + bias > pos.z)
        {
                float M1 = storedDepth.r;
                float M2 = storedDepth.g;
                float v2 = M2 - M1 * M1;
                float pmax = v2 / (v2 + pow(M1 - pos.z, 2));
                light = shadow + (1 - shadow) * pmax;
                
                //light = shadow;
        }
        //return abs( pos.z - storedDepth.z );  
        return light;   
}