source: GTP/trunk/App/Demos/Illum/Ogre/Media/materials/programs/GameTools_HPS_Smoke_S.hlsl @ 1451

struct VS_OUT
{
        float4 hPosition        : POSITION;
        float4 cPosition        : TEXCOORD1;
        float2 texCoord         : TEXCOORD0;
        float r                         : TEXCOORD2;    
        float4 center           : TEXCOORD3;
        float4 Color            : TEXCOORD4;
};

VS_OUT HPS_Smoke_S_VS (float4 position : POSITION,      
                float4 texCoord : TEXCOORD0,
                float4 Color: COLOR0,
                uniform float4x4 worldView,
                uniform float4x4 Proj,
                uniform float4x4 worldViewProj)
{
        VS_OUT OUT;
  
        float2 offset = texCoord.zw;
        float4 cPosition;   
        cPosition = mul(worldView, position);
        OUT.center = cPosition; 
        cPosition.xy += offset;                         
        OUT.cPosition = cPosition;
        OUT.r = abs(texCoord.z);                
 
    OUT.hPosition = mul( Proj, cPosition );
     
    OUT.texCoord = texCoord.xy;
    OUT.Color = Color;    
        return OUT;
} 


float4 HPS_Smoke_S_PS(VS_OUT IN,
                                                uniform float4x4 Proj,
                                                uniform sampler2D Texture       ) : COLOR
{
        float4 Color = 0;
        float f = 0;
        float b = 1;
        float alpha = 0;
                
        float d = length( IN.cPosition.xy- IN.center.xy);
        
        if( d < IN.r )
        {        
         float w = sqrt( IN.r * IN.r - d * d );
         float4 fPosition = IN.cPosition;
         float4 bPosition = IN.cPosition;
         fPosition.z -= w;
         bPosition.z += w;
         fPosition = mul(Proj, fPosition);
         bPosition = mul(Proj, bPosition);
         f = fPosition.z / fPosition.w;
         b = bPosition.z / bPosition.w;
         
        // alpha = pow(w / IN.r, 4);            
        }
        else
         discard;
        
        Color.r = b;
        Color.g = 1 - f;
        
        alpha = 1;
        Color.a = alpha * IN.Color.a;
        Color.a *= tex2D(Texture, IN.texCoord).r * 0.7;
        
        
        return Color; 
}