source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/ssao.cg @ 2809

struct fragment
{
    float4 pos: WPOS; // normalized screen position
    float4 view: COLOR;
    float4 texcoord: TEXCOORD0;      
    float4 lindepth: TEXCOORD1;
};


struct pixel
{
    float4 col: COLOR0;
};


float3 reflect(float3 pt, float3 n)
{
  // distance to plane
  float d = dot(n, pt);
  // reflect around plane
  float3 rpt = pt - d * 2.0f * n;
  
  //return pt;
  return rpt;
}


pixel main(fragment IN, 
           uniform sampler2D lindepth,
           uniform sampler2D scene,
           uniform sampler2D normal,
           uniform float invTexSize,
           uniform float radius,
           uniform float3 eyevec,
           uniform float3 samples[32])
{
    pixel OUT;
 
    // eye space z
    float eyez = tex2D(lindepth, IN.texcoord.xy).x;

    float3 viewvec = IN.view.xyz * 2.0f - float3(1.0f);
    viewvec /= viewvec.z;

    //return float4(viewvec.xyz, 1.0f);
    // eye point
    //float3 eyept = eyez * viewvec;
    float3 eyept = float3(IN.texcoord.xy, eyez);

    float4 pl = tex2D(normal, IN.pos.xy * invTexSize);
    pl = pl * 2.0 - float4(1.0);

    float occlusion = 0.0;

    // gather occlusion from surrounding samples
    for (int i = 0; i < 32; i ++)
    {
        // generate new sample point
        //float3 samplepos = eyept + radius * samples[i];
        // create some dithering by reflecting the sample point alond some random plane
        float3 samplepos = eyept + radius * reflect(samples[i], pl.xyz);

        // project to texture space q: why the scaling?
        float2 sampletex = (samplepos.xy / samplepos.z);// * float2(0.75, 1.0);
        
        //float2 sampletexn = sampletex;
        // normalize to [0 .. 1], move eye point to center
        //float2 sampletexn = sampletex * 0.5f + float2(0.5f);
        float2 sampletexn = sampletex + float2(0.5f);

        // look up depth at sample point
        float depth = tex2D(lindepth, sampletexn).x;
        // compare: is point occluded?
        //float zdist = 50.0f * max(-samplepos.z + depth, 0.0f);
        float zdist = 50.0f * max(samplepos.z - depth, 0.0f);
        // occlusion factor shrinks quadratic with distance to occluder
        occlusion += 1.0 / (1.0 + zdist * zdist);
        //occlusion += 1.0 / (1.0 + zdist);
   }

   // normalize
   occlusion /= 32.0f;
  
   OUT.col = 1.0f - occlusion;
   //   OUT.col = tex2D(scene, IN.texcoord.xy) * 0.5 + (1.0f - occlusion);

   return OUT;
}