// Kuwahara Filter for Painting effect
  sampler2D image;
  
  float p1 = 1.0f / 512.0f;
  float p2 = 2.0f / 512.0f;
  float p0 = 0.0f;
                                     
  float4 main( float4 Pos : POSITION0,
                  float2 Tex : TEXCOORD0 ) : COLOR0
  {
     int i;
     float4 color;
     float4 mean, sum;
     float4 r[9];
     float minvar, variance;
     
     // compute the left up region
     r[0] = tex2D( image, Tex + float2( -p2, -p2 ) );
     r[1] = tex2D( image, Tex + float2( -p2, -p1 ) );
     r[2] = tex2D( image, Tex + float2( -p2, -p0 ) );
     r[3] = tex2D( image, Tex + float2( -p1, -p2 ) );
     r[4] = tex2D( image, Tex + float2( -p1, -p1 ) );
     r[5] = tex2D( image, Tex + float2( -p1, -p0 ) );
     r[6] = tex2D( image, Tex + float2( -p0, -p2 ) );
     r[7] = tex2D( image, Tex + float2( -p0, -p1 ) );
     r[8] = tex2D( image, Tex + float2( -p0, -p0 ) );  
  
     // compute the mean
     mean = 0.0f; sum = 0.0f;
     for (i = 0; i < 9; i ++) 
           mean += r[i];
      mean /= 9.0f;   
     for (i = 0; i < 9; i ++) 
           sum += (mean - r[i]) * (mean - r[i]);
      variance = dot(sum, 0.1111111f);         
     minvar = variance;
     
     // compute the right up region
     r[0] = tex2D( image, Tex + float2( p2, p2 ) );
     r[1] = tex2D( image, Tex + float2( p2, p1 ) );
     r[2] = tex2D( image, Tex + float2( p2, p0 ) );
     r[3] = tex2D( image, Tex + float2( p1, p2 ) );
     r[4] = tex2D( image, Tex + float2( p1, p1 ) );
     r[5] = tex2D( image, Tex + float2( p1, p0 ) );
     r[6] = tex2D( image, Tex + float2( p0, p2 ) );
     r[7] = tex2D( image, Tex + float2( p0, p1 ) );
     r[8] = tex2D( image, Tex + float2( p0, p0 ) );                          
  
     mean = 0.0f; sum = 0.0f;
     for (i = 0; i < 9; i ++) 
           mean += r[i];
      mean /= 9.0f;   
     for (i = 0; i < 9; i ++) 
           sum += (mean - r[i]) * (mean - r[i]);
      variance = dot(sum, 0.1111111f);         
      if (variance < minvar) {
         minvar = variance;
         color = mean;
      }
      
     // compute the left down region
     r[0] = tex2D( image, Tex + float2( -p2, p2 ) );
     r[1] = tex2D( image, Tex + float2( -p2, p1 ) );
     r[2] = tex2D( image, Tex + float2( -p2, p0 ) );
     r[3] = tex2D( image, Tex + float2( -p1, p2 ) );
     r[4] = tex2D( image, Tex + float2( -p1, p1 ) );
     r[5] = tex2D( image, Tex + float2( -p1, p0 ) );
     r[6] = tex2D( image, Tex + float2( -p0, p2 ) );
     r[7] = tex2D( image, Tex + float2( -p0, p1 ) );
     r[8] = tex2D( image, Tex + float2( -p0, p0 ) );
     
     mean = 0.0f; sum = 0.0f;
     for (i = 0; i < 9; i ++) 
           mean += r[i];
      mean /= 9.0f;   
     for (i = 0; i < 9; i ++) 
           sum += (mean - r[i]) * (mean - r[i]);
      variance = dot(sum, 0.1111111f);         
      if (variance < minvar) {
         minvar = variance;
         color = mean;
      }
  
     // compute the right down region
     r[0] = tex2D( image, Tex + float2( p2, -p2 ) );
     r[1] = tex2D( image, Tex + float2( p2, -p1 ) );
     r[2] = tex2D( image, Tex + float2( p2, -p0 ) );
     r[3] = tex2D( image, Tex + float2( p1, -p2 ) );
     r[4] = tex2D( image, Tex + float2( p1, -p1 ) );
     r[5] = tex2D( image, Tex + float2( p1, -p0 ) );
     r[6] = tex2D( image, Tex + float2( p0, -p2 ) );
     r[7] = tex2D( image, Tex + float2( p0, -p1 ) );
     r[8] = tex2D( image, Tex + float2( p0, -p0 ) );  
        
     mean = 0.0f; sum = 0.0f;
     for (i = 0; i < 9; i ++) 
           mean += r[i];
      mean /= 9.0f;   
     for (i = 0; i < 9; i ++) 
           sum += (mean - r[i]) * (mean - r[i]);
      variance = dot(sum, 0.1111111f);         
      if (variance < minvar)
         color = mean;
         
     return color;
  }