// 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;
}