sampler2D Image : register(s0);

// The Laplace filter approximates the second order derivate,
// that is, the rate of change of slope in the image. It can be
// used for edge detection. The Laplace filter gives negative
// response on the higher side of the edge and positive response
// on the lower side.

// This is the filter kernel:
// 0  1  0
// 1 -4  1
// 0  1  0



float4 Laplace_ps ( float4 pos : POSITION,
      float2 texCoord: TEXCOORD0,
			uniform float scale,
			uniform float pixelSize) : COLOR
{

    float2 samples[4] = {
        0, -1,
       -1,  0,
        1,  0,
        0,  1
    };
   float4 laplace = -4 * tex2D(Image, texCoord);

   // Sample the neighbor pixels
   for (int i = 0; i < 4; i++){
      laplace += tex2D(Image, texCoord + pixelSize * samples[i]);
   }

   return (0.5 + scale * laplace);
}