#version 150
#define SIZE 25

// A texture is expected
uniform sampler2D Texture;

// The vertex shader fill feed this input
in vec2 FragTexCoord;

// The final color
out vec4 FragmentColor;

float matr[25];
float matg[25];
float matb[25];

vec4 get_pixel(in vec2 coords, in float x, in float y) {
   return texture(Texture, coords + vec2(x, y));
}

float convolve(in float[SIZE] kernel, in float[SIZE] matrix) {
   float res = 0.0;
   for (int i = 0; i < 25; i++)
      res += kernel[i] * matrix[i];
   return clamp(res, 0.0, 1.0);
}

void fill_matrix() {
   float dxtex = 1.0 / float(textureSize(Texture, 0));
   float dytex = 1.0 / float(textureSize(Texture, 0));
   float[25] mat;
   for (int i = 0; i < 5; i++)
      for(int j = 0; j < 5; j++) {
        vec4 pixel = get_pixel(FragTexCoord,float(i - 2) * dxtex, float(j - 2) * dytex);
         matr[i * 5 + j] = pixel[0];
         matg[i * 5 + j] = pixel[1];
         matb[i * 5 + j] = pixel[2];
      }
}

void main() {

  float[SIZE] ker_edge_detection = float[SIZE] (
    .0,.0, -1., .0, .0,
    .0, .0,-1., .0, .0,
    .0, .0, 4., .0, .0,
    .0, .0, -1., .0,.0,
    .0, .0, -1., .0, .0
  );

  fill_matrix();

  FragmentColor = vec4(convolve(ker_edge_detection,matr), convolve(ker_edge_detection,matg), convolve(ker_edge_detection,matb), 1.0);
}