#define KERNEL_SIZE 9

// Gaussian kernel
// 1 2 1
// 2 4 2
// 1 2 1
float kernel[KERNEL_SIZE];

uniform sampler2D sampler0;
uniform float width;
uniform float height;

float step_w = 1.0/width;
float step_h = 1.0/height;

vec2 offset[KERNEL_SIZE];

void main(void) {
    int i = 0;
    vec4 sum = vec4(0.0);

    offset[0] = vec2(-step_w, -step_h);
    offset[1] = vec2(0.0, -step_h);
    offset[2] = vec2(step_w, -step_h);

    offset[3] = vec2(-step_w, 0.0);
    offset[4] = vec2(0.0, 0.0);
    offset[5] = vec2(step_w, 0.0);

    offset[6] = vec2(-step_w, step_h);
    offset[7] = vec2(0.0, step_h);
    offset[8] = vec2(step_w, step_h);

   // Smooth

   kernel[0] = 1.0/16.0;    kernel[1] = 2.0/16.0;   kernel[2] = 1.0/16.0;
   kernel[3] = 2.0/16.0;    kernel[4] = 4.0/16.0;   kernel[5] = 2.0/16.0;
   kernel[6] = 1.0/16.0;    kernel[7] = 2.0/16.0;   kernel[8] = 1.0/16.0;

    // EMBOSS

/*
   kernel[0] = 2.0;     kernel[1] = 0.0;    kernel[2] = 0.0;
   kernel[3] = 1.0; kernel[4] = -1.0;   kernel[5] = 0.0;
   kernel[6] = 0.0;     kernel[7] = 0.0;    kernel[8] = -1.0;
*/


    // SHARPNESS
  /*
    kernel[0] = -1.0;   kernel[1] = -1.0;   kernel[2] = -1.0;
    kernel[3] = -1.0;   kernel[4] = 9.0;    kernel[5] = -1.0;
    kernel[6] = -1.0;       kernel[7] = -1.0;   kernel[8] = -1.0;
  */

  // Who knows?

/*
    kernel[0] = 1.0;    kernel[1] = 0.0;    kernel[2] = 1.0;
    kernel[3] = -1.0;   kernel[4] = 0.0;    kernel[5] = -1.0;
    kernel[6] = 1.0;    kernel[7] = -1.0;   kernel[8] = 1.0;
*/


    for( i = 0; i < KERNEL_SIZE; i++ ) {
        vec4 tmp = texture2D(sampler0, gl_TexCoord[0].st + offset[i]);
        sum += tmp * kernel[i];
    }

    gl_FragColor = sum;
}