#version 330 core
out vec4 FragColor;

in vec2 TexCoords;

uniform sampler2D screenTexture;

const float offset = 1.0 / 300.0;

void main()
{
  vec2 offsets[9] = vec2[](
      vec2(-offset,  offset), // top-left
      vec2( 0.0f,    offset), // top-center
      vec2( offset,  offset), // top-right
      vec2(-offset,  0.0f),   // center-left
      vec2( 0.0f,    0.0f),   // center-center
      vec2( offset,  0.0f),   // center-right
      vec2(-offset, -offset), // bottom-left
      vec2( 0.0f,   -offset), // bottom-center
      vec2( offset, -offset)  // bottom-right
      );

  float kernel[9] = float[](
      1.0 / 16, 2.0 / 16, 1.0 / 16,
      2.0 / 16, 4.0 / 16, 2.0 / 16,
      1.0 / 16, 2.0 / 16, 1.0 / 16
  );

  vec3 col = vec3(0.0);

  for(int i = 0; i < 9; i++) {
    vec3 sampleTex = vec3(texture(screenTexture, TexCoords.st + offsets[i]));
    col += sampleTex * kernel[i];
  }

  FragColor = vec4(col, 1.0);
}