#pragma glslify: luma = require(glsl-luma)

float dither2x2(vec2 position, float brightness) {
  int x = int(mod(position.x, 2.0));
  int y = int(mod(position.y, 2.0));
  int index = x + y * 2;
  float limit = 0.0;

  if (x < 8) {
    if (index == 0) limit = 0.25;
    if (index == 1) limit = 0.75;
    if (index == 2) limit = 1.00;
    if (index == 3) limit = 0.50;
  }

  return brightness < limit ? 0.0 : 1.0;
}

vec3 dither2x2(vec2 position, vec3 color) {
  return color * dither2x2(position, luma(color));
}

vec4 dither2x2(vec2 position, vec4 color) {
  return vec4(color.rgb * dither2x2(position, luma(color)), 1.0);
}

#pragma glslify: export(dither2x2)