4x4.glsl

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

float dither4x4(vec2 position, float brightness) {
  int x = int(mod(position.x, 4.0));
  int y = int(mod(position.y, 4.0));
  int index = x + y * 4;
  float limit = 0.0;

  if (x < 8) {
    if (index == 0) limit = 0.0625;
    if (index == 1) limit = 0.5625;
    if (index == 2) limit = 0.1875;
    if (index == 3) limit = 0.6875;
    if (index == 4) limit = 0.8125;
    if (index == 5) limit = 0.3125;
    if (index == 6) limit = 0.9375;
    if (index == 7) limit = 0.4375;
    if (index == 8) limit = 0.25;
    if (index == 9) limit = 0.75;
    if (index == 10) limit = 0.125;
    if (index == 11) limit = 0.625;
    if (index == 12) limit = 1.0;
    if (index == 13) limit = 0.5;
    if (index == 14) limit = 0.875;
    if (index == 15) limit = 0.375;
  }

  return brightness < limit ? 0.0 : 1.0;
}

vec3 dither4x4(vec2 position, vec3 color) {
  return color * dither4x4(position, luma(color));
}

vec4 dither4x4(vec2 position, vec4 color) {
  return vec4(color.rgb * dither4x4(position, luma(color)), 1.0);
}

#pragma glslify: export(dither4x4)