Dither Bayer.fs

Code

uniform sampler2D inputImage;
uniform float colorize;
uniform int matrixMode;
precision mediump float;
/*{
    "CATEGORIES": [
        "Halftone Effect",
        "Retro"
    ],
    "CREDIT": "Hugh Kennedy, adapted by David Lublin",
    "DESCRIPTION": "Bayer style dithering",
    "INPUTS": [
        {
            "NAME": "inputImage",
            "TYPE": "image"
        },
        {
            "DEFAULT": 0,
            "MAX": 1,
            "MIN": 0,
            "NAME": "colorize",
            "TYPE": "float"
        },
        {
            "DEFAULT": 2,
            "LABELS": [
                "2x2",
                "4x4",
                "8x8"
            ],
            "NAME": "matrixMode",
            "TYPE": "long",
            "VALUES": [
                0,
                1,
                2
            ]
        }
    ],
    "ISFVSN": "2"
}
*/



//	based on https://github.com/hughsk/glsl-dither

float luma(vec3 color)	{
	return (color.r + color.g + color.b) / 3.0;	
}

float luma(vec4 color)	{
	return color.a * (color.r + color.g + color.b) / 3.0;	
}

float dither8x8(vec2 position, float brightness) {
  int x = int(mod(position.x, 8.0));
  int y = int(mod(position.y, 8.0));
  int index = x + y * 8;
  float limit = 0.0;

  if (x < 8) {
    if (index == 0) limit = 0.015625;
    if (index == 1) limit = 0.515625;
    if (index == 2) limit = 0.140625;
    if (index == 3) limit = 0.640625;
    if (index == 4) limit = 0.046875;
    if (index == 5) limit = 0.546875;
    if (index == 6) limit = 0.171875;
    if (index == 7) limit = 0.671875;
    if (index == 8) limit = 0.765625;
    if (index == 9) limit = 0.265625;
    if (index == 10) limit = 0.890625;
    if (index == 11) limit = 0.390625;
    if (index == 12) limit = 0.796875;
    if (index == 13) limit = 0.296875;
    if (index == 14) limit = 0.921875;
    if (index == 15) limit = 0.421875;
    if (index == 16) limit = 0.203125;
    if (index == 17) limit = 0.703125;
    if (index == 18) limit = 0.078125;
    if (index == 19) limit = 0.578125;
    if (index == 20) limit = 0.234375;
    if (index == 21) limit = 0.734375;
    if (index == 22) limit = 0.109375;
    if (index == 23) limit = 0.609375;
    if (index == 24) limit = 0.953125;
    if (index == 25) limit = 0.453125;
    if (index == 26) limit = 0.828125;
    if (index == 27) limit = 0.328125;
    if (index == 28) limit = 0.984375;
    if (index == 29) limit = 0.484375;
    if (index == 30) limit = 0.859375;
    if (index == 31) limit = 0.359375;
    if (index == 32) limit = 0.0625;
    if (index == 33) limit = 0.5625;
    if (index == 34) limit = 0.1875;
    if (index == 35) limit = 0.6875;
    if (index == 36) limit = 0.03125;
    if (index == 37) limit = 0.53125;
    if (index == 38) limit = 0.15625;
    if (index == 39) limit = 0.65625;
    if (index == 40) limit = 0.8125;
    if (index == 41) limit = 0.3125;
    if (index == 42) limit = 0.9375;
    if (index == 43) limit = 0.4375;
    if (index == 44) limit = 0.78125;
    if (index == 45) limit = 0.28125;
    if (index == 46) limit = 0.90625;
    if (index == 47) limit = 0.40625;
    if (index == 48) limit = 0.25;
    if (index == 49) limit = 0.75;
    if (index == 50) limit = 0.125;
    if (index == 51) limit = 0.625;
    if (index == 52) limit = 0.21875;
    if (index == 53) limit = 0.71875;
    if (index == 54) limit = 0.09375;
    if (index == 55) limit = 0.59375;
    if (index == 56) limit = 1.0;
    if (index == 57) limit = 0.5;
    if (index == 58) limit = 0.875;
    if (index == 59) limit = 0.375;
    if (index == 60) limit = 0.96875;
    if (index == 61) limit = 0.46875;
    if (index == 62) limit = 0.84375;
    if (index == 63) limit = 0.34375;
  }

  return brightness < limit ? 0.0 : 1.0;
}

vec3 dither8x8(vec2 position, vec3 color) {
  return color * dither8x8(position, luma(color));
}

vec4 dither8x8(vec2 position, vec4 color) {
  return vec4(color.rgb * dither8x8(position, luma(color)), 1.0);
}

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);
}

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);
}


void main()	{
	vec4		inputPixelColor = vec4(0.0);
	vec2		loc = gl_FragCoord.xy;
	//	both of these are the same
	inputPixelColor = IMG_THIS_PIXEL(inputImage);
	
	float		val = 1.0;
	
	if (matrixMode == 0)	{
		val = dither2x2(loc, luma(inputPixelColor));
	}
	else if (matrixMode == 1)	{
		val = dither4x4(loc, luma(inputPixelColor));
	}
	else if (matrixMode == 2)	{
		val = dither8x8(loc, luma(inputPixelColor));
	}
	
	inputPixelColor = inputPixelColor * vec4(val,val,val,1.0);

	gl_FragColor = mix(vec4(val,val,val,inputPixelColor.a),inputPixelColor,colorize);
}