precision mediump float;

uniform sampler2D u_texture;

varying float v_lighting;
varying vec2 v_texcoord;

float dither8x8(vec2 position, float alpha) {
  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 alpha < limit ? 0.0 : 1.0;
}

/*
const float ditherThreshold[64] = float[64](
  0.015625, 0.51562, 0.14062, 0.64062, 0.04687, 0.54687, 0.17187, 0.67187,
  0.76562, 0.26562, 0.89062, 0.39062, 0.79687, 0.29687, 0.92187, 0.42187,
  0.20312, 0.70312, 0.07812, 0.57812, 0.23437,  0.73437, 0.10937, 0.60937,
  0.95312, 0.45312, 0.82812, 0.32812, 0.98437, 0.48437, 0.85937, 0.35937,
  0.0625, 0.5625, 0.1875, 0.6875, 0.03125, 0.53125, 0.15625, 0.65625,
  0.8125, 0.3125, 0.9375, 0.4375, 0.78125, 0.28125, 0.90625, 0.40625,
  0.25, 0.75, 0.125, 0.625, 0.21875, 0.71875, 0.09375, 0.59375,
  1.0, 0.5, 0.875, 0.375, 0.96875, 0.46875, 0.84375, 0.34375
);
*/

void main() {
  vec2 tex = vec2(v_texcoord.x, 1.0 - v_texcoord.y);
  vec4 diffuse = texture2D(u_texture, tex).rgba;

  float alpha = dither8x8(gl_FragCoord.xy, diffuse.a);
  if (alpha < 0.5)
  {
    discard;
  }

  gl_FragColor = vec4(diffuse.rgb * v_lighting, 1.0);
}