sample-groupGore/data/media/shaders/threshold.glsl

extern number threshold;

vec4 effect(vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords) {
  vec4 result = Texel(texture, texture_coords);
  float luminance = dot(result.rgb, vec3(.2125, .7154, .0721));
  float val = clamp(luminance - threshold, 0, 1) / (1 - threshold);
  result = vec4(val);

  return vec4(result.rgb * color.rgb, result.a);
}