gistfile1.h

float sample_delta(sampler src, float x, float y) {
  return 1.0 - sample(src, samplerCoord(src) + vec2(x, y)).r;
}

float fun_a(float p2, float p3, float p4, float p5, float p6, float p7, float p8, float p9) {
  float b1 = step(0.5, p3 - p2);
  float b2 = step(0.5, p4 - p3);
  float b3 = step(0.5, p5 - p4);
  float b4 = step(0.5, p6 - p5);
  float b5 = step(0.5, p7 - p6);
  float b6 = step(0.5, p8 - p7);
  float b7 = step(0.5, p9 - p8);
  float b8 = step(0.5, p2 - p9);
  
  return b1 + b2 + b3 + b4 + b5 + b6 + b7 + b8;
}

float fun_b(float p2, float p3, float p4, float p5, float p6, float p7, float p8, float p9) {
  return p2 + p3 + p4 + p5 + p6 + p7 + p8 + p9;
}

kernel vec4 thinEffectStepOne(sampler src) {
  float p2 = sample_delta(src, 0.0, 1.0);
  float p3 = sample_delta(src, 1.0, 1.0);
  float p4 = sample_delta(src, 1.0, 0.0);
  float p5 = sample_delta(src, 1.0, -1.0);
  float p6 = sample_delta(src, 0.0, -1.0);
  float p7 = sample_delta(src, -1.0, -1.0);
  float p8 = sample_delta(src, -1.0, 0.0);
  float p9 = sample_delta(src, -1.0, 1.0);
  
  // COMMON
  float c1 = 1.0 - step(2.5, abs(fun_b(p2, p3, p4, p5, p6, p7, p8, p9) - 4.0));
  float c2 = 1.0 - step(0.5, abs(fun_a(p2, p3, p4, p5, p6, p7, p8, p9) - 1.0));

  // FIRST
  float c1_3 = 1.0 - p2 * p4 * p6;
  float c1_4 = 1.0 - p4 * p6 * p8;
  
  // SECOND
  // float c2_3 = 1.0 - p2 * p4 * p8;
  // float c2_4 = 1.0 - p2 * p6 * p8;
  
  float color = sample_delta(src, 0.0, 0.0);
  
  // RESULT
  float result = 1.0 - color * (1.0 - c1 * c2 * c1_3 * c1_4);
  // float result = 1.0 - color * (1.0 - c1 * c2 * c2_3 * c2_4);
  
  return vec4(result, result, result, 1.0);
}

kernel vec4 thinEffectStepTwo(sampler src) {
  float p2 = sample_delta(src, 0.0, 1.0);
  float p3 = sample_delta(src, 1.0, 1.0);
  float p4 = sample_delta(src, 1.0, 0.0);
  float p5 = sample_delta(src, 1.0, -1.0);
  float p6 = sample_delta(src, 0.0, -1.0);
  float p7 = sample_delta(src, -1.0, -1.0);
  float p8 = sample_delta(src, -1.0, 0.0);
  float p9 = sample_delta(src, -1.0, 1.0);
  
  // COMMON
  float c1 = 1.0 - step(2.5, abs(fun_b(p2, p3, p4, p5, p6, p7, p8, p9) - 4.0));
  float c2 = 1.0 - step(0.5, abs(fun_a(p2, p3, p4, p5, p6, p7, p8, p9) - 1.0));

  // FIRST
  // float c1_3 = 1.0 - p2 * p4 * p6;
  // float c1_4 = 1.0 - p4 * p6 * p8;
  
  // SECOND
  float c2_3 = 1.0 - p2 * p4 * p8;
  float c2_4 = 1.0 - p2 * p6 * p8;
  
  float color = sample_delta(src, 0.0, 0.0);
  
  // RESULT
  // float result = 1.0 - color * (1.0 - c1 * c2 * c1_3 * c1_4);
  float result = 1.0 - color * (1.0 - c1 * c2 * c2_3 * c2_4);
  
  return vec4(result, result, result, 1.0);
}