#version 120
varying vec2 frag;
// input
uniform sampler2D texture_sampler;
uniform vec2 seed;
uniform int iteration;

void main() {
  vec2 z = frag;
  int i;
  for (i = 0; i < iteration; i++) {
    float x = (z.x * z.x - z.y * z.y) + seed.x;
    float y = (z.y * z.x + z.x * z.y) + seed.y;
    if ((x * x + y * y) > 4.0) break;
    z.x = x;
    z.y = y;
  }
  if (i == iteration) {
    discard;
  } else {
    gl_FragColor = texture2D(texture_sampler, vec2(float(i)) / 100.0, 0.25);
  }
}