Mandelbrot set plot, implemented as GLSL fragment shader

mandelbrot.frag

// shamelessly stolen from https://p5js.org/reference/#/p5/loadShader
// ported to work with https://thebookofshaders.com/edit.php
precision highp float;
const int I = 500;
void main() {
  vec2 vPos = gl_FragCoord.xy;
  vec2 p = vec2(-0.74364388703, 0.13182590421);
  float r = .00001;
  vec2 c = p + vPos * r, z = c;
  float n = 0.0;
  for (int i = I; i > 0; i --) {
    if(z.x*z.x+z.y*z.y > 4.0) {
      n = float(i)/float(I);
      break;
    }
    z = vec2(z.x*z.x-z.y*z.y, 2.0*z.x*z.y) + c;
  }
  gl_FragColor = vec4(0.5-cos(n*17.0)/2.0,0.5-cos(n*13.0)/2.0,0.5-cos(n*23.0)/2.0,1.0);
}