Function to create shapes with glsl

shape.frag

  float shape(vec2 p, int N, float size){
    p = p * 2. - 1.;
    
    float a = atan(p.x, p.y) + PI;
    float r = TWO_PI / float(N); 
    float l = length(p);
    
    float d = cos(floor(.5 + a / r) * r - a) * l;
    
    return step(size, d);
  }