vec3 circle(in vec2 _st, in float _radius, vec3 color){
    vec2 dist = _st-vec2(0.5);
    return color-smoothstep(_radius-(_radius*0.02),
                         _radius+(_radius*0.02),
                         dot(dist,dist)*4.0);
}

// Inspired by (but modified)
// http://thndl.com/square-shaped-shaders.html
#define TAU 6.28318530718
vec3 polygon(int n, float size, vec2 pos, vec3 color, float rot) {
  float e = 0.01;
  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  st.x *= u_resolution.x/u_resolution.y;
  st = (st-pos)*2.;
  float a = atan(st.x,st.y)+rot;
  float r = TAU/float(n);

  float d = cos(floor(.5+a/r)*r-a)*length(st);

  return color-smoothstep(size-e,size+e,d);
}