// title: stars

#ifdef GL_ES
precision mediump float;
#endif

#define TWO_PI 6.28318530718

uniform vec2 u_resolution;
uniform float u_time;
vec3 hsb2rgb(in vec3 c){
  vec3 rgb=clamp(abs(mod(c.x*6.+vec3(0.,4.,2.),6.)-3.)-1.,0.,1.);
  rgb=rgb*rgb*(3.-2.*rgb);
  return c.z*mix(vec3(1.),rgb,c.y);
}

void main(){
  vec2 st=gl_FragCoord.xy/u_resolution;
  vec3 color=vec3(0.);
  
  // Use polar coordinates instead of cartesian
  vec2 toCenter=vec2(.5)-st;
  float angle=atan(toCenter.y,toCenter.x);
  float radius=length(toCenter)*2.;
  
  // Map the angle (-PI to PI) to the Hue (from 0 to 1)
  // and the Saturation to the radius
  color=hsb2rgb(vec3((10000.*abs(sin(u_time/5.))*angle/TWO_PI)+.5,radius,1.));
  
  gl_FragColor=vec4(color,1.);
}