void setup(){
    size(200, 200);
    background(0);
    smooth();
  
    // create a simple table of gradients
    int columns = 4;
    int radius = (width/columns)/2;
    // create some gradients
    for (int i=radius; i< width; i+=radius*2){
      for (int j =radius; j< height; j+=radius*2){
        createGradient(i, j, radius, 
        color(int(random(255)), int(random(255)), int(random(255))), 
        color(int(random(255)), int(random(255)), int(random(255))));
      }
    }
  }
  
  void createGradient (float x, float y, float radius, color c1, color c2){
    float px = 0, py = 0, angle = 0;
  
    // calculate differences between color components 
    float deltaR = red(c2)-red(c1);
    float deltaG = green(c2)-green(c1);
    float deltaB = blue(c2)-blue(c1);
    // hack to ensure there are no holes in gradient
    // needs to be increased, as radius increases
    float gapFiller = 8.0;
  
    for (int i=0; i< radius; i++){
      for (float j=0; j<360; j+=1.0/gapFiller){
        px = x+cos(radians(angle))*i;
        py = y+sin(radians(angle))*i;
        angle+=1.0/gapFiller;
        color c = color(
        (red(c1)+(i)*(deltaR/radius)),
        (green(c1)+(i)*(deltaG/radius)),
        (blue(c1)+(i)*(deltaB/radius)) 
          );
        set(int(px), int(py), c);      
      }
    }
    // adds smooth edge 
    // hack anti-aliasing
    noFill();
    strokeWeight(3);
    ellipse(x, y, radius*2, radius*2);
  }