円形に切り取られた空

/**
 * sky ball
 * 
 * @author aadebdeb
 * @date 2017/02/23
 */

var canvas;

function setup() {
  canvas = createCanvas(500, 500);
  
}

function draw() {
  background(255);
  noStroke();
  fill(0, 130, 200);
  ellipse(width / 2, height / 2, width, height);
  var img = new p5.Image(width, height, canvas);
  var mask = new p5.Image(width, height);
  mask.loadPixels();
  for (var x = 0; x < mask.width; x++) {
    for (var y = 0; y < mask.height; y++) {
      mask.set(x, y, color(255, noise(x * 0.01 + frameCount * 0.01, y * 0.04 + frameCount * 0.03, frameCount * 0.1) * 255));
    }
  }
  mask.updatePixels();
  image(mask, 0, 0);
}