arc.js

function setup() {
  createCanvas(720, 400);
}

function draw() {
  background(random(128, 255), random(128, 255), random(128, 255));
  noStroke(0);
  for (var i = 0; i < 100; i++) {
    var x1 = random(0, width);
    var y1 = random(0, height);
    var x2 = random(0, width);
    var y2 = random(0, height);
    fill(random(0, 255), random(0, 255), random(0, 255), random(20, 120));
    arc(x1, y1, x2, y2, PI / 2, PI);
  }
  frameRate(1);
}