2017-2018/ISN/P5js/exemple/sketch.js

function setup() {
  createCanvas(640, 480);
  var white = 0;
  var blakck = 255;
}

function draw() {
  if (mouseIsPressed) {
    fill(white);
  } else {
    fill(black);
  }
  ellipse(mouseX, mouseY, 80, 80);
}