let y = 200;

let extraCanvas;

​

function setup() {

  createCanvas(400, 400);

  extraCanvas = createGraphics(400, 400);

  extraCanvas.clear();

  background(0);

}

​

function draw() {

  // No trails!

  background(0);

  x += random(-10, 10);

  y += random(-10, 10);

  if(x < 0 || x > width) x = 200;

  if(y < 0 || y > height) y = 200;

  // trails

  if (mouseIsPressed) {

    extraCanvas.fill(255, 150);

    extraCanvas.noStroke();

    extraCanvas.ellipse(mouseX, mouseY, 60, 60);

  }

  image(extraCanvas, 0, 0);

  fill(255, 0, 220);

  stroke(255, 200, 200);

  strokeWeight(2);

  rectMode(CENTER);

  rect(min(max(0,x), width), min(max(0,y), width), 20, 20);

​

}