​

function setup() {

  createCanvas(400, 400);

  background(220);

  btnRed = createButton('red');

  btnRed.position(0, 0);

  // btnRed.mousePressed();

}

​

function clearScreen() {

  fill(255);

  circle(350, 350, 50);

  if (mouseIsPressed && mouseX>=325 && mouseX<=375 && mouseY>=325 && mouseY<=375) {

    background(220);

  }

}

​

function draw() {

  fill(0);

  circle(mouseX, mouseY, 10);

  clearScreen();

}