createCanvas(600, 600);

  background(0);

}

​

function draw() {

  noStroke();

  if (mouseIsPressed == true) {

    let circleSize = map(mouseX, 0, width, 5, 100);

    let fillColor = map(mouseY, 0, height, 0, 255);

    fill(fillColor);

    ellipse(mouseX, mouseY, circleSize);

  }

}