createCanvas(400, 400);

  noStroke();

}

​

let x = 200;

let y = 200;

let trans = 255;

function draw() {

  background(0);

  fill(255, 255, 255, trans);

  ellipse(x, y, 20, 20);

  trans-=2;

}

​

function mousePressed() {

  x = mouseX;

  y = mouseY;

  trans = 255;

}