let y = 100

​

function setup() {

  createCanvas(400, 400);

}

​

function mousePressed() {

  x = mouseX;

  y = mouseY;

}

​

function draw() {

  background(220);

  // still circle

  fill('black');

  circle(200, 200, 120);

  // moving circle

  fill('blue');

  noStroke();

  circle(x, y, 120);

​

  // text

  fill('black')

  text("Click to move the blue circle to cover the black circle completely", 30, 25)

}