createCanvas(400, 400);

   slider = createSlider(-80, 80, -80);

  slider.position(10, 10);

}

​

function draw() {

  background(220);

  translate(width/2,height/2)

  val = slider.value();

  fill('yellow')

  circle(0,0,80)

  fill('white')

  circle(val,0,80)

}