let n = 10;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  beginShape();

  noFill();

  for (let i=0; i<width; i++) {

    let y0 = map((1-(1-i)*(1-i)), 0, (1-(1-width)*(1-width)), 0, width);

    vertex(i, y0);

  }

  endShape();

  if (x < width) {

    x++; 

  } else {

    x = 0;

  }

  y = map((1-(1-x)*(1-x)), 0, (1-(1-width)*(1-width)), 0, width);

  ellipse(x, y, 10, 10);

  fill(255, 0, 0);

  ellipse(y, width/2, 30, 30);

}