var playbackIndex = 0; 

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(200); 

  noFill(); 

  beginShape(); 

  for (var i=0; i<points.length; i++){

    vertex(points[i].x, points[i].y); 

  }

  endShape(); 

  var px = width/2;

  var py = height/2;

  if (points.length > 0){

    px = points[playbackIndex].x

    py = points[playbackIndex].y;

    playbackIndex = (playbackIndex+1)%(points.length);

  }

  fill(255);

  ellipse(px,py, 40, 40);

}

​

function mousePressed(){

  playbackIndex = 0; 

  points = []; 

}

​

function mouseDragged(){

  points.push(createVector(mouseX, mouseY));

}