function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(255);

  //translate(width/2,height/2);

  noFill();

  ellipse(width/2,height/2,2*r,2*r);

  if(dist(mouseX,mouseY,width/2,height/2)<r){

     dx = dist(mouseX,height/2,width/2,height/2);

     dy = dist(width/2,mouseY,width/2,height/2);

  }

  ellipse(width/2,height/2,2*r,2*dy);

  ellipse(width/2,height/2,2*dx,2*r);

  push();

  noStroke();

  fill(255,0,0);

  ellipse(width/2+dx,height/2+dy,10,10);

  pop();

}