Animation test;
Animation a_box;
Animation an_ellipse;

void setup()
{
  size(400,100);
 
  a_box = new Animation(this, loadImage("image.gif"), 0,0, 20,20);
  a_box.setStep("BOX");
  a_box.showRectangle();
  
  an_ellipse = new Animation(this, loadImage("image.gif"), 0,0, 10,-40);
  an_ellipse.setStep("ELLIPSE");
  an_ellipse.showRectangle();
  
  test = new Animation(this, a_box, 100,40, 200,40);
  test.setDuration(10000);
  test.showRectangle();
}

void loop()
{
  background(127);
  
  if (test.currentPercentage() < 0.5)
    test.setAnimation(a_box); // set nested animation to the box.
  else
    test.setAnimation(an_ellipse); // set nested animation to the ellipse.
      
  test.draw();
}