Animation test;
BImage one;
BImage two;

void setup()
{
  size(400,100);
  one = loadImage("one.gif");
  two = loadImage("two.gif");
 
  test = new Animation(this, one, 100,40, 200,40);
  test.showRectangle();
}

void loop()
{
  background(127);
  
  if (test.currentPercentage() < 0.5)
    test.setImage(one); // set normal image
  else
    test.setImage(two); // set inverted image
      
  test.draw();
}