Call enterLayer() with two different keys, in order to create two Graphics that are drawn side by side.

use enterLayer() to modify the (global) p5.js functions to operate on a Graphics instead of the canvas.

Use a Graphics in order for one object to allow one object to leave a trail, while the rest of the canvas is fully erased.

One shape leaves a trail (because a semi-transparent color is drawn over it), while another does not.