The screen has only one canvas attached to it. This is canvas number 0 and all drawing operations in this canvas are applied to the screen.

Other canvases can be opened and drawing operations can be performed in them. Drawing can be performed in one of these 'invisible' canvases and then copied to the screen.

The reason for doing this is that images can be built without the user having any knowledge of them. They can then be copied to the screen in one move.

Copying the image is probably much faster than building it. This means that if the same image needs to be drawn to the screen repeatedly it can be stored in a background canvas and copied to the screen as often as it is needed.

Handling Multiple Canvases

Lots of canvases can be open at any time. In order to control which one the drawing operations are performed in, the command Canvas can be used.

Copying Between Canvases

The images from each canvas can be copied from one to another using the command Copy Canvas.