Invaders Revenge is the name of our Kivy version of Space Invaders©. The following screenshot shows you the game we will build in this chapter:

There are several tags in yellow and cyan in the screenshot (or gray dashed lines in the printed version). They help identify the structure of our game; the game will consist of one shooter (the player), who shoots (shots) at 32 (8x4) invaders who are trying to destroy the shooter with their missiles. The invaders are organized in a fleet (which moves horizontally) and sometimes an individual invader can break out of the grid formation and fly around the screen before going back to its corresponding position (dock) in the fleet.

The cyan (gray in the printed version) line across the screen indicates an internal division of the screen into the enemy area and shooter area. This division is used to distinguish between actions that should occur according to touches that happen in different sections of the...