In Chapter 5, “Game Animation: Shooting and Bouncing Games,” the games involved simple horizontal and vertical movement. Moving along the horizontal or vertical axis is very easy to program. But arcade games demand more.
In many games, you need to allow the player to turn and move. For instance, a driving game has both steering and forward movement. A space game also requires this, and might even need to allow the player to fire weapons in the direction that the player’s ship is pointing.