Spawning bullets

We need a way to spawn bullets from both the player and each of the invaders. The solutions to both are very similar but not identical. We need a way to allow GameInputHandler to spawn bullets when a keyboard key or gamepad button is pressed, and we need InvaderUpdateComponent to use its already existing logic to spawn bullets.

The GameScreen class has a vector holding all the GameObject instances, so GameScreen is the ideal candidate to move a bullet into position and set it moving up or down the screen, depending on who or what triggered the shot. We need a way for the GameInputHandler class and InvaderUpdateComponenet to communicate with the GameScreen class, but we also need to restrict the communication to just spawning bullets; we don't want them to be able to take control of any other part of the GameScreen class.

Let's code an abstract class that GameScreen can inherit from.

Coding the BulletSpawner class

Create a new header file in the...