Alien Invasion

In this clone of space invaders, there are four different game modes. 

Normal Mode: The aliens move left and right and move down when they hit the ede of the screen.

Gravity Mode: The aliens continuously move down whilst moving left and right.

Quadratic Mode; The aliens move in a curved pattern  and move down when the hit the edge of the screen.

Sine Mode: The aliens move in a wave formation and move down when they hit the edge of the screen.