When no collision has occurred...

If the conditional clause in the if statement in Listing 4 returns false:

• A collision with the wall has not occurred. 

The ball should continue moving in a forward direction.

The x and y coordinates for the center of the ball are both decremented by one in Listing 4.

This will make it appear that:

• The ball has moved one pixel to the left and one pixel towards the top
  • The next time the ball is drawn on the screen.