An example

Consider the case where:

• The current direction of motion is northwest
• The ball collides with the top wall, and
• The new direction of motion is either northwest or northeast.

This could be a problem

Motion to the northwest or northeast would cause the ball to penetrate the wall.

However, in this case (see Listing 4):

• The ball will simply pause at the wall
• Until the same code is executed in a future iteration of the animation loop
• To send the ball off in a southwest or southeast direction.