Time for animation

It's time to throw in a little more excitement. Let's animate the cube so that it rotates. This'll help demonstrate the shading as well.

For this, we need a Time class. This is a singleton utility class that ticks off frames and makes that information available to the application, for example, via getDeltaTime. Note that this is a final class, which explicitly means that it cannot be extended. There is no such thing as a static class in Java, but if we make the constructor private, we can ensure that nothing will ever instantiate it.

Create a new Time class in the renderbox/ folder. It won't be getting extended, so we can declare it final. Here's the code:

public final class Time {
    private Time(){}
    static long startTime;
    static long lastFrame;
    static long deltaTime;
    static int frameCount;

    protected static void start(){
        frameCount = 0;
        startTime = System.currentTimeMillis();
        lastFrame = startTime;
    }
    protected static...