GLART week 9: Timing
Assigment:


Reading:
        Motion


Examples:
        GLART_9_timing.java -- control animation speed
        Requires font_tahoma.png and GLImage.java


Resources:

        NeHe: Introduction To Physical Simulations  -- tutorial on building a physics simulation



NOTES:
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Since cpu performance varies, program execution speed can vary from
one computer to another.  If you move an animation a fixed amount
in each render() the animation will move at different rates on
different computers, as render() is called more often on the faster
cpu.

VSync also affects the framerate.  Display.setVSyncEnabled(true)
will synchronize OpenGL frame updates with the monitor refresh rate.
Most monitors refresh the screen 60 or 75 per second, and VSync will
force Display.update() to wait till the monitor is ready to draw.
This controls the refresh rate somewhat, but monitors can have
different refresh rates, and slower graphics cards will slow this
down the refresh rate.

To insure that animations run at the same rate across various computers,
you need to move animations according to actual time elapsed, not
frame renders.

Check how much time has elapsed since the last frame rendered, then
"step" the simulation forward by that amount of time.  The simulation
advances in proportion to the time elapsed, and keeps track of
how much time has elapsed within the simulatulation.

Java's time function, System.currentTimeMillis(), does not measure
time accurately below 10 milliseconds, and will not give accurate
results when measuring time elapsed between frames.

Functions:

	Sys.getTime()
	LWJGL's hardware timer returns the time in cpu 'ticks'
	very accurate for small durations

	Sys.getTimerResolution()
	LWJGL function to get ticks per second
	varies on different computers

	NOTE: Java's time function, System.currentTimeMillis() is
	not accurate for small durations

	Use double data type for highest accuracy when measuring
	ticks and small time durations.