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Determining Time Differences

After rendering the scene, compare the current time with the one you last took. We will store this in the secsperframe variable.

//first determine how many seconds elapsed
timerdiff = TimerGetTime()-timer;

//the function reads in milliseconds so convert to seconds by dividing by 1000
secsperframe=(float)(timerdiff/1000.0f);

Let's say the number comes out to be .0125. To get the frame rate, simply divide 1 second by that .0125. This gives you an answer of 80, since 80 times that .0125 is equal to 1 second. To determine how much to move, you simply take the desired distance and divide by the frames per second.

Movement = (desired distance)/(frames a second)

In this example, that would be 1 divided by 80 which would give you .0125 as stated above. The equation can be changed, though, if we substitute in the equation for frames per second. Now it reads:

Movement = (distance desired)/(1/seconds per frame)

This can be further simplified to:

Movement = (distance desired)*(seconds per frame)

I find this equation to be the easiest to use. In NeHe Lesson 23, this looks like:

//now compute the movement value
movementval = (float)(desireddistance*secsperframe);

//get the new time
timer = TimerGetTime();

Next : Moving the Character