Creating a game loop (sleep time help)

Question

I've been using this tutorial to create a game loop.

In the section marked "FPS dependent on Constant Game Speed" there is some example code that includes a Sleep command

I googled the equivalent in java and found it is

Thread.sleep();

but it returns an error in eclipse

Unhandled exception type InterruptedException

What on earth does that mean.

And also I was wondering what the

update_game();
display_game(); 

methods may contain in an opengl-es game (ie: where is the renderer updated and what sort of things go on in display_game();

I am currently using a system that uses the GLSurfaceView and GLSurfaceRenderer features

Here is my adaptation of the code in the tutorial

public Input(Context context){
    super(context);
    glSurfaceRenderer = new GLSurfaceRenderer();
    checkcollisions = new Collisions();
    while (gameisrunning) {
    setRenderer(glSurfaceRenderer);


    nextGameTick += skipTicks;
    sleepTime = nextGameTick - SystemClock.uptimeMillis();
    if(sleepTime >= 0) {
        Thread.sleep(sleepTime);
    }else{
        //S*** we're behind
    }

    }

This is called in my GLSurfaceView although I'm not sure whether this is the right place to implement this.

Answer 1

Looks like you need to go through a couple of tutorials on Java before trying to tackle android game development. Then read some tutorials on Android development, then some more general game development tutorials. (Programming is a lot of reading.)

Thread is throwing an exception when it gets interrupted. You have to tell Java how to deal with that.

To answer your question directly, though, here's a method that sleeps till a specific time:

private void waitUntil(long time) {
    long sleepTime = time - new Date().getTime();

    while (sleepTime >= 0) {
        try {
            Thread.sleep(sleepTime);
        } catch (InterruptedException e) {
            // Interrupted. sleepTime will be positive, so we'll do it again.
        }
        sleepTime = time - new Date().getTime();
    }
}

You should understand at least this method before continuing on game development.

Answer 2

Ironically, Ron Romero's code doesn't work. There are two issues with it: the while loop and the sleeptime variable.

The sleepTime variable is set based off of a specified time (in milliseconds) to sleep. It takes the time and subtracts it from current millisecond time. The problem with this is that the current millisecond time is a huge number (hence the long variable type), which provides a NEGATIVE sleepTime number. You'll never enter the while loop with this code.

The second thing that's wrong is the while loop check itself. Utilizing the sleep function in java, you don't need to do a loop like this. All you have to do is pass the sleepTime that you want to sleep for in milliseconds to the sleep function and it will work just fine.

private void waitUntil(long time) {
    try {
        Thread.sleep(time);
    } 
    catch (InterruptedException e) {
    //This is just here to handle an error without crashing
    }
}

Answer 3

Java performs compile-time checking of checked exceptions.