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About Ilias Tsagklis

Ilias Tsagklis
Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

Game loop example

In this example we shall show you how to create a game loop in Android. Before starting, you should check our Basic Game loop example in order to understand the basic concepts.

To create a game loop in Android one should perform the following steps:

  • Create a thread that will be used as the game loop
  • Implement the run() method of the thread
  • Create an infinite while loop
  • Implement the logic inside the while loop
  • Use a boolean variable (running) in order to control the loop

These are demonstrated in the code snippet(s) below:

// desired fps
private final static int 	MAX_FPS = 50;
// maximum number of frames to be skipped
private final static int	MAX_FRAME_SKIPS = 5;
// the frame period
private final static int	FRAME_PERIOD = 1000 / MAX_FPS;	

@Override
public void run() {
	Canvas canvas;
	Log.d(TAG, "Starting game loop");

	long beginTime;		// the time when the cycle begun
	long timeDiff;		// the time it took for the cycle to execute
	int sleepTime;		// ms to sleep (<0 if we're behind)
	int framesSkipped;	// number of frames being skipped 

	sleepTime = 0;

	while (running) {
		canvas = null;
		// try locking the canvas for exclusive pixel editing
		// in the surface
		try {
			canvas = this.surfaceHolder.lockCanvas();
			synchronized (surfaceHolder) {
				beginTime = System.currentTimeMillis();
				framesSkipped = 0;	// resetting the frames skipped
				// update game state
				this.gamePanel.update();
				// render state to the screen
				// draws the canvas on the panel
				this.gamePanel.render(canvas);
				// calculate how long did the cycle take
				timeDiff = System.currentTimeMillis() - beginTime;
				// calculate sleep time
				sleepTime = (int)(FRAME_PERIOD - timeDiff);

				if (sleepTime > 0) {
					// if sleepTime > 0 we're OK
					try {
						// send the thread to sleep for a short period
						// very useful for battery saving
						Thread.sleep(sleepTime);
					} catch (InterruptedException e) {}
				}

				while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS) {
					// we need to catch up
					// update without rendering
					this.gamePanel.update();
					// add frame period to check if in next frame
					sleepTime += FRAME_PERIOD;
					framesSkipped++;
				}
			}
		} finally {
			// in case of an exception the surface is not left in
			// an inconsistent state
			if (canvas != null) {
				surfaceHolder.unlockCanvasAndPost(canvas);
			}
		}	// end finally
	}
}

 
This was an example of how to create a game loop with Android.

Related Article:

Reference: The Game Loop from our JCG partner Tamas Jano at the “Against The Grain” blog.

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