Question

I’m writing a little game as part of a programming assignment. I’ve got my sprites/images moving the way I want to, except they’re very jerky. Here’s how I’m loading up the image:

//missile and paint are private members of the animation thread
missile = Bitmap.createBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.missile));
paint = new Paint();
paint.setAntiAlias(true);
startTime = new Date().getTime();

The run method of my thread is like this:

@Override
public void run() {
    while(running) {
        Canvas canvas = null;

        try {
            canvas = surfaceHolder.lockCanvas(null);

            synchronized (surfaceHolder) {
                updatePhysics();
                doDraw(canvas);
            }
        } finally {
            if(canvas != null) {
                surfaceHolder.unlockCanvasAndPost(canvas);
            }
        }
    }
}

updatePhysics simply performs calculations and stores the value inside a private member of the thread called projectilePosition:

function updatePhysics() {
    projectilePosition = interceptionCalculationService.positionAtTime((startTime - new Date().getTime()) / 1000);
}

Then, in my doDraw method I do:

private void doDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);

    ...

    //I update the position of the missile
    canvas.drawBitmap(missile, (int) projectilePosition.getDistance() * 2, (int) (getHeight() - (95 + projectilePosition.getHeight())), paint);
    canvas.restore();
}

The problem is that the animation is extremely jerky. The missile follows the correct path, but it’s not smooth at all. I assume that’s because I don’t really control the interval when the thread’s run method is called. How can I make my animation more smooth? I was looking at TranslateAnimation, but I can’t figure out how to use it.

This is my first time writing a game and doing graphics/animation, so I’m not well aware of the best practices or even the tools. I got this far by looking up numerous tutorials.

Answer 1

My solution was to stop relying on the system time and to use a variable (that is a private member of the thread) called currentTime that gets incremented in either doDraw or updatePhysics. So updatePhysics becomes:

function updatePhysics() {
    projectilePosition = interceptionCalculationService.positionAtTime(currentTime);
    currentTime++;
}

currentTime is initialized to 0 in the constructor of the thread. This made my animation smooth.