How does animation at 60Hz works?

I'm using a Thread to make a scrolling under Android. The thread run method is classic. I took it on Internet My view is a SurfaceView.

public void run() {
    Canvas canvas = null;
    while (_run) {
        canvas = _surfaceHolder.lockCanvas();
        if (canvas != null) {
            _surface.doDraw(canvas);
            _surfaceHolder.unlockCanvasAndPost(canvas);
        }
    }
}

What I do not understand is: Why the doDraw (that will draw on screen) is called exactly 60 times per second ? And why there is no synchro problem ?

I do not know how LCD works but on a screen, if you make a scrolling without waiting for the screen synchro, it is possible that the top of the screen display the previous image while the bottom display the correct image. I do not have the problem on Android.

Is it the SurfaceView that handle a kind of double buffering ? And if it is the case, whe开发者_开发问答n the flip is done ?

I do not find any information about that on Internet!

Thank's Etienne

It is indeed double buffered, the flip is done in SurfaceHolder.unlockCanvasAndPost().

Check this out: http://developer.android.com/reference/android/view/SurfaceHolder.html#unlockCanvasAndPost(android.graphics.Canvas)

[Edit] Sorry, forgot your first question.

Android always have vsync enabled, and therefore either lockCanvas() or unlockCanvasAndPost() will block the remaining time to sync it. I don't know im my head if it is lockCanvas() or unlockCanvasAndPost() that blocks, but it should be easy enough to check if you'd need it.

At least on Android 2.3, SGS, the lock is in lockCanvas(). I measured it by calling System.nanoTime() before and after this call.