优化Android游戏循环

Question

优化Android游戏循环

3

我正在为一个简单的安卓游戏使用下面的代码作为游戏循环。它可以正常工作，但是偶尔会出现游戏卡顿的情况。所有东西都会冻结一秒钟，然后向前跳了一点比应该更远的距离。我阅读了大量关于游戏循环的资料，但是我仍然有一些困难来实现平滑循环。是否可以通过插值来解决这个问题？我该如何平滑移动？

private final static int MAX_FPS = 30;
private final static int MAX_FRAME_SKIPS = 5;
private final static int FRAME_PERIOD = 1000 / MAX_FPS;

protected Void doInBackground(Void... params) {
    Log.d("MainTask", "starting game task");
    Canvas canvas;

    long begin;     // the time when the cycle began
    long delta;     // the time it took for the cycle to execute
    int sleep;      // ms to sleep if ahead
    int skipped;    // number of frames being skipped

    sleep = 0;

    while (running) {
        canvas = null;
        try {
            canvas = surfaceHolder.lockCanvas();
            synchronized (surfaceHolder) {
                begin = System.currentTimeMillis();
                skipped = 0;

                gamePanel.update();
                gamePanel.draw(canvas);

                delta = System.currentTimeMillis() - begin;
                sleep = (int)(FRAME_PERIOD - delta);

                if (sleep > 0) {
                    try {
                        Thread.sleep(sleep);
                    } catch(InterruptedException e) {}
                }

                while (sleep < 0 && skipped < MAX_FRAME_SKIPS) {
                    gamePanel.update();
                    sleep += FRAME_PERIOD;
                    skipped++;
                }
            }
        } finally {
            if (canvas != null) surfaceHolder.unlockCanvasAndPost(canvas);
        }
    }
    Log.d("MainTask", "the task is complete");
    return null;
}

- Danny Buonocore

请参阅：https://source.android.com/devices/graphics/architecture.html#loops - fadden

2个回答

1

这可能有点晚了，但是这是我如何实现我的游戏循环的方法。通过这个方法，它可以帮助您跟踪游戏的每秒更新次数和帧数。

long lastTime = System.nanoTime();
double nsPerTick = 1_000_000_000D/60D;
int frames = 0;
int ticks = 0;
long lastTimer = System.currentTimeMillis();
double delta = 0;

while (mRunning) {
    Canvas canvas = null;
    long now = System.nanoTime();
    delta += (now-lastTime)/nsPerTick;
    lastTime = now;
    boolean shouldRender = false;

    while (delta >= 1) {
        ticks++;
        gameView.update();
        delta -= 1;
        shouldRender = true;
    }

    if (shouldRender) {
        frames++;
        canvas = surfaceHolder.lockCanvas();
        gameView.render(canvas);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    if (System.currentTimeMillis() - lastTimer >= 1000) {
        lastTimer += 1000;
        Log.d("FPS", "Ticks: " + ticks + ", Frames: " + frames);
        ticks = 0;
        frames = 0;
    }
}

这是基于vanZeben的视频教程制作的Java游戏，但也适用于Android游戏（至少对我来说是这样）。

希望能够有所帮助。

参考资料: https://www.youtube.com/watch?v=VE7ezYCTPe4&list=PL8CAB66181A502179

- Gem Seeker

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可以查看英文原文，
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- Richard Tingle · Accepted Answer

对于这个循环，您实际上已经做得很正确了。但是我可以看到一些潜在的陷阱。

You don't pass the frame time to your update method. This means your update method must assume a certain frame time. This is likely the cause of your jumps. You won't get constant frame rates if you are anywhere near the maximum performance of the machine, you just wont. And this broadly doesn't matter. If you miss a frame your brain fills in the missing frame and it looks fine. What absolutely does matter is a variable object speed. In this case a variable frame rate will cause a variable speed of your objects. Your update method should be:
```
long previousFrameTime=System.currentTimeMillis();
while (running){
    .....
    .....
    long currentTime=System.currentTimeMillis();
    long frameTime=currentTime-previousFrameTime
    previousFrameTime=currentTime
    gamePanel.update(frameTime/1000.0);  //I personally like my frametimes in seconds, hence /1000.0, but thats up to you
    .....
    .....
 }
```
And all movement within the update should take that frametime into account when determining how far to move

为了说明这点的重要性，看下面两张图。一张是假定帧率，另一张是测量出来的帧率。点代表实际渲染的帧数，线代表观众大脑中正在发生的插值。

You also hold on to the Canvas lock for a lot longer than nessissary. All the way through your update method and through the sleep as well you have a lock on the canvas. This saps performance. Get the lock just before you start rendering and release it as soon as you have finished
```
gamePanel.update();
canvas = surfaceHolder.lockCanvas();
gamePanel.draw(canvas);
surfaceHolder.unlockCanvasAndPost(canvas);
```