Android基本游戏循环实例分析

// 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
  }
}