Android测量每秒帧数FramesPerSecond(FPS)的方法

package net.obviam.droidz;
import java.text.DecimalFormat;
import android.graphics.Canvas;
import android.util.Log;
import android.view.SurfaceHolder;
/**
 * @author impaler
 *
 * The Main thread which contains the game loop. The thread must have access to
 * the surface view and holder to trigger events every game tick.
 */
public class MainThread extends Thread {
 private static final String TAG = MainThread.class.getSimpleName();
 // 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;
 // Stuff for stats */
 private DecimalFormat df = new DecimalFormat("0.##"); // 2 dp
 // we'll be reading the stats every second
 private final static int STAT_INTERVAL = 1000; //ms
 // the average will be calculated by storing
 // the last n FPSs
 private final static int FPS_HISTORY_NR = 10;
 // last time the status was stored
 private long lastStatusStore = 0;
 // the status time counter
 private long statusIntervalTimer = 0l;
 // number of frames skipped since the game started
 private long totalFramesSkipped   = 0l;
 // number of frames skipped in a store cycle (1 sec)
 private long framesSkippedPerStatCycle = 0l;
 // number of rendered frames in an interval
 private int frameCountPerStatCycle = 0;
 private long totalFrameCount = 0l;
 // the last FPS values
 private double fpsStore[];
 // the number of times the stat has been read
 private long statsCount = 0;
 // the average FPS since the game started
 private double averageFps = 0.0;
 // Surface holder that can access the physical surface
 private SurfaceHolder surfaceHolder;
 // The actual view that handles inputs
 // and draws to the surface
 private MainGamePanel gamePanel;
 // flag to hold game state
 private boolean running;
 public void setRunning(boolean running) {
  this.running = running;
 }
 public MainThread(SurfaceHolder surfaceHolder, MainGamePanel gamePanel) {
  super();
  this.surfaceHolder = surfaceHolder;
  this.gamePanel = gamePanel;
 }
 @Override
 public void run() {
  Canvas canvas;
  Log.d(TAG, "Starting game loop");
  // initialise timing elements for stat gathering
  initTimingElements();
  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  0) {
      Log.d(TAG, "Skipped:" + framesSkipped);
     }
     // for statistics
     framesSkippedPerStatCycle += framesSkipped;
     // calling the routine to store the gathered statistics
     storeStats();
    }
   } finally {
    // in case of an exception the surface is not left in
    // an inconsistent state
    if (canvas != null) {
     surfaceHolder.unlockCanvasAndPost(canvas);
    }
   } // end finally
  }
 }
 /**
  * The statistics - it is called every cycle, it checks if time since last
  * store is greater than the statistics gathering period (1 sec) and if so
  * it calculates the FPS for the last period and stores it.
  *
  * It tracks the number of frames per period. The number of frames since
  * the start of the period are summed up and the calculation takes part
  * only if the next period and the frame count is reset to 0.
  */
 private void storeStats() {
  frameCountPerStatCycle++;
  totalFrameCount++;
  // check the actual time
  statusIntervalTimer += (System.currentTimeMillis() - statusIntervalTimer);
  if (statusIntervalTimer >= lastStatusStore + STAT_INTERVAL) {
   // calculate the actual frames pers status check interval
   double actualFps = (double)(frameCountPerStatCycle / (STAT_INTERVAL / 1000));
   //stores the latest fps in the array
   fpsStore[(int) statsCount % FPS_HISTORY_NR] = actualFps;
   // increase the number of times statistics was calculated
   statsCount++;
   double totalFps = 0.0;
   // sum up the stored fps values
   for (int i = 0; i