Android游戏开发测量每秒帧数 Frames Per Second (FPS)

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 < MAX_FRAME_SKIPS) {
// we need to catch up
this.gamePanel.update(); // update without rendering
sleepTime += FRAME_PERIOD;	// add frame period to check if in next frame
framesSkipped++;
}

if (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 < FPS_HISTORY_NR; i++) {
totalFps += fpsStore[i];
}

// obtain the average
if (statsCount < FPS_HISTORY_NR) {
// in case of the first 10 triggers
averageFps = totalFps / statsCount;
} else {
averageFps = totalFps / FPS_HISTORY_NR;
}
// saving the number of total frames skipped
totalFramesSkipped += framesSkippedPerStatCycle;
// resetting the counters after a status record (1 sec)
framesSkippedPerStatCycle = 0;
statusIntervalTimer = 0;
frameCountPerStatCycle = 0;

statusIntervalTimer = System.currentTimeMillis();
lastStatusStore = statusIntervalTimer;
//			Log.d(TAG, "Average FPS:" + df.format(averageFps));
gamePanel.setAvgFps("FPS: " + df.format(averageFps));
}
}

private void initTimingElements() {
// initialise timing elements
fpsStore = new double[FPS_HISTORY_NR];
for (int i = 0; i < FPS_HISTORY_NR; i++) {
fpsStore[i] = 0.0;
}
Log.d(TAG + ".initTimingElements()", "Timing elements for stats initialised");
}

}