In the previous entry we have created a game loop that runs at a constant speed and constant (more or less) FPS.
How can we measure it?
Check the new MainThread.java class.
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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"); }} |
I introduced a simple measuring function. I count the number of frames every second and store them in the fpsStore[] array. The storeStats() is called every tick and if the 1 second interval (STAT_INTERVAL = 1000;) is not reached then it simply adds the number of frames to the existing count.
If the one second is hit then it takes the number of rendered frames and adds them to the array of FPSs. After this I just reset the counters for the current statistics cycle and add the results to a global counter. The average is calculated on the values stored in the last 10 seconds.
Line 171 logs the FPS every second while line 172 sets the avgFps value of the gamePanel instance to be displayed on the screen.
The MainGamePanel.java class’s render method contains the the displayFps call which just draws the text onto the top right corner of the display every time the state is rendered. It also has a private member that is set from the thread.
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 | // the fps to be displayedprivate String avgFps;public void setAvgFps(String avgFps) { this.avgFps = avgFps;}public void render(Canvas canvas) { canvas.drawColor(Color.BLACK); droid.draw(canvas); // display fps displayFps(canvas, avgFps);}private void displayFps(Canvas canvas, String fps) { if (canvas != null && fps != null) { Paint paint = new Paint(); paint.setARGB(255, 255, 255, 255); canvas.drawText(fps, this.getWidth() - 50, 20, paint); }} |
Try running it. You should have the FPS displayed in the top right corner.
 |
| FPS displayed |
Reference: Measuring FPS from our JCG partner Tamas Jano from “Against The Grain” blog.
Do not forget to check out our new Android Game ArkDroid (screenshots below). You feedback will be more than helpful!
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I’m also having an issue with the FPS.
I’m using the 4.0 emulator and I’m topping at ~9.5 FPS. My code is the same as yours though.
For the emulator, apparently the act of setting the canvas to null and initializing it “canvas = surfaceHolder.lockCanvas();” takes quite some time. In the original code, it is not considered part of the frame period when it should be. Put “beginTime = System.currentTimeMillis();” right underneath the “while(running) {” line and it will show you that you need to skip a lot of frames because the emulator is slow, as expected. If you leave the beginTime where it is, it makes you think you are faster than 50 fps because it sleeps about 15ms and only takes 5ms to update and… Read more »
System.currentTimeMillis() uses the system clock, so if the game is paused and later resumed, the repeat calls to update in the inner while loop will cause it to totally wig out.
e.g. while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS) {
This is a great code, but I faced a little flickering issue. So I changed the location of the while loop given below after the finally block and it worked fine.
Please let me know if this is right.
while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS) {