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About Byron Kiourtzoglou

Byron Kiourtzoglou
Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Measuring Frames Per Second (FPS)

This is an example of how to measure frames per second (FPS) in an Android application or game. Measuring FPS in an Android game is very important because it allows you to gauge how smooth the game is. In general, the more FPS the better user experience.

For a better understanding, make sure to check the Android Game Loop example before proceeding.

To measure the FPS you may follow this procedure:

  • Create a thread that will simulate the game loop
  • Use local variables that will hold the time of each iteration
  • Create local variables that will hold the frames count
  • Create a variable for the average FPS
  • In each iteration increase the counter and set the variable values accordingly

These are demonstrated in the code snippet(s) below:

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 < 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");
	}

}

 
This was an example of how to measure frames per second with Android.

Related Article:

Reference: Measuring FPS from our JCG partner Tamas Jano at the “Against The Grain” blog.

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