I have the start of an android game. It has a GameLoop (thread) class which keeps track of an fps value and a GameView (surfaceview) which instatiates a GameLoop object and sets it running and so on.
Now i have a separate FpsText object that knows how to draw itself to the screen but to update i need to do something like fpsText.setText(gameloop.getFps());
This isnt a problem if i do it in the GameView class but i wanted to try and have the an FpsText object that could take care of updating itself. I don't have any other experience with threads and I thought it might backfire but none the less i tried passing fpsText the gameloop reference as an argument. Unsurprisingly i get different unwanted results everytime i run the application so i wanted to know what you think the best way to handle this situation would be?
As an alternative to updating fpsText in the GameView i could always just make the fps value in the gameloop class public but i know that's bad practice! Neither sound like good solutions, perhaps there's a better way?
For reference here's my gameloop, with the second change suggested by RedOrav implemented:
package biz.hireholly.engine;
import android.graphics.Canvas;
import android.util.Log;
import android.view.SurfaceHolder;
import biz.hireholly.gameplay.FpsText;
import java.util.ArrayList;
/**
* The GameLoop is a thread that will ensure updating and drawing is done at set intervals.
* The thread will sleep when it has updated/rendered quicker than needed to reach the desired fps.
* The loop is designed to skip drawing if the update/draw cycle is taking to long, up to a MAX_FRAME_SKIPS.
* The Canvas object is created and managed to some extent in the game loop,
* this is so that we can prevent multiple objects trying to draw to it simultaneously.
* Note that the gameloop has a reference to the gameview and vice versa.
*/
public class GameLoop extends Thread {
private static final String TAG = GameLoop.class.getSimpleName();
//desired frames per second
private final static int MAX_FPS = 30;
//maximum number of drawn frames to be skipped if drawing took too long last cycle
private final static int MAX_FRAME_SKIPS = 5;
//ideal time taken to update & draw
private final static int CYCLE_PERIOD = 1000 / MAX_FPS;
private SurfaceHolder surfaceHolder;
//the gameview actually handles inputs and draws to the surface
private GameView gameview;
private boolean running;
private long beginTime = 0; // time when cycle began
private long timeDifference = 0; // time it took for the cycle to execute
private int sleepTime = 0; // milliseconds to sleep (<0 if drawing behind schedule)
private int framesSkipped = 0; // number of render frames skipped
private double lastFps = 0; //The last FPS tracked, the number displayed onscreen
private ArrayList<Double> fpsStore = new ArrayList<Double>(); //For the previous fps values
private long lastTimeFpsCalculated = System.currentTimeMillis(); //used in trackFps
FpsText fpsText;
public GameLoop(SurfaceHolder surfaceHolder, GameView gameview, FpsText fpsText) {
super();
this.surfaceHolder = surfaceHolder;
this.gameview = gameview;
this.fpsText = fpsText;
}
public void setRunning(boolean running) {
this.running = running;
}
@Override
public void run(){
Canvas c;
while (running) {
c = null;
//try locking canvas, so only we can edit pixels on surface
try{
c = this.surfaceHolder.lockCanvas();
//sync so nothing else can modify while were using it
synchronized (surfaceHolder){
beginTime = System.currentTimeMillis();
framesSkipped = 0; //reset frame skips
this.gameview.update();
this.gameview.draw(c);
//calculate how long cycle took
timeDifference = System.currentTimeMillis() - beginTime;
//good time to trackFps?
trackFps();
//calculate potential sleep time
sleepTime = (int)(CYCLE_PERIOD - timeDifference);
//sleep for remaining cycle
if (sleepTime >0){
try{
Thread.sleep(sleepTime); //saves battery! :)
} catch (InterruptedException e){}
}
//if sleepTime negative then we're running behind
while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS){
//update without rendering to catch up
this.gameview.update();
//skip as many frame renders as needed to get back into
//positive sleepTime and continue as normal
sleepTime += CYCLE_PERIOD;
framesSkipped++;
}
}
} finally{
//finally executes regardless of exception,
//so surface is not left in an inconsistent state
if (c != null){
surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
/* Calculates the average fps every second */
private void trackFps(){
synchronized(fpsStore){
long currentTime = System.currentTimeMillis();
if(timeDifference != 0){
fpsStore.add((double)(1000 / timeDifference));
}
//If a second has past since last time average was calculated,
// it's time to calculate a new average fps to display
if ((currentTime - 1000) > lastTimeFpsCalculated){
for (Double fps : fpsStore){
lastFps += fps;
}
lastFps /= fpsStore.size();
synchronized(fpsText){ //update the Drawable FpsText object
fpsText.setText(String.valueOf((int)lastFps));
}
lastTimeFpsCalculated = System.currentTimeMillis();
//Log.d("trackFPS()", " fpsStore.size() = "+fpsStore.size()+"\t"+fpsStore.toString());
fpsStore.clear();
}
}
}
}