【发布时间】：2012-07-31 11:05:06
【问题描述】：
为了创建游戏循环，我关注了this excellent tutorial。但我认为下一个关于显示 FPS 的教程有点不确定，所以我尝试单独进行。我对我所做的trackFps() 方法相当有信心；它在计算帧之间的时间差后调用，每次运行时测量预测的 FPS，将这些预测的 FPS 值存储在 ArrayList 中，然后每经过一秒钟，将这些预测的 FPS 相加并除以添加的值的数量以获得平均 FPS。
当我使用调试器运行它时，它运行正常，但是当我正常运行它时，我得到以下异常：
FATAL EXCEPTION: Thread-11
java.lang.IndexOutOfBoundsException: Invalid index 26, size is 6
at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:257)
at java.util.ArrayList.get(ArrayList.java:311)
at biz.hireholly.engine.GameLoop.trackFps(GameLoop.java:120)
at biz.hireholly.engine.GameLoop.run(GameLoop.java:73)
这很容易解释，出现在fps += fpsStore.get(fpsTrackCount-1); 这一行。但我看不出fpsTrackCount 变量怎么会高达26，它应该只和ArrayList fpsStore 中存储的变量数量一样高。
有人会查看我的GameLoop 类，尤其是底部的trackFps() 方法吗？我会提供整个事情。它被大量评论，但内容不多，对你们中的一些人来说应该非常熟悉。
GameLoop（底部包含trackFps()计算FPS的方法）：
package biz.hireholly.engine;
import android.graphics.Canvas;
import android.view.SurfaceHolder;
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 int fpsTrackCount = 1; // number we'll divide the fpsSTore by to get average
private ArrayList<Double> fpsStore = new ArrayList<Double>(); //For the previous fps values
private long lastTimeFpsCalculated = System.currentTimeMillis(); //used in trackFps
public GameLoop(SurfaceHolder holder, GameView gameview) {
super();
this.surfaceHolder = holder;
this.gameview = gameview;
}
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(){
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){
int fps = 0;
int toDivideBy = fpsTrackCount;
while ((fpsStore != null) && (fpsTrackCount > 0 )){
fps += fpsStore.get(fpsTrackCount-1);
fpsTrackCount--;
}
lastFps = fps / toDivideBy;
lastTimeFpsCalculated = System.currentTimeMillis();
fpsTrackCount = 1;
fpsStore.clear();
}
else{
fpsTrackCount++;
}
}
/* So That it can be drawn in the gameview */
public String getFps() {
return String.valueOf(lastFps);
}
}
【问题讨论】：
-
我没有看到对你的 TextDrawable 的调用，你能把代码贴在你用它来绘制 FPS 值的地方吗？啊，找到了。
-
抱歉，这是我上传到 Pastebin 的 GameView 中的内容，因为我不想让我的问题变得混乱。
标签： java android game-engine frame-rate game-loop