cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   pegasus4747
   Member

   Hi, I'm pretty new to cocos2d and ObjC in general. I was wondering if it's possible to create a timer clock like the ones you'd see in a racing game -- one that keeps track of the official time elapsed. I thought of doing it in my update method, something like:

   - (void)update:(ccTime)dt {
     ticker++;
     timeElapsed = ticker/frameRate;
   }

   and display timeElapsed. I do get something that looks like a nice running clock, but I have no idea how accurate it is. Is there a better way to do this? Any help is much appreciated!

   Posted 1 year ago #
2. 

   robodude666
   Member

   Pssssst, checkout the dt argument being passed into the update selector. dt stands for delta time, which is the amount of time (in seconds) that have passed since the last update was called.

   To find the amount of time that has elapsed just add dt to your timeElapsed variable. You can also set it to 0 when a new lap starts to restart the clock, etc. :)

   You'll even see that if you print out the timeElapsed calculated via your method and the sum of dts via an NSLog you'll get very close numbers showing that they're both valid and accurate methods of accomplishing this task.

   For the heck of it, you can also store the value of time() when a lap starts, and compare it to the current time() (ex: timeElapsed = time() - startTime;) to get an estimated amount of time (in whole seconds - no milliseconds) that have passed.

   As a note, your method will be dependent on the current frame rate which could be bad if the game lags. If your frame rate is set to 60FPS and all of a sudden your framerate drops to ~30FPS due to some particles or too many sprites you'll notice that timeElapsed is smaller than it actually should. dt on the other hand is the amount of time that has passed so it will be independent of the current frame rate (it will take it into account when calculating the time).

   -robodude666

   Posted 1 year ago #
3. 

   finder39
   Member

   I use this for a timer

   in the init:
   

   timeLevelStarted = [[NSDate date] timeIntervalSince1970];
   		timeForLevel = 180;
   		timeLeft = timeForLevel;
   
   		// Create a label for time left purposes
   		if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
   		{
   			//ipad
   			_timeLabel = [CCLabel labelWithString:@"Time Left: 0" dimensions:CGSizeMake(240, 50) alignment:UITextAlignmentLeft fontName:@"Arial" fontSize:25.0];
   		}
   		else
   		{
   			//ipod
   			_timeLabel = [CCLabel labelWithString:@"Time Left: 0" dimensions:CGSizeMake(120, 25) alignment:UITextAlignmentLeft fontName:@"Arial" fontSize:15.0];
   		}
   		_timeLabel.color = ccc3(0,0,0);
   		//if (gameTypeChoice == 1 || gameTypeChoice == 2) {_label.position = ccp(winSize.width-60, winSize.height-(_label.contentSize.height/2));}
   		//else if (gameTypeChoice == 3) {_label.position = ccp(191, winSize.height-(_label.contentSize.height/2));}
   		//_pointsLabel.position = ccp(_pointsLabel.contentSize.width/2, winSize.height-(_pointsLabel.contentSize.height/2));
   		_timeLabel.position = ccp(winSize.width-_timeLabel.contentSize.width/2, winSize.height-(_timeLabel.contentSize.height/2)-13);
   		[self changeTimeLabel];
   		[self addChild:_timeLabel];

   then call this in the update:
   

   if ([self changeTimeLabel] == 0) {
   		[self unschedule:@selector(gameLogic:)];
   		[self unschedule:@selector(gameLogic2:)];
   		[self unschedule:@selector(gameLogicSpecials:)];
   		int numberOfEnemiesLeft = 0;
   		// check for enemies left
   		for (enemy *enemyCheck in _enemies) {
   			numberOfEnemiesLeft++;
   			//NSLog(@"enemy here");
   		}
   		if (numberOfEnemiesLeft == 0) {
   			NSLog(@"game is over");
   		}
   	}

   and here is my function for it
   

   -(int)changeTimeLabel {
   	double curTime = [[NSDate date] timeIntervalSince1970];
   	timeLeft = timeForLevel - (int)(curTime - timeLevelStarted);
   	if (timeLeft < 0) {
   		timeLeft = 0;
   	}
   	//NSLog([NSString stringWithFormat:@"%i", timeLeft]);
   	int minutesLeft = timeLeft/60, secondsLeft = timeLeft%60;
   	if (secondsLeft < 10) {
   		[_timeLabel setString:[NSString stringWithFormat:@"Time Left: %i:0%i", minutesLeft, secondsLeft]];
   	} else {
   		[_timeLabel setString:[NSString stringWithFormat:@"Time Left: %i:%i", minutesLeft, secondsLeft]];
   	}
   	return timeLeft;
   }

   I hope this helps a lot :)

   Posted 1 year ago #
4. 

   finder39
   Member

   Mine is very accurate by the way. no guessing with it which i like :)

   Posted 1 year ago #
5. 

   araker
   Moderator

   @finder Apple recommends using CACurrentMediaTime() instead of NSDate for time critical applications. NSDate draws from the networked synch-clock and will occasionally hiccup when re-synching it against the network.

   Posted 1 year ago #
6. 

   finder39
   Member

   hmm...will look into it, thanks :)

   Posted 1 year ago #
7. 

   pegasus4747
   Member

   Thanks everyone for the tips

   @finder39: thanks for sharing your code, I'm gonna try it out. Thanks!

   Posted 1 year ago #
8. 

   nickthedude
   Member

   im trying to solve a similar problem theproblem is say you're using nsdate to get a reference point in time, the user gets a phone call or otherwise leaves the app, when you come back, your comparison is way out of whack, right? basically im wondering if there is a time class in cocos that respects pausing?

   Posted 1 year ago #

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