Velocity of touches - iphone

Question

I'm making a simple physics game in cocos2d and want to launch a particle on swipe a the speed of the swipe. To get the velocity I need to take two touches and determine the (difference in position)/(difference in timestamp). My problem is that I can't get two touches. I tried a few methods but none of them are working out.
I tried storing the first touch
#property (nonatomic, strong) UITouch *firstTouch;
...
- (void)ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
[self setFirstTouch:touch];
NSLog(#"first touch time 1: %f", self.firstTouch.timestamp);
}
-(void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
NSLog(#"touch ended");
NSLog(#"first touch time 2: %f", self.firstTouch.timestamp);
NSLog(#"end of touch time: %f", touch.timestamp);
}
but this gives me a difference in timestamps of 0 every time. It seems to replace the firstTouch with the most recent touch
Am I doing something wrong with pointers that this is replaced?
Perhaps I can take the last two touches from ccTouchesMoved?

Answer 1

A far easier way of doing what you are trying to do is adding a UIPanGestureRecognizer to your [CCDirector sharedDirector].openGLView and then use the velocityInView property of the gesture recognizer.
UIPanGestureRecognizer* gestureRecognizer = [[[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipe:)] autorelease];
[[CCDirector sharedDirector].openGLView addGestureRecognizer:gestureRecognizer];
and then:
- (void)handleSwipe:(UIPanGestureRecognizer*)recognizer {
... recognizer.velocity...
}
If you want do follow your approach based on ccTouches..., it seems to me that possibly there is a misunderstanding about a swipe gesture, in that it is not made of 2 touches: it is just one touch that has a begin, some moves, and an end. So you need to track the movement of your finger in ccTouchesMoved:; then in touchesEnded determine whether it is a horizontal or vertical swipe, the direction, and send out the bullet.
Hope either of these suggestions may help.