Question

i need to get the touch move velocity in cocos2d. any api for this?

Answer 1

The most basic way of doing this is to do the following:

1. Of course,register a CCLayer with to be a touch event handler, and implement the touch begin, move and end functions.

2. Create in your relevant class, 2 CGPoint variables to store the CURRENT and PREVIOUS touch positions. Also create 2 CCTIme structures to store the CURRENT and PREVIOUSLY polled times.

3. Set up a schedule to update the current time (I’ve done this in the init of any relevant class.

i.e:

- (id)init {
    if((self = [super init])) {
        [self schedule:@selector(update:)];
        timeCURRENT = (ccTime)0;
    }
    return self;
}

-(void)update:(ccTime)deltaTime {
    timeCURRENT += deltaTime;
}

4 . at the start of touch begin, set both the previous and current variables to the current touch location using the following:

-(BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {  
 touchCURRENT= [touch locationInView: [touch view]];  
 touchPREVIOUS = touchCURRENT;
 timePREVIOUS = timeCURRENT;
...

Then, in touch moved, set the PREVIOUS to the CURRENT, and set the CURRENT using the same line of code as above

-(BOOL)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {   
    touchPREVIOUS = touchCURRENT;
    touchCURRENT= [touch locationInView: [touch view]];
    CGPoint deltaPosition = touchCURRENT - touchPREVIOUS;
    ccTime deltaTime = timeCURRENT - timePREVIOUS;
    timePREVIOUS = timeCURRENT;

Velocity = deltaPosition/deltaTime.

Note that CGPoint subtraction may not work as advertised above, you may have to subtract individual members and feed them into a CGPoint factory method.