Pan gesture messes up direction based on rotation

Question

I have a small issue with my gesture recognizers.

I have a class called "Sprite" which is just a UIImageView. Sprite has its own gesture recognizers and handling methods so that a user can pan, rotate, and resize the graphic.

Here is my code:

    -(void)setup{ //sets up the imageview...
//add the image, frame, etc.
    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(handlePinch:)];
    UIRotationGestureRecognizer *rotateGesture = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(handleRotate:)];

    [self addGestureRecognizer:panGesture];
    [self addGestureRecognizer:pinchGesture];
    [self addGestureRecognizer:rotateGesture];
}

//handling methods
-(void)handlePinch:(UIPinchGestureRecognizer *)recognizer{
    recognizer.view.transform = CGAffineTransformScale(recognizer.view.transform, recognizer.scale, recognizer.scale);
    recognizer.scale = 1;
}

-(void)handleRotate:(UIRotationGestureRecognizer *)recognizer{
    recognizer.view.transform = CGAffineTransformRotate(recognizer.view.transform, recognizer.rotation);
    recognizer.rotation = 0;
}
-(void)handlePan:(UIPanGestureRecognizer *)recognizer{
    CGPoint translation = [recognizer translationInView:self];
    recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x, recognizer.view.center.y + translation.y);
    [recognizer setTranslation:CGPointMake(0, 0) inView:self]
}

So basically each of them works fine on their own. However, when I rotate or resize the imageView, panning becomes problematic. For example, if you rotate the imageView upside down, then the panning gestures will move the image in the reverse direction (up is down, dragging left moves it to the right, etc.). Similarly, a resized sprite will not pan at the same speed/distance as before.

Any ideas on how I can fix this? I would prefer to keep this code within the Sprite class rather than the ViewController (if possible). Thank you.

Jerry Jerry · Accepted Answer · 2012-01-09T05:20:56

Instead of translationInView:self, try translationInView:self.superview.

Pan gesture messes up direction based on rotation

1 Answers