How to reduce pinch zoom speed of UIGestureRecognizer

Question

I created UIGestureRecognizeras :

- (void)handlePinchGesture:(UIPinchGestureRecognizer *)gestureRecognizer {

    if([gestureRecognizer state] == UIGestureRecognizerStateBegan) {
        // Reset the last scale, necessary if there are multiple objects with different scales
        lastScale = [gestureRecognizer scale];
    }

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || 
        [gestureRecognizer state] == UIGestureRecognizerStateChanged) {

        CGFloat currentScale = [[[gestureRecognizer view].layer valueForKeyPath:@"transform.scale"] floatValue];

        // Constants to adjust the max/min values of zoom
        const CGFloat kMaxScale = 2.0;
        const CGFloat kMinScale = 1.0;

        CGFloat newScale = 1 -  (lastScale - [gestureRecognizer scale]); 
        newScale = MIN(newScale, kMaxScale / currentScale);   
        newScale = MAX(newScale, kMinScale / currentScale);
        CGAffineTransform transform = CGAffineTransformScale([[gestureRecognizer view] transform], newScale, newScale);
        [gestureRecognizer view].transform = transform;

        lastScale = [gestureRecognizer scale];  // Store the previous scale factor for the next pinch gesture call  
    }
}

This works as expected, but my client wants him to be less sensitive to touch. How to reduce the pinch speed (both inside and outside) so that it increases the speed by about 100% by default?

Answer 1

Have you tried the scalecurrent value of 80%.

if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || 
        [gestureRecognizer state] == UIGestureRecognizerStateChanged) {

    CGFloat maxScale = 2.0;
    CGFloat currentScale = [gestureRecognizer scale];
    currentScale = 0.8 * currentScale;   //80% of scaling

    if(currentScale < 0.8)
        currentScale = 0.8;

    if(currentScale > maxScale)
        currentScale = maxScale;

    [gestureRecognizer view].transform = CGAffineTransformScale([[gestureRecognizer view] transform], currentScale, currentScale);

}

Answer 2

Try it.

- (void)handlePinching:(UIPinchGestureRecognizer *)gestureRecognizer {

    if([gestureRecognizer state] == UIGestureRecognizerStateBegan) {
        if (CGRectIsEmpty(self.initalFrame)) {
            self.initalFrame = gestureRecognizer.view.frame;
            // store view original frame and never change it
        }

        if (self.preScale == 0.f) {
            self.preScale = 1.f; 
        }

        gestureRecognizer.scale = self.preScale;
        // gestureRecognizer and view should share the same scale state at the beginning
    }

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan ||
        [gestureRecognizer state] == UIGestureRecognizerStateChanged) {

        const CGFloat kMaxScale = 2.0;
        const CGFloat kMinScale = 1.0;

        CGFloat newScale = gestureRecognizer.scale;

        newScale = (newScale - self.preScale) * 0.8 + self.preScale;

        newScale = MIN(newScale, kMaxScale);
        newScale = MAX(newScale, kMinScale);


        CGRect newFrame = self.initalFrame;
        newFrame.size.height *= newScale;
        newFrame.size.width *= newScale;
        gestureRecognizer.view.frame = newFrame;
        self.preScale = newScale;
    }

}

Points

• use a frame to implement the scale.
• change the value of the scaling variable to slow / scalable scaling.

Answer 3

It turns out that excessive scaling speed was actually a mistake in the associated response code. Unfortunately, this does not actually answer my actual question (for which I still need an answer!), But it helps solve my problem with the client.

Notice the added line below, which resets the gestureRecognizer identifier to 1:

- (void)handlePinchGesture:(UIPinchGestureRecognizer *)gestureRecognizer {

        ...

        lastScale = [gestureRecognizer scale];  // Store the previous scale factor for the next pinch gesture call  

        gestureRecognizer.scale = 1;
        // ^ added this line
    }
}