ios - 捏/缩放图像，以触摸为中心

Question

我可以像这样使用缩放功能:

- (void)twoFingerPinch:(UIPinchGestureRecognizer *)recognizer
{

    if([recognizer state] == UIGestureRecognizerStateBegan) {
        _lastScale = 1.0;
    }

    CGFloat scale = 1.0 - (_lastScale - [recognizer scale]);

    CGAffineTransform currentTransform = self.imageForEditing.transform;
    CGAffineTransform newTransform = CGAffineTransformScale(currentTransform, scale, scale);

    [self.imageForEditing setTransform:newTransform];

    _lastScale = [recognizer scale];


}

问题是图像根据它的中心缩放，所以如果您先平移图像使其不居中，然后捏/缩放，它不会放大到触摸之间的区域。我认为这一定是一个已解决的常见问题，但我一直未能找到解决方案。

Answer 1

@objc private func pinchHandler(gesture: UIPinchGestureRecognizer) {
    if let view = gesture.view {

        switch gesture.state {
        case .changed:
            let pinchCenter = CGPoint(x: gesture.location(in: view).x - view.bounds.midX,
                                      y: gesture.location(in: view).y - view.bounds.midY)
            let transform = view.transform.translatedBy(x: pinchCenter.x, y: pinchCenter.y)
                                            .scaledBy(x: gesture.scale, y: gesture.scale)
                                            .translatedBy(x: -pinchCenter.x, y: -pinchCenter.y)
            view.transform = transform
            gesture.scale = 1
        case .ended:
            // Nice animation to scale down when releasing the pinch.
            // OPTIONAL
            UIView.animate(withDuration: 0.2, animations: {
                view.transform = CGAffineTransform.identity
            })
        default:
            return
        }


    }
}