convertRect:toView: works different on iPad retina and iPad 2 - iphone

Question

I have this code that works perfectly on an iPad2 but it scales wrong on a Retina iPad.
I executed the app with no change on both iPads and the behaviour is totally different.
On the Retina iPad the images come back to the original position and the transform doesn't take place.
The code takes a group of views, add them to a temporal view, resize the temporal view and them add those views back, so I can resize all of them at the same time.
- (IBAction)scaleParts:(UIPinchGestureRecognizer *)sender {
if (sender.state == UIGestureRecognizerStateBegan) {
self.tempCanvasView = [[UIView alloc] initWithFrame:self.canvas.bounds];
self.tempCanvasView.backgroundColor = [UIColor redColor];
for (UIView *view in [self.canvas subviews]) {
CGRect currentFrame = view.bounds;
CGRect newFrame = [view convertRect:currentFrame toView:self.tempCanvasView];
view.bounds = newFrame;
[self.tempCanvasView addSubview:view];
}
[self.canvas addSubview:self.tempCanvasView];
} else if (sender.state == UIGestureRecognizerStateChanged) {
self.tempCanvasView.transform = CGAffineTransformScale(self.tempCanvasView.transform, sender.scale, sender.scale);
sender.scale = 1.0;
} else if (sender.state == UIGestureRecognizerStateEnded) {
for (UIView *view in [self.tempCanvasView subviews]) {
CGRect currentFrame = view.bounds;
CGRect newFrame = [view convertRect:currentFrame toView:self.canvas];
view.frame = newFrame;
[self.canvas addSubview:view];
}
[self.tempCanvasView removeFromSuperview];
self.tempCanvasView = nil;
}
}

Answer 1

Maybe you need to detect which screen type the app is using (scale=1 for iPad and 2 for iPadRetina).
CGFloat scale = [[UIScreen mainScreen] scale];
after that..
if (scale==1) {
//code from above
} else {
//code from above with small modification
}

Answer 2

Here is a correct method to do it:
SWIFT:
extension UIView {
func convertRectCorrectly(rect: CGRect, toView view: UIView) -> CGRect {
if UIScreen.mainScreen().scale == 1 {
return self.convertRect(rect, toView: view)
}
else if self == view {
return rect
}
else {
var rectInParent = self.convertRect(rect, toView: self.superview)
rectInParent.origin.x /= UIScreen.mainScreen().scale
rectInParent.origin.y /= UIScreen.mainScreen().scale
let superViewRect = self.superview!.convertRectCorrectly(self.superview!.frame, toView: view)
rectInParent.origin.x += superViewRect.origin.x
rectInParent.origin.y += superViewRect.origin.y
return rectInParent
}
}
}