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POHow should I interact with the geometry of a UIView, disregarding any transforms applied?
 

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  1. POHow should I interact with the geometry of a UIView, disregarding any transforms applied?
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    <p>I have a view that I would like the user to rotate around its center, by tapping and holding somewhere and just move their finger round and round.</p> <p>I have all the geometry worked out; What I do is store the initial touch angle relative to the center as offsetAngle, then my touchesMoved method looks like this:</p> <pre><code>- (void) touchesMoved: (NSSet *)touches withEvent:(UIEvent *)event { self.transform = CGAffineTransformMakeRotation(0); CGPoint location = [[touches anyObject] locationInView: self]; CGPoint actualCenter = [self convertPoint: self.center fromView: self.superview]; CGPoint relativeTouch = [MathHelper translatePoint:location relativeTo: actualCenter]; CGPoint zero = CGPointMake(0, 0); float angle = [MathHelper getAngleForPoint:zero andPoint:relativeTouch]; self.transform = CGAffineTransformMakeRotation(offsetAngle-angle); } </code></pre> <p>The ugly bit is the first line, where I have to restore the rotation in order to get the correct event positions in the view. If I don't that, then the locations jump all over the place as there's no continuity, since the view is rotating...</p> <p>Another issue is when you want to manipulate a view's frame (eg. moving it down), when the view has a transform applied:</p> <pre><code>- (IBAction)toggleSettingsView { BOOL state = [settingsSwitch isOn]; float height = optionsView.bounds.size.height; CGRect polygonFrame = polygonView.frame; [UIView beginAnimations:@"advancedAnimations" context:nil]; [UIView setAnimationDuration:0.3]; if (state) { optionsView.alpha = 1.0; polygonFrame.origin.y += height; } else { optionsView.alpha = 0.0; polygonFrame.origin.y -= height; } polygonView.frame = polygonFrame; [UIView commitAnimations]; } </code></pre> <p>This distorts the view heavily.</p> <p>I must mention that both the CGTransform and the CALayer transform have the same effect.</p> <p>This smells like I'm doing something wrong, but I don't know what I should be doing.</p>
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