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    <p>I am not sure I fully understand your description of the problem, so a dummy app would be really helpful. But here's my analysis from what I can seen now:</p> <p>You say that you have two UIImageViews, Background and MaskImage. From this, and from your code, I understand that what you want to do is:</p> <ol> <li>get a CGPath that represents the actual shape of MaskImage, after various transforms have been applied, from the point of view of (presumably) a superview or some higher-than-superview. </li> <li>Use that CGPath to define a CAShapeLayer, which you will use as the mask on the backing layer of some other view, presumably the Background UIImageView</li> </ol> <p>In that case, MaskImage in your text corresponds to your code's <code>currentView</code> (since that's where you're getting the transform), and Background in your text corresponds to your code's <code>currentImageView</code> (since that's where you're changing the layer's mask). Right?</p> <p>If all of that is correct, then there are two key problems with your code:</p> <ol> <li><p>You want to get the a CGPath representing the <em>transformed shape</em> of currentView. But you're grabbing <code>currentView.frame</code>. This is wrong. <code>currentView.frame</code> will represent the smallest rect, in the coordinates of <code>currentView.superview</code>, which can contain the transformed shape of currentView. So, for instance, if currentView is a square rotated by 45 degrees, then currentView.frame is still a square, just a larger square. Instead, what you should be doing is getting <code>currentView.bounds</code>, which is the rect that represents how currentView's shape in its own coordinate system, generating a path from that, and then apply <code>currentView.transform</code> to that path.</p></li> <li><p>You don't specify anywhere, in your code or text, how to map from the coordinate system of <code>currentView.superview</code> to the coordinate system of MaskImage. You also need to do this before applying the shape to MaskImage.layer.mask.</p></li> </ol> <p>For instance, I can imagine an application where the screen was cut into two equal side left and right, which presented a large photo image on the left side of the screen, and on the right side of the screen it allowed you to pan, rotate, and scale an image of a black rectangle. Then the app would use the black rectangle on the right-hand side to define a CAShapeLayer that was applied as a mask over the image on the left-hand side. This sounds like what you're going for. So what I'm saying is, that the logical set of steps you need for this to work is:</p> <ol> <li>Get a CGPath for the <em>bounds</em> of the black rect, which will be an untransfored rect.</li> <li>Transform this CGPath with the same transform being applied on the black rectangle.</li> <li>Represent this CGPath in the coordinate system of a rect containing just the right-hand side of the screen. Since the right-hand and left-hand sides are congruent, it is now also in the coordinate system that can be directly applied to the left-hand side of the screen.</li> <li>Use the CGPath to define a CALayer, apply this CALayer to the view representing the left-hand side of the screen, and call setNeedsDisplay on that view's layer.</li> </ol> <p>P.S. By the way, there's a third problem. Note that, technically, when you add a .mask to a layer, that layer should not have a superlayer. So you shouldn't add a .mask to the backing layer of a UIView already in the view hierarchy, since it will have a super layer.So, I believe, what you should do is temporarily remove the UIView from the view hierarchy, add the mask layer, and then re-add the view to the view hierarchy.</p>
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    1. POCreate CGpath from UIimageview with rotation and scale for use as cglayer mask
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    1. COThanks for the reply. I added in the full example code (with images). Using bounds helped but it still goes to pieces when I rotate or scale but its a lot better now.
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