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Editorial Team
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Asked: 2026-05-31T21:24:47+00:00

I’ve got an image that’s allowed to be rotated and scaled by the user.

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I’ve got an image that’s allowed to be rotated and scaled by the user.
Every time the user clicks the image I try to figure out if the point is transparent or not.

If it’s transparent I return null in my view’s HitTest, if it’s not transparent I return the view. Problems start when user rotates the image. In my hitTest method, I need to transform the point according to the current view’s rotation. Otherwise the point will indicate an irrelevant location on the view (and the image).

How do I do that?

Thank you very much.

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1 Answer

  1. Editorial Team

    This CGAffineTransform Reference might help:

    CGPointApplyAffineTransform

CGRectApplyAffineTransform

    and

    CGSizeApplyAffineTransform

    But before you start thinking that you need to perform the mapping by hand, I would suggest to give it a try ‘as if’ the current transformation was CGAffineIdentity, and code your coordinate detection accordingly. You might be surprised by the results …

    My own experience says that it looks like when you get your points from UITouch locationIn_SomeView_ the inverted matrix of SomeView is applied to the point before it is handed back to you.

    So, you probably don’t need any of the CGxxxApplyAffineTransform unless you generate the points yourself, outside of the events system.

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