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PODetect touches only on non-transparent pixels of UIImageView, efficiently
 

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    <p>How would you detect touches only on non-transparent pixels of a <code>UIImageView</code>, efficiently?</p> <p>Consider an image like the one below, displayed with <code>UIImageView</code>. The goal is be to make the gesture recognisers respond only when the touch happens in the non-transparent (black in this case) area of the image.</p> <p><img src="https://i.stack.imgur.com/OHCHD.png" alt="enter image description here"></p> <h2>Ideas</h2> <ul> <li>Override <a href="http://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/uiview/uiview.html#//apple_ref/occ/instm/UIView/hitTest:withEvent:" rel="noreferrer"><code>hitTest:withEvent:</code></a> or <a href="http://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/uiview/uiview.html#//apple_ref/occ/instm/UIView/pointInside:withEvent:" rel="noreferrer"><code>pointInside:withEvent:</code></a>, although this approach might be terribly inefficient as these methods get called many times during a touch event.</li> <li>Checking if a single pixel is transparent might create unexpected results, as fingers are bigger than one pixel. Checking a circular area of pixels around the hit point, or trying to find a transparent path towards an edge might work better. </li> </ul> <h2>Bonus</h2> <ul> <li>It'd be nice to differentiate between outer and inner transparent pixels of an image. In the example, the transparent pixels inside the zero should also be considered valid.</li> <li>What happens if the image has a transform?</li> <li>Can the image processing be hardware accelerated?</li> </ul>
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    1. COI open-sourced what we ended up doing here: https://github.com/robotmedia/RMShapedImageView
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