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copied!<p>Something I stumbled across while scratching my head over a similar problem is that CALayer uses <code>containsPoint:</code> when you send it <code>hitTest:</code></p> <p>Its default behaviour is to test against bounds, but we can override and get it to check the alpha channel, and just use CALayer's built in hit-testing to handle the rest:</p> <pre><code>- (BOOL) containsPoint:(CGPoint)p { return CGRectContainsPoint(self.bounds, p) && !ImagePointIsTransparent(self.contents, p)) return YES; } </code></pre> <p>There's a discussion of testing for a single pixel's alpha at <a href="https://stackoverflow.com/questions/1042830/retrieving-a-pixel-alpha-value-for-a-uiimage">Retrieving a pixel alpha value for a UIImage</a></p> <p>This worked for my purposes:</p> <pre><code>static BOOL ImagePointIsTransparent(CGImageRef image, CGPoint p) { uint8_t alpha; CGContextRef context = CGBitmapContextCreate(&alpha, 1, 1, 8, 1, NULL, kCGImageAlphaOnly); CGContextDrawImage(context, CGRectMake(-p.x, -p.y, CGImageGetWidth(image), CGImageGetHeight(image)), image); CGContextRelease(context); return alpha == 0; } </code></pre> <p>(If you're using <code>renderInContext:</code> to draw to the CALayer rather than setting its contents property, then it's going to be more complicated. This might be useful in that case: <a href="http://www.cimgf.com/2009/02/03/record-your-core-animation-animation/" rel="nofollow noreferrer">http://www.cimgf.com/2009/02/03/record-your-core-animation-animation/</a>)</p>

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