Question

I have been developing a simple game for iOS which involves dragging and using rotation- and other gesture recognizers. Dragging is realized through touchesBegan/Moved/Ended and rotation – through recognizer.

The views are irregularly shaped, and the view borders sometimes overlap, so I implemented Ole Belgeman’s UIImage+ColorAtPixel in my picture view and overrode isPointInside method in the main element view. isPointInside invokes the method in picture view, which checks alpha at touch point and returns NO if the transparent section has been touched. Essentially, hitTest ignores this branch.

But the side effect of it is that hitTest ignores all touches on the transparent section, and rotation recognizer only works on the non-transparent zone. For some views, which are too small in size, it becomes impossible to use rotation gesture 🙁

Is there any way to somehow avoid this problem and use hitTest logic only for touchesBegan? I tried to work the solution out, but it seems that hitTest works strictly before any touch handling.

Checking the transparency at touchesBegan works, but when you touch the transparent section, which overlaps the non-transparent section of the other view, the latter doesn’t receive the touch.

I just can’t figure out the trick…

Thank you in advance for any help!

Answer 1

I would make the dragging use a UIPanGestureRecognizer, so that you can implement the delegate method -gestureRecognizer:shouldReceiveTouch: to return NO when your pan recognizer is considering touches in the transparent area. Leave it unimplemented or return YES from your rotation recognizer to receive everything.

In addition, using gesture recognizers for both kinds of actions has other benefits, like the ability to specify dependencies with -requireGestureRecognizerToFail:.