CALayer -hitTest: not respecting containsPoint: overload

Question

Back again and have a different question with the same function that I posted before:

- (AIEnemyUnit *) hitTestForEnemyUnit:(CGPoint)where {
    CALayer * layer = [self hitTest:where];

    while (layer) {
        if ([layer isKindOfClass:[AIEnemyUnit class]]) {
            return (AIEnemyUnit *)layer;
        } else {
            layer = layer.superlayer;
        }
    }

    return nil;
}

I have a bomb that the user drags on top of the enemy so that it is displayed directly above the AIEnemyUnit. For this bomb I implemented the CALayer -containsPoint: to return NO during a drag to allow -hitTest: to pass through the layer. Basically this type of hit testing was working fine with these "pass-through" layers as long as I only used CGImageRef contexts. However once I started implementing sublayers for additional effects on the bomb, -hitTest: immediately broke. It was obvious, the new layers were capturing the -hitTest:. I tried implementing the same technique by overloading -containsPoint: for these layers, but it was still returning the bomb's generic CALayer subclass instead of passing through.

Is there a better way?

Answer 1

Maybe the "where" point is not relative to your "self" layer. You need to convert these points between the layers coordinate systems using:

– convertPoint:fromLayer: or – convertPoint:toLayer:

See http://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CALayer_class/Introduction/Introduction.html#//apple_ref/occ/instm/CALayer/convertPoint:fromLayer:

Answer 2

I resolved this by putting everything on a second "root" layer (called "gameLayer") the same size as the original. Then during the UIPanGestureRecognizer, I move the bomb element from "gameLayer" into my UIView.layer. Then while I am testing for a AIEnemyUnit, I only run the hitTest on the "gameLayer".

- UIView.layer --------- gameLayer 
           |                |
     dragObj(bomb)     gameElements
                            |
                           bomb