User Interaction - Core Animation - page 185

When accessing mouseLocation , it gives us the location clicked as screen coordinates
( x and y values). These coordinates are not the same as those used by the application, so
you need to convert them to window coordinates by using one of the methods built into
the NSWindow and NSView classes. Also, because CALayer objects deal in CGPoints instead
of NSPoints , we also need to change the window coordinate's returned NSRect into a
CGRect .

Now that we have the correct mouse coordinates, we need to find out which is the
deepest layer under the mouse. A call to -hitTest: on the rootLayer returns the correct
CALayer information.

The deepest layer is defined as the layer that has no sublayers that would contain the point
being passed in. For instance, if you click on the text within LZButtonLayer , CATextLayer
is returned from the -hitTest: call because it has no sublayers that contain the CGPoint
being passed in. If, however, the edge of the button is clicked, then LZButtonLayer is
returned instead. Finally, the root layer is returned if the background root layer is clicked
(see Figure 11-2).

Mouse Click

Root Layer receives the mouse event
CATextLayer is returned from the hit test

FIGURE 11-2

The Hit Test

However, we care only if the user clicked on LZButtonLayer . It is possible that the user
thought they were clicking on LZButtonLayer , but were in fact clicking its sublayer.
Therefore, an additional check was added. If the clicked layer were not a LZButtonLayer ,
we check that layer's superlayer to see if it is a LZButtonLayer . If the clicked layer is, then
its superlayer is returned instead. If neither the clicked layer nor its superlayer is a
LZButtonLayer , we return nil .

With the hit test method defined, it's now time to handle mouseUp and mouseDown events
using the code shown in Listing 11-9.