dragging between frames?

[David Reitter <david.reitter@gmail.com>]

How does one recognize the target frame/window of a "drag" action?

We've been trying to track the mouse using something like this:

(track-mouse
	(while (print (read-event)))

... which always returns an event that is relative to the selected  
frame, rather than the one the mouse is over.

This does not yield desired results when the window manager does not  
automatically switch focus.

It seems that there is no way to find out where the mouse is unless it  
is over a selected frame.  (mouse-position) and (mouse-pixel-position)  
always return a value that is relative to the origin of the selected  
frame, and there seems to be no function that would return the window  
underneath the mouse or at given global pixel coordinates.

I can probably hack something together to fix our specific problem  
with dragging and dropping on Carbon, but that wouldn't be the general  
solution that would work on other systems.  Shouldn't there be a  
general way to do this?

Thanks in advance for your comments.