Mouse drags and the responder chain

[Adrian Robert]

In Emacs, I have a situation where I need to track a scrollbar drag 
without using a modal loop.  In OS X, the NSWindow containing the 
scrollbar accepts mouse movement events (as does, assumedly, the 
scrollbar), and implementing -mouseDragged: in an NSScroller subclass 
does the trick: it gets fed the drag events.  In GNUstep, however, this 
only works until the mouse pointer leaves the scrollbar area, at which 
point -mouseDragged: is no longer called.  Thus, you cannot drag the 
scrollbar "sloppily".

I traced the behavior to [NSWindow -sendEvent:], which does the 
following:

            case NSLeftMouseDragged:
              v = [_wv hitTest: [theEvent locationInWindow]];
              [v mouseDragged: theEvent];
              break;

Drags are only sent to the object they are over.  Thus, even if the 
scrollbar explicitly requests and gets firstResponder status from the 
window, it still won't get the events.  I'm not sure how the 
implementation on OS X differs, but it might be that the drags are sent 
according to the responder chain instead of or in addition to the hit 
detection.  Any thoughts?  I'd like to get GNUstep working more 
similarly to OS X if we can figure out what it does, unless people 
think there is something incorrect about it.

thanks