Mac emacs scroll bars

[Steven Tamm]

> > I have been trying to get the scrollbar to continuously scroll if
> > for example I hold down the mouse button on the up or down arrows,
> > but so far I have failed since I am a novice with the emacs source
> > code.
> My guess is that it can be done in Lisp-level using track-mouse and
> sit-for.  But it would not be so easy, judging from complicated codes
> in mouse.el.
I'm not sure one can do it at the lisp level. The particular problem is 
that holding down the mouse button doesn't generate the same kind of 
events on the mac that holding down a key would (i.e. autorepeat 
events).  Because of the event model, read-event hangs until you move 
the mouse.  So the following code:

(defun mac-scroll-down-line ()
  (track-mouse
    (let* ((done nil))
      (while (not done)
        (scroll-down 1)
        (setq done (memq (car-safe (read-event))
                    '(mouse-1 double-mouse-1 triple-mouse-1 drag-mouse-1)))
        ))))

does what you'd want if you move the mouse around... But read-event 
wouldn't do the right thing.  So it appears that there would have to be 
a new C function added that would call the new Carbon function 
GetCurrentEventButtonState (or Button on MAC_OS) so that "mouse-down" 
could be "tested" from the lisp code.

Then the code would look something like this

(defun mac-scroll-down-line ()
  (track-mouse
    (let* ((done nil))
      (while (not done)
        (scroll-down 1)
        (sit-for mouse-delay) ;; possibily have initial and subsequent delays
        (setq done (mac-is-button-down)))
      (mac-scroll-ignore-events))))

I added mac-scroll-ignore-events today to CVS.  This would be more Mac 
like, but have the annoying problem of having a 1/4 second delay after 
you let go of the mouse.  Perhaps the better solution would be to make 
a version of (read-event) that would produce null events?

> > I have included a very small patch to keyboard.c to disable emacs
> > from interpreting double and triple clicking in the scrollbar. This
> > makes it much easier for me to use the scrollbar. I am sending you
> > the patch because I see that you have been contributing heavily to
> > the development of emacs, and I'm not sure where else to send the
> > patch.  Please examine and/or try the patch and if you feel that it
> > is useful, feel free to submit the patch.
>
> Maybe similar thing can alternatively be done with
>
>     (defun mac-scroll-down ()
>       (track-mouse
>         (while (not (meeq (car-safe (read-event))
>                           '(mouse-1 double-mouse-1 triple-mouse-1))) nil)
>         (scroll-down)))
>
> (Likewise for mac-scroll-down-line, mac-scroll-up, and
> mac-scroll-up-line in term/mac-win.el.)
>
> Although both of them are not complete (e.g., drag within non-handle
> scrollbar area), they are better than before.

I checked in a change similar to this.  I forgot to add drag-mouse-1 to 
the list of ignorable events, though.

-Steven