bug#9541: mouse-1 inside scroll-margin causes undesirable region activation

bug#9541: mouse-1 inside scroll-margin causes undesirable region activation

[Le Wang]

Repro:

1. emacs -Q
2. eval:

  (setq scroll-margin 5)

3. open some multi-page file
4. left-click in bottom margin (bottom 5 lines)

Notice region is selected and active.

This problem is noted here: http://www.emacswiki.org/emacs/SmoothScrolling

A package attempts to solve it here:
http://adamspiers.org/computing/elisp/smooth-scrolling.el

But the bug is in Emacs.

-- 
Le

bug#9541: Acknowledgement (mouse-1 inside scroll-margin causes undesirable region activation)

[Le Wang]

Here is my work-around.  I don't fully understand the ramifications of
doing this, but so far it seems work.

(defun le::mouse-drag-region (event)
  "mouse-drag-region but clickable in scroll-margin"
  (interactive "e")
  (let ((scroll-margin 0))
    (mouse-drag-region event)))

(global-set-key [(down-mouse-1)] 'le::mouse-drag-region)

-- 
Le

bug#9541: mouse-1 inside scroll-margin causes undesirable region activation

[Stefan Monnier]

> Here is my work-around.  I don't fully understand the ramifications of
> doing this, but so far it seems work.

> (defun le::mouse-drag-region (event)
>   "mouse-drag-region but clickable in scroll-margin"
>   (interactive "e")
>   (let ((scroll-margin 0))
>     (mouse-drag-region event)))

But this goes against the definition of scroll-margin which does not
make any exception for mouse events.

An alternative would be to declare that scroll-margin does not apply to
commands when run via mouse events.

This said, the current behavior of scroll-margin is clearly problematic
and even buggy (e.g. it seems that displaying the EOB prevents the
mouse-clicks from causing a scroll, even when that scroll would be
towards the BOB).


        Stefan

bug#9541: mouse-1 inside scroll-margin causes undesirable region activation

[Johan Bockgård]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> This said, the current behavior of scroll-margin is clearly problematic
> and even buggy (e.g. it seems that displaying the EOB prevents the
> mouse-clicks from causing a scroll, even when that scroll would be
> towards the BOB).

The real bug is that mouse-clicks set the mark (always). (Search for
push-mark in mouse-drag-track.)

bug#9541: mouse-1 inside scroll-margin causes undesirable region activation

[Chong Yidong]

Johan Bockgård <bojohan@gnu.org> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>> This said, the current behavior of scroll-margin is clearly problematic
>> and even buggy (e.g. it seems that displaying the EOB prevents the
>> mouse-clicks from causing a scroll, even when that scroll would be
>> towards the BOB).
>
> The real bug is that mouse-clicks set the mark (always). (Search for
> push-mark in mouse-drag-track.)

No, that's intended behavior.  The OP's suggestion of disabling the
scroll margin while tracking a mouse drag is on the right track.  I've
committed a change along those lines.