Re: Changes in frame/window code

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 16 Aug 2014 15:46:04 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: emacs-devel@gnu.org
> 
> (1) When dragging I cannot move the slider entirely to the right and
>      make the first column of R2L lines visible until I release the mouse
>      button.  I suppose this is due to some off-by-one failure here but
>      there might be more to it.

I'm not sure this is at all related to R2L lines.  I wrote a trivial
function which just displays the mouse event, and bound it to clicks
on the horizontal scroll bar.  When I drag the scroll bar, even in an
entirely L2R buffer, I see some strange phenomena: e.g., more often
than not, when I drag the bar all the way to the right, releasing the
mouse button without moving the mouse reports slightly different
coordinates than the ones reported before releasing the mouse.
Moreover, many time the 2nd coordinate reported after releasing the
mouse is -1.  Try it.  Maybe it's Windows-specific, I don't know.

Btw, it looks like the information returned by mouse events on the
horizontal scroll bar is not described anywhere, not even in NEWS.
Your use of (cdr (nth 2 start-position)) in
scroll-bar-horizontal-drag-1 got my jaw dropped for a few seconds,
before I realized it was not the Y coordinate...

Also, I don't understand the subtlety of +1 in setting up the scroll
info, e.g.:

  /* Allow nPage to be one larger than nPos so we don't allow to scroll
     an already fully visible buffer.  */
  si.nPage = min (portion, si.nMax) + 1;
  si.nPos = min (position, si.nMax);

The comment doesn't correspond to the code, and I couldn't understand
what's behind this trick.

> (2) Sometimes during dragging the slider starts moving for-/backward in
>      some erratic fashion.  I'm not yet sure whether this is caused by an
>      hmargin issue or something else.

I could only see this in the very first line of the tutorial.  There
was an old and very subtle bug in xdisp.c, revealed by
set_horizontal_scroll_bar, which caused broken cursor motion in that
line.  This is now fixed in r117711 on the trunk.  If you still see
something like that, and it's not related to the few L2R lines in the
tutorial, please report a bug with the recipe.

> (3) Line 121 (written backwards as)
> 
> אם הסמן נמצא באמצע מילה, M-f זז לסוף המילה. אם הסמן נמצא בין שתי מלים,
> 
>     of the tutorial presents a special problem: When I'm repeatedly doing
>     `next-line' on the rightmost column before that line and are about
>     to move to that line I enter some strange sort of loop with the
>     slider in the center of the scroll bar trying to move back- and
>     forward.  C-g gets me out of it but I can't tell so far why I'm stuck
>     there.

This is now fixed in r117447 on the release branch.  The previous
revision fixed bug #18277.

> If (2) or (3) are caused by bug#18277 (or a common underlying problem)
> it should be easier to resolve the remaining issues.

They were all separate and completely unrelated problems.