bug#18277: 24.3.93; A problem with positioning point in horizontally scrolled bidirectional text

bug#18277: 24.3.93; A problem with positioning point in horizontally scrolled bidirectional text

[martin rudalics]

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I see the following problem with positioning point in horizontally
scrolled bidirectional text.  To reproduce with Emacs -Q I type

C-u C-h t hebrew RET

split the root window via C-x 3, provoke a horizontal scroll of the left
window by, for example, moving the window's point to the left, move
point of the left window to the "I" of the L2R string EDIT on line 4 and
move my mouse cursor to the according screen position.  At this moment,
my Emacs frame appears as in the first attached screenshot
(mouse-click-ante.png).

Now I try to do `mouse-set-point' by doing <mouse-1>.  The left window
scrolls horizontally back to the position it had before the previous
horizontal scroll and the window's point moves to another position on
the same line as in the second attached screenshot
(mouse-click-post.png).

martin


In GNU Emacs 24.3.93.1 (i686-pc-mingw32)
  of 2014-08-16 on MACHNO
Repository revision: 117445 rgm@gnu.org-20140815040536-bkq3vaj8hmv3h5zj
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Important settings:
   value of $LANG: ENU
   locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
   tooltip-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

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[-- Attachment #3: mouse-click-post.png --]
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bug#18277: 24.3.93; A problem with positioning point in horizontally scrolled bidirectional text

[Eli Zaretskii]

> Date: Sat, 16 Aug 2014 11:27:09 +0200
> From: martin rudalics <rudalics@gmx.at>
> 
> C-u C-h t hebrew RET
> 
> split the root window via C-x 3, provoke a horizontal scroll of the left
> window by, for example, moving the window's point to the left, move
> point of the left window to the "I" of the L2R string EDIT on line 4 and
> move my mouse cursor to the according screen position.  At this moment,
> my Emacs frame appears as in the first attached screenshot
> (mouse-click-ante.png).
> 
> Now I try to do `mouse-set-point' by doing <mouse-1>.  The left window
> scrolls horizontally back to the position it had before the previous
> horizontal scroll and the window's point moves to another position on
> the same line as in the second attached screenshot
> (mouse-click-post.png).

Fixed in revision 117446 on the emacs-24 branch.

It was a thinko in how the X coordinate was mirrored for R2L lines
that are hscrolled.