bug#4426: 23.0.91; posn-at-point returns an incorrect value

bug#4426: 23.0.91; posn-at-point returns an incorrect value

[IRIE Shinsuke]

I was going to acquire the width and height of a character the cursor
is over, by using the following code:

  (posn-object-width-height (posn-at-point))

However, I found that this code gives back a wrong result when a
header line is displayed such as tabbar-mode. This code returns the
size of another character, which is in the position different from the
exact one in the number of objects included in the header line.
For example, when the cursor is in the top left corner of the window,
the size of the object in the left end of the header line is obtained.

Steps to reproduce:

  1. Turn on tabbar-mode.

  2. Evaluate the following expressions in *scratch*:

       (defun char-w-h ()
         (message "%s" (posn-object-width-height (posn-at-point))))
       (add-hook 'post-command-hook 'char-w-h)

  3. Move a cursor from place to place in the window.


In GNU Emacs 23.0.91.1 (i486-pc-linux-gnu, GTK+ Version 2.16.0)
 of 2009-04-05 on palmer, modified by Debian
 (emacs-snapshot package, version 1:20090320-1ubuntu1)
Windowing system distributor `The X.Org Foundation', version 11.0.10600000
configured using `configure  '--build' 'i486-linux-gnu' '--host'
'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib'
'--libexecdir=/usr/lib' '--localstatedir=/var'
'--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes'
'--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.0.91/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.0.91/site-lisp:/usr/share/emacs/site-lisp'
'--with-x=yes' '--with-x-toolkit=gtk' 'build_alias=i486-linux-gnu'
'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN
-DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed'
'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ja_JP.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

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

Recent input:
u i r e SPC ' t C-p C-p C-p C-p C-p C-p C-p C-n C-n
C-n C-n C-n C-f C-f C-f C-f C-f C-f C-f C-f C-b C-b
C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-n
C-n C-e a b b a r ) C-j ( t a b b a r - m o d e ) C-j
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p
C-n C-p C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f
C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f
C-f C-f C-f C-f C-f C-n C-p C-p C-b C-b C-b C-b C-b
C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b
C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b
C-b C-b C-b C-b C-b C-b C-b C-b C-b C-b C-n C-n C-n
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-n C-n
C-n C-p C-p C-p C-p C-p C-n C-n C-b C-p C-p C-n C-a
C-f C-f C-f C-f C-f C-f C-p C-n C-n C-n C-n C-n C-n
C-n C-n C-n C-n C-n C-n C-n C-p C-p C-p C-p C-p C-p
C-p C-p C-p C-p C-p C-p C-p C-p C-a C-a C-f C-f C-f
C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-n C-n
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n ( r e m o v
e - h o o k SPC ' p o s t - c o m m a n d - h o o k
SPC ' c h a r - w - h ) C-j M-x r e p o r t - e m a
<tab> RET

Recent messages:
(7 . 14) [3 times]
(0 . 14)
(7 . 14)
(0 . 14)
(7 . 14)
(0 . 14)
(7 . 14)
(0 . 14)
(7 . 14) [3 times]
(0 . 14) [41 times]

-- 
IRIE Shinsuke, Ph.D.
irieshinsuke@yahoo.co.jp

bug#4426: [PATCH] posn-at-point returns an incorrect value

[IRIE Shinsuke]

[-- Attachment #1: Type: text/plain, Size: 831 bytes --]

6 months ago I reported bug #4426, that is, `posn-at-point' returns
incorrect value when header line is displayed. I've investigated this
bug and found the solution.

I describe again this bug:

   If header line is displayed, `posn-object-width-height' incorrectly
   returns the size of object in position different from specified one.

   For example, an expression

     (posn-object-width-height (posn-at-point (window-start)))

   must return the width and height of character on the top left corner
   of text area, but actually returns the ones on the beginning of
   header line.

It turned out that this problem occurs as a result of confusion between
it.vpos and MATRIX_ROW_VPOS in a function buffer_posn_from_coords
(included in dispnew.c).

So I wrote the small patch to fix this bug. Please check it.


IRIE Shinsuke

[-- Attachment #2: fix_bug4426.patch --]
[-- Type: text/x-diff, Size: 1007 bytes --]

=== modified file 'src/dispnew.c'
*** old/src/dispnew.c	2010-03-16 14:48:29 +0000
--- new/src/dispnew.c	2010-03-16 16:06:28 +0000
***************
*** 5937,5942 ****
--- 5937,5943 ----
    Lisp_Object old_current_buffer = Fcurrent_buffer ();
    struct text_pos startp;
    Lisp_Object string;
+   int matrix_vpos;
    struct glyph_row *row;
  #ifdef HAVE_WINDOW_SYSTEM
    struct image *img = 0;
***************
*** 5974,5981 ****
      }
  #endif
  
!   if (it.vpos < w->current_matrix->nrows
!       && (row = MATRIX_ROW (w->current_matrix, it.vpos),
  	  row->enabled_p))
      {
        if (it.hpos < row->used[TEXT_AREA])
--- 5975,5984 ----
      }
  #endif
  
!   /* it.vpos isn't the same as MATRIX_ROW_VPOS if header line is displayed */
!   matrix_vpos = (w->current_matrix->rows->mode_line_p ? 1 : 0) + it.vpos;
!   if (matrix_vpos < w->current_matrix->nrows
!       && (row = MATRIX_ROW (w->current_matrix, matrix_vpos),
  	  row->enabled_p))
      {
        if (it.hpos < row->used[TEXT_AREA])

bug#4426: [PATCH] posn-at-point returns an incorrect value

[Lars Magne Ingebrigtsen]

IRIE Shinsuke <irieshinsuke@yahoo.co.jp> writes:

>    If header line is displayed, `posn-object-width-height' incorrectly
>    returns the size of object in position different from specified one.
>
>    For example, an expression
>
>      (posn-object-width-height (posn-at-point (window-start)))
>
>    must return the width and height of character on the top left corner
>    of text area, but actually returns the ones on the beginning of
>    header line.
>
> It turned out that this problem occurs as a result of confusion between
> it.vpos and MATRIX_ROW_VPOS in a function buffer_posn_from_coords
> (included in dispnew.c).
>
> So I wrote the small patch to fix this bug. Please check it.

[...]

> !   if (it.vpos < w->current_matrix->nrows
> !       && (row = MATRIX_ROW (w->current_matrix, it.vpos),
>   	  row->enabled_p))
>       {
>         if (it.hpos < row->used[TEXT_AREA])
> --- 5975,5984 ----
>       }
>   #endif
>   
> !   /* it.vpos isn't the same as MATRIX_ROW_VPOS if header line is displayed */
> !   matrix_vpos = (w->current_matrix->rows->mode_line_p ? 1 : 0) + it.vpos;
> !   if (matrix_vpos < w->current_matrix->nrows
> !       && (row = MATRIX_ROW (w->current_matrix, matrix_vpos),
>   	  row->enabled_p))
>       {
>         if (it.hpos < row->used[TEXT_AREA])

As far as I can tell, this patch hasn't been applied yet.  I'm not
familiar enough with this code to say whether this looks correct or
not.  Could someone take a look?

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

bug#4426: [PATCH] posn-at-point returns an incorrect value

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Date: Sun, 18 Sep 2011 10:21:43 +0200
> Cc: 4426@debbugs.gnu.org
> 
> As far as I can tell, this patch hasn't been applied yet.  I'm not
> familiar enough with this code to say whether this looks correct or
> not.  Could someone take a look?

Is the original problem still present?  AFAIR, Chong fixed something
similar some time ago.

bug#4426: [PATCH] posn-at-point returns an incorrect value

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Date: Sun, 18 Sep 2011 10:21:43 +0200
> Cc: 4426@debbugs.gnu.org
> 
> As far as I can tell, this patch hasn't been applied yet.  I'm not
> familiar enough with this code to say whether this looks correct or
> not.  Could someone take a look?

I took a look.  The problem indeed was still there.  I installed a fix
(slightly different from what the OP suggested).

Thanks.