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Re: scroll-preserve-screen-position and tall lines
From: |
Chong Yidong |
Subject: |
Re: scroll-preserve-screen-position and tall lines |
Date: |
Tue, 21 Feb 2006 10:48:26 -0500 |
An old bug:
Ralf Angeli <address@hidden> wrote:
> When `scroll-preserve-screen-position' is set to `always' Emacs
> doesn't manage to keep the vertical position of point relative to
> window boundaries if tall lines are involved. Here is a testcase:
>
> (progn
> (setq scroll-preserve-screen-position 'always)
> (pop-to-buffer (get-buffer-create "*test*"))
> (dotimes (i 50) (insert (concat (number-to-string i) "\n")))
> (insert "TALL\n")
> (put-text-property (line-beginning-position 0) (line-end-position 0)
> 'face '(:height 2.0 :inherit variable-pitch))
> (dotimes (i 50) (insert (concat (number-to-string (+ i 50)) "\n")))
> (search-backward "TALL"))
>
> After executing it, scroll the buffer by one line with `C-u 1 C-v'.
> Notice that point does not keep its vertical position but moves
> upwards together with the string "TALL". (`scroll-down' does not seem
> to be affected.)
How about making window_scroll_pixel_based preserve the value of vpos
instead of current_y? This patch removes the above bug.
*** emacs/src/window.c.~1.535.~ 2006-02-18 10:23:42.000000000 -0500
--- emacs/src/window.c 2006-02-21 10:41:23.000000000 -0500
***************
*** 4720,4726 ****
struct text_pos start;
Lisp_Object tem;
int this_scroll_margin;
! int preserve_y;
/* True if we fiddled the window vscroll field without really scrolling.
*/
int vscrolled = 0;
--- 4720,4726 ----
struct text_pos start;
Lisp_Object tem;
int this_scroll_margin;
! int old_vpos;
/* True if we fiddled the window vscroll field without really scrolling.
*/
int vscrolled = 0;
***************
*** 4788,4797 ****
{
start_display (&it, w, start);
move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
! preserve_y = it.current_y;
}
else
! preserve_y = -1;
/* Move iterator it from start the specified distance forward or
backward. The result is the new window start. */
--- 4788,4797 ----
{
start_display (&it, w, start);
move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
! old_vpos = it.vpos;
}
else
! old_vpos = -1;
/* Move iterator it from start the specified distance forward or
backward. The result is the new window start. */
***************
*** 4921,4934 ****
|| EQ (Vscroll_preserve_screen_position, Qt)))
/* We found PT at a legitimate height. Leave it alone. */
;
! else if (preserve_y >= 0)
{
! /* If we have a header line, take account of it.
! This is necessary because we set it.current_y to 0, above. */
! if (WINDOW_WANTS_HEADER_LINE_P (w))
! preserve_y -= CURRENT_HEADER_LINE_HEIGHT (w);
!
! move_it_to (&it, -1, -1, preserve_y, -1, MOVE_TO_Y);
SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
}
else
--- 4921,4929 ----
|| EQ (Vscroll_preserve_screen_position, Qt)))
/* We found PT at a legitimate height. Leave it alone. */
;
! else if (old_vpos >= 0)
{
! move_it_to (&it, -1, -1, -1, old_vpos, MOVE_TO_VPOS);
SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
}
else
***************
*** 4948,4954 ****
int charpos, bytepos;
int partial_p;
! /* Save our position, for the preserve_y case. */
charpos = IT_CHARPOS (it);
bytepos = IT_BYTEPOS (it);
--- 4943,4949 ----
int charpos, bytepos;
int partial_p;
! /* Save our position, for the old_vpos case. */
charpos = IT_CHARPOS (it);
bytepos = IT_BYTEPOS (it);
***************
*** 4978,4997 ****
|| EQ (Vscroll_preserve_screen_position, Qt)))
/* We found PT before we found the display margin, so PT is ok. */
;
! else if (preserve_y >= 0)
{
SET_TEXT_POS_FROM_MARKER (start, w->start);
start_display (&it, w, start);
! #if 0 /* It's wrong to subtract this here
! because we called start_display again
! and did not alter it.current_y this time. */
!
! /* If we have a header line, take account of it. */
! if (WINDOW_WANTS_HEADER_LINE_P (w))
! preserve_y -= CURRENT_HEADER_LINE_HEIGHT (w);
! #endif
!
! move_it_to (&it, -1, -1, preserve_y, -1, MOVE_TO_Y);
SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
}
else
--- 4973,4983 ----
|| EQ (Vscroll_preserve_screen_position, Qt)))
/* We found PT before we found the display margin, so PT is ok. */
;
! else if (old_vpos >= 0)
{
SET_TEXT_POS_FROM_MARKER (start, w->start);
start_display (&it, w, start);
! move_it_to (&it, -1, -1, -1, old_vpos, MOVE_TO_VPOS);
SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
}
else
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