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bug#10903: 24.0.93; redisplay glitch with before-string and display over
bug#10903: 24.0.93; redisplay glitch with before-string and display overlays
Tue, 28 Feb 2012 22:40:17 +0200
> From: Stephen Berman <firstname.lastname@example.org>
> Date: Mon, 27 Feb 2012 23:04:03 +0100
> 1. emacs -Q
> 2. Type `C-x b a RET' to get a fresh buffer in Fundamental mode, and at
> (point-min) type "012".
> 3. Type `M-<' so that the cursor is over (i.e. just before) `0'.
> 4. Type `M-: (overlay-put (make-overlay (point) (point)) 'before-string
> "*")'. Now you see this:
> 5. Type `M-: (overlay-put (make-overlay (point) (1+ (point))) 'display
> "")'. Now you see this:
> 6. Type `M-: (remove-overlays)' to restore "012".
> 7. Type SPC to advance the cursor and the start of "012" to column one.
> 8. Repeat step 4. Now you see this:
> 9. Repeat step 5. Now you see this:
We were hitting on an old redisplay optimization that didn't play well
with the bidi-aware display engine.
I think I fixed this. Thanks for such a clear-cut test case.
Since Savannah is on the move, I cannot commit the fix, but perhaps
you could test it locally and see if there are any leftovers. Here's
=== modified file 'src/xdisp.c'
--- src/xdisp.c 2012-02-12 09:46:33 +0000
+++ src/xdisp.c 2012-02-28 20:35:41 +0000
@@ -5156,6 +5156,10 @@ next_overlay_string (struct it *it)
it->current.overlay_string_index = -1;
it->n_overlay_strings = 0;
it->overlay_strings_charpos = -1;
+ /* If there's an empty display string on the stack, pop the
+ stack, to resync the bidi iterator with IT's position. */
+ if (it->sp > 0 && STRINGP (it->string) && !SCHARS (it->string))
+ pop_it (it);
/* If we're at the end of the buffer, record that we have
processed the overlay strings there already, so that
@@ -5453,8 +5457,15 @@ get_overlay_strings_1 (struct it *it, EM
xassert (!compute_stop_p || it->sp == 0);
/* When called from handle_stop, there might be an empty display
- string loaded. In that case, don't bother saving it. */
- if (!STRINGP (it->string) || SCHARS (it->string))
+ string loaded. In that case, don't bother saving it. But
+ don't use this optimization with the bidi iterator, since we
+ need the corresponding pop_it call to resync the bidi
+ iterator's position with IT's position, after we are done
+ with the overlay strings. (The corresponding call to pop_it
+ in case of an empty display string is in
+ next_overlay_string.) */
+ if (!(!it->bidi_p
+ && STRINGP (it->string) && !SCHARS (it->string)))
push_it (it, NULL);
/* Set up IT to deliver display elements from the first overlay