Re: Mouse highlighting and fonts

[Chong Yidong]

Chong Yidong <address@hidden> writes:

> Under certain circumstances, the area to the left and/or right of the
> physical cursor doesn't acquire the proper mouse-face.
>
> This appears to be a long-standing bug, but one that didn't show up
> until the new font code.  That's because it arises as follows: when the
> cursor glyph has a nonzero lbearing or rbearing (i.e., it overlaps with
> its neighbors), the neighboring glyphs are redrawn, and this can
> overwrite the mouse-face highlight.  See xdisp.c:19934. 

According to the comments, this code is supposed to redraw glyphs that
are overwritten because of the left/right overhang of the specified
glyph string.  But I've never noticed overlapping glyphs in Emacs.
Under what circumstances can overlapping glyphs occur?

In other words, would there be any effect from simply turning off the
overlap-compensation code, as indicated?  Anyone know?

(Gerd, do you recall why you wrote this code?)

*** trunk/src/xdisp.c.~1.1213.~ 2008-05-24 18:34:24.000000000 -0400
--- trunk/src/xdisp.c   2008-05-24 21:25:06.000000000 -0400
***************
*** 19928,19933 ****
--- 19928,19934 ----
    else
      x_reached = x;
  
+ #if 0
    /* If there are any glyphs with lbearing < 0 or rbearing > width in
       the row, redraw some glyphs in front or following the glyph
       strings built above.  */
***************
*** 20015,20020 ****
--- 20016,20022 ----
            s->clip_tail = clip_tail;
          }
      }
+ #endif
  
    /* Draw all strings.  */
    for (s = head; s; s = s->next)