bug#15273: 24.3.50; Combining character sequences are displayed weirdly

[Eli Zaretskii <eliz@gnu.org>]

> From: Jan Djärv <jan.h.d@swipnet.se>
> Date: Thu, 5 Sep 2013 18:48:43 +0200
> Cc: 15273@debbugs.gnu.org
> 
> 
> >  emacs -Q
> >  !                      ;; input an exclamation mark (#x21)
> >  C-x 8 RET 2 0 E 4 RET  ;; COMBINING ENCLOSING UPWARD POINTING TRIANGLE
> >  RET                    ;; Newline
> >  C-x 8 2 6 A 0 RET      ;; WARNING SIGN
> > 
> 
> I assume you mean C-x 8 RET 2 6 A 0 RET.
> 
> > I tried many fonts, but all results look weird (the first line is
> > incomplete and too large).
> > 
> > (I haven't tried it on other platforms yet, so I'm not sure whether it's
> > NS-port specific.)
> 
> On Fedora 19, the first does not combine, I just get ! followed by an upward pointing triangle.
> The second is very small, see screen shot.
> 
> The NS one looks better, but when moving the cursor over the first row, it redraws funny.  And metrics are off, the distance between the first triangle and the aaa to the right is actually only one space.  The aaa to the left is also followed by a space, but there the distance is too short, and the source of the redraw error.
> 
> W32 anyone?

On w32, the Uniscribe font driver does not compose these two
characters.  So I guess this composition is done by the driver used by
NS, and perhaps the composition information Emacs gets is incorrect.

Once again, please show the full output of "C-u C-x =" on the composed
character, the pixel-level data of the composition shown there will
probably tell us what is wrong.