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

[Eli Zaretskii]

> 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.