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

[Eli Zaretskii <eliz@gnu.org>]

> From: Kenichi Handa <handa@gnu.org>
> Cc: jan.h.d@swipnet.se, xfq.free@gmail.com, 15273@debbugs.gnu.org
> Date: Sun, 08 Sep 2013 22:05:41 +0900
> 
> (aref composition-function-table #x20E4)
> => (["\\c.\\c^+" 1 compose-gstring-for-graphic]
>     [nil 0 compose-gstring-for-graphic])
> 
> This says that a base character (char-category ".") followed
> by a combing character (char-category "^") should be
> composed by the function compose-gstring-for-graphic if
> those character are displayed by the same font.
> 
> But, I found a bug in characters.el.  In it, U+20E4's
> char-actegory is not set as "^".  So, Emacs couldn't compose
> it with the preceding base character.  I've just installed a
> fix.
> 
> Now, Emacs composes U+20E4 with the preceding "!" if the
> same font is selected for those two characters.

Thanks.

> Next, I'm not sure whether Emacs composes them correctly if
> the underlying font driver doesn't support OTF's "mark" and
> "mkmk" features.  The function compose-gstring-for-graphic
> has a code for such a case, but I don't remember that I
> wrote a code for "enclosing combining marks".

Looks like Uniscribe should need this, at least on XP: I do get a
composition, but the left part of the triangle is off-screen.