bug#23292: 24.5; Combining characters do not reliably combine

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 15 Apr 2016 11:32:29 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: hdfssk@gmail.com, 23292@debbugs.gnu.org
> 
> For the record, the composition works for me on MS-Windows using the
> Arial Unicode MS font, and the composition data looks quite different
> (and makes much more sense to me) than what the OP shows:
> 
>   Composed with the following character(s) "̷" using this font:
>     uniscribe:-outline-Arial Unicode MS-normal-normal-normal-sans-13-*-*-*-p-*-iso8859-1
>   by these glyphs:
>     [0 1 111 82 7 1 6 14 4 nil]
>     [0 1 823 671 0 -5 -2 14 4 nil]
> 
> The OP said the composition data he gets is this:
> 
>   Composed with the following character(s) "̷" using this font:
>     xft:-PfEd-DejaVu Sans Mono-normal-normal-normal-*-13-*-*-*-m-0-iso10646-1
>   by these glyphs:
>     [0 1 111 82 8 1 7 7 0 nil]
>     [0 1 823 703 8 0 8 8 1 nil]
> 
> and the offsets in the second vector look wrong to me, FWIW.

I now tried this on Windows 8.1, where the (default) Courier New font
does have a glyph for u+0337, and I see there the same problem as
reported by the OP, including the composition data that shows positive
offsets where I thought negative offsets should be.

Maybe this is something related to the fact that bot DejaVu Sans Mono
and Courier New are monospaced fonts, whereas Arial Unicode MS isn't?

I Hope Handa-san will provide some insight.