[HarfBuzz] harfbuzz.old applies x advances for rtl in the wrong direction

[Khaled Hosny]

X glyph advances should always be applied from left to right regardless
of text direction, however HarfBuzz code used in Qt applies X advances
in negative if text direction is right to left which breaks Arabic
kerning for example.

This have been reported against Qt:
http://bugreports.qt.nokia.com/browse/QTBUG-4475
And though the issue was closed as not being reproducible, I can still
reproduce it (may be Qt on Windows does not use HB?).

The attached screenshots show the string:
بربربربربربربربربر
حوحوحوحوحوحو
rendered in Qt's sample textedit application, both before and after
applying the attached patch. The font used can be downloaded from SF:
http://sourceforge.net/projects/arabeyes/files/kacst_fonts/kacst_one_3.0.tar.bz2 

Regards,
 Khaled

-- 
 Khaled Hosny
 Arabic localiser and member of Arabeyes.org team
 Free font developer
-------------- next part --------------
A non-text attachment was scrubbed...
Name: hb_qt_advance.diff
Type: text/x-diff
Size: 721 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/harfbuzz/attachments/20110113/f25bf604/attachment.diff>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: before.png
Type: image/png
Size: 8100 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/harfbuzz/attachments/20110113/f25bf604/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: after.png
Type: image/png
Size: 7550 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/harfbuzz/attachments/20110113/f25bf604/attachment-0001.png>