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

[Jjgod Jiang]

On Thu, Jan 13, 2011 at 8:45 PM, Khaled Hosny <khaledhosny at eglug.org> wrote:
> "X and Y values specified in OpenType fonts for placement operations are
> always within the typical Cartesian coordinate system (origin at the
> baseline of the left side), regardless of the writing direction."

Note that just after this, "However, it's important to note that the
meaning of “advance width” changes, depending on the writing direction."
Since advance width depends on the writing direction, adjustment to
advance width should depend on the writing direction as well, I assume.

Anyway, I hope someone more familiar with the spec can clarify this.

> I can't comment on this, but I just tested with FireFox 4 and got
> correct kerning.

Firefox 4 hasn't use harfbuzz-ng for Arabic shaping yet.

> The issue is not limited to this font, I can reproduce it with other
> fonts like Arabic Typesetting from MS and many Linotype fonts. Arabic
> fonts from Apple are AAT fonts, so they don't apply here (may be
> TextEdit on your system is not doing OpenType at all; Apple have been
> too late to the game).

I may have used the AAT font, but TextEdit does support OpenType and
Arabic shaping (in fact, Cocoa Text System supports a lot of OpenType
features better than software from Adobe and Microsoft.)

I just verified it with Arabic Typesetting font, it works well here.

- Jiang