[HarfBuzz] HEH GOAL WITH HAMZA ABOVE(0x06C2) error in arabic

[datao zhang]

Hi JK:
Thanks your reply. But, in windows 7, the <U+0628,U+06C2,U+06C2> and <U+0628,U+06C1, U+0654,U+06C2> will be rendered as different glyphs, refer to the attachment. I use the "msuighur.ttf" font file of win 7 to display such text, there is no medial glyph for U+06C2 in the font file. It seems win7 shape engine will treat U+062C as single joining.
I also check other open source font file, example: DroidSansArabic.ttf, there is no medial glyph for U+06C2. So it seems most of font not include medial glyph for U+062C. 
 
I think it better that treat U+062C as a single joining same as win7 shape engine.
 
Br,
Dean
 

> Date: Thu, 12 Jul 2012 08:45:31 +0100
> From: jfkthame at googlemail.com
> To: harfbuzz at lists.freedesktop.org
> Subject: Re: [HarfBuzz] HEH GOAL WITH HAMZA ABOVE(0x06C2) error in arabic
> 
> On 12/7/12 04:12, datao zhang wrote:
> > Hi Behdad:
> > When i try to draw the text "U+0628,U+06C2,U+06C2,U+0020" with harfbuzz,
> > i find it is rendered differently in windows 7. please see attachment
> > file. After checking the hb-ot-shape-complex-arabic-table.hh, I found
> > U+06C2 joining type was JOINING_TYPE_D (double joining). I don’t know
> > why Unicode specifies it double joining, it really does not make any
> > sense. At least, when render the text, it should be treated as single
> > joining type.
> 
> U+06C2 is classified as double-joining because it has a canonical 
> decomposition to <U+06C1, U+0654>, and U+06C1 is double-joining. If 
> U+06C2 were right-joining, we'd have a situation where equivalent text 
> sequences would have different joining behaviors, so that a canonical 
> normalization process might unexpectedly alter the rendering.
> 
> While I agree that the various HEH-related characters in Unicode are a 
> confusing mess, the various compatibility and stability requirements, as 
> well as the different usage patterns needed for various languages and 
> regions, make it difficult to see how we could "fix" them.
> 
> The broken-looking result you're getting from harfbuzz happens because 
> the font used does not have a 'medi' glyph for the U+06C2 character. 
> This is a font bug.
> 
> To reliably produce the "windows 7" result shown in your attachment, I 
> believe the correct text sequence would be <U+0628, U+06C2, U+200C, U+06C2>.
> 
> JK
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