Intro message and why is there a glyph for ZWJ?

[ArchivePoster]

Posted by: dov-g
         
Hello,

This is my first message to this group. My name is Dov Grobgeld and I am one of the developers working on Hebrew support in pango, which is used in Gtk, which is used in the Gnome desktop and in Gimp, which are most frequently used under Linux.

My current status is that almost all examples in the manual render correctly! And it is indeed beautiful. The main problems that I want to solve before I submit my changes to the official pango version are:

1. The nun+CGJ ligature doesn't work.
2. ZWJ are rendered as an x above the characters.
3. The alef+hataf patach+meteg+dehi ligature doesn't work.

I guess that 1 and 3 are "my fault" and I will try to solve. Regarding 2., I don't understand the rational why there is actually a glyph for ZWJ? Shouldn't it at least be pushed into the SALT (Stylistic alternate) table?

Regards,
Dov

         

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Posted by: 
         
This message has been deleted by the author.
         

[ArchivePoster]

Posted by: John Hudson
         
Hello Dov,

First, let me congratulate you on the Hebrew support in pango. Kirk Lowery drew my attention to this yesterday, and it is heartening to see more platforms supporting this font technology.

Regarding your questions:

1. I wouldn't sweat this too much: this is a hack which will not be necessary when Unicode properly encodes the nun hafukha character. I'm not happy about this hack anyway -- it is contrary to the standard -- and will probably not support it in future versions of the font.

2. Some major applications, e.g. MS Word, offer an option for users to display control characters, which is why ZWJ and other control characters have glyphs in SBL Hebrew. Because most of the time one does not want control characters displayed (they are only usefully displayed for editing), rendering engines need to remove them from the glyph stream in the default situation. This is not an OpenType feature.

There are currently two schools of thought about handling control characters, broadly characterised by Microsoft and Adobe's respective approaches. Microsoft paint glyphs for control characters temporarily before applying OpenType Layout features. This enables font developers to use these glyphs in font lookups, as I have done in a few places. Any control character glyphs not consumed in the lookups are removed before the glyph string is displayed. Adobe do not paint glyphs for control characters during rendering. Their preference is that control characters be interpreted by the rendering engine as calls for specific layout features, e.g. the presence of ZWJ would call for ligature features.

I suspect it is going to take Microsoft and Adobe a while to figure out their differences in this regard. Are you subscribed to the OpenType discussion list? I've been thinking about raising this topic (recently discussed on the Unicode Hebrew list), in that forum.

3. This looks like a bug in the font. I was originally presuming that hataf patach with meteg would always take the ligature form with the medial meteg, but then decided to make the left meteg the default rendering, and activate the medial meteg with ZWJ. If the medial meteg ligature is not used, the dehi spaces relative to the meteg, the immediately previous glyph, and this is not far enough right to clear the hataf patach. I need to add contextual positioning for dehi in this situation.

I am attaching a graphic that demonstrates this bug, and the correct rendering with the medial meteg ligature.

Hope this is helpful.

Regards, John
         

[ArchivePoster]

Posted by: dov-g
         
Thanks for your detailed response, John.

I thought that I would update you on the status of this patch.

After I got your reply I, John, I was convinced that the status of my patch was good enough for officially submitting it, which I did. The patch was accepted, and will thus be included in the next version of pango.

Meanwhile, here is a screen shot of the rendering through the example application testtext:

http://imagic.weizmann.ac.il/~dov/tmp/bereshit-sbl.png

(You might also be interested in another application of mine, guci (the gtk unicode inspector), which allows disecting composed glyphs to their components. See:

http://imagic.weizmann.ac.il/~dov/freesw/gtk/guci/ )

Regarding issue 2, pango at the moment lacks the possibility of toggling the rendering of control characters, and they are always rendered if they appear in the font. If time permits, I plan to to fix this.

         

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