[Freetype] Another Indic GSUB problem

[Dave Williss]

I have the latest ftxgsub from CVS (well, as of Tuesday).

The font mangal.ttf (a Devanagari font) has several GSUB

tables.  One in particular is causing me grief.  This font

has one glyph (I-Matra) that extends up and over the next

glyph.  The 'pres' table picks a version of this glyph that

accounts for the width of following glyph.

 

It is a ContextSubst2 lookup with the following set of

conditions...

 

The coverage matches one glyph, the I-Matra

 

The SubClassSetCount is 5, but only SubClassSet[0]

has any rules.

 

The class table lists classes for all the glyphs that

can follow it and cause it to need to change, but

_not_ the initial glyph itself.

 

The result is that when ContextSubst2() calls Get_Class()

on the initial glyph of the context, it gets a Not_Covered

error and gives up.  It seems from how this table is formed

that it's supposed to assume class 0. 

 

The Microsoft OTSPECs seem to confirm this...

 

http://www.microsoft.com/typography/OTSPEC/gsub.htm

 

"For each context, a SubClassRule table contains a

count of the glyph classes in the context sequence

(GlyphCount), including the first class.  A Class array

lists the classes, beginning with the second class (array

index = 1), that follow the first class in the context.

 

This sounds like the first glyph's class is assumed.

Modifying ftxgsub.c to make this assumption causes it to work.

 

An example of text that shows this is:

 

    Unicode: 0x093F 0x0915 0x093F 0x091E

    Glyphs:  0x1D3 0x80 0x1D3 0x87

 

When it works, the "eye brow" width is adjusted so that

the right end of it falls over the vertical line of the next

glyph.  I've attached two screen grabs of this.

 

The good news is that after this fix, it all seems to work

for Indic and It appears that I didn't break my Arabic support

in the process.

 

 -- Dave Williss
------
Meddle not in the affairs of dragons,
   for you are crunchy and taste good with catsup

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