RE: [ft-devel] charmap index should be same with cmap subtable index?

[David Bevan]

The requirement for our software is backwards compatibility with current FT2 
behaviour - not for identity between FT2 charmap index and TrueType cmap 
subtable index.

It is possible, however, that we have never seen "heavily broken subtables" and 
that (some of) our code does in fact depend on the FT2 charmap index and the TT 
cmap subtable index being the same - and would need changing if we did 
encounter a broken TTF.

David %^>


> -----Original Message-----
> From: address@hidden [mailto:address@hidden
> Sent: 12 July 2010 09:31
> To: David Bevan
> Cc: address@hidden
> Subject: Re: [ft-devel] charmap index should be same with cmap subtable
> index?
> 
> Dear David,
> 
> Thank you for information! I'm not pushing the
> charmap sorting features to default behaviour, but
> knowing the exist of softwares that requires the
> consistency between FT2 charmap index versus TTF/OTF
> cmap subtable index.
> 
> I want to ask another question about your software:
> 
>   FT2 charmap index should be exactly same with
>   TrueType cmap subtable index?
> 
> As described in my previous post, FT2 charmap index
> is not exactly same. If TrueType cmap table includes
> heavily broken subtables, FT2 does not assign the
> index to them, they are automatically ignored.
> 
> It is negligible if we use clean fonts only, but if
> FT2 user want to use FT2 as an inspector of TTF/OTF
> this skipping behaviour might be confusing.
> 
> I think it is possible for FT2 to assign the index
> even to broken subtable and make charmap index same
> with TTF/OTF cmap subtable index.
> 
> Regards,
> mpsuzuki
> 
> On Mon, 12 Jul 2010 04:12:28 -0400
> David Bevan <address@hidden> wrote:
> 
> >
> >Hi!
> >
> >Our software uses the FreeType charmap index directly to access the
> appropriate cmap. (In retrospect, that was perhaps a poor design
> decision.)
> >
> >We will need to be able to retain the existing behaviour. However, if the
> original index is available somehow, we would have no problems with a
> change in what we need to do to retrieve it.
> >
> >Thanks.
> >
> >David %^>
> >
> >
> >
> >> -----Original Message-----
> >> From: address@hidden
> >> [mailto:address@hidden On Behalf
> Of
> >> address@hidden
> >> Sent: 7 July 2010 10:47
> >> To: address@hidden
> >> Subject: [ft-devel] charmap index should be same with cmap subtable
> index?
> >>
> >> Hi all,
> >>
> >> When I was working with Savannah bug #30059,
> >>    http://savannah.nongnu.org/bugs/?30059
> >> I had a question about the relation between
> >> the index for FT_Face->charmap[] and
> >> the index for cmap subtable in TTF/OTF.
> >>
> >> When FT2 handles clean TTF/OTF, they are exactly same.
> >>
> >> # In Microsoft TrueType spec, having 2 subtables
> >> # with same platformID/encodingID was prohibited.
> >> # But now ISO/IEC 14496-22 permits such as far
> >> # as languageID are different.
> >>
> >> OpenType spec recommends to sort cmap subtables by
> >> platformID/encodingID/languageID. Looking at the
> >> encodingID naming convention for (Apple's) Unicode,
> >> ISO and Microsoft platforms, the search from the last
> >> to the first is best to find the widest cmap subtable
> >> for Unicode.
> >>
> >> However, the sorting is recommended but not required.
> >> In Apple's TrueType specification, I could not find
> >> any request to sort cmap subtables. Thus, there is
> >> a possibility that the last cmap subtable is the
> >> widest Unicode cmap.
> >>
> >> In the case of Savannah bug #30059, the sample font
> >> including so many cmap subtables (ca. 400, about 100
> >> subtables can be parsed, 300 tables are heavily broken)
> >> was used to make FT2 cache system crashed. This is
> >> extreme case, but it is true that FT2 cannot handle
> >> a TTF/OTF including cmap subtables > 15.
> >>
> >> In addition, if cmap includes some seriously broken
> >> subtables, FT2 ignores them, give no index for them.
> >>
> >> Considering this behaviour, I want to try a re-sort
> >> of cmap subtables in FT2 during the parsing of cmap
> >> table (as an experiment). It will completely disconnect
> >> the index in FT_Face->charmaps[] and the index for
> >> TTF/OTF cmap subtables. Does the disconnection cause
> >> serious problem in FT2 clients?
> >>
> >> Regards,
> >> mpsuzuki
> >>
> >> _______________________________________________
> >> Freetype-devel mailing list
> >> address@hidden
> >> http://lists.nongnu.org/mailman/listinfo/freetype-devel
> >