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

From: David Bevan
Subject: RE: [ft-devel] charmap index should be same with cmap subtable index?
Date: Mon, 12 Jul 2010 04:12:28 -0400


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.


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,
> 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
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