Hi, I guess current discussion is focused to the variation selectors itself, and, you have no attempt to make fontconfig to handle IVS-specific info. For example, a question "this font supports the IVSs defined for Adobe-Japan1 /or not" might be the future task and separated from the current discussion. Am I understanding correctly? Regards, mpsuzuki Behdad Esfahbod wrote: > Hi everyone, > > Currently fontconfig does not support Unicode variation selectors. Lets fix that. > > Unicode defines 256 generic variation selectors, in the following ranges: > > U+FE00 VARIATION SELECTOR-1..U+FE0F VARIATION SELECTOR-16 > U+E0100 VARIATION SELECTOR-17..U+E01EF VARIATION SELECTOR-256 > > OpenType encodes those in cmap subtable format 14. Fonts as such can encode > pairs of characters in the cmap instead of one. The second of the pair is > supposed to be a variation selector, though nothing in the table format > enforces that. > > To support these in fontconfig, two changes are needed: > > - Extend FcCharSet to be able to carry variation sequences as well, > > - Add a FcFreeTypeCharIndex variant that takes a variation selector. (ala > FT_Face_GetCharVariantIndex), > > Adding the latter is rather trivial. For the former, it would be easiest if > we encode the variation selector and the base Unicode character in one 32-bit > integer, and make sure FcCharSet handles that efficiently (this probably is > currently not the case). > > Ideally, we'd want to encode the sequence U followed by VSx (where VSx is the > VARIATION SELECTOR-x) as (U + VSx << 24). This will use the high byte of the > 32bit unsigned for the variation selector number. The only problem is: there > are 256, not 255, variation selectors. I submitted a proposal to Unicode to > commit to not use the last one, but that was not accepted. Currently up to > ~240 are used. > > Failing that most beautiful scheme, we can use a different shift. 21 would be > the next most natural, given that Unicode numbers fit 21 bits. It just would > be much harder to read a hex of a 32bit number in the FcCharSet verbose output > and know what it means. > > So, what do people think? Lets make this happen. > > Thanks, _______________________________________________ Fontconfig mailing list Fontconfig@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/fontconfig
