I have added and tested type 3 lookup handling, and also added the comments you asked for. I will begin on the final branch if there's nothing else to be done.
Thanks for the help! On Mon, Oct 23, 2023 at 12:54 PM Werner LEMBERG <w...@gnu.org> wrote: > > > I need some help figuring out how to handle the type 3 lookups. > > I need to do 2 things: > > - Figure out which features contain type 3 lookups > > - Determine the number of variations the feature contains > > Simply add all glyphs a type 3 lookup provides to the list of glyphs. > No further special handling is necessary. > > > For the second one, this function seems relevant: > > > https://harfbuzz.github.io/harfbuzz-hb-ot-layout.html#hb-ot-layout-feature-with-variations-get-lookups > > But this returns a list of lookups if you already know the variation > > index, when I want to know the range of possible variation indices. > > This function is not relevant – it's about variation fonts, see > > > https://learn.microsoft.com/en-us/typography/opentype/spec/chapter2#device-and-variationindex-tables > > > hb_ot_layout_lookup_get_glyph_alternates > > also looks useful and could partially solve the problem. > > This is the right function, I think. > > > With this function, I can handle the type 3 lookup cases in > > isolation, only finding the glyphs directly resulting from the > > feature and no further transformations. > > Sounds sufficient to me. > > > Also, can I have some advice on testing the code? How should I make > > these changes bulletproof? > > Alas, we don't have a testing framework for such issues. However, as > soon as your code lands in 'master', the Chromium people and other > parties run their fuzzers on FreeType, which usually unveils memory > leaks or segfaults quite soon. They also do intensive comparison of > graphic images; however, I don't know whether they use the auto-hinter > for that. > > > Werner >
