On Tue, 29 Apr 2025 09:55:56 GMT, Nikita Gubarkov <ngubar...@openjdk.org> wrote:
>> It looks like this regression actually fits into a longer series of fixes / >> regressions in this area: >> >> - [JDK-4517298](https://bugs.openjdk.org/browse/JDK-4517298) fixed metrics >> for zero-width characters, but broke some ligatures / glyph substitutions >> - [JDK-7017058](https://bugs.openjdk.org/browse/JDK-7017058) fixed the >> ligatures / glyph substitutions, but broke some zero-width metrics >> - [JDK-8208377](https://bugs.openjdk.org/browse/JDK-8208377) fixed some >> metrics and rendering for zero-width characters, but broke some ligatures / >> glyph substitutions >> - Now, with this PR, we aim to fix the ligatures without re-breaking >> zero-width metrics and display >> >> We have two different types of use cases pulling `CharToGlyphMapper` in two >> different directions: the users who need raw, untransformed glyph info, and >> the users who need normalized / transformed glyph info. >> >> It looks to me like, in the current code base, the only `CharToGlyphMapper` >> user which requires raw font data is HarfBuzz (explicitly confirmed with the >> HarfBuzz team here: https://github.com/harfbuzz/harfbuzz/discussions/5234). >> >> The regression mechanism at play here is that the HarfBuzz font callbacks >> are currently providing HarfBuzz with transformed glyph info (e.g. ZWJ -> >> INVISIBLE_GLYPH_ID), which prevents HarfBuzz from recognizing and applying >> the correct font GSUB substitutions (which involve ZWJ). >> >> In order to fix this without (yet again) breaking metrics and display >> behavior elsewhere, I've added two methods to `CharToGlyphMapper` which >> provide access to raw glyph info, to be used by the HarfBuzz font callbacks: >> `charToGlyphRaw(int)` and `charToVariationGlyphRaw(int)`. >> >> Note two intricacies related to `CompositeGlyphMapper`: >> 1. We need to be careful to only cache raw (untransformed) values, to avoid >> conflicts between requests for a raw version of a glyph and a transformed >> version of the same glyph. Another option would have been two separate >> caches, but I don't think that's necessary. >> 2. Consumers who are using `CompositeGlyphMapper.SLOTMASK` to check glyph >> slots (e.g. `FontRunIterator` and `CTextPipe`) will "see" invisible glyphs >> as having come from slot 0. This isn't new, and I think it's OK, but >> something to be aware of. >> >> The glyph cache handling in `CCharToGlyphMapper` (for macOS) also requires >> care to avoid mixing value types. >> >> Please also note that I'm not sure if the tweak to `sunFont.c` is being >> tested, since FFM is being used by default for Harf... > > By the way, I see that in each implementation, both `charToGlyph` and > `charToGlyphRaw` call a common method, like `getGlyph(int uniciode, boolean > raw)`. At first there was just `charToGlyph`, then `charToVariationGlyph` was > added and now you added a "raw" version for each of them, I see that in the > future we will need other variants and how it's already starting an > exponential explosion. Overriding all of those methods in each implementation > brings quite a bit of boilerplate, and it becomes easier to miss something. > Maybe take a step back and refactor this into a single `charToGlyph(int > unicode, int variationSelector, boolean raw)` version? > Also, this `raw` parameter only really controls `isDefaultIgnorable` check in > the end of each method. Maybe we could factor this out without bringing it > separately into each mapper implementation? @YaaZ: Thanks for the additional feedback, please see my thoughts below: > By the way, I see that in each implementation, both charToGlyph and > charToGlyphRaw call a common method, like getGlyph(int uniciode, boolean > raw). At first there was just charToGlyph, then charToVariationGlyph was > added and now you added a "raw" version for each of them, I see that in the > future we will need other variants and how it's already starting an > exponential explosion. I don't know if I would call two changes to `CharToGlyphMapper` in 20 years an exponential explosion, but I get your point :-) > Overriding all of those methods in each implementation brings quite a bit of > boilerplate, and it becomes easier to miss something. True, but again keep in mind that there are only 5 implementations, only one of which (the macOS `CCharToGlyphMapper`) has been added in the last 20 years. > Maybe take a step back and refactor this into a single charToGlyph(int > unicode, int variationSelector, boolean raw) version? We'd still need separate methods for `int` vs. `char`, but I think this might reduce 5 methods down to 3? The changeset would be a bit more intrusive (lots of callers would need to change to reflect the new method signature). I'd be interested to hear thoughts from some of the reviewers on this one. > Also, this raw parameter only really controls isDefaultIgnorable check in the > end of each method. Maybe we could factor this out without bringing it > separately into each mapper implementation? I prefer to think of it as controlling whether or not any transformations to `INVISIBLE_GLYPH_ID` happen (right now it's just for default-ignorable characters, but there may be other scenarios in the future, e.g. `\r`, `\n` and `\t` which currently are handled elsewhere). Any ideas for what this refactoring might look like? ------------- PR Comment: https://git.openjdk.org/jdk/pull/24412#issuecomment-2845646011
