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[advisory] libXft vs. harfbuzz #2

Open y-ack opened 3 years ago

y-ack commented 3 years ago

emacs 28.1 has this to say about libXft:

** 'configure' now warns about building with libXft support. libXft is unmaintained, and causes a number of problems with modern fonts including but not limited to crashes; support for it may be removed in a future version of Emacs. Please consider using Cairo + HarfBuzz instead.

on june 11, 2021, 12 had these observations about harfbuzz (for ligature support):

st code inspection > looking at maybe ligatures, and > #include > "what the heck is hb?" > oh my gosh harfbuzz is REAL? > 230 + `ATTR_LIGA = 1 << 11,` > wow fuck they really just used a cast to bypass const > declare function as > `hbtransform(XftGlyphFontSpec *specs, const Glyph *glyphs, size_t len, int x, int y)` > then , > ` ((Glyph *)glyphs)[i].mode |= ATTR_LIGA;` > why the fuck did they declare it as const if they're just going to modify it

mm it's starting to get pretty slow now slow slow slow

ok so the speed issues uh at least the new ones, seem to be entirely caused by harfbuzz, ok I'll deal with this later i think, not worth wasting time on a gimmick right now

library capability > also the need for both harfbuzz and freetype seems like > ugh so like > I don't think any of these libraries handle fallback at ALL > so if you can't find the glyph in your main font then you have to do like 15 billion different things and it's just stupidly inefficient > I might just umm > use one specific font for fallback just to keep this reasonable > rather than dynamically searching and > god this is so stupid > I thought libraries were supposed to actually DO things > so like, > freetype does font rasterization, but also does glyph lookup, so like > converting unicode codepoints into glyph indexes > but harfbuzz also does that, > except, harfbuzz can handle ligatures while freetype can't > but i still need freetype because harfbuzz doesn't do rasterization > and neither of these handle LOADING fonts, that's the job of fontconfig > but even fontconfig can't do fallback, or at least > not very well, anyway

leaving a ?TODO: look at harfbuzz again later re: performance?

12Me21 commented 3 years ago

latest release of xft was like a month ago so idk what they're talking about lol I mean xft is definitely obsolete to some extent (as the world slowly moves away from X11), but it's just a wrapper around fontconfig (font loading), freetype (font rasterizing), and xrender (graphics drawing), which are libraries that Cairo also uses (on certain platforms) I haven't encountered any fonts that crash xft so I have no idea what that's about...

harfbuzz itself isn't a exactly a replacement for any of these components, it just handles things like ligatures iirc as an extra step I think the way I was using it wasn't optimal, but it also might just be overkill for this

y-ack commented 3 years ago

it seems like the recent libxft updates are mostly just build fixes 6 weeks, 2 years, 7 years, 9 years

12Me21 commented 3 years ago

It does seem like they are having trouble adding color font (i.e. emoji) support to xft: https://gitlab.freedesktop.org/xorg/lib/libxft/-/merge_requests/1 not sure how far along the alternative libraries are though...