Servo can't render OpenType ligatures in 'mort' or 'morx' format, only in 'GSUB'

[pcwalton]

So there are at least three ways to specify ligatures in TrueType/OpenType fonts: mort, morx, and GSUB. GSUB is the newest. However, all of my fonts only have mort or morx. So ligatures don't render in most fonts.

I guess we have to convert from mort or morx to GSUB.

[khaledhosny]

mort and morx are part of AAT not OpenType, the only way to do glyph substitution in OpenType is with GSUB. So not an old/new distniction, but to different technologies.

[behdad]

We will eventually implement mort / morx in HarfBuzz natively. In the mean time, if you are building on OS X and build HarfBuzz --with-coretext, then you should get mort / morx working. HarfBuzz will internally call into CoreText for those fonts.

[mbrubeck]

If someone wants to enable this on Mac OS, they can clone the servo/rust-harfbuzz repo and edit the makefile.cargo to add --with-coretext to the configure arguments if $TARGET contains "apple-darwin". You can use a path override to test Servo with your local copy of harfbuzz-sys.

(Cross-platform support is outside of the Servo scope; we'll just wait for it to be implemented in Harfbuzz.)

[behdad]

sgtm

[jdm]

All that's left here is upgrading the version of harfbuzz that Servo uses: ./mach cargo-update -p harfbuzz-sys

[mbrubeck]

#11591 includes the harfbuzz-sys update.