Safe-to-break API

[behdad]

Moving from:
https://bugs.freedesktop.org/show_bug.cgi?id=71443

We like to add bits to the buffer to return "safe-to-break-here", which means, if you break text here and shape the two sides separately, you get the same result as shaping together. This is useful for performant line-breaking.

Starting sketch here:
https://gist.github.com/behdad/149ae8947c11afddc560

[behdad]

Work-in-progress branch here: https://github.com/behdad/harfbuzz/commits/wip-unsafe-to-break

[behdad]

Sample run:

$ ./hb-shape Lobster.ttf Lobster  --show-flags
[L=0+776|o=1+899|b_s=2+1636#2|t=4+547#2|e=5+786#2|r=6+770#2]

[behdad]

cc @khaledhosny @simoncozens

[khaledhosny]

Thanks Behdad, I’ll have a look. I’m just wondering, does this help with breaking inside ligatures anyhow? I assume it will be a unsafe-to-break place, but then I’ll just need to reshape, no other shortcut? I’ve been trying to address breaking inside ligatures in Scribus (HOST-Oman/scribus#144) and all we did so far is to just disallow line breaking there.

[behdad]

Yeah, breaking inside a cluster needs reshape. Breaking inside a Unicode grapheme also needs reshape. This API identifies additional places that need a reshape.

[tayloraswift]

any updates on this? if this doesn't work what is everyone using for linebreaking currently then

[eaenet]

Hi Behdad, do you expend to get back to working at this in the near term? Anything I can do to help? We'd like to start using this for line breaking in Blink.
Thanks!

[behdad]

Hi Behdad, do you expend to get back to working at this in the near term? Anything I can do to help? We'd like to start using this for line breaking in Blink.

Yes, I like to. Wasn't high-priority. Will try to have something testable this quarter.