[HarfBuzz] Making hb-shape output for advance values more intuitive

[Behdad Esfahbod]

Hi all,

Currently the hb-shape output is fairly intuitive with regards to GSUB (thanks
to glyph names) and GPOS glyph offsets (no offset if not repositioned).  But
advance values are not that clear.  Two cases specifically I think need to be
more intuitive:

  * Zero advance.  Right now if you see something like <space>, intuitively
you would think a space glyph with nothing extra, whereas in reality it's a
zero-width'ed space.  Not very intuitive.  I want to make it more explicit.
Adding "+0" may do that.

  * Natural glyph advance.  When you see something like <space+1024>, would be
more compact and more informative if you could see that 1024 is the default
advance of the space glyph.  Ie. no kerning or other GPOS advance tweaking
happened.  Would it be confusing to drop advance if it's natural?  Ie. <space>
would mean <space+1024>, and <space+0> would mean what currently <space>
means...  It would be more revealing of kerning values if kerns were shown
relative to natural advance.  Ie. all advances will be relative to natural
advance, except for somehow special-casing 0.

So I'm seeking ideas for how to express these.  I think I want to make the +0
be the case initially, then find syntax for a "relative advance"
representation.  At any rate, there will be an option for "absolute advances"
for sure.

Cheers,
behdad