[HarfBuzz] Inconsistent shaping across systems

[Koji Ishii]

Though I really didn't look into font tables, the instinct tells me that
"880" is the correct value. Adobe fonts usually use "an em-box that is 12%
below the Latin baseline"[1],

The vertical origin is usually determined by VORG, or vmtx if missing, or
ascent if missing. The font has "TypoAscender 880;"[2].

I don't know where Mac took the value from, but 1.4% looks a little large
error. If it uses CoreText, there used to be a few bugs to get vertical
origin in CoreText. I though they were fixed in recent OS X though. Maybe
CoreText tweaks values from OpenType tables for some reasons?

"1000" looks like an em-box. Since all these variations have constant
offset, and advances are the same among the 3 configurations, so I'm not
sure what the real downsides of using "1000" though.

I'm not familiar with the coordinate system in Harfbuzz, sorry if the
coordinate system handles such offset and the above was pointless.

[1]
https://blogs.adobe.com/CCJKType/2012/01/afdko-features-tips-tricks-part-1.html
[2]
https://github.com/adobe-fonts/source-han-sans/blob/master/Light/features.JP

/koji

On Wed, Aug 19, 2015 at 4:14 AM, Simon Cozens <simon at simon-cozens.org>
wrote:

> On 18/08/2015 11:38, Behdad Esfahbod wrote:
> >> Linux
> >> [gid9861=0 at -500,-880+0,-1000|gid27506=1 at -500,-880+0,-1000]
> >> OS X
> >> [gid9861=0 at -500,-894+0,-1000|gid27506=1 at -500,-894+0,-1000]
>
> > Try with --font-funcs=ot.
>
> Thanks; that gives -1000+0 on both OS X and Linux.
>
> Now it is getting more and more important to move SILE to OT rather than
> FT...
>
> S
>
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