Post #905352
2026-03-07 14:19 UTC
RE: https://typo.social/@fontra/116183016588316849
The blog post is a very interesting write-up, I suggest everyone interested in the font making to read it.
The technical part at the end is the most interesting to me. I’m particular proud of the very neat trick that allows #Fontra to emulate glyph positioning while maintaining interaction between it and manually written feature code.
For context. Font editors will generate positioning features from kerning and anchor data in the font.
Sometimes one wants to add some other feature code before or after the generated ones (e.g. move a dot contextual after being positioned by the default anchor to avoid a clash that happens only in a certain context). The order of the generated and manual code is important, since one might depend on the output of the other.
Replies (1)
-
@khaled@typo.social 2026-03-07 14:26
However, #Fontra does not generate positioning feature code during live preview, as it does the glyph positioning itself, while the rest of the shaping is done by #HarfBuzz (as explained in the blogpost). So how would it do this emulation in the middle of lookup application by HarfBuzz? HarfBuzz has a so-called message callback that allows caller to get a message about what HarfBuzz is doing and the HarfBuzz glyph buffer before each shaping step (this is what https://www.corvelsoftware.co.uk/crowbar/ uses to debug OpenType layout).