[vorporeal]

Blog post author here - great questions.

My understanding is that some, but not all, shaping libraries will handle fallback fonts. For example, I believe Core Text (on MacOS) will specify which sections of a laid-out line should be rendered using which fonts, factoring in fallback font selections. Kerning should work within a run of a single font, but I'm not sure there's any way to "properly" kern a glyph pair from two separate fonts - there wouldn't be any information available about proper alignment (as kerning data is part of a font file). In terms of sizing, one would hope that font creators all respect the em-square when constructing glyph vectors, leading to two different fonts using the same point size having comparably-sized glyphs. If one doesn't want to rely on that, font metrics like ascent and descent could be utilized in an attempt to normalize sizing across different fonts.

In terms of cache size: at the moment, we rarely empty out the cache (but we should do it more often). I have some ideas around triggers for emptying the cache and letting it get rebuilt (e.g.: changes to font size, changes to font family), but haven't wired it up yet. In addition, we could consider clearing the cache periodically when the application is sitting in the background (allowing us to re-rasterize the needed glyphs without blocking painting a frame). So tl;dr: we don't currently but we should and will do so in the future.

[billconan]

Thank you for the answers! I built a rust lib to generate multi-channel signed distance field font texture. I wanted to make it a text rendering lib. But after learning how complex it is, I guess I should give up and simply use core text...

[vorporeal]

MSDF seems like a great choice, depending on your use-case. Given that we don't need to draw text at multiple scales, it doesn't seem to provide much benefit for us over caching rasterized glyphs provided by Core Text. (Copying a rasterized glyph is certainly faster than evaluating an SDF.)

Using Core Text also means our text looks the same as it does in other applications, which avoids bug reports from users like "text in Warp looks different than in iTerm". :)