One unfortunate lesson I've had to relearn a couple times is that once your font rendering library is done, you get to start the unbearably complex task of actually using it to render text, which means shaping - taking the text and splitting it out into individual glyphs from one or more fonts and laying them out. This task is simple enough for western character sets that you can ignore it (and people often do) but the moment you've got customers overseas the risk increases that you will suddenly have to do a ton of work.
Unfortunately, the main good shapers out there I'm aware of are either built to be used with FreeType or are built for a specific OS and its platform-specific font infrastructure. I'd love to see a lightweight shaper to go with a library like libschrift. Anyone run across one before?
Don’t forget layout; Freetype + HarfBuzz + FreeBiDi seems to be the defacto combination. Of all the things I want rewrite-it-in-Rust alternatives, these are probably the things I want the most. (I am aware of RustType; certainly it’s a start.)