Slug doesn't use "bitmap" font data but more like parameter lookup tables in storage buffers, pre-processed from TTF files. The lookup data can of course also live in textures (so that it works in WebGL), but using those textures as "poor-man's storage buffers", e.g. fetching the data directly without filtering.

The pixel shader is indeed quite complex compared to SDF:

https://github.com/floooh/sokol-samples/blob/8afa83928ce1870...