Tessera exists because Ridge OS needed text and I refused to link a font library into the kernel. The whole rasterizer — parser, curve flattener and coverage engine — fits in about 900 lines of C.
TrueType stores glyphs as quadratic Bézier curves in the glyf table, indexed through loca and sized through head and maxp. Parsing is mostly careful byte-order work: everything is big-endian, and the flags in a glyph's outline use a compact run-length encoding that rewards reading the spec twice.
Rendering is a scanline rasterizer with analytic anti-aliasing. Instead of supersampling, each scanline accumulates exact signed coverage where edges cross it, so a diagonal stem gets the right grey value in a single pass. It is fast enough to render a full page of text between vsyncs.
The result renders every glyph you see in Ridge OS, at any size, with no hinting hacks and no external code.