One thing I love about digging into rabbit holes such as PDF parsing is stumbling upon phrases like "schizophrenic PDF files".

The code for computing winding for a quadratic Bézier can be simplified a lot by dealing with monotonic quadratics only. Testing if a sample lies to the left/right of the curve becomes extremely cheap in that case.

"Quadratic Approximation of Cubic Curves" contains a neat method of representing one cubic Bézier as two C1-continuous quadratics, maintaining tangents at the endpoints. Combining that with a heuristic for how many times to split the source curve gives excellent results.

I ported my demo to Rust to see if I can make things faster. The goals is to perform queries for arbitrary points and arbitrary vector paths, as fast as possible. I'll try to write everything SIMD-friendly.

I've implemented non-zero fill for quadratic curves without flattening them. Should be numerically robust but I haven't tested it too thoroughly yet. Very happy with the results so far. Coverage is computed per pixel individually.