Foxtrot

Foxtrot is an open-source, fast STEP file viewer built in Rust at a Formlabs hackathon. The writeup covers the full architecture: parsing the EXPRESS schema to auto-generate a nom-based STEP parser (39K LOC generated), parallel triangulation using Constrained Delaunay Triangulation with custom 3D-to-2D surface projections and Steiner points, a wgpu-based GUI, and a WebAssembly port running in the browser via Three.js. The project loads a complex PCB model in under 1 second on desktop (vs. 23x slower in Onshape), though it handles only a subset of the 915 entity types defined in AP214. Key challenges include the complexity of the EXPRESS language, ad-hoc union types in STEP files, and surface parameterization for cylinders, spheres, and toruses.