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EngrCAD

EngrCAD

A CAD kernel for modern .NET built around a hybrid geometry engine that natively supports three representations:

  • B-Rep — parametric surfaces (planes, conics, NURBS) wrapped in topology, for precision modeling and STEP exchange.
  • Implicit — signed distance fields (SDF) composed as an AST of primitives and operators, for lattices, shells, and organic blends.
  • Mesh — discrete half-edge triangle meshes, for rendering, FEA, and 3D printing.

The unified Shape API lets you model once with one vocabulary and choose the representation at the end:

var body = Shape.Box(40, 30, 10) - Shape.Cylinder(4, 12).Translate(10, 8, 0);


BrepSolid    exact = body.ToBrep();      // precision modeling, STEP export
Sdf          field = body.ToImplicit();  // blends, shells, lattices
HalfEdgeMesh mesh  = body.ToMesh();      // rendering, FEA, 3D printing

Where to go

  • Getting started — install, build a first model, and run the live-modeling loop (dotnet watch + hot reload).
  • Examples — one page per feature, each with runnable code and the render it produces. Every snippet is compiled, executed, and screenshotted by the documentation build itself, so the examples cannot drift from the code.
  • API reference — generated from the source XML documentation.

Highlights

  • LINQ-native querying — a custom IQueryable provider routes spatial predicates to BVH indexes instead of linear scans; B-Rep topology is LINQ-queryable and drives feature selectors (queries, chamfer & fillet).
  • Sketch-first modeling — fluent 2D sketches (lines, arcs, béziers, primitive shapes, holes) consumed by extrude/revolve/sweep, exact in every representation (sketching).
  • Parametric features — FeatureScript-style history with [Param] properties, prefix-cached regeneration, and JSON parameter round-tripping (features).
  • Standards-aware holes — metric clearance / counterbore / countersink / tap pilot catalogs behind one Drill call (holes).
  • Modeled threads — the ISO metric coarse catalog with real helical geometry and 3D-printing clearances (threads).
  • Assemblies — shared parts posed by rigid frames, nested sub-assemblies, and flattened instances for viewers and exporters (assemblies).
  • A viewer that is a library — build a Scene, call EngrCad.Show, or render headless PNGs for CI and agents (viewer).

A note on how this was built

EngrCAD is written by one person, with substantial help from AI coding assistants, and I would rather say so plainly than have you guess.

A hybrid geometry kernel of this scope — three interoperating engines, a full FEA suite, a renderer, and an ECAD stack — is normally the work of a team over many years, and the research behind almost any single part of it is worth multiple PhD-years on its own. I am one person. AI assistance is what made attempting that breadth realistic at all.

The counterweight is verification, and it is deliberate. Nothing here is trusted because it “looks right”: every algorithm is checked against closed-form solutions, exact identities, twin-decoder round-trips, and measured convergence orders, and those checks live in the test suite and in this documentation — every example on this site is compiled, run, and rendered by the build, so it cannot drift from the code. Where the kernel cannot do something exactly, it is designed to refuse by name rather than return a plausible wrong answer. Read the code and the results with their origin in mind, and please report anything that looks off.