InventorRayOptics

An Autodesk Inventor add-in that adds an optical ray-tracing environment for the currently open part (.ipt) or assembly (.iam). The properties of each body can be altered in the environment to simulate transmissive materials, phosphorescent materials, perfectly absorbing materials, or to produce light. Individual surfaces can be configured with a fixed reflectivity, to be a dichroic mirror or phosphorescent reflector, or to be a surface on which the projected light pattern can be observed. Lights can be configured with a custom light spectrum, emission pattern, and intensity.

It is the Inventor-native sibling of StepRayOptics (the standalone browser version). This project is Inventor-only.

How it works

1. The Environments tab gets a "Ray Optics" entry, next to Stress Analysis and Inventor Studio. Clicking it switches the document into a dedicated "Ray Optics" environment — its own ribbon tab becomes active, while the normal modeling tabs stay available (this tool is a passive viewer, not an exclusive editing mode) — and Inventor automatically provides the standard Finish/return affordance out of that environment.
2. The C# add-in exports the active document to a temporary STEP file (true B-rep geometry).
3. It opens a dockable panel hosting a WebView2 browser control (unchanged across environment switches — it's a docked panel beside the model, not merged into Inventor's own 3D view; see "Environment vs. same-window rendering" below).
4. The web app reads the STEP with OpenCascade (WASM) and ray-traces light against the analytic B-rep surfaces — not a triangulated mesh — rendering with three.js.

The Ray Optics tab's "Refresh Model" button re-exports and reloads without leaving the environment — useful after editing geometry in another tab.

Environment vs. same-window rendering

Inventor's Environment API only swaps ribbon tabs/panels — it does not replace or merge with the 3D graphics view. Stress Analysis/Inventor Studio get their "results in the same window" look by drawing directly into Inventor's native 3D view via its ClientGraphics API, not by embedding another control over it. This project deliberately keeps the simpler architecture: the ray-traced view lives in its own WebView2/three.js panel beside Inventor's native view, not drawn into it. Merging the two would mean replacing the three.js rendering of rays with native ClientGraphics calls from C# — a real rearchitecture, intentionally not done here.

Core guarantee: all intersection and all surface normals used in the physics come from the exact analytic surfaces (GeomAPI_IntCS for intersection, GeomLProp_SLProps for normals). Triangles are used only to draw the model on screen and never appear in the optical result.

Status

✅ Implemented and verified live in Autodesk Inventor 2025: ribbon button → Environment switch → STEP export → WebView2 panel → OpenCascade load → live B-rep ray-trace rendering, all confirmed via screenshot capture of the running app. Also stress-tested standalone in a browser against real STEP files (a 7-surface part and an 18-body, 160-surface assembly; 15 consecutive retraces up to ~15k rays, zero crashes). See docs/DEVELOPMENT_SPEC.md for the full architecture, phased build plan, and verified API reference this was built from — including a gotchas section on two hard-won bugs (an OCCT memory-corruption double-free, a WebView2 navigation race) worth reading before touching brepTracer.js/occt.js again.

Building

addin/InventorRayOptics/InventorRayOptics.csproj    — MSBuild, .NET Framework 4.8, x64

Build with MSBuild (no dotnet SDK required):

MSBuild.exe addin/InventorRayOptics/InventorRayOptics.csproj -p:Configuration=Debug -p:Platform=x64

This also copies webapp/ into bin/Debug/webapp/ next to the DLL (see the CopyWebApp target in the .csproj). Deploy the build output folder (DLL + .addin manifest + webapp/ + WebView2Loader.dll) into %APPDATA%\Autodesk\Inventor 2025\Addins\ and restart Inventor.

webapp/vendor/opencascade/ holds the vendored OpenCascade WASM build (~119 MB across 6 files: the base module plus the core/modelingAlgorithms/visualApplication/ dataExchangeBase/dataExchangeExtra dynamic-library profiles, all required — see js/occt.js for why). It is committed directly; no separate fetch step is needed.

Dev-time verification without Inventor

webapp/ can be exercised standalone in any browser (python webapp/serve.py 8360), since the OpenCascade/three.js pipeline has no Inventor dependency — only the "export the active document" trigger does. window.__iro.loadModelFromUrl(url) in the browser console drives the same load path the add-in's postMessage uses. webapp/samples/ holds two STEP files used for this (not part of the shipped add-in).

Repository layout

addin/     C# Inventor add-in (Visual Studio-compatible MSBuild project)
webapp/    Web app hosted by WebView2 (opencascade.js + three.js)
  js/occt.js        OpenCascade init, STEP loading, B-rep face-table + display mesh
  js/brepTracer.js  ray tracer against the analytic B-rep face table
  js/optics.js      Snell/Fresnel/TIR/dispersion math (ported from StepRayOptics)
  js/materials.js   Cauchy/Sellmeier IOR models + glass presets (ported verbatim)
  js/app.js         three.js scene, UI wiring
docs/      DEVELOPMENT_SPEC.md — architecture, phased build plan, verified API notes
tools/     nuget.exe (vendored; no system NuGet/dotnet SDK required to build)

Known limitations

• Per-body/per-model transform gizmos (move/rotate/scale) are not implemented — the model is shown at the pose Inventor exported it in. (StepRayOptics has these; they were scoped out here since Inventor already supplies a fixed pose.)
• Two-way selection (viewer ↔ Inventor face highlight) is not implemented — STEP export doesn't preserve Inventor's internal face IDs, so this would need a geometric best-effort matching pass (see DEVELOPMENT_SPEC §7 Phase 4).
• B-rep intersection is brute-force per face (with a bbox broad phase, including a per-body aggregate bbox pre-filter for assemblies). It comfortably handles the documented "hundreds to a few thousand" rays; a 160-surface, 18-body assembly at ~1,000 rays takes a few seconds rather than being instant — expected given exact analytic intersection is far more expensive than a triangle BVH.