# v0.3.1 — First public release: 3D STEP viewer with measurement & assembly fit-check

A lightweight Windows desktop viewer for STEP / STL / DXF — open a part, measure it,
and check how two parts fit together, without firing up a heavyweight CAD suite.

## ✨ New features

**View & assembly tree**
* Import multiple CAD files at once (STEP / STL / DXF) via the toolbar, drag-and-drop,
  or the command line (`STPViewer.exe a.stp b.stp`).
* STEP product structure is rebuilt into an **assembly tree** — toggle visibility, recolor
  (cascades to children), and zoom-to any node; whole-file remove and outline-edge toggle.
* Smooth orbit / zoom / pan even on large assemblies (hundreds of thousands of triangles).

**Measurement** (pick a mode, click the model)
* Point (snaps to nearby vertices), two-point distance + ΔX/ΔY/ΔZ, edge length
  (line / curve / arc with radius), face area + surface type, circle center / radius /
  diameter / circumference, angle between two faces or edges, and face-to-face minimum gap.
* Edge length, radius and angle use **exact B-rep values**; area and gap are mesh-based.
* Switch units **mm ⇄ inch** anytime — existing measurements and 3D labels convert live.

**Assembly fit-check** (mate a male/female pair and verify)
* **Two-point align** — click a point on the part to move, then the target point, to slide
  the whole file into place.
* **Three-point align** — pick 3 feature points on each file to solve a full rotate+translate
  in one shot, for parts that aren't already oriented the same way.
* **Axis rotate** — rotate the selected file ±90° about X / Y / Z to square it up.
* **Drag mode** (hand cursor) — left-press a part and drag it along the screen plane.
* **Gizmo** — XYZ arrows to move along an axis (independent of view angle, ideal for pushing
  along a mating axis) and rings to rotate any angle. The gizmo always renders on top, so it
  is never hidden inside a solid part.
* **Interference check** — for two visible files, shows red intersection lines where they
  collide, or the minimum gap when they don't (gap ≈ 0 means a clean fit).

**Section & export**
* Section view along X / Y / Z with a position slider and flip, to inspect mating internals.
* Export measurements to CSV (opens cleanly in Excel) and save a 2× PNG screenshot of the view.

## 📦 Downloads

Two builds are produced:

| Build | Needs .NET 8 Desktop Runtime? | Notes |
|-------|-------------------------------|-------|
| **Standard** (`STPViewer_v0.3.1`) | ✅ Yes | Smaller; for machines that already have the runtime |
| **Portable** (`STPViewer_v0.3.1_portable`) | ❌ No | Runtime bundled — unzip and run, no install / admin needed |

Run `STPViewer v0.3.1.exe`.

## 🔗 Links
* Overview & usage:
  [README.md](https://github.com/ETWen/STPViewer/blob/main/README.md)
* Architecture & design:
  [ARCHITECTURE.md](https://github.com/ETWen/STPViewer/blob/main/ARCHITECTURE.md)

**Full changelog:** first public release — [commit history](https://github.com/ETWen/STPViewer/commits/v0.3.1)