monster-step-viewer

A 3D viewer for STEP (ISO 10303-21) CAD files, built with monstertruck, bevy and egui. Optional path-traced overlay via 3Delight (NSI).

Features

• Load and display STEP files with full assembly support.
• Model hierarchy panel showing shells and faces.
• Per-face visibility toggling.
• Random colors mode for visualizing individual faces.
• STEP-defined colors from the file.
• Adjustable tessellation density.
• Wireframe edge display (boundary edges).
• Polygon-edge overlay (triangulated mesh edges) and isoparametric curve overlay.
• Per-axis clip planes (X/Y/Z, flippable, with optional solidify).
• Manual Y/Z up-axis toggle for files saved in either convention.
• Bounding box visualization.
• Pan/orbit camera controls with keyboard shortcuts.
• Optional 3Delight (NSI) path-traced overlay — see 3Delight Rendering.
• File metadata display.

Installation

cargo install monster-step-viewer

The installed binary is called mstpv.

Usage

# Run with a STEP file
mstpv path/to/model.step

# Or run and use the file dialog
mstpv

Controls

Mouse

• Left-drag or right-drag: Orbit. Left-drag keeps this reachable on a touchpad, where a single-finger drag is all you need.
• Middle-drag: Pan.
• Scroll wheel: Zoom (dolly).
• Left-click: Pick face/hierarchy item. A click only selects if the pointer stays put; move it and the gesture orbits instead.

Keyboard

• R: Reset view to the initial vantage.
• F: Frame the scene with the current camera angle.
• C: Center on the selected face.
• Ctrl++/-/0: Zoom UI in/out/reset.
• Esc: Quit.

Toolbar Icons

Icon	Action
	Random face colors
	STEP-defined colors
	Bounding box
	STEP curve wireframe
	Isoparametric curves
	Polygon (mesh) edges
Z/Y	Up-axis toggle -- current axis first; clicking swaps
	3Delight NSI overlay (requires nsi-render)

Per-axis clip planes (X/Y/Z) cycle Off → +axis → −axis → Off. The toolbar also has a tessellation-quality slider and a shading-mode picker.

3Delight Rendering

Build with the nsi-render Cargo feature for a 3Delight (NSI) progressive-render overlay:

cargo run --features nsi-render -- path/to/model.step

3Delight must be installed locally. mstpv looks it up at runtime — checking standard install paths and the $DELIGHT environment variable — and only enables the ③ toolbar button if it's found. Clicking it starts an interactive rendering session in 3Delight Display; camera moves translate in real time.

Native-only; wasm builds are unaffected.

Building

Requires Rust 1.89+ (2024 edition).

cargo build              # debug
cargo build --release    # release
cargo build --release --features nsi-render
cargo test

Linux Dependencies

# Debian/Ubuntu
sudo apt-get install libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev libxkbcommon-dev libssl-dev libudev-dev

# Fedora
dnf install clang clang-devel clang-tools-extra libxkbcommon-devel pkg-config openssl-devel libxcb-devel systemd-devel

Dependencies

• bevy – game engine for rendering.
• egui – immediate-mode GUI.
• monstertruck – STEP parsing, BRep topology, tessellation.
• bevy_editor_cam – orbit/pan/dolly camera controls.
• meshopt – mesh post-processing (vertex cache/fetch reordering); native-only.
• nsi – 3Delight scene interface bindings (nsi-render only).

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.