Vela

Vela is a C++17 project built around VSR ("Vela Scene Runtime"), a scene graph library designed to pair a live, editable scene description with one or more ANARI devices. Applications build a scene once in VSR and render it through any ANARI implementation, which makes VSR useful both as a scene-authoring layer and as a way to compare device behavior side by side.

This repository contains:

• The VSR library collection (core utilities, scene, I/O, rendering, app glue, UI, scripting)
• ANARI device implementation backed by VSR for capturing ANARI state from other applications
• Interactive ImGui-based viewer
• SciVis Studio, a project/shot-oriented scientific visualization application
• Additional interactive apps: multi-device viewer, data tree editor, networked client/server, and an experimental MPI distributed viewer
• Focused interactive demos
• Single-file tutorials showing specific concepts
• Command-line tools for conversion, inspection, headless rendering, and scripting
• Unit tests

VSR's scene library (vsr_scene) generally follows 1:1 with ANARI's object hierarchy, defined in the ANARI specification here.

Vela is tested on Linux, but is also intended to be usable on other operating systems such as macOS and Windows.

Note that Vela is experimental and does not yet track a versioning system, so there are no API or ABI stability guarantees.

Building from source

The repository uses CMake 3.21+ and requires the ANARI-SDK 0.15.0 or newer to be findable via find_package(anari). Builds must happen in a directory separate from the source directory:

% cd /path/to/vela
% mkdir build
% cd build
% cmake -DCMAKE_BUILD_TYPE=Release ..
% cmake --build . --parallel

Using a tool like ccmake or cmake-gui will let you see which options are available to enable. The most commonly used ones are:

• VSR_BUILD_APPS : build the applications and command-line tools
• VSR_BUILD_INTERACTIVE_APPS : build the windowed applications
• VSR_BUILD_UI_LIBRARY : build the ImGui-based UI library
• VSR_USE_CUDA : enable CUDA code paths where relevant
• VSR_USE_LUA : enable Lua scripting support
• VSR_USE_MPI : enable MPI support
• VSR_USE_NETWORKING : enable networking support via Boost.Asio

Many file importers carry additional build dependencies and are therefore off by default, each behind its own option: VSR_USE_ASSIMP, VSR_USE_HDF5, VSR_USE_OIIO, VSR_USE_SILO, VSR_USE_TORCH, VSR_USE_USD, and VSR_USE_VTK. If an expected format is missing at runtime, check whether its option was enabled in your build.

Running the applications

The best starting point for understanding how the libraries compose is src/apps/tutorial/, which holds single-file examples covering rendering, image pipelines, the Forest container, DataTree serialization, and USD export.

vsrViewer

vsrViewer is the main interactive application. It loads scene data from the supported file formats, lets you inspect and edit objects, layers, parameters, animations, and transfer functions, and can save and reload full sessions as .vsr files.

The list of devices offered in the UI comes from a comma-separated list in the VSR_ANARI_LIBRARIES environment variable. If it is unset the app falls back to a small set of defaults, but defining it in your environment (e.g. in a .bashrc) gives you control over what appears:

% export VSR_ANARI_LIBRARIES=helide,visrtx
% ./vsrViewer

Files can be loaded on the command line using a pattern of:

% ./vsrViewer -[loader type] [file1] [file2...]

Once a loader type is selected, every filename after it uses that loader until the next loader type appears. Common loader types are assimp, dlaf, hdri (environment light), obj, and ply. See vsr_io for the full set of supported formats, and vsr::app::Context::parseCommandLine() for the definitive list of available options.

Command-line tools

src/apps/tools/ contains headless utilities, including vsrOffline and vsrRender for offline rendering, vsrPrint for inspecting serialized .vsr files, vsrVolumeToNanoVDB for volume conversion, and vsrLua for scripted workflows.

anari_vsr

anari_vsr is an ANARI device that mirrors ANARI object state into a VSR scene and writes a live_capture.vsr archive as frames are committed. Point an existing ANARI application at it to capture what that application actually submits, then open the result in vsrViewer. It can also forward rendering to a real backend device, selected with the ANARI_VSR_LIBRARY environment variable (helide by default).

Scripting

With VSR_USE_LUA=ON, scenes can be authored and automated from Lua. vsrLua is a standalone interpreter and REPL, while vsrViewer embeds a Lua terminal and builds its Actions menu from Lua modules. Both expose a pre-bound scene variable. See src/vsr/scripting/ for the API and scripts/examples/ for worked examples.

Documentation

• src/vsr/README.md — index of the libraries and what each one covers
• AGENTS.md — architecture overview, dependency layers, and key design patterns
• CONTEXT-MAP.md — how the project's domain contexts relate, with links to per-area glossaries
• docs/adr/ — architecture decision records
• STYLEGUIDE.md — C++ coding conventions used throughout the project

Licensing

Vela is licensed under the Apache License 2.0 — see LICENSE. Contributions are accepted under the Developer Certificate of Origin; see CONTRIBUTING.md.

Third-party components vendored under external/ remain under their own licenses, listed in THIRD-PARTY-NOTICES.md. Three of them preserve their upstream license text in place:

• external/vela_fmtlib — {fmt}, MIT License (external/vela_fmtlib/LICENSE).
• external/vela_glm — OpenGL Mathematics (GLM), dual-licensed under The Happy Bunny License (Modified MIT License) OR the MIT License, at your option (external/vela_glm/LICENSE, which contains the full text of both). The Happy Bunny License is the MIT License plus a non-binding restriction regarding military use; the plain MIT option is available without that restriction.
• external/vela_agx — agx (Animated Geometry eXchange), an independently published third-party project by Jefferson Amstutz (upstream), Apache License 2.0 (external/vela_agx/LICENSE).