Production-Ready PBR: Integrating BRL-CAD geometry ray tracing with Appleseed rendering

[brlcad]

Outline

BRL-CAD recently introduced "art," a command-line renderer that integrates the appleseed rendering engine. While BRL-CAD provides the geometry and intersection logic, appleseed handles the light transport and shading. Currently, "art" is in an experimental state, supporting only basic, single-file Open Shading Language (OSL) shaders. This project aims to bring "art" to production-readiness by implementing support for complex shader networks (OSL and MaterialX), advanced material properties like subsurface scattering and emission, and robust texture mapping for BRL-CAD primitives.

Details

The focus of this project is to transition "art" from a prototype to a reliable production tool. Key development areas include:

• Shader Network Integration: Move beyond single-file .osl shaders to support full shader networks and MaterialX files. This involves creating a robust mapping system between BRL-CAD material properties and appleseed’s shading nodes.
• Texture Mapping & UVs: Solving the "mapping problem" by ensuring that BRL-CAD’s implicit primitives (ellipsoids, tori, etc.) correctly pass coordinate data to appleseed for procedural and image-based texturing.
• Advanced Light Transport: Implementing and testing advanced optics features within the "art" framework, including:
  -- Emission: Allowing BRL-CAD geometry to act as light sources.
  -- Subsurface Scattering (SSS): Essential for realistic skin, wax, and plastic.
  -- Volumetrics: Basic support for fog or smoke within the appleseed optics pipeline.

Expected Outcome

• A production-stable version of the art utility capable of rendering complex scenes with full PBR fidelity.
• Support for OSL shader networks, allowing users to use industry-standard material workflows.
• A suite of "Production-Ready" demo scenes showing off complex materials (translucency, metallic flakes, textures) rendered directly from BRL-CAD .g files.
• Documentation for the updated material system and an "art" manual page for PBR rendering in BRL-CAD.

Project Properties

Skills

Languages: C++, Open Shading Language (OSL).
Concepts: Physically-Based Rendering (PBR), Light Transport (Path Tracing), MaterialX.
APIs: appleseed API, BRL-CAD librt.

Difficulty

Hard (Reasoning: Requires a deep understanding of path tracing math and the ability to bridge two very different software architectures.)

Size

Long (350h)

Additional Information

• Potential mentor(s): Sean Morrison
  Erik Greenwald
• Organization website: https://brlcad.org
• Communication channels: https://brlcad.zulipchat.com

[vishwakarmanilesh7398-driod]

"Hi @brlcad, @erikg,

I have been studying the art utility's current architecture and I'd like to share my proposed approach for transitioning it to a production-ready tool. My idea focuses on three critical technical areas:

1. Shader Network Orchestration:
   Instead of simple OSL files, my approach involves building a mapping layer that can interpret complex MaterialX graphs and OSL shader networks. This will allow BRL-CAD material properties to interface directly with Appleseed’s shading nodes, providing industry-standard material fidelity.

2. Solving the UV Mapping Problem:
   For BRL-CAD’s implicit primitives (Ellipsoids, Tori, etc.), I propose a robust coordinate-passing logic. By calculating and passing precise surface parameters to Appleseed during the intersection phase, we can ensure that procedural and image-based textures wrap correctly without distortion.

3. Advanced Light Transport Integration:
   I plan to extend the optics pipeline to support:

Emission: Allowing any geometry to be sampled as a light source.

Subsurface Scattering (SSS): Implementing a BSSRDF model for realistic translucent materials like wax or skin.

Volumetrics: Integrating basic fog and smoke scattering within the path-tracing loop.

I am aiming for a Long (350h) project size to ensure that all features are thoroughly tested with a suite of production-ready demo scenes. I would love to hear your thoughts on this architectural direction."