mr-sanders

mr-sanders is a "production-style" Monte Carlo rendering engine written from scratch in C++20. Unlike research renderers, the priority is artist usability: fast interactive feedback, a broad feature set, and as few technical controls as possible. Heavy emphasis was also placed on developer tooling: profiling, logging, diagnostics, and testing tools for performance and correctness.

This is my biggest project to date. I've tried to combine everything I've learned about rendering and software engineering into a single robust, genuinely usable renderer.

It is named after my first cat. 🐱

The current roadmap is to finish full Blender compatibility, and then adding GPU/XPU support.

Notable Features

Interactive

• Render preview window with progressive refinement.
• Interactive camera (-ipr): fly through the scene with WASD / mouse while it renders.

Geometry

• Triangle meshes, spheres, quads, disks.
• Curves / hair: B-spline strands (ribbon / thick / oriented).
• Embree 4 BVH acceleration: hardware-optimised ray traversal and multi-level instancing.
• Catmull-Clark subdivision with adaptive dicing (OpenSubdiv).
• Scalar displacement mapping, per-object ray visibility masks.
• 3D Gaussian splats.
• Heterogeneous volumes (fog, atmosphere, OpenVDB / NanoVDB) with the Henyey-Greenstein phase function.
• Emissive volumes with physically-based blackbody / thermal radiation.
• Volume motion blur from VDB velocity fields (Eulerian semi-Lagrangian advection).

Shading

• Full Open Shading Language (OSL) integration: JIT-compiled, thread-safe shader networks.
• OpenPBR surface shader (full spec).
• Physically-based hair BCSDF (Chiang et al. 2016).
• MaterialX support: .mtlx networks compiled to OSL and mapped onto native lobes.
• Procedural metallic-flakes shader and procedural textures (noise, image, checkerboard, normal map, displacement).
• Programmable shaders: scenes can reference .osl on disk with no recompile.
• Texture system with caching, mipmapping, and filtering (OIIO).
• Nested dielectric medium priority stack.

Lighting & sampling

• Point, distant, spot, area (quad / disk / sphere / mesh), skydome (lat-long HDR), and IES photometric lights.
• Light-tree importance sampling for many-light scenes.
• Sobol quasi-random sampling (OpenQMC).
• Next event estimation + MIS, Russian roulette.
• Delta tracking and ratio tracking for participating media.
• Adaptive sampling: per-pixel error-driven termination.
• Filter importance sampling with box, Gaussian, and windowed-sinc reconstruction filters.
• A "one-click" Caustics Solver (Conty & Kulla 2020): guided photon mapping with photon beams for difficult light paths.

Camera

• Perspective and orthographic, thin-lens depth of field, aperture blades.
• Linear camera and object motion blur.
• Ray differentials for texture filtering.

Colour & output

• OpenColorIO colour management: ACEScg render space, configurable display / view transforms.
• EXR, PNG, JPEG, TIFF, HDR and more (OIIO).
• AOVs: normal, albedo, depth, emission, background, direct / indirect lighting, raycount, cputime.
• Cryptomatte (v1.2) for per-object / material ID mattes.
• Intel Open Image Denoise using albedo / normal guide buffers.

Developer tooling

• GoogleTest suite, Tracy profiler instrumentation.
• Structured logging, CPU / memory diagnostics, per-render stat accumulators.

Renders

Coming soon...