💡 kajiya

Experimental real-time global illumination renderer made with Rust and Vulkan

Its general goal is to get as close as possible to path-traced reference at real-time rates in dynamic scenes, without any precomputed light transport, or manually placed light probes.

kajiya does not currently aim to be a fully-featured renderer used to ship games, support all sorts of scenes, lighting phenomena, or a wide range of hardware. It's a hobby project, takes a lot of shortcuts, and is perpetually a work in progress.

For more context, check out our announcement article on Embark's Medium. You'll also get to learn how kajiya connects to our rendering work, and the rust-gpu project!

Ruins environment rendered in kajiya. Scene by Crebotoly

Features

• Hybrid rendering using a mixture of raster, compute, and ray-tracing
• Dynamic global illumination
  • Fully dynamic geometry and lighting without precomputation
  • Volumetric temporally-recurrent irradiance cache for "infinite" bounces
  • Ray-traced diffuse final gather for high-frequency details
  • Ray-traced specular, falling back to diffuse after the first hit
• Sun with ray-traced soft shadows
• Standard PBR with GGX and roughness/metalness
  • Energy-preserving multi-scattering BRDF
• Reference path-tracing mode
• Temporal super-resolution and anti-aliasing
• Natural tone mapping
• Physically-based glare
• Basic motion blur
• Contrast-adaptive sharpening
• Optional DLSS support
• glTF mesh loading (no animations yet)
• A render graph running it all

Technical details

• Global illumination overview
• Repository highlights:
  • HLSL shaders: assets/shaders/
  • Rust shaders: crates/lib/rust-shaders/
  • Main render graph passes: world_render_passes.rs

Primary platforms

kajiya currently works on a limited range of operating systems and hardware.

Hardware:

• Nvidia RTX series
• Nvidia GTX 1060 and newer with 6+ GB of VRAM (slow: driver-emulated ray-tracing)
• AMD Radeon RX 6000 series

Operating systems:

• Windows
• Linux

Secondary Platforms

kajiya has a rudimentary "RTX Off" mode which runs on a wider range of systems, but most of its visual features are disabled.

Hardware:

• Older GPUs with support for Vulkan 1.2

Operating systems:

• macOS

Dependencies

(Some) Linux dependencies

• uuid-dev
• In case the bundled libdxcompiler.so doesn't work: https://github.com/microsoft/DirectXShaderCompiler#downloads

(Some) MacOS dependencies

• ossp-uuid (brew install ossp-uuid)

Building and running

To build kajiya you need Rust.

Once Rust is installed, open a command prompt in the project folder, then build and run the viewer app via:

cargo run --bin view --release

This will compile a binary in the target/release folder, and then run it.

For a list of supported command-line switches see --help. In order to pass it through cargo to the renderer, you need to separate the cargo arguments from view arguments using -- e.g.:

cargo run --bin view --release -- --help

Loading assets

kajiya supports meshes in the glTF 2.0 format, and also has its own tiny RON-based scene format which can refer to multiple glTF 2.0 meshes.

To load either, simply drag-n-drop the .gltf, .glb, or .ron file onto the window of the view app. See the assets/ folder for a few bundled examples.

The first time a mesh is loaded, it is converted to a runtime format: the vertices are packed, and textures are compressed. The next time the same mesh is used, it's loaded from the cache/ folder.

Please note that only the roughness-metalness workflow in glTF is supported. In Blender that corresponds to Principled BSDF.

kajiya can also load image-based lights (examples). To do so, drag-n-drop an .exr or .hdr file onto window of the view app.

The loaded assets can be manipulated in the Scene section of the UI. The app state is persisted in view_state.ron.

Controls in the view app

• WSAD, QE - movement
• Mouse + RMB - rotate the camera
• Mouse + LMB - rotate the sun
• Shift - move faster
• Ctrl - move slower
• Space - switch to reference path tracing
• Tab - show/hide the UI

Resolution scaling

DPI

For the view app, DPI scaling in the operating system affects the physical number of pixels of the rendering output. The --width and --height parameters correspond to logical window size and the internal rendering resolution. Suppose the OS uses DPI scaling of 1.5, and the app is launched with --width 1000, the actual physical width of the window will be 1500 px. Rendering will still happen at 1000 px, with upscaling to 1500 px at the very end, via a Catmull-Rom kernel.

Temporal upsampling

kajiya can also render at a reduced internal resolution, and reconstruct a larger image via temporal upsampling, trading quality for performance. A custom temporal super-resolution algorithm is used by default, and DLSS is supported on some platforms. Both approaches result in better quality than what could be achieved by simply spatially scaling up the image at the end.

For example, --width 1920 --height 1080 --temporal-upsampling 1.5 will produce a 1920x1080 image by upsampling by a factor of 1.5 from 1280x720. Most of the rendering will then happen with 1.5 * 1.5 = 2.25 times fewer pixels, resulting in an almost 2x speedup.

Technical guides

• Using DLSS
• Working on Rust shaders
• Using kajiya as a crate

Known issues

• Vulkan API usage is extremely basic. Resources are usually not released, and barriers aren't optimal.
• There are hard limit on mesh data and instance counts. Exceeding those limits will result in panics and Vulkan validation errors / driver crashes.
• Window (framebuffer) resizing is not yet implemented.
• Denoising needs more work (always).

Acknowledgments

This project is made possible by the awesome open source Rust community, and benefits from a multitude of crates 💖🦀

Special shout-outs go to:

• Felix Westin for his MinimalAtmosphere, which this project uses for sky rendering.
• AMD, especially Dominik Baumeister and Guillaume Boissé for the FidelityFX Shadow Denoiser, which forms the basis of shadow denoising in kajiya.
• Maik Klein for the Vulkan wrapper ash, making it easy for kajiya to talk to the GPU.
• Traverse Research and Jasper Bekkers for a number of highly relevant crates:
  • Bindings to the DXC shader compiler: hassle-rs
  • SPIR-V reflection utilities: rspirv-reflect
  • Vulkan memory management: gpu-allocator
  • Blue noise sampling: blue-noise-sampler
• Troy Sobotka for guidance and mind-bending discussions about color.

Contribution

We welcome community contributions to this project.

Please read our Contributor Guide for more information on how to get started. Please also read our Contributor Terms before you make any contributions.

Any contribution intentionally submitted for inclusion in an Embark Studios project, shall comply with the Rust standard licensing model (MIT OR Apache 2.0) and therefore be dual licensed as described below, without any additional terms or conditions:

License

This contribution is dual licensed under EITHER OF

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

For clarity, "your" refers to Embark or any other licensee/user of the contribution.