💡 Experimental real-time global illumination renderer 🦀

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
  • Multi-bounce temporally-recurrent voxel-based diffuse
  • Short-range ray-traced diffuse for high-frequency details
  • Single bounce 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 overview

• A quick presentation about the renderer
• Repository highlights:
  • HLSL shaders: assets/shaders/
  • Rust shaders: crates/lib/rust-shaders/
  • Main render graph passes: world_render_passes.rs
• Notable branches:
  • restir-meets-surfel - latest experimental branch, with new GI in the works

Platforms

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

Hardware:

• Nvidia RTX series
• Nvidia GTX 1060 and newer (slow: driver-emulated ray-tracing)
• AMD Radeon RX 6000 series

Operating systems:

• Windows
• Linux

(Some) Linux dependencies

• libtinfo5
• uuid-dev

Building and running

There's a very minimal asset pipeline in bake.rs, which converts meshes from GLTF to an internal flat format, and calculates texture mips. In order to bake all the provided meshes, run:

• Windows: bake.cmd
• Linux: ./bake.sh

When done, run the renderer demo (view app from crates/bin/view) via:

• Windows: build_and_run.cmd [scene_name]
• Linux: ./build_and_run.sh [scene_name]

Where [scene_name] is one of the file names in assets/scenes, without the .ron extension, e.g.:

build_and_run.cmd battle

or

cargo run --bin view --release -- --scene battle --width 1920 --height 1080 --no-debug

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
• Backspace - reset view to previous saved state
• 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.

Adding Meshes and Scenes

To add new mesh(es), open bake.cmd (Win) / bake.sh (Linux), and add

• cargo run --bin bake --release -- --scene "[path]" --scale 1.0 -o [mesh_name]

To add new scenes, in \assets\scenes, create a [scene_name].ron with the following content:

(
    instances: [
        (
            position: (0, 0, 0),
            mesh: "[mesh_name]",
        ),
    ]
)

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.
• The voxel GI uses a fixed-size volume around the origin by default.
  • Use --gi-volume-scale to change its extent in the view app
  • It can be configured to use camera-centered cascades at an extra performance cost (see CASCADE_COUNT and SCROLL_CASCADES in csgi.rs)
• 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

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.