bevy_solari.md

---

title: Initial raytraced lighting progress (bevy_solari)
authors: ["@JMS55", "@SparkyPotato"]
pull_requests: [19058, 19620, 19790, 20020, 20113, 20156, 20213, 20242, 20259, 20406, 20457, 20580, 20596, 20622, 20658, 20659]

---

Overview

(TODO: Embed solari example screenshot here)

With the new bevy_solari crate, we're making our first steps towards realtime raytraced lighting.

For some background, lighting in video games can be split into two parts: direct and indirect lighting.

Direct lighting is light that is emitted from a light source, bounces off of one surface, and then reaches the camera. Indirect lighting by contrast is light that bounces off of different surfaces many times before reaching the camera. Indirect lighting is also often called global illumination.

(TODO: Diagrams of direct vs indirect light)

In Bevy, direct lighting comes from analytical light components (DirectionalLight, PointLight, SpotLight) and shadow maps. Indirect lighting comes from a hardcoded AmbientLight, baked lighting components (EnvironmentMapLight, IrradianceVolume, Lightmap), and screen-space calculations (ScreenSpaceAmbientOcclusion, ScreenSpaceReflections, specular_transmission, diffuse_transmission).

The problem with these methods is that they all have large downsides:

• Emissive meshes do not cast light onto other objects, either direct or indirect.

• Shadow maps are very expensive to render and consume a lot of memory, so you're limited to using only a few shadow casting lights. Good shadow quality can be difficult to obtain in large scenes.

• Baked lighting does not update in realtime as objects and lights move around, is low resolution/quality, and requires time to bake, slowing down game production.

• Screen-space methods have low quality and do not capture off-screen geometry and light.

Bevy Solari is intended as a completely alternate, high-end lighting solution for Bevy that uses GPU-accelerated raytracing to fix all of the above problems. Emissive meshes properly cast light and shadows, you can have hundreds of shadow casting lights, quality is much better, it requires no baking time, and it supports fully dynamic scenes!

Try it out

While Bevy 0.17 adds the bevy_solari crate, it is not yet production ready.

However, feel free to run the solari example to check out the progress we've made. There are two different modes you can try out:

A non-realtime "reference" mode that uses pathtracing: cargo run --release --example solari --features bevy_solari -- --pathtracer.

A realtime mode that uses a combination of techniques, and currently supports only diffuse materials: cargo run --release --example solari --features bevy_solari.

Additionally, if you have a NVIDIA GPU, you can enable DLSS Ray Reconstruction with the realtime mode for a combination of denoising (Bevy Solari does not currently come with any alternate denoisers), lower rendering times, and anti-aliasing: cargo run --release --example solari --features bevy_solari,dlss.

How it works

TODO: Showcase the different aspects/steps of Solari (direct initial+temporal+spatial, indirect initial+temporal+spatial, world cache, DLSS RR)

Look forward to more work on Bevy Solari in future releases!

(TODO: Embed bevy_solari logo here, or somewhere else that looks good)

Special thanks to @Vecvec for adding raytracing support to wgpu.