Strolle: pretty lightning, 🌈 global illumination 🌈, 6D hashmaps, progress report with a dungeon scene!
Strolle is a real-time rendering engine that uses ray-tracing to achieve aesthetic lightning effects such as 🌈 global illumination 🌈:
\(you might wanna bump your screen's backlight a bit to see all of the effects\)
tl;dr GI is when you simulate how light bounces around a scene before it it seen by the camera - on the screenshot above it is apparent in two places:
\- the floor underneath the sphere is tinted red,
\- the inside of the left-corridor is visible even though the direct lightning (as guarded by the shadow) doesn't get there.
For comparison, here's the same scene with direct lightning only - you can intuitively feel it is somewhat less realistic, more rough, less deep:
... and the same scene using Bevy's default renderer:
Note that on the screenshot above you can also see the inside of the left-corridor, but that's just because Bevy uses ambient lightning to light everything visible in the camera - the difference is best seen with a larger corridor:
For fun, here's how everything looks like without textures:
And, as is the custom, here's The Cornell Box!
As for the algorithmic side - Strolle approximates global illumination by ad-hoc voxelizing the scene into a 6D hashmap of position and normal (you might want to zoom-in to see the voxels):
\(voxel map, kinda extra-smoothed-out by image compression here\)
... estimating GI for each visible voxel, and then sampling a few (1-3) nearby voxels for each visible pixel, which performs kind-of-denoising at once (since one could consider voxels to be like a world-space spatial & temporal denoising mechanism).
Note that on all of the screenshots above, there's no denoising applied per-se - that's just how it looks like when you sample the voxel map directly.
For simplicity (and performance), the algorithm doesn't perform any collision-resolving - we just utilize Z-order curve to prevent nearby cells from colliding with each others, which turned out to work pretty well in practice (at least on the current test scenes).
Technical-wise, we're using software ray-tracing backed-by a couple of rust-gpu shaders (and raster pass for detecting primary hits) - the goal here is to create a relatively simple engine that doesn't require GPU with hardware ray-tracing capabilities, and can still generate a good-looking image.
All goes pretty well so far:
\- Cornell Box runs at 90 FPS (1024x1024) on my M1 Pro,
\- The Dungeon Scene™️ gets around 40-60 FPS (1024x1024, M1 Pro), but I've still got a few optimizations left to apply, so I'm hoping to extract some more frames here.
More info & a couple of videos:
\- https://twitter.com/Piterolex/status/1649148596627861520
\- https://twitter.com/Piterolex/status/1642254962427154433
... and, of course, link to the code:
https://github.com/Patryk27/strolle
(voxel\~ish GI hasn't been merged yet, and there's lots of missing documentation, so it's not really usable yet, though 😇)