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Voxel Direct Lighting on the GPU

Josh

Entry posted by Josh ·

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We left off on voxels when I realized the direct lighting needed to be performed on the GPU. So I had to go and implement a new clustered forward renderer before I could do anything else. Well, I did that and now I finally have voxel lighting calculation being performed with the same code that renders lighting. This gives us the data we need to perform cone step tracing for real-time dynamic global illumination.

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The shadows you see here are calculated using the scene shadowmaps, not by raycasting other voxels:

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I created a GPU timer to find out how much time the lighting took to process. On the CPU, a similar scene took 368 milliseconds to calculate direct lighting. On the GPU, on integrated graphics, (so I guess it was still the CPU!) this scene took 11.61064 milliseconds to process. With a discrete GPU this difference would increase, a lot. So that's great, and we're now at the third step in the diagram below:

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Next we will move this data into a downsampled cube texture and start performing the cone step tracing that gives us fast real-time GI.

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Josh

Here's the scene using a higher voxel resolution. It looks interesting!

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This is a 256x256x256 grid with a voxel size of 10 cm, so that gives you an idea of how much area that can cover. It's bigger than I thought it would be. Then you can have maybe 3-4 of these at bigger sizes, cascading out around the camera.

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SpiderPig

Great work!  How much memory does the voxel grid use and is it stored on the GPU?  I'm thinking about large open worlds; would you generate all voxel data at large voxel sizes, then simply update in real-time the higher density voxel grid around the camera?

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Josh
3 hours ago, SpiderPig said:

Great work!  How much memory does the voxel grid use and is it stored on the GPU?  I'm thinking about large open worlds; would you generate all voxel data at large voxel sizes, then simply update in real-time the higher density voxel grid around the camera?

At a resolution of 256x256x256 voxels, each grid will require 384 mb VRAM.

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Josh

Whew, that was difficult! I changed the the direct lighting routine to use transform feedback to render the direct lighting into a vertex buffer instead of using a texture, which was creating a lot of waste. The next step is to take the lit voxels and put them into a 3D texture. This is one of the hardest features I've ever implemented.

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