Ray Tracing Support

[5nefarious]

Khronos has recently released the final specification for ray tracing on Vulkan. At this point, DX12, Vulkan, and Metal all seem to have some form of acceleration for ray tracing. Are there any plans to eventually consolidate and expose these APIs in wgpu and wgpu-rs?

I foresee real-time rendering making increasing use of ray tracing in the future, so this may be an essential feature to have. However, I imagine it may be very difficult to support this on the DX11 and OpenGL backends through software emulation.

[kvark]

See also:

• VKTrace/DXR Support wgpu-rs#247 (dupe in wgpu-rs)
• RTX Extensions for DX12, Vulkan and OpenGL gfx#2418 (graphics abstraction we use)
• Ray Tracing extension gpuweb/gpuweb#535 (Web upstream feature request)

It's too early to consider this an essential feature on all backends, but rolling it out at least where the backends do have support for it seems very useful today.

[Sebbl0508]

Are there any updates on this?

[cwfitzgerald]

Not currently. There's interest from upstream WebGPU, but that would be well after v1.

We could make it a native extension and I think it would be great, but the apis are quite large (including shader side transformations), and given very few of us actually have hardware to support this, the chance of it happening any time soon without a champion is low.

[OriginLive]

Hi, when is this comming out?

[cwfitzgerald]

There's no one actively working on it to my knowledge.

[OriginLive]

It would be nice to atleast get native extension or some bindings. Would be a nice start

[expenses]

I'm curious about getting basic ray-tracing support working. I think that a first draft wouldn't be too hard, with some limitations. I think we'd initially want to:

• Focus on Vulkan
• Ignore the full ray tracing pipeline (https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_ray_tracing_pipeline.html) and just focus on ray queries (https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_ray_query.html)
• Ignore support in naga for now, just support ray tracing in SPIR-V via SPIRV_SHADER_PASSTHROUGH.

The remaining part is then creating an abstraction for acceleration structures (https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_acceleration_structure.html).

You probably want to focus on getting a simple acceleration structure abstraction for triangle mesh and instance ASes that are built on the GPU. Anything else can come later.

I can't promise anything, but I'll try and look into this when I'm back with my home setup.

[expenses]

My progress so far is at master...expenses:wgpu:hal-acceleration-structures. I plan on merging in wgpu-hal support first, probably with a 'hello world' ray-traced triangle example like https://github.com/SaschaWillems/Vulkan#basic-ray-tracing.

[kvark]

@expenses thank you for championing Ray Tracing! It's very exciting for the community to get access to it 🚀 .

Our main concerns are the maintenance costs for a large API surface added to the fact it will need to change in order to abstract over DXR efficiently. Ideally, there would be a proper investigation on the API differences between VkRT and DXR before wgpu-hal API is prototyped. However, we are somewhat confident that the amount of changes needed for DXR will be limited, and it would be fine to do as the next step.

My advice, if I may, would be to not try to copy Vulkan into wgpu-hal. Our HAL is low level and zero/low overhead, but it doesn't have to be extremely low level. For example, it doesn't have the API for allocating memory and binding objects to it, like Vulkan. So if you have a choice of 1) put complexity in the Vulkan backend, or 2) expose it in wgpu-hal, please put a bigger weight on 1). We can make it more complex as a follow-up for DXR if needed.

Again, thank you for all the amazing contributions. Looking forward to see the opportunities that your work opens to all of us!

[expenses]

My impression is that as Vulkan raytracing was based on DXR, the APIs should be fairly similar. Beyond acceleration structures, the main thing I've focused on is the ray query extension: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_ray_query.html. This allows ray tracing in the normal vertex/fragment/compute shader stages as opposed to requiring a new ray tracing shader stage and shader binding tables and all that stuff.

This is equivalent to inline ray tracing in DXR 1.1: https://devblogs.microsoft.com/directx/dxr-1-1/#inline-raytracing