Microsoft has announced DirectX Raytracing (DXR), a major new feature addition to DirectX 12. This API will offer hardware accelerated ray tracing to DirectX applications.
Demo video:
What is DirectX Raytracing?
At the highest level, DirectX Raytracing (DXR) introduces four, new concepts to the DirectX 12 API:
- The acceleration structure is an object that represents a full 3D environment in a format optimal for traversal by the GPU. Represented as a two-level hierarchy, the structure affords both optimized ray traversal by the GPU, as well as efficient modification by the application for dynamic objects.
- A new command list method, DispatchRays, which is the starting point for tracing rays into the scene. This is how the game actually submits DXR workloads to the GPU.
- A set of new HLSL shader types including ray-generation, closest-hit, any-hit, and miss shaders. These specify what the DXR workload actually does computationally. When DispatchRays is called, the ray-generation shader runs. Using the new TraceRay intrinsic function in HLSL, the ray generation shader causes rays to be traced into the scene. Depending on where the ray goes in the scene, one of several hit or miss shaders may be invoked at the point of intersection. This allows a game to assign each object its own set of shaders and textures, resulting in a unique material.
- The raytracing pipeline state, a companion in spirit to today’s Graphics and Compute pipeline state objects, encapsulates the raytracing shaders and other state relevant to raytracing workloads.
You may have noticed that DXR does not introduce a new GPU engine to go alongside DX12’s existing Graphics and Compute engines. This is intentional – DXR workloads can be run on either of DX12’s existing engines. The primary reason for this is that, fundamentally, DXR is a compute-like workload. It does not require complex state such as output merger blend modes or input assembler vertex layouts. A secondary reason, however, is that representing DXR as a compute-like workload is aligned to what we see as the future of graphics, namely that hardware will be increasingly general-purpose, and eventually most fixed-function units will be replaced by HLSL code. The design of the raytracing pipeline state exemplifies this shift through its name and design in the API. With DX12, the traditional approach would have been to create a new CreateRaytracingPipelineState method. Instead, we decided to go with a much more generic and flexible CreateStateObject method. It is designed to be adaptable so that in addition to Raytracing, it can eventually be used to create Graphics and Compute pipeline states, as well as any future pipeline designs.
Source: https://blogs.msdn.microsoft.com/directx/2018/03/19/announcing-microsoft-directx-raytracing/
| Vendor | Support |
|---|---|
| AMD | Indeterminate |
| NVIDIA Volta | Hardware + Software (RTX) |
| NVIDIA Pre-Volta | Software |
Source: https://www.anandtech.com/show/12547/expanding-directx-12-microsoft-announces-directx-raytracing
The Tensor cores in a Volta card, like the TITAN V, are what allow for the hardware support. Tensor cores are normally used for deep learning applications, as such they have not appeared in Pascal cards. The potential for Tensor cores to be used for ray tracing has been known, but this might be the first mainstream application.
Additional demo of NVIDIA's RTX technology with DXR running on a Volta card:
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