Ray Tracing and Variable-Rate Shading Design Goals for AMD RDNA2

Hardware-accelerated ray tracing and variable-rate shading will be the design focal points for AMD's next-generation RDNA2 graphics architecture. Microsoft's reveal of its Xbox Series X console attributed both features to AMD's "next generation RDNA" architecture (which logically happens to be RDNA2). The Xbox Series X uses a semi-custom SoC that features CPU cores based on the "Zen 2" microarchitecture and a GPU based on RDNA2. It's highly likely that the SoC could be fabricated on TSMC's 7 nm EUV node, as the RDNA2 graphics architecture is optimized for that. This would mean an optical shrink of "Zen 2" to 7 nm EUV. Besides the SoC that powers Xbox Series X, AMD is expected to leverage 7 nm EUV for its RDNA2 discrete GPUs and CPU chiplets based on its "Zen 3" microarchitecture in 2020.

Variable-rate shading (VRS) is an API-level feature that lets GPUs conserve resources by shading certain areas of a scene at a lower rate than the other, without perceptible difference to the viewer. Microsoft developed two tiers of VRS for its DirectX 12 API, tier-1 is currently supported by NVIDIA "Turing" and Intel Gen11 architectures, while tier-2 is supported by "Turing." The current RDNA architecture doesn't support either tiers. Hardware-accelerated ray-tracing is the cornerstone of NVIDIA's "Turing" RTX 20-series graphics cards, and AMD is catching up to it. Microsoft already standardized it on the software-side with the DXR (DirectX Raytracing) API. A combination of VRS and dynamic render-resolution will be crucial for next-gen consoles to achieve playability at 4K, and to even boast of being 8K-capable.