Capable of rendering realistic lighting effects in real-time, the AMD Capsaicin Graphics Framework is now available and features the incorporation of the GI-1.0 solution.

Today, the GPUOpen website was updated with the new AMD Capsaicin graphics rendering research framework based on Microsoft’s DirectX12 API.

AMD Capsaicin (not to be confused with the GPUs released around seven years ago) is a graphics rendering framework designed to encourage fast prototyping of new features. Its core principle includes creating simpler abstractions of common rendering operations so that game developers may focus on writing algorithms instead of having to deal with complex API specifics.

The framework is based on a modular design to better support multiple concurrent developers and research implementations. AMD Capsaicin’s 1.0 release includes several HLSL functions for material sampling, light sampling, spherical harmonics, and more. There are also several common rendering techniques like TAA, SSGI, Tone Mapping, and Ambient Occlusion, among others.

The most interesting feature by far currently available in the AMD Capsaicin framework is the GI-1.0 real-time global illumination solution, based on the paper A Fast Scalable Two-Level Radiance Caching Scheme for Real-Time Global Illumination (Guillaume Boissé, Sylvain Meunier, Heloise de Dinechin, Matthew Oliver, Pieterjan Bartels, Alexander Veselov, Kenta Eto, Takahiro Harada).

The main goal of GI-1.0 is to use additional lighting structures to reduce the sample rates for ray tracing and thus improve performance. The two-level scheme caches the radiance and uses it for sampling. AMD Senior Graphics Programmer Guillaume Boisse explained in this GDC 2023 presentation:

Screen probes are our first level of caching. They position directly onto the primary surfaces and only onto the primary surfaces. They cache the incoming radiance across the hemisphere, and they’re high fidelity simply by virtue of the fact that we have many probes.

Then the hash cells, they’re the second level of caching. They’re positioned anywhere in the world. They cache the reflected radiance for a given direction. They’re far less detailed than the screen probes, but they’re stable and persistent, so it’s a nice complement.

The paper also includes performance figures for GI-1.0. The rendering time cost in AMD’s tests ranges from 1.932ms to 3.124ms on an AMD Radeon RX 6900 XT GPU.

GI-1.0 was also implemented as an Unreal Engine 5 plugin so the engineers could compare it with UE5’s Lumen renderer. That said, the UE5 integration is still incomplete due to the engineering effort to accurately evaluate UE5’s material system.

The AMD Capsaicin graphics rendering framework lets users switch between renderers. In this version, a reference Path Tracer renderer is available in addition to GI-1.0.