AMD explains ray tracing support in RDNA 2

With the introduction of AMD’s graphics cards in the Radeon RX 6000 series, the architecture RDNA 2 also premiered in graphics cards, shortly after it did the same as the graphics part in Xbox Series X and Series S. One of the news is support for hardware accelerated ray tracing. In a developer video, one of AMD’s graphics engineers discusses how developers can use the new hardware in conjunction with Microsoft’s DirectX Raytracing 1.1 (DXR 1.1) developer interface.

One of the news in the DXR 1.1 version update is what is called inline ray tracing. In short, developers have better control over when calculations are related to ray tracing is performed in the rendering process, which consists of different steps that determine how the pixels of the scenes are colored (shader stages). The extended control is given by the developer being able to control the scheduling of tasks, and also makes it possible to introduce ray tracing in all steps of the rendering process.

For the developer who performs a certain type of calculation at an earlier stage in the process, this means that ray tracing-calculations can be performed during the same step, which optimizes the burden on both the developer and the hardware. For AMD, hardware-accelerated computing is supported by ray tracing first with the architecture RDNA 2, where each resource group (Work Group Processor, WGP) is equipped with two hardware devices called Ray Accelerator (RA) for the task.

Each RA can independently perform calculations of whether light beams cross “boxes” or “ray triangles” when traveling in 3D environments. AMD also shares what the company sees as the best approach to support DXR 1.1 on RDNA 2 hardware. It includes tracking as few light beams as possible while achieving good image quality, and that one beam per pixel on the screen gives good results.

In order to achieve the good result, this should also be combined with an effective system for cleaning up the visual noise that occurs when calculating ray tracing, a process called denoising. Developers who develop particularly effective denoisingTechnicians can get away with fewer tracked light rays than one per pixel, resulting in better performance. AMD has developed two specialized denoisingRDNA 2 features made publicly available under an MIT license.

In addition to ray tracing-calculations can be performed anywhere in the rendering process, they can be performed asynchronously via the same Asynchronous Compute system AMD has long applied in the company’s graphics architectures. The video also contains a number of tips that are primarily of interest to those who develop games with ray tracingsupport for RDNA 2. This includes the size of groups of wires for optimal execution, and how traversal of light beams can be optimized so that calculations are not performed in parts of the image that are not visible or unimportant.

AMD’s interpretation of ray tracing is currently available in the graphics cards Radeon RX 6800 and RX 6800 XT and soon with the flagship Radeon RX 6900 XT. Among game consoles, this applies to the Xbox Series X and sibling Series S, as well as competing hardware Playstation 5.

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