Valve’s Samuel Pitoiset has been changing the Radeon Vulkan (RADV) driver to offer more control over how variable rate shading (VRS) works. Phoronix notes that the higher degree of control might relate to whether a Steam Deck is running on its battery or connected to AC. Microsoft introduced VRS to DirectX 12 in 2019 as a performance-saving feature. Essentially it can make a game render different parts of the screen with varying levels of clarity and precision depending on how important they are. Someone playing a racing game isn’t necessarily looking at the scenery or the sky most of the time, so VRS might make a game spend less effort on the pixels in those areas than the car, cockpit, or the road.
The feature is supposed to save performance on pixels players won’t notice, like things covered up by motion blur or pure black pixels inside shadows. Something like that could be critical for a portable PC running on batteries, like the Steam Deck. Pitoiset’s changes make dynamic scaling of VRS rates possible, and now that rate can be written to a new configuration file. The Steam Deck’s AMD Van Gogh APU will enable this by default. While Pitoiset confirmed the change is meant to save power, Phoronix speculates this could allow the VRS rate to change between different settings when the Steam Deck is on AC or battery power. Theoretically, this could also have results for other AMD devices running Vulkan applications. Late last summer, Valve and AMD collaborated on a new Linux CPU driver for better performance. Any Zen 2 PC could benefit from it. Around the same time, Valve announced changes to the Steam Big Picture user interface designed for the Steam Deck but will also apply to full PCs. Steam Decks start shipping on February 28.
