The Gamecube and Wii emulator, Dolphin, implements “Ubershaders” to solve stuttering

Dolphin [Official Site] is one of my favorite open source projects and the progress they’ve made in the past few years is truly impressive. In their latest project blog post, the developers have outlined a very exciting new feature in the emulator, one which helps mitigate the issue of stuttering.

The problem of shader compilation stuttering is something of a recurring problem when it comes to rendering. If there’s no shader cache present, GPUs generally spend precious time compiling shaders which then results in jerkiness as things struggle to be rendered properly. To complicate things, shader caches are unique to driver versions, configurations and the actual game so, that, if there’s any change, they need to be re-compiled. In short, and I know I’m simplifying things for the sake of brevity, being able to have a reliable shader cache is something that can vastly improve user experience.



The Dolphin team is confident that they’ve implemented a very “ridiculous” but good solution to this stuttering problem. They’ve written an interpreter that emulates the actual Gamecube/Wii rendering pipeline. It avoids compilation during the game and instead relies upon flexible shaders that compile when you initially start up the game. It required a very specialized knowledge of not only the hardware but also the APIs and drivers, so it’s a massive achievement to get something like this done.

The write up by the Dolphin team details the nature of these challenges and the technical considerations that had to be made in order to get all of this working. I recommend that you give it a read if you’re more technically-minder or simply curious to learn more.

So, what does this mean, in practical terms, to the average user? With these so-called “Ubershaders” a lot, if not nearly all, of the stuttering in the emulator is gone. The current recommended “hybrid” option greatly reduces performance cost while keeping games running smoothly. I tried them out for myself and found that the implementation seems to work as promised. Shaders compiled at startup and I didn’t notice any stutter as I played a bit of Super Mario Sunshine and Twilight Princess. These Ubershaders ought to work on both OpenGL and Vulkan backends, though I only tried it out with the latter.



There’s a few caveats to all of this, mostly for a few specific hardware vendors and driver combinations. For Linux users, there’s a few quirks that mostly affect those who use Nvidia cards with proprietary drivers. First and foremost, the compiled shaders are much slower on OpenGL and Vulkan than their (Windows) D3D backend. The Dolphin team is limited by the lack of tools provided by Nvidia to disassemble shaders, despite every other vendor providing the tools. Likewise, there’s also a quirk in the driver that causes some slight stutter when shaders are compiled which again does not happen in D3D.

Mesa users like myself are all good, however, and the project gets some praise for smartly sharing shaders between pipelines and thus eliminating any potential stutter with new blending modes. Both Intel and AMD users are recommended to use the Vulkan backend as anv and radv behave well with the emulator.

The Dolphin team are still hard at work adding new features and optimizing things and I, for one, can’t wait to see what other things they have in store for the future. You’ll have to grab a development version or compile from source to check out Ubershaders for now. Article taken from GamingOnLinux.com.