'This game is extremely broken': The dev of VKD3D-Proton, software for running Direct3D 12 games on Linux, isn't enjoying Forza Horizon 6 very much

In my performance analysis of the PC version of Forza Horizon 6, I found that the game ran very well on a wide range of PCs, with nary a bug or glitch. However, these were all using Windows, and many Linux gamers are finding that the game has considerable problems on that platform. Fortunately, the maker of the software that translates Windows game code to work on Linux has perhaps discovered the root cause of the issues.

As spotted by GamingOnLinux, Hans-Kristian Arntzen has recently submitted a whole bunch of tweaks for merging with the latest version of VKD3D-Proton. This bit of software is called a translation layer, and is akin to someone converting instructions from French to English. In this instance, it's translating the Direct3D 12 into Vulkan, so that games using the API can run on PCs using Linux.

But along with the code, Arntzen has offered one or two thoughts on Forza Horizon 6's coding, starting with a fairly damning overview: "This game is extremely broken."

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To the average PC enthusiast, a lot of what the developer is criticising won't mean anything, because it's all related to the very deep levels of code and processes that the game's engine is doing. One thing did stand out to me, though: "There are also bugs with 'use-before-alloc' where the application allocates resources after submit and writing descriptors pointing to them to the descriptor heap while GPU is in flight."

In the world of Direct3D 12, allocating resources, writing everything required into them, and then telling the GPU it's all ready is an absolute must for avoiding odd behaviours, rendering glitches, or full-blown crashes. You absolutely don't want to be flinging out a command list to the GPU before or during that whole process, because it could be requesting the wrong data or a resource that isn't even there yet.

A lot of the issues also seem to relate directly to code for AMD RDNA 2 or newer GPUs, though it turns out that GeForce RTX GPUs have issues too. Nvidia is aware of this and has said that it will release a fix in "an upcoming driver release."

Linux gamers have been reporting numerous problems with the game via ProtonDB, though interestingly, the handful of comments from Steam Deck owners are mostly quite positive. This latter point is important because if Xbox Games Studio never intended for Forza Horizon 6 to run on devices using a translation layer, it wouldn't have bothered working with Valve to achieve Steam Deck verification.

Using Proton Experimental and disabling ray-tracing in FH6 seems to help quite a bit, and given just how popular the game is right now, I dare say that Valve and Arntzen will eventually get on top of things. How much Xbox Games Studio will chip in is anyone's guess, though, given that it's their mess in the first place.

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