Comment by MindSpunk
10 hours ago
Depends what you're precompiling.
For Vulkan you already ship "pre-compiled" shaders in SPIR-V form. The SPIR-V needs to be compiled to GPU ISA before it can run.
You can't, in general, pre-compile the SPIR-V to GPU ISA because you don't know the target device you're running on until the app launches. You would have to precompile ISA for every GPU you ever plan to run on, for every platform, for every driver version they've ever released that you will run on. Also you need to know when new hardware and drivers come out and have pre-compiled ISA ready for them.
Steam tries to do this. They store pre-compiled ISA tagged with the GPU+Driver+Platform, then ship it to you. Kinda works if they have the shaders for a game compiled for your GPU/Driver/Platform. In reality your cache hit rate will be spotty and plenty of people are going to stutter.
OpenGL/DirectX11 still has this problem too, but it's all hidden in the driver. Drivers would do a lot of heroics to hide compilation stutter. They'd still often fail though and developers had no way to really manage it out outside of some truly disgusting hacks.
There's two tiers of precompiled though. Even if you can't download them precompiled, you can compile before the game launches so there are no stutters after.
Yes, many games do that too. Depending on how many shaders the game uses and how fast the user's CPU is an exhaustive pre-compile could take half an hour or more.
But in reality the exhaustive pre-compile will compile way more than will be used by any given game session (on average) and waste lots of time. Also you would have to recompile every time the user upgraded their driver version or changed hardware. And you're likely to churn a lot of customers if you smack them with a 30+ minute loading screen.
Precisely which shaders get used by the game can only be correctly discovered at runtime in many games, it depends on the precise state of the game/renderer and the quality settings and often hardware vendor if there are vendor-specific code paths.
Some games will get QA to play a bunch of the game, or maybe setup automated scripts to fly through all the levels and log which shaders get used. Then that log gets replayed in a startup pre-compile loading screen so you're at least pre-compiling shaders you know will be used.
I don't think this is as much of an issue as you are making it out to be. I have my Steam Deck on the main branch release which seems to exclude it from downloading precompiled shaders. When a game updates it has to compile the shaders first, but even on a big game this does not take an unreasonable amount of time. Less time than it takes for game updates to download at least.
Steam could improve the experience here by having the shaders compile overnight in the background so it presents zero delay but the current way doesn't bother me much at all.
2 replies →
So is this why on my laptop when I start a game after an update it starts "compiling vulkan shaders" for a few minutes? I've never understood what that was actually for but it takes 100% CPU on all cores so it's clearly doing something