Comment by jayd16

Even this is just guesswork for the way these engines work, because they literally don't know what set of shaders to compile ahead of time. Arbitrary scripting can change that on a frame-by-frame basis, shader precompilation in these engines mostly relies on recording shader invocations during gameplay and shipping that list. [1]

Like, on the one hand, you have engines/games which always stutter, have more-or-less long "shader precompilation" splashscreens on every patch and still stutter anyway. The frametime graph of any UE title looks like a topographic cross-section of Verdun. On the other hand there are titles not using those engines where you wouldn't even notice there were any shaders to precompile which... just run.

[1] https://dev.epicgames.com/documentation/en-us/unreal-engine/...

> In a highly programmable real-time rendering environment such as Unreal Engine (UE), any application with a large amount of content has too many GPU state parameters that can change to make it practical to manually configure PSOs in advance. To work around this complication, UE can collect data about the GPU state from an application build at runtime, then use this cached data to generate new PSOs far in advance of when they are used. This narrows down the possible GPU states to only the ones used in the application. The PSO descriptions gathered from running the application are called PSO caches.

> The steps to collect PSOs in Unreal are:

> 1. Play the game.

> 2. Log what is actually drawn.

> 3. Include this information in the build.

> After that, on subsequent playthroughs the game can create the necessary GPU states earlier than they are needed by the rendering code.

Of course, if the playthrough used for generating the list of shadersdoesn't hit X codepath ("oh this particular spell was not cast while holding down shift"), a player hitting it will then get a 0.1s game pause when they invariably do.

Uvix 3 days ago

That's why I said "precompilation at startup". That has users compile for their precise hardware/driver combination prior to the game trying to use them for display.

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formerly_proven 3 days ago

Even this is just guesswork for the way these engines work, because they literally don't know what set of shaders to compile ahead of time. Arbitrary scripting can change that on a frame-by-frame basis, shader precompilation in these engines mostly relies on recording shader invocations during gameplay and shipping that list. [1]
Like, on the one hand, you have engines/games which always stutter, have more-or-less long "shader precompilation" splashscreens on every patch and still stutter anyway. The frametime graph of any UE title looks like a topographic cross-section of Verdun. On the other hand there are titles not using those engines where you wouldn't even notice there were any shaders to precompile which... just run.
[1] https://dev.epicgames.com/documentation/en-us/unreal-engine/...
> In a highly programmable real-time rendering environment such as Unreal Engine (UE), any application with a large amount of content has too many GPU state parameters that can change to make it practical to manually configure PSOs in advance. To work around this complication, UE can collect data about the GPU state from an application build at runtime, then use this cached data to generate new PSOs far in advance of when they are used. This narrows down the possible GPU states to only the ones used in the application. The PSO descriptions gathered from running the application are called PSO caches.
> The steps to collect PSOs in Unreal are:
> 1. Play the game.
> 2. Log what is actually drawn.
> 3. Include this information in the build.
> After that, on subsequent playthroughs the game can create the necessary GPU states earlier than they are needed by the rendering code.
Of course, if the playthrough used for generating the list of shadersdoesn't hit X codepath ("oh this particular spell was not cast while holding down shift"), a player hitting it will then get a 0.1s game pause when they invariably do.

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