Reduce Input Lag for Steam Deck Built-In FPS Limiter

[iiGiovanni]

#Description:
The built-in FPS limiter in SteamOS (Gamescope) provides excellent frametime consistency and smooth framerate matching. However, it introduces noticeable input lag compared to using external tools like MangoHud for limiting FPS.

#Steps to Reproduce:

1. Enable the built-in FPS limiter in SteamOS (e.g., set to 30 FPS).
2. Play a game and observe the input latency.
3. Compare this with MangoHud’s FPS limiter (e.g., mangohud_config=fps_limit=30).

#Expected Behavior:
The built-in FPS limiter should provide smooth frametimes and consistent framerate without adding noticeable input lag, matching or exceeding MangoHud’s performance.

#Actual Behavior:
While the built-in limiter provides smooth frametimes, the added input lag makes it feel less responsive compared to external FPS limiters like MangoHud.

#Additional Notes:
• The MangoHud limiter creates a console-like experience with no noticeable input lag, while the SteamOS limiter feels frustrating for games requiring fast responses.
• Reducing the input lag for the built-in limiter would make it more convenient and competitive with external solutions.

#Suggestion:
Investigate and optimize how the built-in limiter handles frametimes and input latency, potentially reducing redundant buffering or V-Sync-like effects introduced by Gamescope.

This improvement would enhance the overall gaming experience on the Steam Deck.

[matte-schwartz]

there used to be a low-latency frame limiter but it had to be removed as explained in this comment on an older issue about the same topic: #474 (comment), but I believe there's currently work underway to bring it back.