[BUG] Stuttering on Vulcan, Extreme stuttering when VSync Double Buffering

[Pengu]

Hi,
Not sure if this is two bugs or one, but the stuttering always feels the same, so I think it might be related.
Only happens with the Vulcan rendering mode. The default mode is fine and perfect.

Here are the full-screen and V-Sync / FPS limit settings and when the bug(s) appear:

1. When V-Sync is disabled and framerate unlimited (no matter if full-screen or windowed) I get weird stuttering in the game. It feels like the time and physics engine continue, I just stay on one frame for a moment. *
Here it is especially noticeable:
Liftoff Arena, especially in the corners
Bardwell's Yard, when looking at the grass in the corner of the field near the birdhouse. The rest of Bardwell's Yard appears stutter-free.
I did not notice it on Pine Valley, but maybe it's there just in a specific spot.

2. Triple-buffered V-Sync no matter if full-screen or windowed: No stuttering, just 30FPS (obviously). It feels kind of different than the same settings in default rendering mode, not sure what it is though.

3. Full-screen and Double-Buffered V-Sync: the stuttering is constant, and each stutter is longer, and it is even visible in all maps and the main menu (the rotating props of the drone stutter and the UI is lagging).

4. Windowed (NOT "Windowed maximized") and Double-buffered V-Sync: The same kind of stuttering like in "1", NOT the kind of stuttering like in "3".

5. Full-screen and 59/60FPS limit and no V-Sync: on 59FPS No stuttering at all, 60FPS tiny stutters, feels butter-smooth but frame tearing (the kind of frame tearing that you usually fix by enabling V-Sync),

6. Windowed (NOT "Windowes maximized"), no V-Sync and 60 FPS cap: feels basically like "5" but I think there are stutters like "1", just much less noticeable.

Video showing the issue: https://youtu.be/psrSbbpVn5Q
(Video starts with 3, then 1, then 2, then 5 but you also see me changing the graphics settings)

The type of full-screen doesn't matter.

*I hope you understand what I mean. It's also visible in the video. For example, in Witcher 3 there is a different kind of stuttering when you quicksave. During the quicksave it feels like the entire game pauses for a moment. Here, in Liftoff this stutter feels more like if I blink or close my eyes for a moment while flying. The game and time continue, the drone continues on its path, I just don't see where I'm going for a moment.

Specs:
Ryzen 5-2600x
16GB RAM
Nvidia RTX 2060Super Founder Edition
2560x1440p60 Monitor

Liftoff 1.3.10 - 25/03/2021
Latest GPU Driver 465.89
Windows 10 2004 Build 19041.867

I sent you the output_log.txt by email.
This bug makes Liftoff basically unplayable for me in Vulcan mode. But luckily, I can still play Liftoff just fine in the default rendering mode. Just wanted to report this to you so you don't remove the default mode or that you can fix this and allow me to enjoy the performance benefits of Vulcan.
Thank you! :D

[JuniorDiscart]

Hi

Funny to see you using Windows with that avatar. ;)

Thanks for the extensive report and sending over the log file (though I wasn't able to find anything related to performance issues). I'd say the Vulkan stuff is pretty experimental and a hit-or-miss on many systems. Where it works, it works well, where it doesn't it creeps up with a lot of stutters. We see that Vulkan is pretty susceptible for VSync, full screen mode and which display it is running on, and I'm not sure it is something we are able to do much about currently (as it's just an option we can expose for people to use in case they prefer it), but everything else on our end is supposed to be agnostic of the rendering API selected and is further handled by the engine. So we can only hope it becomes better as we update the engine and more issues are ironed out on their end, but doing that has some additional challenges in and of itself.

It seems in your case you better stick with default rendering. :)

As a side-note though, the smoothest Liftoff experience I had was on our Linux text machine using the Vulkan API with a GTX980Ti. Compared to OpenGL, it ran with near 80% increase of FPS but depending on the VSync or full screen settings, quality varied in terms of perceived stutters.

[Pengu]

Thank you for the answer :D
Yeah, I'm not always on Linux, mostly because not all the games work that well so I have Windows on the gaming PC. I think I should try Liftoff in Linux though.

It just really intrigued me how weird this issue was so I played around with the settings. :D
As long as you keep the default API around for now, I will stay happy.

[JuniorDiscart]

Yeah, we don't intend to remove DX11 support. ;) For Mac however, we soon might have no choice as Apple has deprecated OpenGL support, so we are forced to use Metal (though Vulkan is not available for that platform). But since we checked out Metal, Vulkan was also available to us to enable for Windows and Linux(and ran fine except in some cases) we thought to make it available for those it works well. But I get the impression that Vulkan support on Linux overall is better, so it will probably work best there. DX was already much better than OpenGL in terms of performance, so the increase is not as much, but nonetheless, some systems might see a benefit from using it. :)

[Pengu]

sounds good and thanks for all the background info. Normally I play a game and it runs well or it runs bad and I have no idea why, now I at least know why.