VSync Framerate Issue

Development Rendering
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We’ve been having some issues obtaining a high and stable framerate with V-Sync.

We were initially using DirectX12, it was reported that in packaged builds only the game was running at 30fps with V-Sync on (or half the monitor in question, I hadn’t noticed it as my monitors refresh rate is 180 so it was running at 90) - with V-Sync off it was exceeding 200fps. We have been unable to fix this, and even removing all of the rendering overrides doesn’t seem to have resolved the issue. We tried all combinations of setting the variables mentioned here:

https://dev.epicgames.com/documentation/en\-us/unreal\-engine/low\-latency\-frame\-syncing\-in\-unreal\-engine

Including the obvious offender of rhi.SyncInterval. What options could we have overlooked?

We needed a build so tested Vulkan which seemed to work correctly but only if we passed in -vulkanpresentmode=2, looking at the default settings it should default to mailbox which shouldn’t tear. Can you think of any reason why it might be necessary to specify this override? Also if we leave vsync on when using a high refresh monitor the framerate seems confined to 60 regardless of the refresh rate of the monitor (again we confirmed obvious candidates like t.maxfps were not overriding the framerate).

2

Steps to Reproduce
We have not yet been able to reproduce the issue with any sample projects and are not sure why it is occurring only in our main project.

3

Hi there,

Just as a sanity check I put together my own small project to test VSync both in the editor and in a build in 5.4, and as with your sample projects, I cannot reproduce this issue.

It does seem to be project dependent, so we can rule out any NVIDIA Control Panel (or equivalent) settings.

Does your project use any platform specific plugins, such as Intel’s XeSS plugin? (or more generally, any plugins with a rendering focus at all?)

If you would be able to attach your project’s DefaultEngine.ini, that would also be helpful to review.

Thanks,

Hayden

4

Hi Hayden,

Thanks for your response - it prompted me to take another look at the upscaling plugins - the offender seemed to be AMD FSR​. We’d confirmed it was still happening with it disabled in options (and by default) but removing the plugin resolved the issue.

Thanks

Alex

5

Excellent, glad I could help point you in the right direction.

I will go ahead and close this case now.

Thanks,

Hayden