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VSync framerate is sometimes 30

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I enable VSync in my dx application and expect the framerate to be around 60 fps. But sometimes it's 30 instead. It's not only my application, but also others that I've tried that are made in DX. Is there any settings that can be wrong, cause it should be 60 shouldnt it? :)

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Assuming your monitor refreshes at 60Hz (some newer LCDs are now 75Hz), then your application must render everything in less than 16 milliseconds - or one frame.

If the application takes 20ms to render a frame then you'll only be able to update the screen every other frame. 60Hz / 2 = 30Hz.

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Yeah, but I only render a box so it cant be that(when I turn off Vsync, it runs at about 2000 FPS). It doesnt happen all the time, sometimes the app runs at 60 fps. And it's not changing, either it's 30 or 60 from the start of the execution.

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If you have a way to enable triple buffering, that will typically fix the 60->30 jump issue.

Or more accurately triple buffering will not be blocked as hard by vsync, which will let your other code run smoothly instead of also locking to 30fps.

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Hmmm, I'm out of (good) ideas! Here's a few less obvious ones...

1) Does the really app look like it's running at 30Hz? Maybe the FPS counter is misreading?

2) Do you have some weird message loop design that occasionally hogs the cpu?

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