Why does vsync sometimes lock to 30fps?

[PiKe]

In a couple of games, Bulletstorm and Red Faction Guerrilla when vsync is on it reduces the framerate to 30fps in parts, is this simply due to the way vsync works or something more sinister?

 

[PGdude]

If the FPS drops below 60, the next factor of 60 it drops to is 30. If it dips below 30 it drops to 20, below that to 15, below that to 10.


Multiples/Factors of 60 is what it will jump to.

 

[Sin_Chase]

Exactly the above.

This is why nVidia introduce daptive VSYNC.

All the benefits of VSYNC when you have >= 60FPS but none of the cons when you drop below (Turns it off, and you risk tearing also)

I use a combination of Adaptive VSYNC and locking the games max FPS to 60 (where available)

 

[PiKe]

Right thought it might be something like that, cheers.

 

[Gregster]

Exactly the above.

This is why nVidia introduce daptive VSYNC.

All the benefits of VSYNC when you have >= 60FPS but none of the cons when you drop below (Turns it off, and you risk tearing also)

I use a combination of Adaptive VSYNC and locking the games max FPS to 60 (where available)

I take it, that a 120hz monitor will cope better, unless it goes over 120fps? (then tearing would be evident?)

 

[Rroff]

I use a combination of Adaptive VSYNC and locking the games max FPS to 60 (where available)

Not sure if thats actually a good idea tho I've not tested. In theory you could be causing duplicate frames (plus increased input latency) to be drawn because your artificially preventing the next one being ready when it would normally be.

 

[pgi947]

I take it, that a 120hz monitor will cope better, unless it goes over 120fps? (then tearing would be evident?)

I don't notice tearing that much at 120hz (over 120fps) as much as i noticed tearing over 60fps on 60hz.

@PiKe, are the 30fps drops durring game play or other parts of the game? As allot of cut scenes etc will tend to lock to 30fps.

 

[PiKe]

During gameplay in Bulletstorm, moving your view over an area with lots of lighting or textures or even the main menu with the characters stood next to each other causes 30fps.

 

[PGdude]

Sounds about right if it drops at the more graphics intensive sections (causing a slight dip in FPS forcing Vsync to jump to 30fps)