FPS setting in KSP?

[JedTech]

Something I've wondered about for a year or more, but have yet to come to conclusion about is the FPS (frames per second) setting in KSP. What exactly does it do?

If my monitor(like most) only does 60 FPS, then is there any value to leaving the setting in KSP above 60 FPS?

[JedTech]

The Wiki isn't very helpful:

Quote

 

Frame Limit

• Sets the max FPS. Basically a top on how fast the game can run.
• Default: 120 FPS

 

Edited February 4, 2016 by JedTech

[peachoftree]

That limits the maximum FPS the game will run at, it's useful for getting a constant frame rate if your FPS constantly jumps from high to low.

[steve_v]

It's also useful if you don't want your GPU sucking full power and generating heat rendering simple scenes / loading screens at 300FPS.

[JedTech]

If my monitor(like most) only does 60 FPS, then is there any value to leaving the setting in KSP above 60 FPS?

If not then why is the default setting 120?

Is this default setting telling our computers to do work for 120 fps when our monitors can only do 60?

Edited February 4, 2016 by JedTech

[steve_v]

Your monitor refresh rate has nothing to do with the framerate limit in KSP, unless you have V-sync on.

If your monitor can only do 60Hz, so be it, it doesn't stop the GPU from refreshing faster than this - you just won't see it.

If you have V-sync (sync to v-blank) on then the GPU will render at the monitor refresh rate, and the framerate limiter won't do anything unless set below that.

The default cap is there to stop your GPU running away rendering simple stuff at silly FPS. or to smooth out framerate spikes. 120FPS is a reasonable default because some have 120Hz monitors, and you usually don't want it set below your refresh rate.

35 minutes ago, JedTech said:

Is this default setting telling our computers to do work for 120 fps when our monitors can only do 60?

No, it's a limit, not a target. The only thing it "tells our computers to do" (eh whut?) is not render faster than what you set here.

If you want to synchronise to your refresh rate (and eliminate tearing) use the tool for the job - V-sync.

If you want to limit FPS without using V-sync (it comes with a small performance hit), then use the FPS limiter.

4 hours ago, JedTech said:

The Wiki isn't very helpful:

Frame Limit

• Sets the max FPS

The wiki is not only helpful, it's entirely correct. What more is there to say? "Sets the max FPS" is precisely what it does.

Edited February 4, 2016 by steve_v

[JedTech]

34 minutes ago, steve_v said:

The wiki is not only helpful, it's entirely correct. What more is there to say? "Sets the max FPS" is precisely what it does.

It was helpful if you need a thesaurus for the word "limit", but it wasn't helpful in helping me to understand  the implications of a max fps setting.

Thank you for your great information. I was worried that leaving it at 120 would sometimes cause my graphic card to refresh this fast even though my monitor could not display it. I think I understand from your post that this is not a concern?

It sounds like for optimal performance, I should look up this V-sync thing and synchronize my refresh rate. While leaving the KSP setting nice and high so it does not disturb the synchronization. 

[steve_v]

47 minutes ago, JedTech said:

I was worried that leaving it at 120 would sometimes cause my graphic card to refresh this fast even though my monitor could not display it.

If you have V-sync off, that's exactly what it will do - the GPU will render as fast as it can (up to the FPS limit) regardless of your monitor refresh rate.

47 minutes ago, JedTech said:

I understand from your post that this is not a concern?

It's not a problem and nothing bad will come of it (except possibly some image tearing), though rendering frames faster than they can be displayed is a little wasteful.

Setting the framerate limiter won't fix tearing, but it will prevent the GPU doing pointless work that the monitor can't display.

47 minutes ago, JedTech said:

It sounds like for optimal performance, I should look up this V-sync thing and synchronize my refresh rate.

V-sync is more of an image-quality thing really - if your GPU is rendering frames out of sync with the refresh rate of the monitor you will likely see a bit of tearing.
Monitors draw an image line-by-line, top to bottom - without V-sync a new frame may be sent to the monitor before it has finished drawing the last, and this can produce ugly horizontal breaks in the image where the screen effectively shows part of two different frames.

V-sync instructs the GPU to only push a new frame to the monitor during vertical blank - the period where the monitor blanks out the current frame before starting on the next. It eliminates tearing, but it may introduce a slight performance decrease by making the GPU wait on the monitor. Most GPU drivers offset this using (double/triple)buffering or "pre-rendered frames" drawn to a memory buffer until the display is ready for them.

Edited February 4, 2016 by steve_v