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What's the point of adaptive VSync?

#11Snuckie7(Topic Creator)Posted 10/6/2013 5:46:13 PM
nIMr0D888 posted...
And how are you going to tell if your monitor can only supply a new frame every 16.67ms?


Because lots of game engines will still read the quicker inputs, regardless of what your monitor's refresh rate is.
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#12nIMr0D888Posted 10/6/2013 5:49:28 PM(edited)
Input lag is the time it takes from when you do something with I/O (Mouse and keyboard) until you see the change on the output (screen).

Regardless of how fast the game engine is running you are still limited by the screens refresh rate, and part of closed loop control as an operator you need to see the change in order to react to it, which means the refresh rate is a limiting factor in input lag.
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#13Snuckie7(Topic Creator)Posted 10/6/2013 6:05:00 PM
nIMr0D888 posted...
Input lag is the time it takes from when you do something with I/O (Mouse and keyboard) until you see the change on the output (screen).

Regardless of how fast the game engine is running you are still limited by the screens refresh rate, and part of closed loop control as an operator you need to see the change in order to react to it, which means the refresh rate is a limiting factor in input lag.


There's a whole pipeline to rendering a frame, and display lag is merely one additional factor tacked onto the end. The less time the GPU spends to render a frame, the more current the information will be by the time the display lag gets added on.
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#14DV8ingSourcesPosted 10/6/2013 6:36:07 PM
Snuckie7 posted...
There's a whole pipeline to rendering a frame, and display lag is merely one additional factor tacked onto the end. The less time the GPU spends to render a frame, the more current the information will be by the time the display lag gets added on


Yeah a lot of people don't seem to understand this.

Having a higher framerate behind the scenes means you are getting closer to realtime with the actual input. Its true that you can only SEE every 16ms at 60 hz but your input can be from anywhere within that 16ms or worse with triple buffering.

If your input is read and it takes a full 16ms to render that frame with that input, it will be put in the next frame which effectively just doubled the input 'lag'.

If you render something at say 300 fps internally and it gets output to the screen every 16.66ms, the input has only 'rested' for 3ms versus the full 16.6ms 60fps would create. So you are closer to reality in your input.
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#15MrApplePosted 10/6/2013 7:14:33 PM
nIMr0D888 posted...
Snuckie7 posted...
nIMr0D888 posted...
If you are running at the refresh rate of your monitor there shouldn't be any input lag, adaptive vsync just turns off vsync when your framerate drops below the refresh rate so that when you do drop below, your framerate isn't decreased by a multiple of the refresh rate.

It is meant to provide a smoother experience, and has the backing of John Carmack.


Having any kind of VSync on introduces input lag, and higher framerates will always decrease input lag too.


For some games this it is true, but at 60Hz there is a minimum of 16.67ms between frames that is going to be the same whether or not you are running vsync or not. With triple buffering you will see a noticeable amount of input lag (a whole frame which is another 16.67ms).

Lots of people think vsync causes input lag mainly because of the transition between 60fps and 30fps (16.67ms and 33.33ms).


so whats the difference between vsync and vsync with triple buffering? is the input lag the same or different between them?
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#16DV8ingSourcesPosted 10/6/2013 7:41:38 PM
[This message was deleted at the request of the original poster]
#17DV8ingSourcesPosted 10/6/2013 7:50:59 PM
MrApple posted...
so whats the difference between vsync and vsync with triple buffering? is the input lag the same or different between them?


Sorry for the delete, but my explanation was getting too convoluted and hard to understand.

Triple buffering can reduce input lag a fair bit.

Normally a gpu only uses 2 buffers when rendering its frames. One that sits completed ready for handoff and another that prepares the next frame. If both are full (waiting on the monitor's refresh), the gpu sits there doing nothing and you have a guaranteed 16ms+refresh wait of input lag (minimum as there is generally a lot more delays before it even gets to the rendering stage).

Triple buffering adds another hand to the two. Now when the gpu finishes rendering a frame it can be placed into buffer 2 or 3 awaiting transfer into buffer 1 (the handoff position where it gets delivered to the monitor).

What makes triple buffering better for input lag is that between buffer 2 and 3, the latest fully rendered frame will always be transferred into the handoff position. That means that sometimes it skips one of the processed frames. That skipping also means that you just shaved off some input lag.

So with triple buffering you are much more likely to get closer to your actual refresh rate with your input lag than you would without it.
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#18PraetorXynPosted 10/6/2013 8:06:02 PM
With normal Vsync:
If you're running at 60 FPS, your framerate will drop to a multiple of 30, i.e. 30 FPS.
With adaptive Vsync:
Your framerate will drop usually to somewhere between 50 and 59 usually.
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