Wrapping It Up
So there you have it. Triple buffering gives you all the benefits of double buffering with no vsync enabled in addition to all the benefits of enabling vsync. We get smooth full frames with no tearing. These frames are swapped to the front buffer only on refresh, but they have just as little input lag as double buffering with no vsync at the start of output to the monitor. Even though "performance" doesn't always get reported right with triple buffering, the graphics hardware is working just as hard as it does with double buffering and no vsync and the end user gets all the benefit with out the potential downside. Triple buffering does take up a handful of extra memory on the graphics hardware, but on modern hardware this is not a significant issue.
Just to recap, from our previous example, here are what the three frames we looked at rendering stack up side by side.
Triple Buffering
Double Buffering
Double Buffering with vsync
We've presented the qualitative argument and the quantitative argument in support of triple buffering. So, now the question is: does this data change things? Are people going to start looking for that triple buffering option more now than without this information? Let's find out.
{poll 135:300}
The major difference in the technique we've described here is the ability to drop frames when they are outdated. Render ahead forces older frames to be displayed. Queues can help smoothness and stuttering as a few really quick frames followed by a slow frame end up being evened out and spread over more frames. But the price you pay is in lag (the more frames in the queue, the longer it takes to empty the queue and the older the frames are that are displayed).
In order to maintain smoothness and reduce lag, it is possible to hold on to a limited number of frames in case they are needed but to drop them if they are not (if they get too old). This requires a little more intelligent management of already rendered frames and goes a bit beyond the scope of this article.
Some game developers implement a short render ahead queue and call it triple buffering (because it uses three total buffers). They certainly cannot be faulted for this, as there has been a lot of confusion on the subject and under certain circumstances this setup will perform the same as triple buffering as we have described it (but definitely not when framerate is higher than refresh rate).
Both techniques allow the graphics card to continue doing work while waiting for a vertical refresh when one frame is already completed. When using double buffering (and no render queue), while vertical sync is enabled, after one frame is completed nothing else can be rendered out which can cause stalling and degrade actual performance.
When vsync is not enabled, nothing more than double buffering is needed for performance, but a render queue can still be used to smooth framerate if it requires a few old frames to be kept around. This can keep instantaneous framerate from dipping in some cases, but will (even with double buffering and vsync disabled) add lag and input latency. Even without vsync, render ahead is required for multiGPU systems to work efficiently.
So, this article is as much for gamers as it is for developers. If you are implementing render ahead (aka a flip queue), please don't call it "triple buffering," as that should be reserved for the technique we've described here in order to cut down on the confusion. There are games out there that list triple buffering as an option when the technique used is actually a short render queue. We do realize that this can cause confusion, and we very much hope that this article and discussion help to alleviate this problem.
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Scalarscience - Saturday, June 27, 2009 - link
...I'm posting this as a reply but please use the reply button on the previous post unless you're really wanting to reply to this particular post...The next thing that I see COMPLETELY neglected in this article and most of the comments--outside of 1 or 2 mentions of higher framerates increasing your movement rate--is that many games will use the engine's currently processing frame for collision & 'hitscan' decisions. My experience/understanding is that this is in addition to the input latency issues covered above, and in fact is MORE important to me than just worrying about visual tearing.
Hitscan is a term I learned more from the original UT game, I know there was a term CS players used back in the 1.x days too but it slips my mind (and probably more terms now). Basically it applies to projectiles who have 'infinite' velocity, ie, hit their targets immediately when calculated. Hitscan isn't the only type of calculation used for in-game weapons by any means, but the it's the one who (imo) is most affect by latency & discontinuities in the gameplay (caused by bad prediction or perhaps a stalling render thread) so it's the one that is most discussed. My impression is that the hitscan issues apply to other collisions & weapon hits as well, modified by how their weapons work.
As FPS players are not only concerned with 'what they see' but also what their 'shots' and 'movements' are translating into (especially in competitive online fps games) this is one of the main reasons that players used to force vsync off even if they could get their CRT to do 100hz or higher. Older games do have things directly tied to the render thread (physics, movement speed etc) but as time has gone on that's been reduced and methods of 'prediction' have been added, which means that the discussions get complicated over time. Also some games will use client side detection for certain things (instead of correlating things from the server's perspective to make the final 'decision') which can reduce apparent latency for hitscan style shots
Konstantineb - Saturday, June 27, 2009 - link
Would like to know if anandtech is considering an Arma 2 review with some GPUs performance data.The game is realy good looking, and it deserves a review from anandtech....StarRide - Friday, June 26, 2009 - link
Since WoW's triple buffering actually says it might cause input lag, I'm beginning to wonder if WoW's triple buffering implementation is actually just 3 frame render ahead...profoundWHALE - Monday, January 19, 2015 - link
"I'm beginning to wonder if WoW's triple buffering implementation is actually just 3 frame render ahead... "Congradulations, you just accurately described a triple-buffer as a "3 frame render ahead", which it is. It's really not that difficult a concept.
We apply the same concept to a youtube video. We buffer ahead so we get a smooth, steady frame-rate, although in the case of video streaming, we are buffering many, many frames.
This means that if you have terribly low fps, you'll see a bigger hit to latency with triple-buffering than someone with 100 fps.
30 fps = 33.3 ms per frame, meaning that you can end up with latency of about 100 ms with triple buffering
120 fps = 8.33 ms per frame, meaning that you can end up with latency of about 25 ms with triple buffering
Vsync will continue rendering as usual, but will simple make sure that only an exact multiple is displayed, so if your average fps is about 45 fps and you have a 60 Hz refresh rate, you'll get a steady output of 30 fps. The downside is you'll probably get an effect similar to the 3:2 pulldown where some frames will last as short of a time as 25 ms, and as long as 33 ms.
This is why things like Gsync and Freesync are awesome, because we can just throw vsync and buffering out the window and instead of trying to sync the input the the output, we sync the output to the input.
profoundWHALE - Monday, January 19, 2015 - link
I should clarify that the real world lag from triple buffer isn't as bad as the numbers I put out there, but because you have vsync, you will have greater input lag so it still gives a good idea of what latencies you could be looking at.MamiyaOtaru - Friday, June 26, 2009 - link
Triple buffering is obv. better than double, but I'd still not use it.In the final set of comparison shots, two thirds of the screen on the double buff without vsync example is newer than the corresponding screen in the triple buffering example. This means tears, yes, but that's newer info you aren't getting until later with triple buffering.
With double, a mouse movement that starts halfway between screen refreshes can (if the framerate is high enough) show up as soon as a new frame is rendered and swapped to the front to be read by the monitor. Granted, it will only show up on some bottom portion of the screen, with older info above, but in triple buffering that movement will not show up at all until the monitor finishes the current refresh and starts another.
In the horse example posted, the max time between input and reaction on screen is 3 times greater with triple buffering than with double w/o vsync, even if with the latter that reaction is only shown on the bottom 2/3rds or 1/3rd of the screen. It's *there* and it isn't until later with triple buffering.
But it's sure as hell better than double buff with vsync :) And visually better than double buff w/o vsync. A nice compromise. But let's not pretend there are precisely 0 drawbacks. If you'd prefer faster reaction time and can accept tearing to get it, you'll not want triple buffering, as that shuts out any new info until the monitor has drawn a completed, now out of date frame.
It's similar to interlaced vs progressive. Progressive looks nicer, no artifacts. But given the same bits per second, interlaced will have a higher framerate as it isn't drawing the whole frame each time. With double buffering you get bits of several frames rendered onto the screen at once. Artifacts, but you're getting more up to date info *even if that more up to date info isn't on the whole screen*.
justniz - Friday, June 26, 2009 - link
This article makes it sound like triple-buffering is always best, which is just not true.If you play games that require fast reactions and you have powerful enough hardware that you dont get tearing on double-buffering then DONT USE TRIPLE BUFFERING.
Why?
Because triple buffering adds an extra frame's worth of delay before you see the picture. Its only maybe 1/30 to 1/60th of a second extra, but in twitch/frag games removing that delay may be enough to give you the edge.
DerekWilson - Friday, June 26, 2009 - link
triple buffering does not add an extra frame of delay.triple buffering is always the best option, even for twitch shooters where a bad tear can look like something that's actually there and distract the gamer.
having powerful hardware does not reduce tearing. in fact, at higher framerates there is always a higher chance of tearing than at lower frame rates (at 300 FPS tears will happen every frame, whereas at 40 FPS, tears cannot possibly happen every frame -- the lower the frame rate, the less likely or often tearing occurs).
you still get the reduce lag "edge" that is apparent in double buffering without vsync, but you get the most recently fully completed frame of animation rather than a composite of multiple frames starting with the one that triple buffering would have given you in full.
MamiyaOtaru - Friday, June 26, 2009 - link
ou get the most recently fully completed frame of animation rather than a composite of multiple frames starting with the one that triple buffering would have given you in full.starting with, but ending with newer stuff, which is exactly the point. Triple buffering is offering the most up to date feedback on your input only up until the point a tear would happen in double buffering.
DerekWilson - Friday, June 26, 2009 - link
i did note that this is the only potential advantage of double buffering without vsync, but that in order to actually benefit from it, it needs to be a visible artifact (the frames need to be different enough to cause a visible tear) and you only get the benefit in the percentage of the frame that comes after the tear.part of the double buffered frame is the same as the triple buffered frame ... if you need information from this part of the screen (if you're looking there) you still won't get the benefit and the peripheral distraction of tearing can ... well ... distract.
some people may see this as a real advantage, but i certainly think the downside certainly outweighs any potential upside.