What causes tearing when Vsunc is off?

[Link19]

Ok, I know what tearing can be caused when the games FPS exceeds the refresh rate of the monitor.

But the real question is, why is it that the FPS can be higher than the monitor refresh rate and not cause any tearing, while sometimes there is tearing? It seems it is different for every situation. Why is tearing sometimes not a problem when the FPS is consistently higher than the monitor refresh rate?

I am looking at buying an LCD good for gaming. Is the refresh rate on an LCD important for gaming? I see that the refresh rate on almost all LCDs is stuck at 60Hz? I have seen some at 75Hz for their native resolution, but it seems as if 60Hz is always recommended? Is it really important to get a fast refresh rate on an LCD for gaming?

Are there any LCDs out there with fast response times and a refresh rate of 85Hz? I have seen some say 85Hz, but it seems that they aren't really true 85Hz because that 85Hz cannot keep up with the signal or something?

Any recommendations for a good widescreen gaming LCD.

 

[nullpointerus]

Ok, I know what tearing can be caused when the games FPS exceeds the refresh rate of the monitor.

No, not quite. Your monitor displays a new image 60 times per second (60Hz) which means that the interval between refreshes is constant. The problem is that the interval between game frame draws is not constant. Every time you or the environment moves or otherwise changes, the amount of GPU power needed to render the scene also changes. Tearing is when your game tries to update the screen while the monitor is in the middle of a refresh. So the total refresh rates aren't strictly what causes tearing.

But the real question is, why is it that the FPS can be higher than the monitor refresh rate and not cause any tearing, while sometimes there is tearing? It seems it is different for every situation. Why is tearing sometimes not a problem when the FPS is consistently higher than the monitor refresh rate?

Tearing only happens when the game tries to redraw the screen while the monitor is in the middle of a refresh. If you have a 60Hz monitor, with v-sync on you won't see much (if any) difference above 60fps because the game has to fit those, say, 73fps into 60Hz without any overlap (i.e. tearing). IOW, you never see at least 13 of those frames. I say "at least" because the difficulty of scene rendering may fluctuate wildly in less than a second:

X-X-X-X-X-X-X-X-X-X (X = monitor refreshes)
R-R-RRR------RR-R-RR (R = game frames)

Note that the large gap in the middle where the game misses three refreshes cannot be made up later on in the same second because monitor refresh intervals are constant, and v-sync dictates that each refresh can show one frame at the most.

 

[Link19]

Originally posted by: nullpointerus

Ok, I know what tearing can be caused when the games FPS exceeds the refresh rate of the monitor.

No, not quite. Your monitor displays a new image 60 times per second (60Hz) which means that the interval between refreshes is constant. The problem is that the interval between game frame draws is not constant. Every time you or the environment moves or otherwise changes, the amount of GPU power needed to render the scene also changes. Tearing is when your game tries to update the screen while the monitor is in the middle of a refresh. So the total refresh rates aren't strictly what causes tearing.

But the real question is, why is it that the FPS can be higher than the monitor refresh rate and not cause any tearing, while sometimes there is tearing? It seems it is different for every situation. Why is tearing sometimes not a problem when the FPS is consistently higher than the monitor refresh rate?

Tearing only happens when the game tries to redraw the screen while the monitor is in the middle of a refresh. If you have a 60Hz monitor, with v-sync on you won't see much (if any) difference above 60fps because the game has to fit those, say, 73fps into 60Hz without any overlap (i.e. tearing). IOW, you never see at least 13 of those frames. I say "at least" because the difficulty of scene rendering may fluctuate wildly in less than a second:

X-X-X-X-X-X-X-X-X-X (X = monitor refreshes)
R-R-RRR------RR-R-RR (R = game frames)

Note that the large gap in the middle where the game misses three refreshes cannot be made up later on in the same second because monitor refresh intervals are constant, and v-sync dictates that each refresh can show one frame at the most.

I played NFS Hot Pursuit 2 on my 19'' CRT and got 150FPS with my monitor set at 1280*1024 at 75Hz refresh rate. There was no tearing? Why was there no tearing? Is it because my video card was able to deal with the overlap and fit 150 FPS in 75Hz?

How much overlap is possible when the FPS exceeds the refresh rate of the monitor? For instance, can 200 FPS per second be ahcieved with a 60Hz refresh rate without any tearing?

 

[nullpointerus]

Originally posted by: Link19

Originally posted by: nullpointerus

Ok, I know what tearing can be caused when the games FPS exceeds the refresh rate of the monitor.

No, not quite. Your monitor displays a new image 60 times per second (60Hz) which means that the interval between refreshes is constant. The problem is that the interval between game frame draws is not constant. Every time you or the environment moves or otherwise changes, the amount of GPU power needed to render the scene also changes. Tearing is when your game tries to update the screen while the monitor is in the middle of a refresh. So the total refresh rates aren't strictly what causes tearing.

But the real question is, why is it that the FPS can be higher than the monitor refresh rate and not cause any tearing, while sometimes there is tearing? It seems it is different for every situation. Why is tearing sometimes not a problem when the FPS is consistently higher than the monitor refresh rate?

Tearing only happens when the game tries to redraw the screen while the monitor is in the middle of a refresh. If you have a 60Hz monitor, with v-sync on you won't see much (if any) difference above 60fps because the game has to fit those, say, 73fps into 60Hz without any overlap (i.e. tearing). IOW, you never see at least 13 of those frames. I say "at least" because the difficulty of scene rendering may fluctuate wildly in less than a second:

X-X-X-X-X-X-X-X-X-X (X = monitor refreshes)
R-R-RRR------RR-R-RR (R = game frames)

Note that the large gap in the middle where the game misses three refreshes cannot be made up later on in the same second because monitor refresh intervals are constant, and v-sync dictates that each refresh can show one frame at the most.

I played NFS Hot Pursuit 2 on my 19'' CRT and got 150FPS with my monitor set at 1280*1024 at 75Hz refresh rate. There was no tearing? Why was there no tearing? Is it because my video card was able to deal with the overlap and fit 150 FPS in 75Hz?

How much overlap is possible when the FPS exceeds the refresh rate of the monitor? For instance, can 200 FPS per second be ahcieved with a 60Hz refresh rate without any tearing?

If you (or the game) enables both v-sync and triple-buffering, your fps can exceed the refresh rate of the monitor without tearing. Normally, games use only double buffering since it frees up some video RAM for other aspects of rendering. With double buffering and v-sync, your game basically does the following:

draw frame on primary buffer
schedule it to display when the monitor has time
draw frame on secondary buffer
schedule it to display when the monitor has time
wait for monitor to finish with the primary buffer...
repeat at step 1

Triple buffering adds an extra buffer in the mix. Since the monitor can only "lock" one buffer at a time, the game can continue rendering frames on the other two buffers until the monitor is finally ready for its next buffer to display on the screen. So there's no waiting involved, and your game can hit 200fps on a 60Hz display even with v-sync on.

Unfortunately, I'm not familiar enough with what happens at high fps with v-sync off to speak confidently about it, but if you google for it, you'll likely find some more experienced gamers discussing why they turn it off. Perhaps with 150fps on a 75Hz display the tearing is so frequent and/or consistent that you simply stop noticing it?

 

[JRW]

Originally posted by: nullpointerus

If you (or the game) enables both v-sync and triple-buffering, your fps can exceed the refresh rate of the monitor without tearing.

Problem with that statement.. with Vsync enabled the framerate will never exceed the monitors refresh rate. triple buffering helps maintain stable framerates while vsync is enabled but can introduce a small input lag in the process.

If you plan on running with Vsync enabled on an LCD it will most likely be 60hz refresh which means 60FPS max. Im used to running without Vsync on my CRT but when I tried this on a 2001FP LCD the screen tearing was pretty bad.

 

[nullpointerus]

Originally posted by: JRW

Originally posted by: nullpointerus

If you (or the game) enables both v-sync and triple-buffering, your fps can exceed the refresh rate of the monitor without tearing.

Problem with that statement.. with Vsync enabled the framerate will never exceed the monitors refresh rate. triple buffering helps maintain stable framerates while vsync is enabled but can introduce a small input lag in the process.

If you plan on running with Vsync enabled on an LCD it will most likely be 60hz refresh which means 60FPS max. Im used to running without Vsync on my CRT but when I tried this on a 2001FP LCD the screen tearing was pretty bad.

I already explained why v-sync with triple buffering allows framerate to exceed the monitor's refresh rate. Please see my previous post. If you're just going by practical experience, then apparently you must be careful which numbers you go by. Fraps's display stays capped at 60fps with v-sync and triple buffering whereas F.E.A.R.'s internal game counter clearly goes much higher (70+) during the same benchmark run.

Note: if you want triple buffering in Direct3D games on nVidia hardware, you must enable it via a third-party tool like DirectX Tweaker.

 

[Matt2]

Originally posted by: JRW

Originally posted by: nullpointerus

If you (or the game) enables both v-sync and triple-buffering, your fps can exceed the refresh rate of the monitor without tearing.

Problem with that statement.. with Vsync enabled the framerate will never exceed the monitors refresh rate. triple buffering helps maintain stable framerates while vsync is enabled but can introduce a small input lag in the process.

If you plan on running with Vsync enabled on an LCD it will most likely be 60hz refresh which means 60FPS max. Im used to running without Vsync on my CRT but when I tried this on a 2001FP LCD the screen tearing was pretty bad.

When I was playing Doom 3 with my 7800GT SLI @ 510/1200 using 1280x1024 res I only got like 150fps in timedemo 1 and the demo seemed to "lag". It would go through super fast for about 5 seconds and then hitch or stutter. This was with V-Sync off.

If I turned V-Sync on, I expected to get 70fps (my old LCD's refresh rate), but in fact, the FPS I acheived actually broke the 200fps barrier and didnt stutter at all??