Prepar3D Vsync/Triple Buffering... Placebo?

[MadDog 353]

3 minutes ago, laserit said:

Also, if Prepar3d's  Vsync does nothing then why does my frame rate change when I deactivate Vsync?

I'm not stating for a fact that it does nothing... but I am stating that it appears to be doing something other than providing Vsync.  If you go through the steps I outlined in the original post, you can witness it for yourself.

[laserit 93]

I don't know whats its doing inside of P3D but it absolutely is having a positive effect for me and its definitely not a placebo ;)

Without the Vsync my frames jump around from a low of around 39 to a high of about 58 and I get microstutters. If I use the frame rate limiter I get microstutters. Limiting my frames by way of the Vsync inside of v4 gives me the smoothest experience and best feeling of speed that I've ever had with ESP. I haven't experimented with settings outside the sim yet as for the first time, I haven't felt the need to.

[jayren 5]

I think you are right, it is a well known trick in Xplane 11 to run the sim in windowed mode to get rid of screen tearing. p3d is just running windowed mode in full screen.

 

[SteveW 1,792]

VSync in P3D steers the GPU output to the Monitor refresh frequency. Check out my other post:

 

 

[MadDog 353]

10 hours ago, SteveW said:

VSync in P3D steers the GPU output to the Monitor refresh frequency. Check out my other post:

Ah...that makes sense - so it basically limits the framerates based on refresh rate (a la traditional vsync).  I normally keep P3D internally locked at 30... so didn't notice that.  It's interesting that desktop composition does not limit frames by default so it must be adaptive;  I assume that the P3D vsync option must disable the adaptive functionality.  So that just leaves the question of what the P3D Triple Buffering option does (since I'm pretty sure that desktop composition is already triple buffered).

[SteveW 1,792]

 

2 hours ago, MadDog said:

Ah...that makes sense - so it basically limits the framerates based on refresh rate (a la traditional vsync).  I normally keep P3D internally locked at 30... so didn't notice that.  It's interesting that desktop composition does not limit frames by default so it must be adaptive;  I assume that the P3D vsync option must disable the adaptive functionality.  So that just leaves the question of what the P3D Triple Buffering option does (since I'm pretty sure that desktop composition is already triple buffered).

Yes, simply takes the monitor vsync frequency for output fps, actual frame vsync is handled by the desktop as you correctly worked out.

Triple buffer allows the renderer to start drawing a spare frame while one backbuffer is in mid-read and the other has just completed drawing. So it will be hard to see if that's operating, looking at processor graphs will be no use. Having the frame in hand is of benefit to the overall timing and accuracy of the physics and locations of objects in the sim. With the locked fps on the slider, this keeps up to three frames in hand but more important is the fact that the position of the terrain and objects in the next frame is calculated from the exact same period of each next frame, and is designed to run so that these are displayed exactly in the positions they were calculated to be in. With Unlimited the time of the next frame and the location of the objects is calculated on the average fps at the time. If the fps is wandering when the sim displays the next frame it's not showing the objects where they should be and shaves off accuracy. The triple buffer helps ensure the average fps is maintained as the timing from that is more stable. Whether it makes a difference to the GPU/Monitor coordination I'm not sure.

[bean_sprout 1,201]

Seems vsync works best on lower-end systems or systems that have a pronounced bottle-neck somewhere.  I don't ( and never did even in FSX) use vsync as I want full throughput at all times.  V4 is nice because unlike V3.4, FPS stays fairly consistent with unlimited.

 

Cheers

bs

[MadDog 353]

1 hour ago, bean_sprout said:

I don't ( and never did even in FSX) use vsync as I want full throughput at all times.

That was kind of the point of my post.  Unless you specifically disabled Desktop Composition in Windows, you've actually been using Vsync all along...you just didn't know it.

[bean_sprout 1,201]

When vsync is enabled panning is unacceptable both in cockpit and external.  If it defaults to adaptive I can see your point as my FPS is generally over 100.
 

Cheers
bs