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G-Sync with DirectDraw games

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag. List of G-SYNC Monitors.

G-Sync with DirectDraw games

Postby Glide » 21 Jun 2017, 09:15

I was wondering if anyone knows of a way to improve the performance of G-Sync with DirectDraw games.
An example of what I'm talking about is Adventure Game Studio games.
While many of those games have an option for a D3D9 renderer, on Win10 CU I just get a black screen and have to fall back to the DirectDraw 5 renderer.

The games run at a fixed 40 FPS rate, but with G-Sync active the monitor's refresh rate is constantly jumping around between 35-45 FPS and the games stutter terribly.
What I've had to do is create an 80Hz refresh rate and disable G-Sync to get the games to play smoothly.
But while 40 FPS at a fixed 80Hz is mostly smooth, you do still get an occasional stutter.
1/2 refresh rate V-Sync does not appear to do anything, nor do framerate limiters.
Unfortunately trying to manually create a 40Hz refresh rate does not seem to work, unless there's some trick to it.

Is there a reason why the refresh rate gets so erratic with games like these?
I've noticed similar behavior in some other games/apps too.
Perfectly smooth performance with G-Sync disabled, but lots of framerate fluctuations/stuttering with it enabled.
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Re: G-Sync with DirectDraw games

Postby RealNC » 21 Jun 2017, 09:33

G-sync cannot work with DirectDraw, since it has no way to detect when new frames are output. Only hardware buffer flips can be detected. Even OpenGL cannot work with g-sync if flipping is disabled and instead frame buffers are copied (fortunately, nobody uses that mode.)

You might have some luck using DXGL, which is a wrapper that translates DirectDraw to OpenGL:

However, I have not tried it and have no idea if it works or not. It is a very new project and pretty much still in alpha.
Twitter: @realnc

The views and opinions expressed in my posts are my own and do not necessarily reflect the official policy or position of Blur Busters.
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Re: G-Sync with DirectDraw games

Postby Glide » 21 Jun 2017, 10:20

Oh, I thought it must have been "working" since the monitor was at least reporting something in the 40Hz range instead of being locked to 100Hz.

DXGL seems to do the trick though.
I haven't spent any real time with the games yet, so I can't confirm if things are going to be problem-free all the way through, but just tried playing the intro for a couple of them.
Refresh rate is pretty much locked to 40Hz and images are panning smoothly without any stutters now.

Thank you.
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