QOpenGLWidget VSync

rtavakko

@mcleary Thanks again for trying it! I also ran the same code with two top level widgets on another PC and it worked ok so I'm guessing this is something with my laptop. I'm not sure if its still recommended to give each OpenGL widget its own context to make sure the code runs the same way on different PCs.

mcleary

@rtavakko If you absolutely need to share the contexts then I guess you should try to find the problem with your laptop. Which graphics processor do you have on the laptop? Is the driver updated?

rtavakko

@mcleary Good point. I updated the drivers recently (about a month ago). My laptop specs are:

GPU: GeForce GTX 950M
OS + Driver: Windows 10, driver NVIDIA 4.5.0 385.54
Qt version: 5.12.0 MINGW (64 bit)

I also have an Intel HD Graphics 530 (NVIDIA Optimus tech) for the built-in display which may have something to do with this. I've set my GTX 950M for OpenGL rendering and as the high-performance card. I'll dig a little deeper to see what could be the issue and update the thread.

mcleary

@rtavakko You could also try the MSVC build of Qt. I don't know if you are willing to install Visual Studio just to test this but it might be worth a shot.

rtavakko

@mcleary I tried the QT MSVC 2017 compiler with the same results. My Optimus setup has betrayed me before...

Patterson

Could you provide more details of your issue, such as screenshot of FPS, Monitor type, and the application you run. Note there are a set of applications can override v-sync settings in-app McDVOICE

rtavakko

@Patterson sure, I will get more details on this and post here

riyana

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rtavakko

@mcleary @Patterson

Its been a long time since this thread was started but I think it makes sense to post the updates here. I put together a basic project with native OpenGL and also using Qt's QOffscreenSurface and QWindow classes.

The github repository can be found here:

https://github.com/rtavakko/VSync

In this setup there is a single renderer that render to an FBO texture using its own thread and 3 display windows that share the GUI thread with all of them sharing OpenGL contexts together.

On my machine I see a clear lag with VSync on when there are 2 or more display windows. Turning VSync off clears the lag. The calcualted FPS values do not indicate any issues in either case which doesn't help but I see a clear difference when I start the application with say 2 displays and then close one of them.

I have my internal laptop display and an RCA RT1970 (both running at 1920x1080 - 60Hz) and both connected to my integrated Intel HD 530 GPU. My discrete GPU is an NVIDIA GeForce GTX 950M and I'm running Qt 5.12.0 MSVC2017 64 bit.

I'll dig in further myself also with other machines but if anyone has any ideas on what could be causing this, it would really help debug further.

Cheers!

Mylincoln Portal

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liamerickson

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