QOpenGLWidget VSync

rtavakko · wrote on 23 Feb 2020, 16:29

Any thoughts on this guys? I've verified the same thing on my machine with various QT OpenGL examples. The top level windows divide the refresh rate between them. If I have two QMainWindows for example, each will render at 30 fps with the default 60 Hz refresh rate. Each one can have many child widgets all running at the same 30 fps rate.

I have a feeling I will need to create a context for each top level window. Any thoughts on how and where (in main?) to do this. Does the top level window need to be a QWindow for this to work?

Cheers!

mcleary · wrote on 24 Feb 2020, 19:40

Unfortunately I also don't know how to proceed and would need to see the application. Could you share one of the examples you mentioned?

rtavakko · wrote on 25 Feb 2020, 00:53

Sure. I modified the qopenglwindow and qopenglwidget example adding an extra window. Qopenglwidget is easier to do since it displays framerate and also you can add child widgets on the fly.

mcleary · wrote on 25 Feb 2020, 10:22

I'll see if I can try it today. Will report back.

mcleary · 25 Feb 2020, 20:43

Is it that what you're talking about? As you can see, all widgets are running at 60fps.

rtavakko · 26 Feb 2020, 10:10

@mcleary Thanks for trying it, thats exactly it! I added a second top level window in main and that caused the framerate for both winows and their child widgets to be divided in half.

I just finished modifying the contextinfo example also creating two RenderWindow objects contained by two QWidgets in a single window and the two render at the correct 60 Hz refresh rate since each has a separate context. I think that's what I'll need to do but I'm not sure if this just my machine or its Windows or its just the way it is overall.

mcleary · 26 Feb 2020, 16:07

@rtavakko I also tried creating a new top level window but I still have no problems. Hopefully you can find the problem

rtavakko · 27 Feb 2020, 09:26

@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 · 27 Feb 2020, 11:28

@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 · 27 Feb 2020, 11:39

@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 · 27 Feb 2020, 16:09

@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 · wrote on 27 Feb 2020, 16:09

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

Patterson · 3 Nov 2020, 08:53

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 · wrote on 9 Jun 2020, 00:55

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

riyana · wrote on 19 Dec 2020, 08:26

This post is deleted!

rtavakko · wrote on 13 Jan 2021, 21:05

@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 · wrote on 24 Sept 2021, 08:13

This post is deleted!

liamerickson · 2 Apr 2022, 11:23

This post is deleted!