[Interest] QOpenGLWidget's performance drop

[Tor Arne Vestbø]

Thanks for the detailed report Sivan. Can you file an issue about in https://bugreports.qt.io/ with the sample code, and a diff of the changes you made to improve performance? Thanks!

On 16 Feb 2022, at 11:53, sivan nanthiran <nanthiran2005 at gmail.com<mailto:nanthiran2005 at gmail.com>> wrote:

Hi,

Recently I have upgraded from Qt-5.4.1 to Qt-5.15.2. The following is my system configuration:
- MacOS
- External display connected to External GPU, and made as the primary screen, connected to a macbook

In my simple testApp, I have 2 QOpenGLWidget and 1 QWidget. I just simply render a triangle in those QOpenGLWidgets which changes color every 16ms.

The rendering performance in my app used to be 60fps as it was rendering on the external GPU. However, after Qt-5.15 upgrade, I noticed the performance is about 45fps and there are load in my macbook's Intel GPU.

Upon investigating, I found out that its due to QOffscreenSurface's change to be not window-backed anymore. Since QOpenGLWidget internally uses QOffscreenSurface, I believe this is causing the rendering to not happen on the screen's GPU. When I hack the code to make the QOffscreenSurface to window-backed, I'm able to get the same performance as before.

So is there any clean way to achieve the same performance I used to achieve? If not, are there any effects if I force the QOffscreenSurface to be window backed for MacOS?

Thanks in advance.

Regards,
Sivan


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