[Interest] QOpenGLWidget's performance drop

sivan nanthiran nanthiran2005 at gmail.com
Thu Feb 17 04:48:52 CET 2022

Hi Tor,

I have created a bug report (https://bugreports.qt.io/browse/QTBUG-100943)
as you requested. Please note that my Qt patch only forces the
QOffscreenSurface to be window-backed.


On Wed, Feb 16, 2022 at 6:58 PM Tor Arne Vestbø <Tor.arne.Vestbo at qt.io>

> 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> 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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