Have you tried Qt 3D or Qt RHI for your woes ?
I had the same experience with QOpenGLWidget, there are a few bug reports open about its performance especially with multiple viewports. See also this thread on the mailing list: https://lists.qt-project.org/pipermail/interest/2020-Decembe...
Well, ... the Qt3D is a higher level framework that isn't really relevant to the stuff I'm doing considering that I'm basically running my own "framework", i.e. my game engine that renders to my rendering surface.
In my use case what I really need is just to have Qt provide me a rendering surface with good performance (and ideally with working integration with the rest of the widget system) and then get out of the way.
Well, ... the Qt3D is a higher level framework that isn't really relevant to the stuff I'm doing considering that I'm basically running my own "framework", i.e. my game engine that renders to my rendering surface.
In my use case what I really need is just to have Qt provide me a rendering surface with good performance (and ideally with working integration with the rest of the widget system) and then get out of the way.