Looking at the video it seems related to the drawing of offscreen textures because during that phase we change the active render target and viewport.
Do you restore main render target's Viewport after calling Noesis renderer->RenderOffscreen() and before calling renderer->Render()?

I'd say yes. The relevant code is here: https://github.com/rschurade/Ingnomia/blob/master/src/gui/mainwindow.cpp#L561

Looking at the code, renderer->paintWorld() is not calling glViewport, and I don't see that QOpenGLWindow::makeCurrent calling it either: https://code.woboq.org/qt5/qtbase/src/gui/kernel/qopenglwindow.cpp.html#_ZN13QOpenGLWindow11makeCurrentEv
Could you do a quick test and always call glViewport (with the appropriate sizes) before renderer->paintWorld()?

That seems to fix it.

Great, so that was the missing piece. It should be enough to call it after makeCurrent:

if ( m_view->GetRenderer()->RenderOffscreen() )

{

// Restore state managed by QOpenGLWindow

makeCurrent();

glViewport(...);

}

Well I have to call it at the beginning of paintWorld() but that basically the same location in execution order. So this could be closed. Thanks