@AlexMax
The issues is marked fixed in 6.3 and 6.4, so it it still persists in 6.5, that would probably warrant a new issue, linking to the old one. Or is it captured by linked and still-open https://bugreports.qt.io/browse/QTBUG-99602?

Hi,

Since you have a commercial licence, I would recommend opening an issue directly from your account as you have access to support.

@JKSH Yes, I created two simple console applications and added required libraries to them. Compiler keys are identical. I checked carefully. A one project have a mistake, and another doesn't have For example, a project with subprojects have this error, but QT Widgets does not have (but not always). Heisenbug?

Assuming you have an OpenGL context and you can draw/create objects in it you would make that context current, then create a QOpenGLPaintDevice and use it to render() the widget into that. Please note that a widgets require a QApplication instance and a running Qt's event loop, so you would need to ensure you have that.

As for DirectX Qt doesn't have any direct support for it, but you could probably grab() a widget into a QPixmap, transfer the pixels to a DirectX texture and draw a quad with it.
If you feel adventurous you could also implement your own QPaintEngine, then subclass QPaintDevice to return that engine and use it like with the OpenGL version.

There's a Qt Canvas 3D module in Qt 5.5 that provides WebGL-like interface to hardware accelerated 3D. It is layered on top of existing Qt's OpenGL support.
As for non-QML stuff, on WinRT Qt uses ANGLE, so if you stick to functions provided by Qt (e.g. QOpenGLFunctions) and not try to talk to the driver directly it should work just fine cross-platform.

@Chris-Kawa Hi thanks for your reply. For some reason, though, it has started working again. All i changed was I added QWidget::resizeEvent(pEvent); to the GameView class and it started working. However, here is where it gets weird. when i remove that line it still works, so effectively i have changed nothing and it started working