Is there any way to transform output image from QWebEngine in realtime?

[Bendertron]

Hi, Everyone!
May be it's a bit unclear, but i'll try to explain. I'd like to split output image (frame) that produces QWebEngine in a few images and stack them one above another. Input content looks like this:

and I'd like to transform into image like this:

The problem is that html content has some animation.
QWebEngineView is added to QGraphicsScene that has no parents, so WebEngine works offscreen. Resulting image is produced in another widget.
I tried to use render() (webView->page()->view()->render(&painter);) where painter uses QPixmap (also tried to use QOpenGLPainterDevice) but it takes too much time to render, that's why output animation becomes jerky.
Is there any way to transform the image directly on gpu (I'm not an expert in OpenGL, but maybe I can get framebuffer object, or get opengl context)?