[Development] QT_XCB_NATIVE_PAINTING makes worse that without of it

[Allan Sandfeld Jensen]

On Sonntag, 24. März 2019 10:07:06 CET Denis Shienkov wrote:
> Allan,
> 
> so, do we need in OpenGL support for 2-d acceleration in QtWidget
> applications running via X11? When, e.g. we use QPainter?
> 
> I'm already confused... What we need to have to be use the GPU
> acceleration on X11 with QtWidgets?
> 
There are currently three ways.

1) Use the old scene-graph and set a QOpenGLWidget as the view of a 
QGraphicsView. 
2) Create a QOpenGLFrameBufferObject and a QOpenGLPaintDevice, and paint 
inside that for offscreen accelerated OpenGL painting inside a QPainter.
3) Use a QOpenGLWindow as the root window

In the widgets/painting examples you can find a pattern that uses the 
QOpenGLFrameBufferObject and blitting to have an otherwise rasterized 
application switch to opengl acceleration. Though the pattern is still a bit 
too Qt4'ish even after I tried cleaning it up last year.

Note though that the recommended way of doing hardware accelerated painting 
these days with Qt, is using QML or the QtQuick scenegraph from C++. QPainter 
being so sequential and imperative will never be able to take full advantage 
of OpenGL because the API wasn't designed for it.

'Allan