Qt GLWidget in GraphicsScene for fast video display from image data (C++ , Windows)?

Question

There are a few questions about displaying video more efficiently in Qt than by showing it as QLabel. There seem to be two approaches:

• Write directly to a window's / widget's image buffer (but I could not find information whether this is possible with Qt, while MSVC / MSC applications apparently can write to a window handle)

• Use OpenGL to display via hardware

  • Image scaling (KeepAspectRatioByExpanding) through OpenGL
  • What is the most efficient way to display decoded video frames in Qt?

Since my current approach involves a QPixmapItem created from a QImage populated with my image data, even at small resulutions (<1 MP, 30 Hz) my Core2Duo is reporting 40 % load.

I would like to keep using QGraphicsScene in order to show multiple images/videos, but I don't know whether it's possible to show (multiple) QGLWidgets in a scene - is it?

Answer 1

Perhaps not several GLWidget, but several GraphicsItem, calling painter->beginNativePaintingwhich allows openGL commands to be issued.

The viewport of the graphicView must be a QGLwidget, the latter initialized with QGLFormat(QGL::SampleBuffers) in the constructor. see Qt widgets using opengl

The case is simpler when OpenGL active item is in the background, because calls to glClear erase the viewport background as well, clearing any item below with a lower zorder.