title: Qt5: Drawing some graphics on top of QOpenGLWidget
body: <p>I'm building an app which uses Qt5 that aims to display a video from a digital camera (using Gstramer pipeline). Then with the help of QPainter I'm drawing some graphics on top of it (some text shapes, and icons).</p>
  <p>The thing is that the video refresh rate is ~30 FPS, and I only need to update the graphics in ~10 FPS or so. Currently I redraw the graphics overlay for every video frame which is very wasteful in terms of CPU.</p>
  <p>Is there a better approach in which I can re-use the overlay from the previous frame, and only update the background (the frame from the camera)?</p>
  <p>One idea that I had was to paint the overlay into a QImage, and then just paint the image onto the QOpenGLWidget, but it just feels wrong.</p>
  <p>Thank you...</p>