/*!   \page opengl-overlay-example.html  \ingroup opengl-examples  \title OpenGL Overlay ExampleThis example demonstrates how to use OpenGL overlays with the Qt OpenGLExtension. It features a QGLWidget with a relatively expensive redrawingoperation, and rubber-band drawing in the overlay plane. Using theoverlay has the advantage that the rubber-band may be drawn and erasedwithout damaging the image in the main plane, so costly redraws areavoided.See \c{$QTDIR/examples/opengl/overlay} for the source code.*/