Return information about current OpenGL rendering state.
‘targetwindow’ is the window handle of the window that is currently enabled for
drawing. That is, the last window a Screen drawing command was drawing to, or
the window which is the current target for OpenGL rendering commands.
‘IsOpenGLRendering’ if equal to zero, then normal 2D Screen drawing is active.
If greater than zero, then Matlab OpenGL drawing is active, ie. a
Screen(‘BeginOpenGL’); command was executed and OpenGL code can draw into