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
'targetwindow'.