glRotate

1
Hi,

there is the function Screen('glRotate',...)
I just want to rotate, say the character 'F', around the z-axis.
If i use the extern gl-Operations with Screen('BeginOpenGL') it seems
that it works. But to bring an simple F on the Window in that way is
too complicate.
The easier way i suppose, is to use Screen('glRotate'...) together
with the other Screen-commands. Here the code:
[OnScreen, screenRect]=Screen('OpenWindow',0,white,[]);
Screen('FillRect', OnScreen, white);
Screen('TextFont', OnScreen, 'Arial');
Screen('TextStyle', OnScreen, 1);
textbox = Screen('TextBounds', OnScreen, R);
textbox = OffsetRect(textbox, x, y);
Screen('glPushMatrix', OnScreen);
Screen('glRotate', OnScreen, 90, 0, 0, 1);
Screen('DrawText', OnScreen, R, x, y, [255, 255, 0]);
Screen('glPopMatrix', OnScreen);
Screen('Flip',OnScreen);

This do not work. Do you have an example for the use of Screen
('glRotate'...)? Would be very helpful.

thanks a lot
m.