Screen(‘BeginOpenGL’)

Psychtoolbox>Screen.{mex*} subfunction

Prepare window ‘windowPtr’ for OpenGL rendering by external OpenGL code. This
allows to use OpenGL drawing routines other than the ones implemented in
Screen() to draw to a Psychtoolbox onscreen- or offscreen window via execution
of OpenGL commands. Typical clients of this function are mogl (Richard F.
Murrays OpenGL for Matlab wrapper), the new Eyelink-Toolbox and third party
Matlab Mex-Files which contain OpenGL rendering routines. You *have to* call
this command once before using any of those external drawing commands for the
window. After drawing, you *must* switch back to PTB’s rendering via the
Screen(‘EndOpenGL’, windowPtr); command. Normally, you won’t provide the
optional flag ‘sharecontext’, so PTB will automatically isolate the OpenGL state
of your code from its internal state. However, if you provide sharecontext=1,
then PTB will allow your code to use and affect PTBs internal context. Only do
this if you really know what you’re doing! If you provide sharecontext=2 then
PTB will give you your own private context, but it will synchronize the state of
that context with its internal state - Seldomly needed, but here for your
convenience. Caution: sharecontext=2 is not supported on all operating systems
and gpu’s, e.g., not on OSX, so avoid if you can! The context state isolation is
as strict as possible without seriously affecting performance and functionality:
All OpenGL context state is separated, with two exceptions: The framebuffer
binding (if any) is always synchronized with PTB (and reset to zero when calling
‘EndOpenGL’ or another Screen command) to allow external code to transparently
render into PTBs internal framebuffers - Needed for the imaging pipeline to
work. Ressources like textures, display lists, FBOs, VBOs, PBOs and GLSL shaders
are shared between PTB and your code as well for efficiency reasons. Both types
of ressource sharing shouldn’t be a problem, because either you are a beginner
or advanced OpenGL programmer and won’t use those facilities anyway, or you are
an expert user - in which case you’ll know how to prevent any conflicts easily.

###See also: EndOpenGL SetOpenGLTexture GetOpenGLTexture moglcore