Apart from marshaling GLX commands and managing Pbuffers, VirtualGL also reads back the rendered pixels at the appropriate time (usually by monitoring codice_1 or codice_2) and then draws those pixels into application's X window using standard X image drawing commands. Since VirtualGL is redirecting the GLX commands away from the 2D X Server, it can be used to add accelerated 3D support to X proxies (such as VNC) as well as to prevent indirect OpenGL rendering from occurring when using a remote X display.