How 3D acceleration work??

[QH]

I follow the source code of virtualbox. Virtualbox implement the 3D acceleration using the Chromium, the Guest will send the render code to the Host. Host complete the render.
I'm confused how the Guest get the result(frame buffer) and show the result to the window??
I debug a OpenGL app in the guest and follow the render command send and receive. but there no render data receive back. The Guest and Host communication use the HGCM, so I guess the showing work is done by the VBoxGuest.sys. I'm right???
Thanks for help!

[Technologov]

I think host displays rendered data, just using guest's _window_ limits. (viewport)
You can try asking on vbox-dev mailing list to get better answers.

As for Direct3D: guest additions use parts of "Wine" code to translate guest's D3D->OpenGL.