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kommt nochHow the remote graphics reach your client (Sun Shared Visualization Software)
How the remote graphics reach your client (Sun Shared Visualisation Software)
This method is implemented in Suns Shared Visualisation Software, which consists mainly of the two open-source projects VirtualGL and TurboVNC. There are basically two modes to use these tools: The direct mode (aka "VGL image transport"), which involves only VirtualGL and requires an X-server on the client machine, and the raw mode (aka "X11 image transport") for which only TurboVNC is required on the client (this is the recommended mode for windows clients).
DIRECT MODE (aka "VGL image transport"): In this case only the 3D grahics commands are executed on the server. The 2D commands (e.g. for drawing the GUI) are sent to the client exactly like in the standard remote X11 approach (ssh -X). The 3D commands, however, are executed on the server graphics cards and the generated 2D images are read back, compressed, and sent to the client by VirtualGL. This is not done over the normal X11/ssh-connection, but over a own connection, which is set up by the vglrun application on the server and requires the vglclient application to run on the client (i.e. connecting to the remote visualisation server by means of 'vglconnect'). VirtualGL (vglclient) receives the compressed images on port 4242 and copies them into the X-server of the client.
advantage: up to 20 percent faster than the raw mode for high bandwidths; only 3D viewport is sent as jpeg image, text and menus are drawn locally and therefore appear crisp.
disadvantage: requires X-server.
RAW MODE (aka "X11 image transport"): This is the recommended mode when there is no X-server available on the client, e.g. in case of Microsoft Windows machines. In this mode a second "virtual" X-server, the vncserver, is running on the server machine, which transfers the screen contents (in JPEG-compressed form) to a client application, the vncclient. Standard VNC servers do not allow the execution of 3D graphics commands and use a compression method that is not very suitable for 3D graphics. These problems have been removed in the TurboVNC server, which hands 3D commands over to the "real" X-server that executes them on the server's graphics cards.
advantage: does not require X-server (easier to configure under Microsoft Windows).
disadvantage: compression artefacts visible in text areas due to jpeg-compression of whole desktop.
A more detailed description of the two modes is available at www.virtualgl.org.