In practice, most commonly used at present are a remote server machine running Unix or Linux as well as a remote viewing tool such as VNC. As already mentioned, the X Windows System has an integrated concept for rendering over a network. By simply setting the DISPLAY environment variable, an application can be run on a computer and rendered on any accessible X server on the network. A machine can have an X server that has the screen of the connected monitor(s). It can also run additional X servers such as Xvnc that are not connected to a physical screen. This allows multiple graphics applications to run on the same server computer that is connected to different X servers without conflict with the connected screens (or even use of the screen).

When remote rendering is enabled, Open Inventor (on a Unix server machine) opens a normal X window on the target display, but does not attempt to initialize OpenGL in that window. Instead, Open Inventor creates an off-screen buffer on the server machine and initializes OpenGL on that buffer. All 3D rendering is done in the off-screen buffer on the remote machine. Rendering can be hardware accelerated if the remote machine supports the OpenGL extension “pbuffer”. When each 3D image is finished, Open Inventor reads back the rendered image and sends it to the target display.

In most cases, this process is transparent to the Open Inventor application. If the application has callbacks or custom nodes that make direct calls to OpenGL, they should work as long as they use the OpenGL render context of Open Inventor. This context is linked to the off-screen buffer.

Limitations of remote rendering.

Stencil buffer support. Accumulation buffers, anti-aliasing and other OpenGL features depend on the capabilities of the remote server. OpenGL extensions required for advanced rendering techniques such as bump mapping and job-independent transparency may not be available on the server machine.

OpenGL hardware (Quad Buffered) Stereo is not supported because OpenGL commands are not sent to the local machine. However, software stereo modes such as anaglyph (red/green) and interlaced images are supported.

Overlay layers are not supported when using remote rendering.

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