Chapter 14. Configuring GLX in Xinerama
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## Chapter 14. Configuring GLX in Xinerama

The NVIDIA Linux Driver supports GLX when Xinerama is enabled on similar GPUs. The Xinerama extension takes multiple physical X screens (possibly spanning multiple GPUs), and binds them into one logical X screen. This allows windows to be dragged between GPUs and to span across multiple GPUs. The NVIDIA driver supports hardware accelerated OpenGL rendering across all NVIDIA GPUs when Xinerama is enabled.

To configure Xinerama

1. Configure multiple X screens (refer to the XF86Config(5x) or xorg.conf(5x) man pages for details).

2. Enable Xinerama by adding the line

           Option "Xinerama" "True"

   to the "ServerFlags" section of your X config file.

Requirements:

- Using identical GPUs is recommended. Some combinations of non-identical, but similar, GPUs are supported. If a GPU is incompatible with the rest of a Xinerama desktop then no OpenGL rendering will appear on the screens driven by that GPU. Rendering will still appear normally on screens connected to other supported GPUs. In this situation the X log file will include a message of the form:

      (WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of
      (WW) NVIDIA(2):      the GPUs composing the desktop.  OpenGL rendering will
      (WW) NVIDIA(2):      be disabled on screen 2.

- NVIDIA's GLX implementation only supports Xinerama when physical X screen 0 is driven by the NVIDIA X driver. This is because the X.Org X server bases the visuals of the logical Xinerama X screen on the visuals of physical X screen 0.

  When physical X screen 0 is not being driven by the NVIDIA X driver and Xinerama is enabled, then GLX will be disabled. If physical X screens other than screen 0 are not being driven by the NVIDIA X driver, OpenGL rendering will be disabled on them.

- Only the intersection of capabilities across all GPUs will be advertised.

  The maximum OpenGL viewport size depends on the hardware used, and is described by the following table. If an OpenGL window is larger than the maximum viewport, regions beyond the viewport will be blank.

  OpenGL Viewport Maximums in Xinerama

  GeForce GPUs before GeForce 8: | 4096 x 4096 pixels
  GeForce 8 and newer GPUs: | 8192 x 8192 pixels
  Quadro: | as large as the Xinerama desktop

- X configuration options that affect GLX operation (e.g.: stereo, overlays) should be set consistently across all X screens in the X server.

Known Issues:

- Versions of XFree86 prior to 4.5 and versions of X.Org prior to 6.8.0 lack the required interfaces to properly implement overlays with the Xinerama extension. On earlier server versions mixing overlays and Xinerama will result in rendering corruption. If you are using the Xinerama extension with overlays, it is recommended that you upgrade to XFree86 4.5, X.Org 6.8.0, or newer.

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