Stereo on Linux

Introduction

Using stereo in a window is more complicated with Linux^® than IRIX^®. This section contains information about configuring a Linux machine so that stereo in a window can be used by SYBYL^® and other "stereo ready" Linux applications. Hardware stereo requires both a stereo ready graphics card and monitor. Changes to the Linux configuration may also be necessary.

Hardware Requirements

1. Refresh rate of 118 Hz (or better) at a resolution of 1280 x 1024 
2. Refer to http://www.reald.com/scientific/stereo_ready_monitors.asp   for Real D information on stereo ready CRT monitors.

1. A wide variety of NVidia Quadro cards support stereo, but not all have the stereo connector for the Real D emitter. NVidia Quadro cards with the stereo connector include NVidia Quadro 4 750-980 XGL & FX 1100, 1300, 1400, 3000, 3400, 4400, 4500, 5500 
2. FireGL X1 256p
3. Refer to http://www.reald.com/scientific/stereo_ready_graphics_cards.asp for Real D graphics card compatibility information.
4. Refer to Linux Hardware and Graphics Cards for most up-to-date list of Tripos information on graphics cards.

In general, the stereo emitter from an older SGI machine will not work with a PC graphics card. Emitters that are known to work with PC graphics cards are:

1. CrystalEyes emitter model ENT
2. CrystalEyes emitter model E2

Additional information about emitters can be found on the Real D web site at: http://www.reald-corporate.com/scientific/emitters_faq.asp.

Any type of CrystalEyes compatible glasses should work, including ones used with SGIs.

Before You Proceed

The default Linux configuration is for mono mode. Changes must be made to the default Linux configuration to enable stereo mode. Two steps must be performed:

1. Modify the xorg.conf file.
2. Restart the X-server to enable the stereo mode of the card.

It is essential to understand the importance of the xorg.conf file in the Linux system and to read the manufacturer's notes about your graphics cards. Warning: Incorrect modifications to the xorg.conf file may render your machine unusable or, in extreme cases, even damage your monitor.

xorg.conf manages the configuration of the graphics card, the mouse, the keyboard, the desktop, the fonts, etc. This central configuration file is critical to the functioning of the X-server.
Red Hat Enterprise Linux version 4 (RHEL 4) it is located in: /etc/X11/xorg.conf
It may have a different name or location for other versions of Linux.

Before making changes to xorg.conf, it is a good idea to make a backup copy. (Note: You must be an administrator to change the xorg.conf file.) It is also essential to know about its syntax. Read and understand the xorg.conf man page before making any changes to your system. To access the man page, at the Linux prompt, type: man xorg.conf 

Graphic card configuration is different for each card vendor. In addition, stereo or mono mode is accomplished differently by the different graphics cards. Therefore, it is important to read the release notes for your particular graphics driver.

Enabling Stereo

Detailed information should be provided in the release notes for your particular graphics cards

• For the NVidia Quadro cards:
  Add the following to the "Device" section of the XF86Config file (/etc/X11/XF86Config in Red Hat EL/WS 3):
  Option "Stereo" "3"
• For the ATI FireGL X1 256p card:
  Add the following to the "Device" section of the XF86Config file (/etc/X11/XF86Config in Red Hat EL/WS 3):
  Option "Stereo" "on"

This will enable the stereo visuals and activate the stereo emitter connector on the graphics card. You must restart the X Server for the change to take effect.

Stereo mode should now be enabled. If a stereo ready application, such as SYBYL, uses stereo mode, stereo images should be visible. If stereo images are not available, see the sections below for more settings.

In stereo mode, two images (one for the left eye and another for the right eye) are displayed. Displaying two images reduces the display refresh rate in half, which may result in "flicker." Most people will perceive flickering if the refresh rate is less than 118 Hz for stereo. See the next section (Increasing Screen Frequency) for instructions on increasing the refresh rate.

Increasing Screen Frequency

You can change the frequency by editing the capabilities of the monitor in the xorg.conf file. You may also have to write a modeline (see Creating Modelines below).

For best results, a refresh rate of 118 Hz is required for stereo. The refresh rates supported by a monitor varies with the resolution. In general, the supported refresh rate decreases as the resolution increases. The ideal combination for SYBYL is a refresh rate of 118 Hz or better, with a resolution of 1280 x 1024.

Warning: An incorrect modification may inflict permanent damage to your monitor. Proceed with caution.

Modifying Monitor Capabilities

Many vendors will provide the frequency information in monitor specification sheets that came with the monitor. Specification sheets also can be found on the vendor's web site. Turn to the documentation for your monitor and search for the vertical and horizontal sync rate. If you find the frequency ranges, add them to the "Monitor" section of the xorg.conf file:

Example:
VertRefresh 50 - 80
HorizSync 31.0 - 100.0

If changing/adding these values does not increase the refresh rate of the monitor, first try rebooting the machine and retrying the edits. If that fails, you may need to set additional options in the "Device" section to get the X Server to try non-default refresh rates (look in the documentation for options involving DDC or EDID). In some cases, you may need a different monitor cable to allow the graphics card to "talk" to the monitor and retrieve the available refresh rates.

Creating Modelines

If, after trying the changes discussed above, the refresh rate still does not improve, you will have to create a modeline entry in the xorg.conf file. Modelines are used to define display modes with specific frequencies. Modeline creation is not thoroughly described in the manual page. There is some documentation about it in Appendix B (Programming Modes) of the NVidia release notes and there are some programs which assist in testing these lines (e.g., xvidtune). Note that the modeline must correspond with the monitor and the settings of "VertRefresh" and "HorizSync."

ATI video cards supplied with older drivers use a modeline for a 1280x1024 120Hz mode (60Hz in stereo). Not all monitors support such high refresh rates. If the monitor does not support the specified rate, it may go black or display only "static." In this case, you will have to use console mode to revert your changes, and restart the X Server. (See How do I revert my changes in the console?).

For example: the ATI modeline may also work for NVidia cards:
Modeline "1280x1024" 233.793 1280 1384 1528 1776 1024 1025 1028 1097 +hsync +vsync

The website http://www.sh.nu/nvidia/gtf.php provides an interface to calculate modelines for arbitrary resolution and refresh rates.

Warning: Improper modification may result in permanent damage to your hardware.

Known Issues with Stereo on Linux

1. In general, the graphics performance of an application in stereo mode is approximately half of the performance in mono mode. This is because everything must be drawn twice in stereo mode.
2. NVidia drivers 76.64 and 76.67 work well, but older drivers in the NVidia Quadro 4 family have a known performance problem when stereo is enabled. The solution is to upgrade to the newer drivers.
3. Stereo emitters from older SGI machines are not compatible with PC graphics cards. In general, you cannot reuse the emitter from your SGI on a Linux machine.