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     stereo - stereo viewing on Silicon Graphics systems


     All SGI graphics systems have one or more ports for connecting stereo
     viewing equipment to enable 3-D stereo presentation of computer graphics
     imagery.  The Stereo port provides power for the external viewing
     equipment, and provides a Stereo Field sync signal to synchronize the
     external viewing equipment to the time-multiplexed stereo video.

     When the Stereo Sync signal is High, the system is displaying the Right-
     Eye view; when it is low, the system is displaying the Left-Eye view.
     External stereo viewing equipment uses this signal to synchronize its
     time-multiplexing of the video into the viewer's left and right eyes,
     creating the illusion of a stereoptic presentation of the graphics
     images.  For more information on creating Left-Eye and Right-Eye views,
     see the article, High Resolution Virtual Reality, by Michael Deering in
     ACM Computer Graphics, vol. 26, number 2, the 1992 SIGGRAPH proceedings,
     page 195.

     To display stereo images, a stereo-capable software application must be
     running on a stereo-capable graphics system, to which the appropriate
     external stereo viewing equipment has been attached.  The system must be
     running a stereo-video format.  See xsetmon(1), setmon(1G) and
     setmonitor(3G) for details on setting the system to stereo video format.

     Three different kinds of stereo are supported on SGI equipment.  The
     first two methods use the stereo connection described above to
     synchronize external viewing equipment, such as the CrystalEyes stereo
     goggles.  The third method is used for head mounted displays.

     1.  The most common is 1280x492 pixels per left/right field, at 60
     field-pairs per second.  All Silicon Graphics workstation models support
     this kind of stereo.  This method has been called divided screen or split
     screen stereo in various documents, because the frame buffer is divided
     into 2 parts, one for each eye.  Stereo applications render the left-eye
     view into the top half of the frame buffer, using lines 0-491.  The
     right-eye view is rendered into the bottom half of the frame buffer using
     lines 532-1023 (on all systems except O2, which uses lines 512-1003).
     The application must adjust the transformation matrix to correct for the
     fact that pixels are not square in this format.  There are two variations
     on split screen stereo.  In the first, called old-style stereo, a single
     application takes over the entire screen and is responsible for all
     rendering, typically using the older IRIS GL application program
     interface.  This kind of stereo is selected by giving the STR_RECT option
     to setmon.  In the second variation, which uses the SGI Stereo X
     extension, applications can render stereo into a window on a desktop that
     includes other windows.  The SGI Stereo X extension includes these
     functions: XSGIStereoQueryExtension, XSGIStereoQueryVersion,
     XSGIQueryStereoMode, XSGISetStereoMode, and XSGISetStereoBuffer.  This
     kind of stereo is selected by giving the STR_TOP or STR_BOT option to
     setmon, or by selecting "Top" or "Bottom" when prompted by xsetmon after
     the user chooses a split-screen stereo timing table. The windowing system
     is responsible for putting up menus, popups, etc. in both the top and
     bottom halves of the screen, in order to make stereo-in-a-window work.

     2.  Another stereo method, Quadbuffer Stereo, dedicates separate frame
     buffers to each eye, so it uses four buffers when displaying double
     buffered stereo images.  This method renders and displays square pixels,
     and does not require the windowing system to render its widgets in two
     places. Stereo applications render the left-eye and right-eye views to
     the same pixel locations in the screen or window, but select either the
     left buffer or right buffer when rendering views for the left or right
     eye, respectively.  This method allows several different display
     resolutions, and has the advantage of allowing the software application
     to render to a square-pixel space.  This results in higher image quality,
     especially for anti-aliased rendering.  This method is typically selected
     by using setmon or xsetmon to load, for example, the 1024x768_96s timing

     3.  The third way of doing stereo is with the Multi-channel option (MCO),
     which dedicates a video channel per eye.  This method is popular for
     virtual reality helmets, but is beyond the scope of this document.  No
     Stereo Sync is needed for this kind of stereo.  The two video channels
     must be genlocked together.  See setmon(1G) and setmonitor(3G) for
     details on enabling the genlock function.

     In some multi-screen stereo applications it is desirable to genlock the
     stereo screens together.  Care must be taken to ensure that right-eye
     views are locked together.  For some older stereo formats, this may
     require several tries.  See setmon(1G) for details on enabling the
     genlock function.


     There are four different types of stereo ports found on various Silicon
     Graphics systems.

     The DIN-8 powered serial port connectors, which are found on the Onyx and
     Crimson models, provide Stereo Sync in addition to serial communication
     signals for other types of peripherals.  The serial signals are not used
     by external stereo viewing equipment, but the pin-out description of all
     signals on the DIN-8 is provided here for completeness.

     In order to support peripherals which draw power from the host system,
     the Challenge and Onyx systems provide two powered-peripheral serial
     ports.  These ports have a DIN-8 connector.  These ports share the tty2
     and tty3 signal lines with the standard DB-9 connectors; if the DB-9
     connector for tty2 is already in use, you cannot use the powered
     peripheral connector for tty2.  Similarly, if tty3's DB-9 connector is
     connected to a peripheral, the powered peripheral port connected to the
     tty3 signal lines cannot also be used.  The Stereo SYNC signal is brought
     out in parallel to both ports. The powered peripheral ports have the
     following pin assignments:

                                     /   2   \
                                    /4       5\
                                   /           \
                                  ( 1    8    3 )
                                   \           /
                                    \ 6     7 /

                     |Pin | Name | Description                |
                     | 1  | DTR  | Data Terminal Ready        |
                     | 2  | CTS  | Clear To Send              |
                     | 3  | SYNC | Stereo Sync/GND (jumpered) |
                     | 4  | RD   | Receive Data               |
                     | 5  | TD   | Transmit Data              |
                     | 6  | SG   | Signal Ground              |
                     | 7  | GND  | Ground point               |
                     ||_8  ||_V10P ||_10V supply                 |

     The Onyx and Crimson also provide Stereo Sync and Stereo Power as part of
     the 13W3 RGB video port.  Note: the Elan and Indy products do NOT have
     stereo support in its 13W3 port.  This connector has the following pin

                          \ A1   1  2  3  4  5   A2  A3 /
                           \   6  7  8  9  10          /

          |Pin | Name       | Description                               |
          |A1  | RED        | Analog Red signal                         |
          |A2  | GRN        | Analog Green signal + optional video sync |
          |A3  | BLU        | Analog Blue signal                        |
          | 1  | N/C        |                                           |
          | 2  | MONTYPE_0  | Monitor ID bit 0                          |
          | 3  | N/C        |                                           |
          | 4  | STEREO     | Stereo Sync signal                        |
          | 5  | STEREO_PWR | Stereo Power, +10V                        |
          | 6  | MONTYPE_1  | Monitor ID bit 1                          |
          | 7  | MONTYPE_2  | Monitor ID bit 2                          |
          | 8  | GND        |                                           |
          | 9  | GND        |                                           |
          ||10  ||_GND        ||___________________________________________|

     Indy, Indigo, Indigo2 (Elan, Extreme, XS, or XZ), and O2 models use a
     micro-DIN connector for the following Stereo port:

                                     /   3   \
                                    /         \
                                   / 2       1 \
                                  (             )
                                   \     #     /
                                    \         /

                          |Pin | Name   | Description   |
                          | 1  | PWR    | +12V          |
                          | 2  | GND    | Signal Ground |
                          ||_3  ||_STEREO ||_Stereo Sync   |

     Indigo2 and Octane models with IMPACT graphics use a DB9 connector for
     stereo.  This connector has the following pin assignments:

                                \  5  4  3  2  1  /
                                 \   9  8  7  6  /

                          |Pin | Name   | Description   |
                          | 1  | STEREO | Stereo Sync   |
                          | 6  | GND    | Signal Ground |
                          | 7  | GND    | Signal Ground |
                          ||_8  ||_PWR    ||_+12V          |


     xsetmon(1), setmon(1G), setmonitor(3G)

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