STEREO(7) STEREO(7)
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 RightEye
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
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STEREO(7) STEREO(7)
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
table.
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.
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STEREO(7) STEREO(7)
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 |
|____|______|____________________________|
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STEREO(7) STEREO(7)
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
assignments:
-------------------------------
\ 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 | |
|____|____________|___________________________________________|
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STEREO(7) STEREO(7)
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 |
|____|________|_______________|
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 |
|____|________|_______________|
xsetmon(1), setmon(1G), setmonitor(3G)
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