Matrox G450 PCI (PCI 2:0:0) dual head - driving
Sony projector & NEC LCD panel
Depending on which projectors are available (powered up
and not switched to other devices, e.g.
Viewstation),
different X11 configurations may be used:
When the displays are independant, each has a different value for
the environment variable DISPLAY. On a system with only one
screen, this is usually :0.0. The second screen becomes
:0.1, the third :0.2 etc. Each screen has an independant
coordinate system starting at (0,0) in the top left corner.
Tasks may be launched on a given screen by either using the mouse in
that screen (right-click on desktop or left-click a launcher icon), or
by specifying the DISPLAY, e.g.
DISPLAY=:0.1; mozilla &
Any popup windows or alerts spawned by a task will appear on the same screen.
Xinerama/merged mode
The Matrox cards support a "merged mode", where the two outputs appear
to X11 as a single double-width display. In addition, X11 supports
"Xinerama", where multiple cards may be grouped into a single display.
In these modes, the screens share a single DISPLAY value. A single
coordinate system extends across the grouped screens, so that
the top left of the second screen becomes pixel (1024,0).
A task may be started at a particular location using the standard
X11 methods, e.g.
xeyes -geometry +300+100
However, not all applications will honour this argument. Applications
may launch popups and alert windows seeming at random on any one of the
grouped displays. If one of the projectors is not operating, the
popup may be hard to locate.
The advantage of Xinerama and Merged mode is that applications may straddle
two projectors or be dragged from one screen to another.
OpenGL
It appears that direct render mode (DRI) is not available on the
second output of the Matrox cards, and that OpenGL programs (such
as certain of the xscreensaver graphics) will not run
in Merged or Xinerama mode (they will crash X11)
Several different XF856Config files are available in /etc/X11 to
start X11 in different states. Shortcut scripts startx1, startx2 etc.
are provided to start X11 using these configurations.
Start X11 with both Dell projectors running independantly.
Use this mode if only the right Dell projector is required - it is
not possible to enable only the second output on the Matrox dual-head
cards.
Start X11 with both Dell projectors in merged mode, plus
the Sony projector to the left, plus the NEC flat panel below
the left Dell . Move the mouse into a display to use it. To find the
mouse pointer more easily, right-click. This will usually bring up a
popup menu which is easier to see.
Note: It takes about 20 seconds to start the G550 card alone (startx1,
startx2). It takes about 2 minutes to start both the G550 and G450
cards (startx4 etc.)
Start X11 with all displays independant. Use this mode if the
Sony and only one Dell projector are required.
More on Xinerama
The difference between Xinerama and Merged mode is subtle. In Merged mode,
the two displays can share a taskbar, and only the two outputs on one Matrox
card can be grouped. In Xinerama, the displays have separate taskbars,
and all displays are grouped. It is possible to have both Xinerama and
Merged modes together.
