Each line in X*screens lists a separate screen device (except in combined mode). A screen device can be a physical device, the CRT screen, or the image planes or overlay planes of a physical device.
The syntax for each line of an X*screens file is:
. [{ depth
{~4}
[doublebuffer] }1
/ dey / device [ # comment]
depth 16 doublebuffer
/dev/device
Specifies the name of the device file that the X server should read for this display.
Specifies the number of image and overlay planes available to the server (one pixel per plane).
Specifies double buffer. Double buffering divides video memory into halves and displays one half while drawing the other. Double buffering is used with graphics programs that double buffer their screen output. This avoids "flashing" during screen redraw.
Specifies the division of the image planes into two 8-bit, double buffered halves.
Specifies the size of the monitor in inches (when number~100)
or millimeters (when number> 100).
This example shows how to specify a particular screen configuration consisting of a high-resolution screen on which you want to run XII and Starbase
applications. The image plane of this screen is accessed by the device file / dey / i'Yimge_device. The overlay plane is accessed by the device file / dey / overlay_device. You want to switch between four different screen configurations:
• One screen with XII running in the image planes (image mode).
• Two screens with Starbase running in the image planes and XII running in the overlay planes (overlay mode). You may have only one Starbase application running in this mode, and you can see it only if you open a
"transparent" window to look through the overlay planes.
• Two screens running on the same display (stacked mode). One screen runs 3 in the image planes, and the other runs in the overlay planes. You move
between the two screens by moving the pointer to the edge of the display.
The order in which the screens appear is specified by the order in which their designations appear in the X*screens file. Starbase is not normally run in this mode.
• One screen with two visuals, one with depth 24, and the other with depth 8 (combined mode). Starbase applications are run in windows that can be moved or resized like any other window. You can have several Starbase applications running at once, each in its own window. The order in which the screens are described is unimportant.
Here is the XOscreens file that creates these four configurations. To use a particular configuration, un comment the line (two lines for Stacked Screens Mode) that create it, and make sure all other lines are commented.
### Default Configuration ###
/dev/i~ge_device
### Overlay Screens Mode ###
# / dev / overlay_device
### Stacked Screens Mode ###
# /dev/i~ge_device
# / dev / overlay_device
### Combined Screens Mode ###
# / dev / i~ge_device / dev / overlay_device depth 24 depth 8
More examples can be found in the system XOscreens file. Note that the first configuration is the default screen configuration provided with XII.
Multiple Screen Configurations
On systems that support multiple display devices, it is possible to configure X to use these multiple devices in two ways:
Preliminary Configuration 3·"
• A single X server can treat multiple devices as individual screens within a single display.
Configure the X*screens file so that each device is listed on a separate line.
The order of the lines in the file determines the number given to each screen, beginning with zero.
S /dev/crtO #display 0, screen
°
/dev/crt1 #display 0, screen 1
10 address a specific device, use the screen parameter of the DISPLAY variable. For instance, DISPLA Y=local: 0.1 addresses the second device .
• Multiple X servers can treat each device as a separate display.
Create an X*screens file for each device. For example:
XOscreens:
10 address a specific device, use the display parameter of the DISPLAY variable. In this case, DISPLAY=local: 1.0 addresses the second device.
Mouse Tracking with Multiple Screen Devices
If you use a multi-screen configuration, the mouse pointer can move from one screen to another. You can arrange the screens in a vertical, horizontal, or matrix orientation by adding the appropriate lines to the X*pointerkeys configuration file described in chapter 9. The sample X*pointerkeys file in your system directory contains examples that show how to specify the orientation of multiple screens.
Note
"
The sample X*pointerkeys file is placed in /usr/lib/X11 at install time. If you subsequently update your system, the X*pointerkeys file in /usr/lib/X11 is not overwritten, and the sample file is placed in /etc/newconfig.
Moving the mouse pointer off one edge of a screen causes the pointer to move to another screen, depending on the screen orientation you have specified.
configuration files, the order of entry determines the tracking order of the mouse pointer. The first line in the file is the device on which the pointer appears when you start XII.
Other lines correspond to the screens that appear when the mouse is moved to the right or left side of the current screen. Moving off the right side goes to the next higher display, the left side the to next lower. If you are on the highest display and move right, you move to the lowest display. If you are on the lowest display and move left, you move to the highest display.
Making a Device Driver File
Devices specified in screen configuration files must correspond to device files. If you don't have the appropriate device file, you must create it using the mknod command. For information on mknod see the system administration manual for your operating system.
Preliminary Configuration 3·13
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