XNEST(1)XNEST(1)NAMEXnest - a nested X server
SYNOPSISXnest [-options]
DESCRIPTIONXnest is a client and a server. Xnest is a client of the real server
which manages windows and graphics requests on its behalf. Xnest is a
server to its own clients. Xnest manages windows and graphics requests
on their behalf. To these clients Xnest appears to be a conventional
server.
OPTIONSXnest supports all standard options of the sample server implementa‐
tion. For more details, please see the manual page on your system for
Xserver. The following additional arguments are supported as well.
-display string
This option specifies the display name of the real server that
Xnest should try to connect with. If it is not provided on the
command line Xnest will read the DISPLAY environment variable in
order to find out the same information.
-sync
This option tells Xnest to synchronize its window and graphics
operations with the real server. This is a useful option for
debugging, but it will slow down the performance considerably. It
should not be used unless absolutely necessary.
-full
This option tells Xnest to utilize full regeneration of real server
objects and reopen a new connection to the real server each time
the nested server regenerates. The sample server implementation
regenerates all objects in the server when the last client of this
server terminates. When this happens, Xnest by default maintains
the same top level window and the same real server connection in
each new generation. If the user selects full regeneration, even
the top level window and the connection to the real server will be
regenerated for each server generation.
-class string
This option specifies the default visual class of the nested
server. It is similar to the -cc option from the set of standard
options except that it will accept a string rather than a number
for the visual class specification. The string must be one of the
following six values: StaticGray, GrayScale, StaticColor, Pseudo‐
Color, TrueColor, or DirectColor. If both, -class and -cc options
are specified, the last instance of either option assumes prece‐
dence. The class of the default visual of the nested server need
not be the same as the class of the default visual of the real
server; although, it has to be supported by the real server. See
xdpyinfo for a list of supported visual classes on the real server
before starting Xnest. If the user chooses a static class, all the
colors in the default colormap will be preallocated. If the user
chooses a dynamic class, colors in the default colormap will be
available to individual clients for allocation.
-depth int
This option specifies the default visual depth of the nested
server. The depth of the default visual of the nested server need
not be the same as the depth of the default visual of the real
server; although, it has to be supported by the real server. See
xdpyinfo for a list of supported visual depths on the real server
before starting Xnest.
-sss
This option tells Xnest to use the software screen saver. By
default Xnest will use the screen saver that corresponds to the
hardware screen saver in the real server. Of course, even this
screen saver is software generated since Xnest does not control any
actual hardware. However, it is treated as a hardware screen saver
within the sample server code.
-geometry W+H+X+Y
This option specifies geometry parameters for the top level Xnest
windows. These windows corresponds to the root windows of the
nested server. The width and height specified with this option
will be the maximum width and height of each top level Xnest win‐
dow. Xnest will allow the user to make any top level window
smaller, but it will not actually change the size of the nested
server root window. As of yet, there is no mechanism within the
sample server implementation to change the size of the root window
after screen initialization. In order to do so, one would probably
need to extend the X protocol. Therefore, it is not likely that
this will be available any time soon. If this option is not speci‐
fied Xnest will choose width and height to be 3/4 of the dimensions
of the root window of the real server.
-bw int
This option specifies the border width of the top level Xnest win‐
dow. The integer parameter must be a positive number. The default
border width is 1.
-name string
This option specifies the name of the top level Xnest window. The
default value is the program name.
-scrns int
This option specifies the number of screens to create in the nested
server. For each screen, Xnest will create a separate top level
window. Each screen is referenced by the number after the dot in
the client display name specification. For example, xterm -display
:1.1 will open an xterm client in the nested server with the dis‐
play number :1 on the second screen. The number of screens is lim‐
ited by the hard coded constant in the server sample code which is
usually 3.
-install
This option tells Xnest to do its own colormap installation by
bypassing the real window manager. For it to work properly the
user will probably have to temporarily quit the real window man‐
ager. By default Xnest will keep the nested client window whose
colormap should be installed in the real server in the WM_COL‐
ORMAP_WINDOWS property of the top level Xnest window. If this col‐
ormap is of the same visual type as the root window of the nested
server, Xnest will associate this colormap with the top level Xnest
window as well. Since this does not have to be the case, window
managers should look primarily at the WM_COLORMAP_WINDOWS property
rather than the colormap associated with the top level Xnest win‐
dow. Unfortunately, window managers are not very good at doing
that yet so this option might come in handy.
-parent window_id
This option tells Xnest to use the window_id as the root window
instead of creating a window. This option is used by the xrx xnest‐
plugin.
USAGE
Starting up Xnest is as simple as starting up xclock from a terminal
emulator. If a user wishes to run Xnest on the same workstation as the
real server, it is important that the nested server is given its own
listening socket address. Therefore, if there is a server already run‐
ning on the user's workstation, Xnest will have to be started up with a
new display number. Since there is usually no more than one server
running on a workstation, specifying Xnest :1 on the command line will
be sufficient for most users. For each server running on the worksta‐
tion the display number needs to be incremented by one. Thus, if you
wish to start another Xnest, you will need to type Xnest :2 on the com‐
mand line.
To run clients in the nested server each client needs to be given the
same display number as the nested server. For example, xterm -display
:1 will start up an xterm in the first nested server and xterm -display
:2 will start an xterm in the second nested server from the example
above. Additional clients can be started from these xterms in each
nested server.
XNEST AS A CLIENTXnest behaves and looks to the real server and other real clients as
another real client. It is a rather demanding client, however, since
almost any window or graphics request from a nested client will result
in a window or graphics request from Xnest to the real server. There‐
fore, it is desirable that Xnest and the real server are on a local
network, or even better, on the same machine. As of now, Xnest assumes
that the real server supports the shape extension. There is no way to
turn off this assumption dynamically. Xnest can be compiled without
the shape extension built in, and in that case the real server need not
support it. The dynamic shape extension selection support should be
considered in further development of Xnest.
Since Xnest need not use the same default visual as the the real
server, the top level window of the Xnest client always has its own
colormap. This implies that other windows' colors will not be dis‐
played properly while the keyboard or pointer focus is in the Xnest
window, unless the real server has support for more than one installed
colormap at any time. The colormap associated with the top window of
the Xnest client need not be the appropriate colormap that the nested
server wants installed in the real server. In the case that a nested
client attempts to install a colormap of a different visual from the
default visual of the nested server, Xnest will put the top window of
this nested client and all other top windows of the nested clients that
use the same colormap into the WM_COLORMAP_WINDOWS property of the top
level Xnest window on the real server. Thus, it is important that the
real window manager that manages the Xnest top level window looks at
the WM_COLORMAP_WINDOWS property rather than the colormap associated
with the top level Xnest window. Since most window managers appear to
not implement this convention properly as of yet, Xnest can optionally
do direct installation of colormaps into the real server bypassing the
real window manager. If the user chooses this option, it is usually
necessary to temporarily disable the real window manager since it will
interfere with the Xnest scheme of colormap installation.
Keyboard and pointer control procedures of the nested server change the
keyboard and pointer control parameters of the real server. Therefore,
after Xnest is started up, it will change the keyboard and pointer con‐
trols of the real server to its own internal defaults. Perhaps there
should be a command line option to tell Xnest to inherit the keyboard
and pointer control parameters from the real server rather than impos‐
ing its own. This is a future consideration.
XNEST AS A SERVERXnest as a server looks exactly like a real server to its own clients.
For the clients there is no way of telling if they are running on a
real or a nested server.
As already mentioned, Xnest is a very user friendly server when it
comes to customization. Xnest will pick up a number of command line
arguments that can configure its default visual class and depth, number
of screens, etc. In the future, Xnest should read a customization
input file to provide even greater freedom and simplicity in selecting
the desired layout. Unfortunately, there is no support for backing
store and save under as of yet, but this should also be considered in
the future development of Xnest.
The only apparent intricacy from the users' perspective about using
Xnest as a server is the selection of fonts. Xnest manages fonts by
loading them locally and then passing the font name to the real server
and asking it to load that font remotely. This approach avoids the
overload of sending the glyph bits across the network for every text
operation, although it is really a bug. The proper implementation of
fonts should be moved into the os layer. The consequence of this
approach is that the user will have to worry about two different font
paths - a local one for the nested server and a remote one for the real
server - since Xnest does not propagate its font path to the real
server. The reason for this is because real and nested servers need
not run on the same file system which makes the two font paths mutually
incompatible. Thus, if there is a font in the local font path of the
nested server, there is no guarantee that this font exists in the
remote font path of the real server. Xlsfonts client, if run on the
nested server will list fonts in the local font path and if run on the
real server will list fonts in the remote font path. Before a font can
be successfully opened by the nested server it has to exist in local
and remote font paths. It is the users' responsibility to make sure
that this is the case.
AUTHOR
Davor Matic, MIT X Consortium
X Version 11 Release 6.6 XNEST(1)
