XNEST(1)
NAME
Xnest - a nested X server
SYNOPSIS
Xnest [-options]
DESCRIPTION
Xnest 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.
OPTIONS
Xnest supports all standard options of the sample server
implementation. 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 regener-
ates. 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 follow-
ing six values: StaticGray, GrayScale, StaticColor,
PseudoColor, TrueColor, or DirectColor. If both,
-class and -cc options are specified, the last
instance of either option assumes precedence. 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 window.
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 ini-
tialization. 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 specified 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 window. 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 -dis-
play :1.1 will open an xterm client in the nested
server with the display number :1 on the second
screen. The number of screens is limited by the hard
coded constant in the server sample code which is usu-
ally 3.
-install
This option tells Xnest to do its own colormap instal-
lation by bypassing the real window manager. For it
to work properly the user will probably have to tem-
porarily quit the real window manager. By default
Xnest will keep the nested client window whose col-
ormap should be installed in the real server in the
WM_COLORMAP_WINDOWS property of the top level Xnest
window. If this colormap is of the same visual type
as the root window of the nested server, Xnest will
associate this colormap with the top level Xnest win-
dow as well. Since this does not have to be the case,
window managers should look primarily at the WM_COL-
ORMAP_WINDOWS property rather than the colormap asso-
ciated with the top level Xnest window. Unfortu-
nately, 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 xnestplugin.
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 running
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 workstation 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 command 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 CLIENT
Xnest 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 assump-
tion 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 win-
dows' colors will not be displayed properly while the key-
board or pointer focus is in the Xnest window, unless the
real server has support for more than one installed col-
ormap 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_COL-
ORMAP_WINDOWS property of the top level Xnest window on
the real server. Thus, it is important that the real win-
dow manager that manages the Xnest top level window looks
at the WM_COLORMAP_WINDOWS property rather than the col-
ormap associated with the top level Xnest window. Since
most window managers appear to not implement this conven-
tion 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 controls 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 imposing its own. This is a future
consideration.
XNEST AS A SERVER
Xnest 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 num-
ber 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 pass-
ing 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 imple-
mentation 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.
BUGS
Won't run well on servers supporting different visual
depths. Still crashes randomly. Probably has some memory
leaks.
AUTHOR
Davor Matic, MIT X Consortium