X Version 11 (Release 6.1)

Xnest(X1M)

Xnest -- 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 Xsco(X1M) server implementation. The following additional arguments are supported:

-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 Xsco(X1M) 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, 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 the xdpyinfo(X1M) manual page 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(X1M) manual page 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 Xsco 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 Xsco 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 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 -display :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 Xsco server 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 manager. By default Xnest will keep the nested client window whose colormap 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 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 window.

Usage

Starting up Xnest is as simple as starting up xclock(X1) 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. Therefore, 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 displayed 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 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 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.

Notices

This server has not been thoroughly tested and debugged. It:

will not run well on servers supporting different visual depths.
still crashes randomly.
probably has some memory leaks.

References

X(X1M), Xsco(X1M).