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Xprint
- The "X print service" - a portable, network-transparent printing system
based on the X11 protocol
Xprint is a very flexible, extensible,
scaleable, client/server print system based on ISO 10175 (and some other
specs) and the X11 rendering protocol.
Using Xprint an application can search, query
and use devices like printers, FAX machines or create documents
in formats like PDF. In particular, an application can seek a
printer, query supported attributes (like paper size, trays, fonts
etc.), configure the printer device to match its needs and print on
it like on any other X device reusing parts of the code which is used
for the video card Xserver.
The "X Print Service" technology
allows X rendering to devices such as printers and fax. Most of the service
is available in the X11 technology stack as Xp, with the remainder in single
toolkit stacks (e.g. DtPrint for CDE). Modifications have also been made to
the LessTif/Motif/Qt technology stacks to support Xprint.
The Xp portion
consists of:
- Xp Extension for the X-Server (included in the X-Server Xprt)
- Xp Extension API for the client side (libXp/libXprintUtils)
- PCL ddx driver
that converts core X to native PCL
- PDF ddx driver that converts core X
to native PDF
- PostScript ddx driver that converts core X to native PostScript
- Raster ddx driver that generates xwd rasters which can be converted to
PCL, PDF or PostScript rasters
From an X clients perspective, it can attach
to one of two nearly identical X-Servers, a "Video" X-Server, and a "Print"
X-Server which has the additional Xp capability but otherwise looks and
behaves the same.
The X Print Service expands
on the traditional X-Server and Xlib world in four ways.
- Most obvious is
the use of "print ddx drivers" instead of
- "video ddx drivers". While a
video ddx driver modifies pixels in a video frame buffer, a print ddx driver
generates "page description language (PDL)" output (such as PCL, PDF or
PostScript) or sends the print rendering instructions to a platform-specific
print API (like Win32/GDI).
Once a print ddx driver generates PDL output,
it can be sent to a spooler such as lp(1)
or retrieved by the client (to
implement functionality like "print-to-file").
Though not currently done,
a single X-Server can support both print and video ddx drivers.
- Since printers
support "paged" output, unlike video, a portion
- of the Xp Extension supports
APIs to delineate printed output. For example, XpStartPage and XpEndPage
tell the X-Server where a physical page starts and ends in an otherwise
continuous stream of X rendering primitives. Likewise, XpStartJob and XpEndJob
determine when a collection of pages starts and ends. XpEndJob typically
causes the generated PDL to be submitted to a spooler, such as lp(1)
.
- Since
printers have extensive capabilities, another portion of
- the Xp Extension
supports APIs to manipulate "print contexts".
Once a printer is selected
using the Xp Extension API, a print context to represent it can be created.
A print context embodies the printer selected - it contains the printer's
default capabilities, selectable range of capabilities, printer state,
and generated output. Some "attributes" within the print context can be
modified by the user, and the X-Server and print ddx driver will react accordingly.
For example, the attribute "content-orientation" can be set to "landscape"
or "portrait" (if the printer supports these values - which can be queried
using the Xprint API as well).
- Since printers can have "built in" fonts,
the Xp Extension in
- the X-Server works with the print ddx drivers to make
available (for printing only) additional fonts on a per print context basis.
When a print context is created and set for a given printer, the X font
calls may be able to access additional printer fonts. To do this (typically),
the X-Server must have access to "printer metric files" (.pmf) that describe
at minimum the metrics of the built in fonts.
There are three tasks
to start the X Print Service:
- configuring the X Print Server,
- starting
the X Print Service
- configuring the user session so that clients can find
the running X Print Service
The tasks are described in detail below.
The X Print Server (Xprt) can read a number of configuration
files which control its behavior and support for printers. Each vendor
platform has a default location for this information. Xprt can also read
the environment variable XPCONFIGDIR to locate alternate configuration
directories. Common settings include:
export XPCONFIGDIR=/X11/lib/X11/XpConfig/
export XPCONFIGDIR=/proj/x11/xc/programs/Xserver/XpConfig/
Xprt has many
built-in defaults, and lacking any configuration files, will immediately
try to support all printers visible via lpstat(1)
.
In order of importance
for configuration by a system administrator, the configuration files for
a "C" locale are as follows (see Xprt(__mansuffix__) for more details (including
support for non-"C" locales)):
- ${XPCONFIGDIR}/C/print/Xprinters
- 'Xprinters'
is the top most configuration file. It tells Xprt which specific printer
names (e.g. mylaser) should be supported, and whether lpstat(1)
or other
commands should be used to automatically supplement the list of printers.
- ${XPCONFIGDIR}/C/print/attributes/printer
- The 'printer' file maps printer
names to model configurations (see 'model-config' below). For example, "mylaser"
could be mapped to a "HPDJ1600C", and all other arbitrary printers could
be mapped to a default, such as "HPLJ4SI". When depending on lpstat(1)
in the Xprinters file, setting up defaults in 'printer' becomes all the more
important.
- ${XPCONFIGDIR}/C/print/attributes/document
- The 'document' file
specifies the initial document values for any print jobs. For example,
which paper tray to use, what default resolution, etc.
- ${XPCONFIGDIR}/C/print/attributes/job
- The 'job' file specifies the initial job values for any print jobs. For example,
"notification-profile" can be set so that when a print job is successfully
sent to a printer, e-mail is sent to the user.
- ${XPCONFIGDIR}/C/print/models/PSdefault/model-config
- ${XPCONFIGDIR}/C/print/models/PSdefault/fonts/fonts.dir
- ${XPCONFIGDIR}/C/print/models/PSdefault/fonts/9nb00051.pmf
- ${XPCONFIGDIR}/C/print/models/PSdefault/fonts/9nb00093.pmf
- The 'model-config'
file has attributes that describe the printer models capabilities and default
settings. Printer model fonts may also be present. The model-config file
also identifies the print ddx driver to be used. For each printer model
supported, a complete hierarchy of files should exist. In most cases, these
files do not need to be modified.
- ${XPCONFIGDIR}/C/print/ddx-config/raster/pcl
- ${XPCONFIGDIR}/C/print/ddx-config/raster/pdf
- ${XPCONFIGDIR}/C/print/ddx-config/raster/postscript
- The print ddx drivers can have highly specific configuration files to control
their behavior. In most cases, these files do not need to be modified. More
information in how to configure and customize the X print server can be
found in the Xprt(__mansuffix__) manual page.
The summary checklist
for starting the X Print Service is as follows:
- Choose an execution model
for the X Print Service. The X
- Print Service can be run on a per-user session
basis, per machine basis, or can be run on a few machines globally available
to a number of users.
- If print jobs are to be submitted to a spooler (almost
always
- the case), make sure all needed printers are available to the spooler
subsystem (most often lp(1)
) on the same machine running the X Print Service.
- Configure the X Print Server. See ``X Print Server
- Configuration''.
- Depending
on #1, start the X Print Server process "Xprt", and
- then the toolkit-specific
Print Dialog Manager Daemon process (such as CDEnext's "dtpdmd") at the
appropriate times. Note that libXprintUtils-based applications/toolkits do
not need a Print Dialog Manager Daemon process to use Xprint. The details
are described below.
Because the X Print Service is based on X, it can be
easily distributed. The most significant factors in which execution model
to choose will be driven by:
- how many printers will be accessable through
the printer subsystem on any given machine. A system administrator may
choose to cluster printers on a few given machines, or scatter them across
an organization and possibly make extensive use of remote spoolers to make
them globally available.
- how many machines will need a copy of the X Print
Server configuration files. The files have been architected so that one
super-set version of them can be maintained and distributed (e.g. via NFS),
and a per-machine or per-user version of the `Xprinters' is all that is needed
to have the appropriate information in them utilized or ignored.
- how many
users can demand services from a given X Print Service. With the above in
mind, some obvious execution models include:
- Global - in this model, the
system administrator is choosing to run the X Print Service on a *few*
select machines with appropriate printers configured, and allow clients
access to the global resource. This can centralize the administration of
printers and configuration files, but may have to be monitored for performance
loading.
Startup would likely be done by boot-up scripts (such as /etc/init.d/xprint).
- Per-machine - every machine with potential X Print Service users would run
the service. Printer and configuration file administration is decentralized,
and usage would be limited to the users on the machine.
Startup would likely
be done by boot-up scripts (such as /etc/init.d/xprint).
- Per-user session -
every user would run an entire X Print Service for themselves. In the future,
the Video X Server normally started may contain Print X Server capability,
so this model becomes very natural.
Startup would likely be done at session
login or by launching actions or processes manually once the user logs
in. Note: Deamons like "dtpdmd" must be started after Xprt.
Starting of
the processes is straight forward. In strict order (example is for manually
starting the X print server for CDEnext usage):
- [machineA] % Xprt [-XpFile Xprinters file] [:dispNum]
- Note that Xprt will
look for configuration files in either a default location or where XPCONFIGDIR
points.
-XpFile specifies an alternate `Xprinters' file, rather than the default
one or `${XPCONFIGDIR}/C/print/Xprinters'.
- [machineA] % dtpdmd -d machineA[:dispNum] [-l /tmp/dtpdmd.log]
- The dtpdmd
will maintain an X-Selection on the X-Server, and will start dtpdm's as required
to service requests.
In all but the per-user session model, the machine running
the dtpdmd (thus dtpdm's) will need display authorization to the users video
display.
Once a X Print Server and dtpdmd have been
started -- many of them in some cases -- clients will need to find and use
them. There are two mechanisms that allow clients to discover X Print Servers
and printers.
- "X Print Specifier" - assuming usage of the DtPrint/XprintUtils-based
print applications, the following notation is understood:
printer_name@machine[:dispNum]
For example:
colorlj7@printhub:2
In the above example, the X Print Server running at `printhub:2' is assumed
to support the printer named `colorlj7'.
- ${XPSERVERLIST} - assuming usage of
the DtPrint print dialogs, the environment variable ${XPSERVERLIST} can
contain a list of X Print Servers. For example:
XPSERVERLIST="printhub:2 printhub:3 otherdept:0"
Then in the dialogs, only a printer name needs to be entered. The dialog
will then search the X Print Servers in ${XPSERVERLIST} for a server than
supports the printer, and then establish contact.
From most
CDEnext applications, printing is accomplished by bringing down the File
menu and selecting Print.... This will result in the DtPrintSetupBox dialog,
which will request the name of a printer, and offer limited capability
to configure print options (e.g. number of copies). If the user wishes, they
can select Setup..., which will start a dtpdm capable of modifying additional
print options. Finally, the user should select Print.
- ${XPCONFIGDIR}
- This environment variable points to the root of the Xprint server configuration
directory hierarchy. If the variable is not defined, the default path
is be assumed. The default path may be /usr/X11R6/lib/X11/xserver/, /usr/lib/X11/xserver/,
/usr/share/Xprint/xserver/ or /usr/openwin/server/etc/XpConfig, depending
on the system, and may be configured in /etc/init.d/xprint.
- ${LANG}
- This
environment variable selects the locale settings used by the Xprint server.
Xprt allows language-specific settings (stored in ${XPCONFIGDIR}/${LANG}/print/)
which will override the default settings (stored in ${XPCONFIGDIR}/C/print/).
If ${LANG} is not set "C" is assumed.
- ${XPSERVERLIST}
- The environment variable
${XPSERVERLIST} contains a list of display identifiers (separated by whitespace)
which tell an application where it can find the Xprint servers. Usually
${XPSERVERLIST} is set by the profile startup scripts (e.g. /etc/profile
or /etc/profile.d/xprint.sh) using the output of /etc/init.d/xprint get_xpserverlist.
Example:
export XPSERVERLIST="`/etc/init.d/xprint get_xpserverlist`"
Alternatively ${XPSERVERLIST} can be set manually. Example:
export XPSERVERLIST="littlecat:80 bitdog:72"
instructs an application to find an Xprint server at display 80 on the
machine "littlecat" and at display 72 on the machine bigdog.
- ${XPRINTER}
- The environment variable ${XPRINTER} defines the default printer used
by print applications. The syntax is either printername or printername@display.
Examples:
- XPRINTER=ps003
- tells an application to look for the first printer
named "ps003" on all Xprint servers.
- XPRINTER=hplaser19@littlecat:80
- tells
an application to use the printer "hplaser19" on the Xprint server at display
"littlecat:80".
If ${XPRINTER} is not set the applications will examine
the values of the ${PDPRINTER}, ${LPDEST}, and ${PRINTER} environment
variables (in that order).
X11(7)
, xplsprinters(__mansuffix__),
xprehashprinterlist(__mansuffix__), xphelloworld(__mansuffix__), xpxmhelloworld(__mansuffix__),
xpawhelloworld(__mansuffix__), xpxthelloworld(__mansuffix__), xpsimplehelloworld(__mansuffix__),
Xserver(__mansuffix__), Xprt(__mansuffix__), libXp(3x)
, libXprintUtils(3x)
,
libXprintAppUtils(3x)
, XmPrintShell(3x)
, XawPrintShell(3x)
, Xprint FAQ
(http://xprint.mozdev.org/docs/Xprint_FAQ.html <URL:http://xprint.mozdev.org/docs/Xprint_FAQ.html>),
Xprint main site (http://xprint.mozdev.org/
<URL:http://xprint.mozdev.org/>)
This manual page was written by Roland Mainz <roland.mainz@nrubsig.org>
based on the original X11R6.6 xc/programs/Xserver/XpConfig/README.
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