Tribblix: manual page: Xprint.5

Xprint(5) File Formats and Configurations Xprint(5)

NAME

Xprint - The "X print service" - a portable, network-transparent
printing system based on the X11 protocol

SYNOPSIS

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 it's needs and print on it like
on any other X device reusing parts of the code which is used for the
video card Xserver.

OVERVIEW

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:

+o Xp Extension for the X-Server (included in the X-Server Xprt)

+o Xp Extension API for the client side (libXp/libXprintUtils)

+o PCL ddx driver that converts core X to native PCL

+o PDF ddx driver that converts core X to native PDF

+o PostScript ddx driver that converts core X to native PostScript

+o 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.

HOW THE X PRINT SERVICE WORKS

The X Print Service expands on the traditional X-Server and Xlib
world in four ways.

1. 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.

2. 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).

3. 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).

4. 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.

USAGE

There are three tasks to start the X Print Service:

1. configuring the X Print Server,

2. starting the X Print Service

3. configuring the user session so that clients can find the running
X Print Service

The tasks are described in detail below.

SERVER CONFIGURATION

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(1)
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 model's 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(1) manual page.

STARTING UP

The summary checklist for starting the X Print Service is as follows:

1. 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.

2. 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.

3. Configure the X Print Server. See ``X Print Server
Configuration''.

4. 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:

+o 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.

+o 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.

+o how many users can demand services from a given X Print Service.

With the above in mind, some obvious execution models include:

+o 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).

+o 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).

+o 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):

1.

[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'.

2.

[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.

CLIENT CONFIGURATION

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.

+o "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'.

+o ${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.

END-USER SEQUENCE
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>.

ENVIRONMENT

${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).

AUTHORS

This manual page was written by Roland Mainz
<roland.mainz@nrubsig.org> based on the original X11R6.6
xc/programs/Xserver/XpConfig/README.

8 October 2004 Xprint(5)