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NAME
dps - Display PostScript imaging for the X Window System
DESCRIPTION
This manual page provides information about the Display
PostScript system, implemented as an extension to the X Win-
dow System.
The INTRODUCTION section contains a brief, nontechnical
description of the Display PostScript system.
The remaining sections provide the application developer
with more detailed technical information about the archi-
tecture.
The REFERENCES section describes additional documentation
and tells you how to use Adobe's public access file
server.
INTRODUCTION
The PostScript language is a simple interpretive programming
language with powerful graphics capabilities. Its primary
purpose is to describe the appearance of text, graphical
shapes, and images on printed or displayed pages. If an
application, such as a word processing system or graphics
package, produces a page description using the PostScript
language, you can print the pages on a wide variety of
PostScript printers and view them on monitors where the
Display PostScript system is available.
The Display PostScript system is a high-performance imple-
mentation of the PostScript language for interactive com-
puter displays. The use of the Display PostScript system
ensures true WYSIWYG (What You See Is What You Get) between
the display and any PostScript printer.
DISPLAY POSTSCRIPT SYSTEM ARCHITECTURE
The Display PostScript system is part of the X Window System
and is implemented as an X extension. Display PostScript
applications use window system features for window placement
and sizing, menu creation, and event handling, while using
Display PostScript features to take care of imaging inside
the window.
Display PostScript system components include:
The PostScript interpreter.
The Client Library - a C language interface to the basic
facilities of the Display PostScript system.
pswrap - a preprocessor that prepares PostScript language
programs for invocation from a C program.
These components are discussed below.
APPLICATION BUILDING BLOCKS
Most of a Display PostScript application is written in C or
another high-level language. It calls Client Library pro-
cedures to start a PostScript execution context, send pro-
grams and data to the PostScript interpreter, and get
results from the interpreter. The Client Library is the
application's primary interface to the Display PostScript
system.
In addition, it calls wraps - custom PostScript language
procedures developed specifically for the application. Wraps
are generated by the pswrap translator from application-
specific PostScript language code.
USING PSWRAP
pswrap is a preprocessor that takes PostScript language code
as input and embeds it in C-callable procedures, or wraps.
The output of pswrap is compiled and linked with the rest of
your application, which can then call the wraps to transmit
PostScript language code to the PostScript interpreter.
A Display PostScript application uses C or another high-
level language to perform calculations, communicate with the
window system, read and write files, and do other applica-
tion processing. It uses wraps primarily for imaging tasks.
Consider a procedure, PSWDisplayText, that places text on
the screen at a particular x,y coordinate. A call to this
wrap from the application program might look something like
this:
PSWDisplayText(72.0, 100.0, "Hello World");
The body of the PSWDisplayText procedure is actually written
in the PostScript language. It was defined to pswrap as
follows:
defineps PSWDisplayText(float X,Y; char *text)
X Y moveto
(text) show
endps
In the wrap definition, the defineps and endps keywords tell
pswrap where a given PostScript language program begins and
ends. The defineps statement defines the resulting
procedure call. The pswrap translator processes this input
and produces a C language source-code file. When compiled
and linked with the application, the PSWDisplayText pro-
cedure sends a PostScript language program to the inter-
preter (binary-encoded for more efficient processing), caus-
ing "Hello World" to be displayed on the screen.
See the Programming the Display PostScript System with X for
further information.
THE CLIENT LIBRARY
The Display PostScript Client Library is a linkable library
of compiled C procedures that provides an interface between
the application and the Display PostScript system. It
creates an environment for handling imaging calls to
specific Client Library procedures like DPSmoveto and to
custom wraps written for the application.
To the application programmer, it appears that Client
Library procedures directly produce graphical output on the
display. In fact, these procedures generate PostScript
language statements and transmit them to the PostScript
interpreter for execution; the PostScript interpreter then
produces graphical output that is displayed by device-
specific procedures in the Display PostScript system. In
this way, the Client Library makes the full power of the
PostScript interpreter and imaging model available to a C
language program.
The Client Library includes procedures for creating, commun-
icating with, and destroying PostScript execution contexts.
A context consists of all the information (or "state")
needed by the PostScript interpreter to execute a PostScript
language program. In the Client Library interface, each con-
text is represented by a DPSContextRec data structure.
PostScript execution contexts are described in the
PostScript Language Reference Manual, Second Edition.
REFERENCES
Information about the PostScript Language and the Display
PostScript system is available in a number of manuals and
via the public access file server described below.
POSTSCRIPT LANGUAGE MANUALS
If you're new to the PostScript language, you should first
read the following manuals (published by Addison-Wesley and
available from Adobe Systems Incorporated or through your
technical bookstore):
PostScript Language Reference Manual, Second Edition
The standard reference for the PostScript language.
Describes the PostScript imaging model and the concepts
and facilities of the PostScript interpreter. Documents
the PostScript language. Required reading.
PostScript Language Tutorial and Cookbook
Introduction to the PostScript language in an informal,
interactive style. Contains a collection of example pro-
grams that illustrate the PostScript imaging model.
PostScript Language Program Design
Guidelines for the advanced developer to use in designing
and debugging PostScript language programs. Printer-
oriented, but most of the information is relevant to writ-
ing a Display PostScript application.
DISPLAY POSTSCRIPT MANUALS
Once you're up to speed in the PostScript language, read
Programming the Display PostScript System with X, available
from Addison-Wesley. This book is collection of manuals that
explain how to render text and graphics with the Display
PostScript extension to X. It contains the following manu-
als:
Programming Guide
Explains how to render text and graphics with the Display
PostScript extension to X.
Client Library Reference Manual
Describes the procedural interface to the Display
PostScript system. Tells how to send programs and data to
a PostScript execution context, how to handle context out-
put, how to create and terminate a context. Contains pro-
cedure definitions, programming tips, and a sample appli-
cation program.
Client Library Supplement for X
Describes Display PostScript features that are specific to
the X Window System, such as context creation and addi-
tional error codes.
pswrap Reference Manual
Describes how to define C-callable procedures that contain
PostScript language programs. Tells how to declare input
arguments and output to be received from the interpreter.
Documents the pswrap command line options.
Display PostScript Toolkit for X
Describes the Display PostScript Toolkit for the X Window
System. It also contains information about locating
PostScript language resources and about the makepsres
utility.
THE PUBLIC ACCESS FILE SERVER
Adobe Systems Incorporated provides a public access file
server. If you have access to Internet or UUCP electronic
mail, you can use the public access file server to obtain
the following information:
Display PostScript system manuals
Code examples
AFM files
Documentation updates
The public access file server is a mail-response program.
That is, you send it a request by electronic mail and it
mails back a response. (The ``Subject:'' line is treated as
part of the message by the file server.)
To send mail to the file server, use one of the following
addresses:
Internet ps-file-server@adobe.com
UUCP ...!decwrl!adobe!ps-file-server
To receive a quick summary of file server commands, send the
following message:
help
To receive detailed information on how to use the file
server, send the following message:
send Documents long.help
COLORMAP USAGE
The Display PostScript system uses entries from the default
X colormap to display colors and grey values. You can con-
figure this usage. Giving the Display PostScript system
more colormap entries improves the quality of its rendering,
but leaves fewer entries available to other applications
since the default colormap is shared.
Resources in your .Xdefaults file control the colormap
usage. Each resource entry should be of the form
DPSColorCube.visualType.depth.color: size
where
visualType is one of GrayScale, PseudoColor, or
DirectColor.
depth is 1, 2, 4, 8, 12, or 24 and should be the largest
depth equal to or less than the default depth.
color is one of the strings "reds", "greens", "blues", or
"grays".
size is the number of values to allocate of that color.
These resources are not used for the static visual types
StaticGray, StaticColor, or TrueColor. Specifying 0 for
reds directs the Client Library to use only a gray ramp.
This specification is particularly useful for gray-scale
systems that incorrectly have PseudoColor as the default
visual.
For example, to configure a 5x5x4 color cube and a 17-
element gray ramp for an 8-bit PseudoColor screen, specify
these resources:
DPSColorCube.PseudoColor.8.reds: 5
DPSColorCube.PseudoColor.8.greens: 5
DPSColorCube.PseudoColor.8.blues: 4
DPSColorCube.PseudoColor.8.grays: 17
These resources use 117 colormap entries, 100 for the color
cube and 17 for the gray ramp. For the best rendering
results, specify an odd number for the gray ramp.
Resources that are not specified take these default values:
DPSColorCube.GrayScale.4.grays: 9
DPSColorCube.GrayScale.8.grays: 17
DPSColorCube.PseudoColor.4.reds: 2
DPSColorCube.PseudoColor.4.greens: 2
DPSColorCube.PseudoColor.4.blues: 2
DPSColorCube.PseudoColor.4.grays: 2
DPSColorCube.PseudoColor.8.reds: 4
DPSColorCube.PseudoColor.8.greens: 4
DPSColorCube.PseudoColor.8.blues: 4
DPSColorCube.PseudoColor.8.grays: 9
DPSColorCube.PseudoColor.12.reds: 6
DPSColorCube.PseudoColor.12.greens: 6
DPSColorCube.PseudoColor.12.blues: 5
DPSColorCube.PseudoColor.12.grays: 17
DPSColorCube.DirectColor.12.reds: 6
DPSColorCube.DirectColor.12.greens: 6
DPSColorCube.DirectColor.12.blues: 6
DPSColorCube.DirectColor.12.grays: 6
DPSColorCube.DirectColor.24.reds: 7
DPSColorCube.DirectColor.24.greens: 7
DPSColorCube.DirectColor.24.blues: 7
DPSColorCube.DirectColor.24.grays: 7
If none of the above defaults apply to the display, the
Client Library uses no color cube and a 2-element gray ramp;
that is, black and white.
SEE ALSO
pswrap(1), dpsexec(6)
NOTES
Copyright 1988-1992 Adobe Systems Incorporated.
PostScript and Display PostScript are trademarks of Adobe
Systems Incorporated which may be registered in certain jur-
isdictions.
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