XFree86 and DPS <author>Juliusz Chroboczek, <email/jch@xfree86.org/ <date>27 February 2001</date> <ident>$XFree86: xc/programs/Xserver/hw/xfree86/doc/sgml/dps.sgml,v 1.2 2003/01/20 03:43:07 dawes Exp $</ident> <toc> <sect>Introduction Display Postscript (or DPS for short) is a rendering extension for X11. DPS is slightly atypical in that it is based on <it/code mobility/, the ability to send executable code from client to server. Thus, a DPS client does not request that a line should be rendered; instead, it uploads code to the server which, when executed, causes a line to be drawn. This document does not aim at teaching programming with DPS; it is only a summary description of the DPS support code included with XFree86. More information about DPS, including a DPS bibliography, is available from <url url="http://dps.sourceforge.net" name="the DPS extension site">. <tscreen> <it>Note: Adobe, PostScript and Display PostScript are trademarks of Adobe Systems Incorporated which may be registered in certain jurisdictions.</it> </tscreen> As all X11 extensions, DPS consists of client-side and server-side components. The DPS client side consists of a number of libraries and a number of tools for programming and configuration. The DPS server side may consist either of an X server extension, or of a client-side process known as the ``DPS agent.'' In this latter case, the term ``server-side'' is somewhat misleading. At the time of writing, only the client side is included with XFree86; the server side must be obtained separately. Please see <ref id="sec:server-side" name="server side"> later in this document for more information. <sect>The DPS client side The DPS client side consists of four libraries and a number of basic tools for programming and configuration; these are all included with XFree86. <sect1>Libraries The <tt/libpsres/ library is a library for management of <it/PostScript resources/, on-disk files representing PostScript data structures such as fonts, font encodings, procsets, <it/etc./ It is closely related to the <tt/makepsres/ tool (see <ref id="sec:tools" name="client-side tools"> later in this document). The basic DPS client library is <tt/libdps/. This library contains a number of functions for connection establishment, resource management, as well as stubs for all standard PostScript operators. Normally, all DPS clients should link with <tt/libdps/; in addition, <tt/libdps/ may be used for printing by non-DPS clients (this is done, for example, by Sun's JDK). This library is documented in [CLRM] and [CLSX]. The <tt/libdpstk/ library contains a number of additional utilities for managing DPS contexts, user paths and user objects, and for previewing EPS files. It is documented in [DPTX]. The <tt/libdpstkXm/ library contains four Motif widgets. The <it/DPS Scrolling Widget/ is a DPS drawing area that automatically manages issues such as scrolling, scaling, client-side backing store, incremental redisplay, <it/etc./ The <it/Font Selection Box/, and its associated <it/Font Preview/, present a convenient and powerful interface for choosing scalable fonts. Finally, the <it/Color Picker/ presents an interface for choosing colours using either of the RGB or HSV spaces. The latter three widgets are documented in [DPTX]; some summary Scrolling Widget documentation is available in the <tt/doc/ subdirectory of the <tt/DPS.tar.gz/ file, available from <url url="ftp://dps.sourceforge.net/pub/dps/DPS.tar.gz">. The source code for <tt/libdpstkXm/ is included with XFree86; however, as it depends on Motif, this library is not built by default. A GTK-based library providing some of the functionality of <tt/libdpstkXm/ is available from <url url="http://www.gyve.org/gtkDPS/" name="the gtkDPS site">. <sect2>Libdps and Xt In X11R5, <tt/libdps/ did not depend on <tt/libXt/. In X11R6, however, code was added to make the Xt main loop dispatch to sundry code on DPS events; with this addition, all programs that link with <tt/libdps/ need to link with <tt/libXt/, whether they use Xt or not. This state of affairs is unfortunately true of the version of <tt/libdps/ included with XFree86. We are currently considering various solutions to this problem (including the use of weak linker symbols or splitting off the guilty functions into a separate library). <sect1>Client-side tools <label id="sec:tools"> In addition to the libraries, the client side of DPS consists of two utilities. The <tt/makepsres/ utility is used for managing PostScript resources. Its basic operation consists in walking recursively a filesystem tree, noting all resources, and then writing out a ``Unix PostScript Resources,'' file, basically a directory of all the resources found. This utility is documented in the <htmlurl name="makepsres(1)" url="makepsres.1.html"> manual page. The <tt/pswrap/ utility is a stub generator for PostScript clients. Roughly speaking, it takes as its input textual PostScript code, and generates a collection of C functions that transmit that code in pre-tokenised form to the DPS extension. <tt/Pswrap/ is documented in [PSWRAP]. <sect1>Sample clients XFree86 contains three sample DPS clients, <tt/dpsinfo/, <tt/dpsexec/ and <tt/texteroids/. They are documented in their respective manual pages. A number of sample clients that depend on Motif are available in <url url="ftp://dps.sourceforge.net/pub/ftp/DPS.tar.gz">. Additional sample clients can be found as part of GtkDPS (see above). The GNUstep environment can be compiled to use DPS for all rendering; for more information, please see <url url="http://www.gnustep.org" name="the GNUstep site">. <sect>The DPS server side <label id="sec:server-side"> In order to use DPS clients, you need to install a DPS server side, which can be either a server extension (a ``DPS/X extension''), or a separate process (referred to, variously, either as a ``DPS/NX agent'' or, rather confusingly, as ``Client-Side DPS'' (CSDPS). <sect1>Display Ghostscript Display Ghostscript (note the capitalisation), or DGS, is a client-side implementation of DPS based on the Ghostscript PostScript interpreter. DGS is still in beta at the time of writing; it does, however, provide a very usable implementation of DPS, although it still has some problems with the semantics of multiple DPS contexts. DGS is available from <url url="http://www.gnustep.org/resources/sources.html" name="the GNUstep download area">. <sect1>The DPS extension The DPS extension is a much younger project aiming at producing an efficient server-side implementation of DPS. The extension is currently in a state best described as alpha; current versions are known to crash the X server under some circumstances. The DPS extension is available from <url url="http://dps.sourceforge.net" name="the DPS extension site">. <sect>References Links to electronic versions of all of these, and more, are available from <url url="http://dps.sourceforge.net" name="the DPS extension site">. [PLRM2] PostScript language reference manual. Adobe Systems, 2nd ed. Addison-Wesley, 1990. ISBN 0-201-18127-4. [PLRM] PostScript language reference. Adobe Systems Incorporated, 3rd ed. Addison-Wesley, 1999. ISBN 0-201-37922-8. [INTRO] Display PostScript System. Introduction: Perspective for Software Developers. 15 April 1993. [CLRM] Display PostScript System. Client Library Reference Manual. 15 April 1993. [CLSX] Display PostScript System. Client Library Supplement for X. 15 April 1993. [DPTX] Display PostScript System. Display PostScript Toolkit for X. 15 April 1993. [PSWRAP] Display PostScript System. pswrap Reference Manual. 15 April 1993. </article>