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Archive-name: postscript-faq/part7-10
Last-modified: 1992/10/29
Version: 2.0

Subject: 7 Programming in PostScript 


Subject: 7.1 What is PostScript level 2? 

    PostScript Level Two is a major upgrade to PostScript Level One. 

    Starting from PostScript Level One as a basis, PostScript Level Two 
    represents the confluence of many features: 



    * Composite fonts -- fonts with the capability of supporting 
      character sets with more than 256 characters. Such fonts are 
      needed in the Asian marketplace, for example. 


    * Patterns -- provide a device-independent way to describe patterns 
      which tile an area. A pattern can be thought of as another kind 
      of ``color'' in PostScript Level Two. 


    * Forms -- to meet the demands of the forms market, forms describe 
      static information which can be repeated many times on one page 
      or printed on many separate pages, or both. 


    * Color -- the previous ill-defined color models are now enhanced 
      with the addition of CMYK color, support for color images, CIE 
      device-independent color (if anybody can understand the damned 
      thing). 


    * Halftones -- new highly accurate halftone screening methods to 
      meet the needs of high end typesetting equipment. 


    * Display PostScript -- many enhancements and efficiency 
      improvements to support the needs of screen rendering. 
      Enhancements include: 



       * efficient rectangle operators, 


       * efficient font and text operators, 


       * multiple contexts 


       * shared memory models 


       * hit detection 

    A detailed description of PostScript 2 is available in the section 
    on PostScript 2. 


Subject: 7.2 Should I learn level 2 PostScript? 

    Yes, because Level Two will soon become the standard. Application 
    developers using PostScript need to become aware of the new 
    capabilities and how to take advantage of them. 

    See the books section for info on what books teach level 2 
    PostScript. 


Subject: 7.3 Where can I find examples of PostScript code? 

    Many other books on PostScript make example PostScript code 
    available. (See the section on books.) 

    All the examples in ``the blue book'' are available from the Adobe 
    file server (See the section on Adobe.) 

    See the question ``How can I browse through PostScript programs?'' 
    in the section on utilities. 


Subject: 7.4 How do I get the physical size of a page? 

    The initial clipping path gives you the size of the imagable area. 
    Use ``clippath pathbbox'' to get these coordinates. If you must 
    know the size of the device's imageable area, use the sequence 
    ``gsave initclip clippath pathbbox grestore'', but this will 
    prevent an enclosing application from using the clippath to achieve 
    some special effects (such as multiple pages per page). 


Subject: 7.5 Why can't I do a pathforall after a charpath ? 

    See the section on fonts, question ``Why are Adobe fonts hidden?''. 


Subject: 7.6 How do I center a string of text around a point? 

    Level 1 PostScript has two operators that can extract information 
    about the metrics of characters: ``stringwidth'' and ``charpath''. 

    The ``stringwidth'' operator returns the advance width of its 
    string operand. This is the distance the current point would be 
    moved by a ``show'' operation on the same string. ``stringwidth'' 
    returns two numbers on the stack, representing the x and y 
    components of the advance width. Usually the y component is zero 
    because most fonts are displayed along a horizontal line, moving 
    the current point only in the x direction. 

    Also note that the ``stringwidth'' operator includes any side 
    bearings in its result. It usually does not give an exact measure 
    of the area of the page that will be touched by its operand. 

    If all that an application requires is horizontal centering of a 
    long string of text, the result returned by ``stringwidth'' is 
    sufficient. A common technique is 


        x y moveto
        (string) dup stringwidth pop 2 div neg 0 rmoveto show

    (This code makes the assumption that the y component of advance 
    width is irrelevant.) 

    The ``charpath'' operator extracts the graphic shapes of its string 
    operand and appends them to the current path in the graphic state. 
    These shapes can then be processed by other PostScript operators. 
    To get the actual size of the area touched by a character a simple 
    approach is 


        gsave
        newpath
        0 0 moveto
        (X) true charpath flattenpath pathbbox
        grestore

    This code places four numbers on the stack, representing the 
    coordinates of the lower left and upper right corners of the 
    bounding box enclosing the character ``X'' rendered with the 
    current point at (0,0). 

    There are two things to be careful about when using the code shown 
    above: 



   1. There are severe limits on the size of the string operand, 
      related to the limit on the number of elements in a graphic path. 
      The PostScript Language Reference Manual recommends taking 
      ``charpath''s one character at a time. 


   2. If user space is rotated or skewed with respect to device space, 
      the result from ``pathbbox'' may be larger than expected; 
      ``pathbbox'' returns a rectangle oriented along the user space 
      coordinate axes, which fully encloses a (possibly smaller) 
      rectangle oriented along the coordinate axes of device space. If 
      user space is rotated at an integer multiple of 90 degrees these 
      two rectangles will be the same, otherwise the rectangle in user 
      space will be larger. 

    So, to center text vertically one must get the bounding boxes of 
    all the characters in the string to be displayed, find the minimum 
    and maximum y coordinate values, and use half the distance between 
    them to displace the text vertically. 

    If an application does this repeatedly, it would be wise to store 
    the bounding boxes in an array indexed by character code, since 
    ``charpath'' is a slow operation. 

    Font metric information is available outside of a PostScript 
    printer in font metrics files, available from Adobe. A program 
    generating PostScript output can obtain metrics from these files 
    rather than extracting the metrics in the printer. 


Subject: 7.7 How can I concatenate two strings together? 


%% string1 string2 append string
% Function: Concatenates two strings together.
/append {
         2 copy length exch length add  % find the length of the new.
         string dup     % string1 string2 string string
         4 2 roll       % string string string1 string2
         2 index 0 3 index
         % string string string1 string2 string 0 string1
         putinterval    % stuff the first string in.
         % string string string1 string2
         exch length exch putinterval
} bind def


Subject: 8 Computer-specific PostScript 

    This section describes PostScript information specific to a 
    particular type of computer or operating system. 


Subject: 8.1 Sun Workstations 

    What is Open Look? 

    Open Look is Sun Microsystems ``Look and Feel'' Graphical User 
    Interface. Open Look is the user-visible part of Open Windows. 
    There is a lot of competition in industry over graphical user 
    interface (GUI) systems. Some of the players are Sun with OpenLook 
    and the Open Software Foundation (OSF) with MOTIF. 

    What is Open Windows? 

    Open Windows is Sun Microsystems window system for the Sun 
    Workstation. Open Windows is based on the X/NeWS window server(s) 
    and includes many tools and utilities. Don't confuse 
    OpenWindows/OpenLook with Open Desktop from Santa Cruz Operation. 
    Open Windows is the underpinnings of OpenLook. 

    What is NeWS? 

    NeWS is Sun Microsystems PostScript-based window system for the Sun 
    Workstation. NeWS was a project within Sun (started around 1985) to 
    create a window system to supplant SunView (a very successful 
    kernel-based window system). NeWS is a client-server model window 
    system (like X) but among many of NeWS novel features was the use 
    of PostScript as the language to describe the appearance of objects 
    on the screen. Because there are few ways to design a knee joint, 
    NeWS has many features in common with Display PostScript, but NeWS 
    predates Adobe Display PostScript and was neither connected with 
    Adobe Display PostScript nor endorsed by Adobe. NeWS is not an 
    Adobe product, nor is it a Sun/Adobe joint venture. 

    NeWS had the potential to become a world-class window system had 
    not a coalition of computer vendors ganged together to endorse the 
    X window system from MIT, sending Sun into a frenzy to support both 
    X and NeWS in the same window server. 

    One respected engineer from DEC remarked they all feared Sun would 
    ignore the industry X coalition and go on to make NeWS a standard. 
    They were overjoyed when Sun reacted by taking on X and merging it 
    with NeWS, causing additional work which made it harder for Sun to 
    make progress with NeWS. Also it made X the de facto standard; 
    whether or not this is a good thing depends on who you talk to. 

    Sun management has signed a deal to adopt Display PostScript. Will 
    they put NeWS aside then? 

    And how does PostScript run on them? 

    PostScript runs (mostly) on NeWS. Due to lack of support from Sun 
    management, NeWS never made it as a fully-compliant PostScript 
    interpreter. There were incompatibilities between the NeWS 
    PostScript interpreter and ``official'' PostScript interpreters as 
    defined by Adobe and the Apple LaserWriter family of printers, such 
    that many PostScript files which would print fine on a LaserWriter 
    would not render under NeWS. The most critical incompatibility was 
    the lack of support for Adobe Type 1 fonts, Sun having gone with 
    their own font format known as F3. Given the NeWS PostScript 
    interpreter was not even PostScript Level One compliant, the 
    chances of bringing NeWS to Level Two compliance was remote, 
    lending further to NeWS decline. 


Subject: 8.2 IBM PC 

    You can find nenscript for OS/2 1.x--2.0 and MSDOS on 
    ftp-os2.nmsu.edu in pub/uploads/nensc113.zip. 


Subject: 8.3 Apple Macintosh 

    For more details about printing with the Macintosh, read the 
    comp.sys.mac.apps FAQ. 

    How can I convert a PostScript file created with a UNIX program to 
    the Mac? 

    A way that is clumsy, but works, is this: 



   1. Display the UNIX-based PostScript file on screen 


   2. Use window dumping facility to get a bitmap file 


   3. Convert the above bitmap file to TIFF format and then export it 
      to Adobe Illustrator on the Mac. 

    The PostScript section of the FAQ for the Macintosh newsgroup 
    comp.sys.mac.app (maintained by Elliotte Harold) answers the 
    following questions: 



    * How do I make a PostScript file? 


    * How do I print a PostScript file? 


    * Why won't my PostScript file print on my mainframe's printer? 

      Full documentation of this process provided with a utility called 
      macps. 


    * Why are my PostScript files so big? 


Subject: 9 Encapsulated PostScript 


Subject: 9.1 What is Encapsulated PostScript? 

    An Encapsulated PostScript file (EPSF) is a standard format for 
    importing and exporting PostScript language files in all 
    environments. It is usually a single page PostScript language 
    program that describes an illustration. The purpose of the EPS file 
    is to be included as an illustration in other PostScript language 
    page descriptions. The EPS file can contain any combination of 
    text, graphics, and images. An EPS file is the same as any other 
    PostScript language page description, with some restrictions. 

    EPS files can optionally contain a bitmapped image preview, so that 
    systems that can't render PostScript directly can at least display 
    a crude representation of what the graphic will look like. There 
    are three preview formats: Mac (PICT), IBM (tiff), and a platform 
    independent preview called EPSI. 

    An EPS file must be a conforming file, that is, it must conform to 
    the Adobe Document Structuring Conventions (DSC). At a minimum, it 
    must include a header comment,%!PS-Adobe-3.0 EPSF-3.0, and a 
    bounding box comment,%%BoundingBox: llx lly urx ury, that 
    describes the bounds of the illustration. 

    (The specification does not require the EPSF version, but many 
    programs will reject a file that does not have it.) 

    The EPS program must not use operators that initialize or 
    permanently change the state of the machine in a manner that cannot 
    be undone by the enclosing application's use of save and restore 
    (eg. the operators starting with ``init'' like initgraphics). As a 
    special case, the EPS program may use the showpage operator. The 
    importing application is responsible for disabling the normal 
    effects of showpage. 

    The EPS program should make no environment-sensitive decisions (the 
    importing application may be trying to attain some special effect, 
    and the EPS program shouldn't screw this up), although it can use 
    some device-dependent tricks to improve appearance such as a 
    snap-to-pixel algorithm. 

    The complete EPS specification is available from Adobe (see the 
    section on Adobe). 

    An optional component of an EPS file is a ``preview'' image of the 
    file's content. The preview image is a bitmapped representation of 
    the image which may be displayed by programs using the EPS file 
    without having to actually interpret the PostScript code. 

    The recommended form for a preview image is ``Interchange'' format 
    and is described fully in the ``red book'', second edition. 
    Interchange format represents the image as a series of hex strings 
    placed in the EPS file as PostScript comments. The entire file 
    remains an ASCII file. 

    A variation of EPS embeds the preview image and PostScript text in 
    a binary file which contains a header and the preview image in 
    either a TIFF or MetaFile format. The header defines where in the 
    file each section (EPS, TIFF, or MetaFile) starts and ends. On the 
    Macintosh, the preview is stored as a PICT in the file's resource 
    fork. 

    What is EPSI? 

    EPSI is EPS. EPSI is an all ASCII (no binary data or headers) 
    version of EPS. EPSI provides for a hexadecimal encoded preview 
    representation of the image that will be displayed or printed. 


Subject: 9.2 How do I convert PostScript to EPS? 

    To convert from PostScript to EPS, one must guarantee that the 
    PostScript file meets the above requirements. If the actual program 
    conforms to the programming requirements, then one can simply add 
    the required comments at the top of the file saying that the file 
    is EPS and giving its BoundingBox dimensions. 

    Optional comments include font usage (%%DocumentFonts: or%% 
    DocumentNeededResources: font), EPSI preview comments (%% 
    Begin(End)Preview:) extensions (%%Extensions:) and language 
    level (%%LanguageLevel:). 

    There are some operators that should not be used within an EPS 
    file: 


        banddevice     cleardictstack   copypage     erasepage
        exitserver     framedevice      grestoreall  initclip
        initgraphics   initmatrix       quit         renderbands
        setglobal      setpagedevice    setshared    startjob

    These also include operators from statusdict and userdict operators 
    like legal, letter, a4, b5, etc. 

    There are some operators that should be carefully used: 

        nulldevice     setgstate        sethalftone  setmatrix
        setscreen      settransfer      undefinefont

    To convert a PostScript file to EPS format, you must edit the file 
    using a text editor or word processor to add lines that will define 
    the file as an EPS-format file. 



   1. Using your normal method of printing, print the PostScript file 
      to a PostScript printer. You can choose to view it on the screen 
      instead, but keep in mind that all the below distance 
      measurements assume that you are printing on a normal-sized piece 
      of paper. 

      NOTE: If the PostScript image does not get displayed properly, it 
      probably will not work either once you have converted it to EPS 
      format. Correct the PostScript program so that it works before 
      you convert it to EPS format. 


   2. Use a tool (see below) to find the bounding box, which shows how 
      much space the PostScript image occupies when printed. You 
      specify the dimensions of the bounding box when you convert the 
      PostScript file to EPS format. 


   3. If you don't have a bounding box tool, you can just use a ruler 
      and draw one on your printout. With two horizontal lines and two 
      vertical lines, draw a box around the image that includes the 
      entire image while minimizing white space. 

      This box represents your bounding box. You may want to leave a 
      small amount of white space around the image as a precautionary 
      measure against minor printing problems, such as paper stretching 
      and paper skewing. 


   4. Measure distance ``a'' from the lower-left corner of the image to 
      the left edge of the paper. 


   5. Write the measurement in points. If your ruler does not show 
      points, calculate the total number of points: 1 inch = 72 points, 
      1 cm = 28.3 points, and 1 pica = 12 points. Designate this 
      measurement as ``measurement a.'' 


   6. Measure distance ``b'' from the lower-left corner of the image to 
      the bottom edge of the paper. 

      Designate this measurement in points as ``measurement b.'' 


   7. Measure distance ``c'' from the upper-right corner of the image 
      to the left edge of the paper. 

      Designate this measurement in points as ``measurement c.'' 


   8. Measure distance ``d' from the upper-right corner of the image to 
      the bottom edge of the paper. 

      Designate this measurement in points as ``measurement d.'' 


   9. Using any text editor, open the PostScript file for editing. 

      You'll see several lines of text. These lines are the PostScript 
      description of the image. The lines at the top of the file are 
      the header. 


  10. Add these lines to, or modify existing lines in, the header (the 
      first group of lines in any PostScript file): 


        %!Adobe-2.0 EPSF
        %%Creator: name
        %%CreationDate: date
        %%Title: filename
        %%BoundingBox: a b c d

      Note: Make sure that the first line in the file is `` Also, do 
      not separate the header lines with a blank line space. The first 
      blank line that PostScript encounters tells it that the the next 
      line begins the body of the program. 

      For ``name,'' type your name or initials. For ``date,'' type 
      today's date using any format (for example, MM-DD-YY, MM/DD/YY, 
      July 5, 1987, and so on). For ``filename,'' type the name of the 
      PostScript file. After ``BoundingBox: ,'' type the measurements 
      you took in steps 3, 4, 5, and 6, separating each with a space: 
      ``a'' is the measurement from Step 3, ``b'' is the measurement 
      from Step 4, ``c'' is the measurement from Step 5, and ``d'' is 
      the measurement from Step 6. 


  11. Save the file in text-only format. 

    If you are interested in learning how to further edit your 
    PostScript files, these books are available at most bookstores: 

    Understanding PostScript Programming and the green book. 

    Encapsulated PostScript is discussed in Appendix C of the old red 
    book. The new red book has a lot of information about Encapsulated 
    PostScript. 

    There will be a technical note available from Adobe called 
    'Guidelines for Specific Operators' that will talk about why some 
    operators are prohibited and how to use the others. 


Subject: 9.3 How do I get the bounding box of a PostScript picture? 

    Use bbfig or epsinfo.ps. 

    Or if you would rather construct the bounding box by hand, use 
    Ghostview, which has a continuous readout of the mouse cursor in 
    the default user coordinate system. You simply place the mouse in 
    the corners of the figure and read off the coordinates. 

Subject: 10 About The Comp.Lang.PostScript FAQ (and Usenet Guide to 
    PostScript) 


Subject: 10.1 The PostScript FAQ: What is it? 

    The PostScript FAQ is a set of answers to frequently asked 
    questions (FAQs) that have appeared on the Usenet newsgroup 
    comp.lang.postscript. It is broken into many useful sections. 

    The Usenet Guide to PostScript is a larger set of help and answers 
    to PostScript questions, plus a tutorial for new users. It is still 
    in the process of being created. There is one file ``Exactly What 
    Does a Transformation Matrix Do?'', that is definitely not part of 
    the FAQ. Please send more! 

    I need help writing and revising answers for common questions 
    relating to PostScript. Almost all of the information in the 
    documents has been written by kind volunteers. The answers will be 
    published in either or both documents. A very long answer in the 
    Usenet Guide may be summarized, referred to briefly, or not 
    mentioned at all in the FAQ. 


Subject: 10.2 How to get the FAQ files 

    The FAQ is available by anonymous ftp to 
    wilma.cs.brown.edu:pub/comp.lang.postscript/ You can get it 
    formatted in plain text ASCII, LaTeX, or PostScript. 

    I would be happy to email a copy of the FAQ in any format to you if 
    you do not have FTP. 


Subject: 10.3 How to write a FAQ answer 

    I greatly appreciate your time and effort to help improve the 
    quality of the FAQ. Thank you for being willing to contribute! 


    * Please check to see if the topic is already in an FAQ. Perhaps 
      you really mean to submit a revision to an existing section. 

    * Start with a clear statement about what problem you are solving. 

    * Write for novice users, in ``tutorial format'', even if the 
      answer is meant for experienced programmers. 

    * Be specific when you make references. 

    * Be complete, and take the time to look over your draft and 
      revise. 

    * Answers should not be too wordy, unless you intend to write a 
      long answer for the Usenet Guide and have a shorter summary or a 
      pointer to the description placed in the FAQ. If you want to 
      write the summary yourself, thanks! 

    * Obviously, I cannot accept copyrighted material without 
      permission. Don't write the FAQ by paraphrasing from a 
      copyrighted book! 


Subject: 10.4 The FAQ can contain LaTeX and PostScript inserts 

    The FAQ is actually written with LaTeX, so feel free to submit with 
    that text formatting language. There is a PostScript version of the 
    FAQ also, so feel free to send along PostScript pictures to 
    include. 


Subject: 10.5 Revising the FAQ 

    Suggestions and comments are welcomed. My favorite way of receiving 
    a change suggestion is if you make a copy of the FAQ, edit the 
    copy, and mail me the modification, or a context diff (include the 
    version number). 


Subject: 10.6 How to submit new information 

    If you know something that you think is worthwhile to be put in a 
    FAQ, definitely send it to me! 

    Don't hold back if your information is very specific. If there's 
    too much information to post I will archive it at an ftp site and 
    place a pointer to it in the FAQ. 


Subject: 10.7 How to add a program description to the FAQ index 

    If the program is original, please send it to me, or tell me where 
    I can get it. Please put your name and email address at the top of 
    each file. Your program will be doubly useful if you clean up the 
    program so that other people can use it as an example to learn. 

    If the program was written by someone else, please send me just the 
    title, description, and where to get it. I may already have it. 

    For programs the FAQ needs to know: 


    * What is the name of the program? 

    * What does it claim to do, and does it do it well? Is it worth 
      using? 

    * Where is it available? What ftp sites can I get it from? 

    * How much does it cost? Is it free? 

    * What kinds of computers does it run on? 

    * Who is the author and does the author give an email address? 

    * Does it handle PostScript 2? 

    If the program is a PostScript interpreter, then the FAQ also needs 
    to know: 


    * Does it let you go backwards one page? 

    * Does it display the number of pages in the document? 

    * Does it let you print PostScript to a non-PostScript printer? 

    * What formats can it convert to? 


Subject: 10.8 How to add a book description to the FAQ 

    For books the FAQ needs to know: 


    * What is the name of the book or document? 

    * What does it claim to do, and does it do it well? Is it worth 
      using? 

    * Can I get it on-line? 

    * Who wrote it? Does the author give an email address? 

    * Who is the publisher, and what is the copyright date? 

    * Does the publisher list an address and phone number or fax 
      number? 

    * What is the ISBN number of the book? 

    * What is the library call number of the book? 

    * How much does the book cost? 

    * Does it cover PostScript 2? 

    * Are coding examples from the book available by email or anonymous 
      ftp? 

    * Do the authors sell the coding examples on a diskette? 


Subject: 10.9 Questions that need answers 



   1. Where are ftp sites that have PostScript freeware? 


   2. What vendors sell fonts for PostScript printers? Where are the 
      free ftp sites for them? 


   3. Are there any free encapsulated PostScript converters? 


   4. What is the charter for comp.lang.postscript? 


   5. How do I make a downloaded font (ie: PFA) persistent? 


   6. What questions should the FAQ have? 


   7. What book information is wrong or missing in the FAQ? 


   8. What program information is wrong or missing in the FAQ? 


   9. What ftp site have good examples of PostScript code?