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Archive-name: postscript/faq/part7-10
Last-modified: 1993/05/21
Version: 2.1

                              -- PostScript -- 

                            Answers to Questions 

                    (the comp.lang.postscript FAQ v2.1) 

                               Jon Monsarrat 

                              jgm@cs.brown.edu 






                     This FAQ is formatted as a digest. 

                Most news readers can skip from one question 

                     to the next by pressing control-G. 


    Changes since the last version are marked with a '|' in the table 
    of contents and in the sections in the text-only format of the FAQ. 

    Now that there is Linux and BSD 386 UNIX IBM PC (and clone) users 
    can run any of the X-windows and UNIX programs in the utilities 
    section. See comp.os.linux. Also, there is now GhostScript for the 
    Macintosh. 

    Section 12, Utilities, will be posted in comp.sources.postscript 
    along with the global index from now on. 

    Please help fix the FAQ! All comments should be mailed to 
    jgm@cs.brown.edu. My favorite way to receive a change suggestion is 
    when it is accompanied by a section of the FAQ that is edited and 
    mailed to me verbatim as an example. If you would like to 
    contribute, please read the section ``about the FAQ'' first. Thank 
    you! 

    Books and programs are referred to by name only. See the book
    sections for book information, and the comp.sources.postscript FAQ
    for a full list of all PostScript related programs. I have
    archived a number of the small utilities in
    wilma.cs.brown.edu:pub/postscript.  You can get the
    comp.sources.postscript FAQ from
    wilma.cs.brown.edu:pub/comp.sources.postscript.

Subject: 7 Programming in PostScript 


Subject: 7.1 What is PostScript level 2? 

    (See the Section 11, ``About 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. 

    There are many good books on PostScript 2. (See Section 5, 
    ``Books''.) 


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

    Many other books on PostScript make example PostScript code 
    available. ``Thinking in PostScript'', by Glenn Reid, is the only 
    book I know of that allows its examples to be freely distributed. 
    (See Section 5, ``Books''.) 

    All the examples in ``the blue book'' are available from the Adobe 
    file server (See Section 5, ``Books''.) 

    See the question ``How can I browse through PostScript programs?'' 
    in the comp.sources.postscript FAQ. 


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 Section 4, ``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'' usually does not give an exact 
    measure of the area of the page that will be touched by its 
    operand. The letters can either project a little over the 
    boundaries or fall a little within (leaving a touch of whitespace). 

    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) false 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). Leaving the flattenpath out will cause it 
    to be less accurate, but it will take up less memory and be faster. 

    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. This still may not do a very 
    good job, since this provides centering based on extrema, not on 
    the optical center of the string (which is more related to a sort 
    of ``center of mass'' of the text). 

    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 the font vendor. 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: 7.8 What do I do when I get stack overflow/underflow? 

    These errors are among the most common in PostScript. 

    When I get a stack overflow, that is usually a sign that a routine 
    is leaving an object on the stack. If this routine gets called 2000 
    times, it leaves 2000 objects on the stack, which is too many. 

    When I get a stack underflow, that is a sign that either: (A) one 
    of the routines in the program doesn't work, and never has or (B) 
    one of the routines in the program works, but expects to be called 
    with some arguments left on the stack. 

    There is no such thing as a PostScript debugger right now. For now, 
    the best that you can do to debug your program is to put in lots of 
    print statements. Learn to use the PostScript pstack command, and 
    use an online interpreter so you don't have to run to the printer 
    for each debugging cycle. 

    Use an error handler to learn more about what exactly is happening 
    when your program crashes. (see the comp.sources.postscript FAQ for 
    a list of all PostScript related programs.) 

    If your code has never worked yet (i.e. you are still writing it) 
    then I find that it helps to put little comments in the margin 
    about the state of the stack. Like this: 

  
         Heart pathbbox             % lowerx lowery upperx uppery
         exch 4 -1 roll             % lowery uppery upperx lowerx
  
  
    I generally put these comments in originally, and then take them 
    out when the program works. Maybe this is a bad practice, in case I 
    ever want to go back and look at the code to modify it!! 


Subject: 7.9 How can I print in landscape mode? 

|   Landscape (the opposite of portrait) means that the page is turned 
|   on its side. You can redefine showpage in terms of the current 
|   definition of showpage. 
|
|   Do something like: 

  
  /oldshowpage /showpage load def
  
  90 rotate llx neg ury neg translate   % for the first page
  /showpage
  {
          oldshowpage
          90 rotate llx neg ury neg translate
  } def
  
|   This won't work if the PostScript file you're editing uses 
|   initgraphics or grestoreall. 

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 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. 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. 

    As of October 1992, Sun management signed a deal with Adobe to 
    adopt Display PostScript for the Sun. The future of NeWS is still 
    undecided (but it looks bad). 

    And how does PostScript run on them? 

    PostScript runs on NeWS, although NeWS is not 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. 


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. 

    There are rumors that Word Perfect and Microsoft Word don't produce 
    ``clean'' PostScript that follows the DSC conventions (See Section 
    9, ``Encapsulated PostScript''). This means that a lot of 
    PostScript utilities like Ghostview and psnup, etc., that require 
    the DSC conventions, will not work on them. 

    Creating a PostScript file from MS Word 

    Install the LaserWriter driver that comes with Windows.In the 
    printer setup, select a PostScript printer. Then click on the setup 
    button to get that pop-up. Then clik the Options button. Then 
    select the print to Encapsulated PostScript File. If you don't 
    specify a file name, Word will prompt you for one when you tell it 
    to print. 

    When printing Microsoft Windows files that have been captured on a 
    PC's LPT port, you mostly need to define two ctrl-d's in a row as 
    well to remove all of them in the document: 

  
  (\004\004) cvn {} def
  

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? 

o
    * 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? 

    Encapsulated PostScript (EPS) 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). Read Appendix G (Document Structuring 
|   Conventions, V3.0) and Appendix H (Encapsulated PostScript File 
|   Format, V3.0) in the new PostScript red book: PostScript Language 
|   Reference Manual, Second Edition. 

    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. 

    That book contains all of the information that you need to fix your 
    program to correctly output EPS. It is what I use for our software. 

    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. 


Subject: 9.2 What are EPSI and EPSF? 

    EPSI is EPS with a device independent bitmap preview. 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. 

    EPSF is a version of EPS with a TIFF preview instead of a bitmap 
    preview. 


Subject: 9.3 How do I convert PostScript to EPS? 

    Use pstoepsi, or do it by hand. 

    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 ``% 
      !Adobe-2.0 EPSF.'' 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: 9.4 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? 

    * What packages does it rely on? 

    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. What are TrueType fonts? 


   4. Are there any free encapsulated PostScript converters? 


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


   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?