1. Forms

Forms (also called Form XObjects in PDF) are cached graphical objects that can be rendered multiple times efficiently. They provide a powerful optimization technique for repetitive graphics.

1.1. Overview

Forms in PostScript allow you to:

  • Cache complex graphics - Define once, render many times

  • Improve performance - Avoid recalculating paths and transformations

  • Reduce memory - Shared representation of repeated content

  • Create templates - Reusable graphic components

Forms are particularly useful for:

  • Logos and watermarks

  • Repeated design elements

  • Page headers and footers

  • Backgrounds and borders

  • Complex illustrations used multiple times

1.2. Basic Form Concepts

1.2.1. What is a Form?

A form is a self-contained graphic that:

  • Has its own coordinate system

  • Can be transformed independently

  • Is rendered with a single operator

  • Maintains its own resources

% Simple form definition (Level 1 compatible approach)
/MyForm {
  gsave
    % Draw form content
    newpath
    0 0 100 100 rectfill
  grestore
} def

% Use form multiple times
100 100 translate
MyForm

200 200 translate
MyForm

1.2.2. Form as Procedure

The simplest form is a PostScript procedure:

% Define form
/Logo {
  gsave
    % Logo graphics
    newpath
    0 0 moveto
    50 0 lineto
    25 43.3 lineto
    closepath
    1 0 0 setrgbcolor
    fill
  grestore
} def

% Use form
gsave
  72 720 translate  % Top left
  Logo
grestore

gsave
  540 720 translate  % Top right
  Logo
grestore

1.3. Creating Reusable Forms

1.3.1. Parameterized Forms

Forms that accept parameters:

/Badge {  % size color -> -
  2 dict begin
    /color exch def
    /size exch def

    gsave
      color aload pop setrgbcolor

      % Draw badge
      newpath
      0 0 size 0 360 arc
      fill

      % Border
      0 setgray
      1 setlinewidth
      0 0 size 0 360 arc
      stroke

      % Text
      1 setgray
      /Helvetica-Bold findfont size 2 div scalefont setfont
      0 0 moveto
      (!) dup stringwidth pop 2 div neg
      size 4 div neg rmoveto
      show
    grestore
  end
} def

% Usage
gsave
  100 100 translate
  30 [1 0 0] Badge  % Red badge, size 30
grestore

gsave
  200 200 translate
  40 [0 0 1] Badge  % Blue badge, size 40
grestore

1.3.2. Forms with State

Forms that maintain internal state:

/Counter {
  % Create counter form with state
  10 dict begin
    /value 0 def

    /increment {
      /value value 1 add def
    } def

    /reset {
      /value 0 def
    } def

    /draw {
      gsave
        % Draw current value
        /Courier findfont 12 scalefont setfont
        0 0 moveto
        value =string cvs show
      grestore
    } def

    currentdict
  end
} def

% Usage
Counter /counter exch def

gsave
  100 100 translate
  counter /draw get exec
grestore

counter /increment get exec
counter /increment get exec

gsave
  100 80 translate
  counter /draw get exec
grestore

1.4. Form Libraries

1.4.1. Icon Library 

/icons <<
  /checkmark {
    gsave
      0.2 0.8 0.2 setrgbcolor
      2 setlinewidth
      1 setlinecap
      1 setlinejoin

      newpath
      5 10 moveto
      12 3 lineto
      25 20 lineto
      stroke
    grestore
  } bind

  /cross {
    gsave
      0.8 0.2 0.2 setrgbcolor
      2 setlinewidth
      1 setlinecap

      newpath
      5 5 moveto
      25 25 lineto
      stroke

      25 5 moveto
      5 25 lineto
      stroke
    grestore
  } bind

  /star {
    gsave
      1 0.8 0 setrgbcolor

      newpath
      15 25 moveto
      11 11 lineto
      25 7 lineto
      13 3 lineto
      15 -11 lineto
      7 3 lineto
      -5 7 lineto
      9 11 lineto
      5 25 lineto
      closepath
      fill
    grestore
  } bind
>> def

/drawIcon {  % x y iconName size -> -
  4 dict begin
    /size exch def
    /name exch def
    /y exch def
    /x exch def

    gsave
      x y translate
      size 30 div dup scale
      icons name get exec
    grestore
  end
} def

% Usage
100 100 /checkmark 20 drawIcon
150 100 /cross 20 drawIcon
200 100 /star 20 drawIcon

1.4.2. Shape Library 

/shapes <<
  /arrow {  % length width -> -
    2 dict begin
      /width exch def
      /length exch def

      newpath
      0 0 moveto
      length width 2 div sub 0 lineto
      length width 2 div sub width 2 div lineto
      length 0 lineto
      length width 2 div sub width -2 div lineto
      length width 2 div sub 0 lineto
      0 0 lineto
      closepath
      fill
    end
  } bind

  /roundedRect {  % width height radius -> -
    3 dict begin
      /r exch def
      /h exch def
      /w exch def

      newpath
      r 0 moveto
      w r sub 0 w 0 w r r arcto 4 {pop} repeat
      w h r sub w h r h r arcto 4 {pop} repeat
      r h 0 h 0 h r arcto 4 {pop} repeat
      0 r 0 0 r 0 r arcto 4 {pop} repeat
      closepath
      fill
    end
  } bind

  /polygon {  % sides radius -> -
    2 dict begin
      /r exch def
      /n exch def

      newpath
      0 1 n 1 sub {
        /i exch def
        /angle i 360 n div mul 90 add def
        r angle cos mul
        r angle sin mul
        i 0 eq { moveto } { lineto } ifelse
      } for
      closepath
      fill
    end
  } bind
>> def

1.5. Complex Forms

1.5.1. Business Card Form 

/BusinessCard {  % name title email phone -> form
  4 dict begin
    /phone exch def
    /email exch def
    /title exch def
    /name exch def

    {
      gsave
        % Card outline (3.5" x 2")
        0.5 setlinewidth
        0 0 252 144 rectstroke

        % Name
        /Helvetica-Bold findfont 16 scalefont setfont
        10 110 moveto
        name show

        % Title
        /Helvetica findfont 12 scalefont setfont
        10 95 moveto
        title show

        % Contact info
        /Helvetica findfont 9 scalefont setfont
        10 70 moveto
        (Email: ) show email show

        10 60 moveto
        (Phone: ) show phone show

        % Logo area (placeholder)
        0.9 setgray
        200 100 40 30 rectfill
      grestore
    } bind
  end
} def

% Create and use
(John Doe) (Senior Developer) (john@example.com) (+1-555-0123)
BusinessCard /myCard exch def

100 100 translate
myCard exec

1.5.2. Letterhead Form 

/Letterhead {  % company address1 address2 phone -> form
  4 dict begin
    /phone exch def
    /addr2 exch def
    /addr1 exch def
    /company exch def

    {
      gsave
        % Company name
        /Helvetica-Bold findfont 24 scalefont setfont
        50 750 moveto
        company show

        % Address
        /Helvetica findfont 10 scalefont setfont
        50 735 moveto addr1 show
        50 725 moveto addr2 show
        50 715 moveto phone show

        % Bottom line
        0.5 setlinewidth
        50 705 moveto
        562 705 lineto
        stroke
      grestore
    } bind
  end
} def

% Create letterhead
(ACME Corporation)
(123 Business Street)
(City, State 12345)
(+1-555-0100)
Letterhead /header exch def

% Use on each page
header exec

1.5.3. Watermark Form 

/Watermark {  % text -> form
  1 dict begin
    /text exch def

    {
      gsave
        % Position and rotate
        306 396 translate
        45 rotate

        % Semi-transparent effect (simulated)
        0.9 setgray

        % Large text
        /Helvetica-Bold findfont 72 scalefont setfont
        text dup stringwidth pop 2 div neg 0 moveto
        show
      grestore
    } bind
  end
} def

% Create watermark
(CONFIDENTIAL) Watermark /wmark exch def

% Apply to pages
gsave
  wmark exec
grestore

1.6. Form Optimization

1.6.1. Cached Form Pattern 

% Cache expensive calculations in form
/OptimizedForm {
  % Pre-calculate values
  20 dict begin
    /points [
      0 1 360 {
        /angle exch def
        50 angle cos mul
        50 angle sin mul
      } for
    ] def

    {
      gsave
        % Use pre-calculated points
        newpath
        points aload pop moveto
        2 2 points length 2 sub {
          points exch get
          exch
          points exch get
          exch
          lineto
        } for
        closepath
        stroke
      grestore
    } bind
  end
} def

1.6.2. Lazy Initialization 

/LazyForm {
  10 dict begin
    /initialized false def
    /cache null def

    /init {
      /cache {
        % Expensive form content here
        newpath
        0 0 100 0 360 arc
        fill
      } bind def
      /initialized true def
    } def

    /draw {
      initialized not {
        init
      } if
      cache exec
    } def

    currentdict
  end
} def

1.7. Form Composition

1.7.1. Combining Forms 

/CompositeForm {  % form1 form2 offsetX offsetY -> compositeForm
  4 dict begin
    /offsetY exch def
    /offsetX exch def
    /form2 exch def
    /form1 exch def

    {
      gsave
        form1 exec
      grestore

      gsave
        offsetX offsetY translate
        form2 exec
      grestore
    } bind
  end
} def

% Create composite
Logo Badge 60 0 CompositeForm /logoBadge exch def

% Use composite
100 100 translate
logoBadge exec

1.7.2. Layered Forms 

/LayeredForm {
  10 dict begin
    /layers [] def

    /addLayer {  % form -> -
      /layers [
        layers aload pop
        4 -1 roll
      ] def
    } def

    /draw {
      layers {
        gsave
          exec
        grestore
      } forall
    } def

    currentdict
  end
} def

% Usage
LayeredForm /composite exch def
composite /addLayer get { background } exec
composite /addLayer get { content } exec
composite /addLayer get { overlay } exec
composite /draw get exec

1.8. Form Templates

1.8.1. Page Template 

/PageTemplate {  % headerProc footerProc -> template
  2 dict begin
    /footer exch def
    /header exch def

    {
      gsave
        % Header
        0 720 translate
        header exec
      grestore

      % Content area marker (optional)
      % 72 72 468 648 rectstroke

      gsave
        % Footer
        0 36 translate
        footer exec
      grestore
    } bind
  end
} def

% Define header and footer
/myHeader {
  /Helvetica-Bold findfont 14 scalefont setfont
  72 0 moveto
  (Document Title) show

  /Helvetica findfont 10 scalefont setfont
  540 0 moveto
  (Page ) show
  1 =string cvs show
} def

/myFooter {
  /Helvetica findfont 9 scalefont setfont
  72 0 moveto
  (© 2024 Company Name) show

  540 0 moveto
  (Confidential) show
} def

% Create template
myHeader myFooter PageTemplate /template exch def

% Use on each page
template exec

1.8.2. Report Template 

/ReportTemplate {
  20 dict begin
    /title exch def
    /subtitle exch def
    /author exch def
    /date exch def

    {
      gsave
        % Title section
        /Helvetica-Bold findfont 24 scalefont setfont
        306 650 moveto
        title dup stringwidth pop 2 div neg 0 rmoveto
        show

        % Subtitle
        /Helvetica findfont 14 scalefont setfont
        306 630 moveto
        subtitle dup stringwidth pop 2 div neg 0 rmoveto
        show

        % Author and date
        /Helvetica findfont 10 scalefont setfont
        306 600 moveto
        author dup stringwidth pop 2 div neg 0 rmoveto
        show

        306 585 moveto
        date dup stringwidth pop 2 div neg 0 rmoveto
        show

        % Decorative line
        1 setlinewidth
        156 570 moveto
        456 570 lineto
        stroke
      grestore
    } bind
  end
} def

1.9. Form Transformation

1.9.1. Scaled Form Instance 

/ScaledForm {  % form scale -> scaledForm
  2 dict begin
    /scale exch def
    /form exch def

    {
      gsave
        scale dup scale
        form exec
      grestore
    } bind
  end
} def

% Usage
Logo 2 ScaledForm /bigLogo exch def
Logo 0.5 ScaledForm /smallLogo exch def

1.9.2. Rotated Form Instance 

/RotatedForm {  % form angle -> rotatedForm
  2 dict begin
    /angle exch def
    /form exch def

    {
      gsave
        angle rotate
        form exec
      grestore
    } bind
  end
} def

% Usage
Arrow 45 RotatedForm /diagonalArrow exch def

1.9.3. Colored Form Instance 

/ColoredForm {  % form r g b -> coloredForm
  4 dict begin
    /b exch def
    /g exch def
    /r exch def
    /form exch def

    {
      gsave
        r g b setrgbcolor
        form exec
      grestore
    } bind
  end
} def

% Usage
Star 1 0 0 ColoredForm /redStar exch def
Star 0 0 1 ColoredForm /blueStar exch def

1.10. Practical Form Examples

1.10.1. Example 1: Invoice Template 

/InvoiceTemplate {  % invoiceNo date dueDate -> form
  3 dict begin
    /due exch def
    /date exch def
    /invNo exch def

    {
      gsave
        % Company header
        /Helvetica-Bold findfont 20 scalefont setfont
        50 750 moveto
        (INVOICE) show

        % Invoice details
        /Helvetica findfont 10 scalefont setfont
        450 750 moveto (Invoice #: ) show invNo show
        450 735 moveto (Date: ) show date show
        450 720 moveto (Due: ) show due show

        % Table header
        0.8 setgray
        50 650 512 20 rectfill

        0 setgray
        /Helvetica-Bold findfont 10 scalefont setfont
        55 655 moveto (Description) show
        350 655 moveto (Quantity) show
        450 655 moveto (Price) show
        500 655 moveto (Total) show

        % Border
        0.5 setlinewidth
        50 650 512 20 rectstroke
      grestore
    } bind
  end
} def

% Usage
(INV-001) (2024-01-15) (2024-02-15) InvoiceTemplate
/invoice exch def

invoice exec

1.10.2. Example 2: Certificate Border 

/CertificateBorder {
  {
    gsave
      % Outer border
      2 setlinewidth
      0.6 0.4 0.2 setrgbcolor
      36 36 540 720 rectstroke

      % Inner border
      1 setlinewidth
      0.8 0.6 0.4 setrgbcolor
      50 50 512 688 rectstroke

      % Corner ornaments
      0.6 0.4 0.2 setrgbcolor
      [ 40 40  572 40  40 756  572 756 ] {
        /y exch def
        /x exch def

        gsave
          x y translate
          newpath
          -10 0 moveto
          0 10 lineto
          10 0 lineto
          0 -10 lineto
          closepath
          fill
        grestore
      } forall
    grestore
  } bind
} def

CertificateBorder /certBorder exch def
certBorder exec

1.10.3. Example 3: Barcode Form 

/SimpleBarcode {  % digits -> form
  1 dict begin
    /digits exch def

    {
      gsave
        % Simple barcode (conceptual)
        /barWidth 2 def
        /barHeight 50 def
        /x 0 def

        0 1 digits length 1 sub {
          /i exch def
          digits i get 48 sub  % Convert char to digit

          2 mod 0 eq {
            0 setgray
          } {
            1 setgray
          } ifelse

          x 0 barWidth barHeight rectfill
          /x x barWidth add def
        } for
      grestore
    } bind
  end
} def

% Usage
(123456789) SimpleBarcode /bc exch def
100 100 translate
bc exec

1.10.4. Example 4: Graph Grid Form 

/GraphGrid {  % width height xDiv yDiv -> form
  4 dict begin
    /yDiv exch def
    /xDiv exch def
    /h exch def
    /w exch def

    {
      gsave
        0.8 setgray
        0.25 setlinewidth

        % Vertical lines
        0 xDiv w {
          dup 0 moveto h lineto stroke
        } for

        % Horizontal lines
        0 yDiv h {
          dup 0 exch moveto w exch lineto stroke
        } for

        % Border
        0 setgray
        1 setlinewidth
        0 0 w h rectstroke
      grestore
    } bind
  end
} def

% Usage
400 300 20 20 GraphGrid /grid exch def
50 50 translate
grid exec

1.11. Form Management

1.11.1. Form Registry 

/FormRegistry <<>> def

/registerForm {  % name form -> -
  FormRegistry 3 1 roll put
} def

/getForm {  % name -> form
  FormRegistry exch get
} def

/hasForm {  % name -> boolean
  FormRegistry exch known
} def

% Usage
/myLogo /Logo registerForm
/myLogo getForm exec

1.11.2. Form Factory 

/FormFactory {
  20 dict begin
    /forms <<>> def

    /create {  % name type params -> -
      3 dict begin
        /params exch def
        /type exch def
        /name exch def

        % Create form based on type
        type /badge eq {
          params /size get
          params /color get
          Badge
          forms name 3 -1 roll put
        } if

        % ... other types
      end
    } def

    /get {  % name -> form
      forms exch get
    } def

    currentdict
  end
} def

1.12. Performance Considerations

1.12.1. When to Use Forms 

% Good: repetitive complex graphics
/ComplexLogo {
  % Many path operations
  % Multiple colors
  % Gradients, etc.
} def

% Use form multiple times
100 100 translate ComplexLogo exec
200 200 translate ComplexLogo exec
300 300 translate ComplexLogo exec

% Bad: simple graphics
/SimpleDot {
  0 0 5 0 360 arc fill
} def
% Just draw directly instead

1.12.2. Form vs Procedure 

% Form (better for repeated use)
/form {
  gsave
    % Graphics here
  grestore
} bind def

% Plain procedure (simpler for single use)
/procedure {
  % Graphics here
} def

1.13. Best Practices

1.13.1. Self-Contained Forms 

% Good: form handles its own state
/GoodForm {
  gsave
    % Set all needed parameters
    1 setlinewidth
    0 0 0 setrgbcolor
    % Draw
  grestore
} bind def

% Bad: depends on external state
/BadForm {
  % Assumes linewidth, color are set
  % Draw
} def

1.13.2. Documented Parameters 

% Good: clear interface
/DocumentedForm {  % x y size color -> -
  % Creates a colored square at position
  % ...
} def

% Bad: unclear parameters
/MyForm {  % ??? -> -
  % ...
} def

1.13.3. Minimal Dependencies 

% Good: standalone
/StandaloneForm {
  gsave
    /Helvetica findfont 12 scalefont setfont
    % Use font
  grestore
} bind def

% Bad: assumes font is set
/DependentForm {
  % Assumes currentfont is correct
  (Text) show
} def

1.14. Common Pitfalls

1.14.1. Forgetting State Isolation 

% Wrong: modifies global state
/BadForm {
  1 0 0 setrgbcolor
  % Draw
} def

% Correct: isolated state
/GoodForm {
  gsave
    1 0 0 setrgbcolor
    % Draw
  grestore
} def

1.14.2. Absolute Positioning 

% Wrong: hardcoded positions
/BadForm {
  100 200 moveto
  (Text) show
} def

% Correct: relative positioning
/GoodForm {
  0 0 moveto
  (Text) show
} def
% Use with translate for positioning

1.14.3. Missing bind 

% Slower: not bound
/SlowForm {
  newpath
  0 0 100 100 rectfill
} def

% Faster: bound
/FastForm {
  newpath
  0 0 100 100 rectfill
} bind def

1.15. See Also

Back to top

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