path: root/Master/tlpkg/tlgs/lib/pdf_ops.ps

%    Copyright (C) 1994, 2000 Aladdin Enterprises.  All rights reserved.
% 
% This software is provided AS-IS with no warranty, either express or
% implied.
% 
% This software is distributed under license and may not be copied,
% modified or distributed except as expressly authorized under the terms
% of the license contained in the file LICENSE in this distribution.
% 
% For more information about licensing, please refer to
% http://www.ghostscript.com/licensing/. For information on
% commercial licensing, go to http://www.artifex.com/licensing/ or
% contact Artifex Software, Inc., 101 Lucas Valley Road #110,
% San Rafael, CA  94903, U.S.A., +1(415)492-9861.

% $Id: pdf_ops.ps 8156 2007-07-31 14:19:45Z alexcher $
% Definitions for most of the PDF operators.

.currentglobal true .setglobal

% Define pdfmark.  Don't allow it to be bound in.
% Also don't define it in systemdict, because this leads some Adobe code
% to think this interpreter is a distiller.
% (If this interpreter really is a distiller, don't do this.)
systemdict /pdfmark known not
 { userdict /pdfmark { cleartomark } bind put } if

/renderingintentdict mark
  /Perceptual 0
  /RelativeColorimetric 1
  /Saturation 2
  /AbsoluteColorimetric 3
.dicttomark readonly def

userdict /GS_PDF_ProcSet 127 dict dup begin

% ---------------- Abbreviations ---------------- %

/bdef { bind def } bind def

% ---------------- Graphics state stack ---------------- %

% PDF adds a number of parameters to the graphics state.
% We implement this by pushing and popping a dictionary
% each time we do a PDF gsave or grestore.
% The keys in this dictionary are as follows:
%	self			% identifies the dictionary as one of ours
%	ClipRect		% (optional)
%	Show
%	TextSaveMatrix		% matrix at time of BT (iff within BT/ET)
% (The following correspond directly to PDF state parameters.)
%	AlphaIsShape
%	FillConstantAlpha
%	FillColor
%	FillColorSpace
%	FillOverprint
%	SoftMask
%	StrokeConstantAlpha
%	StrokeColor
%	StrokeColorSpace
%	StrokeOverprint
%	TextSpacing
%	TextHScaling
%	Leading
%	TextFont
%	TextLineMatrix
%	TextMatrix
%	TextRise
%	TextRenderingMode
%	WordSpacing

/nodict 1 dict def
nodict /self { //nodict } executeonly put
nodict readonly pop

/dictbeginpage {	% <initialdict> dictbeginpage -
  //nodict 20 dict .copydict begin { def } forall
  graphicsbeginpage textbeginpage
} bdef
/endpage {	% - endpage -
  showpage end
} bdef

/graphicsbeginpage {
  initgraphics
  currentdict /ClipRect knownoget { aload pop rectclip } if
  0 g  0 G  false op  false OP  0 OPM
  1 ca  1 CA  null SMask  false AIS  /Compatible BM  true TK
} bdef

/gput		% <value> <key> gput -
 { exch currentdict //nodict eq { /self dup load end 5 dict begin def } if
		% If we're in a Level 1 system, we need to grow the
		% dictionary explicitly.
   currentdict length currentdict maxlength ge %eq
    { currentdict dup length 3 mul 2 idiv 1 add dict .copydict end begin 
    }
   if def
 } bdef

% Restore graphics state, but do not modify path. Paths are not part
% of the PDF graphics state; see 4.4.1 of PDF reference 3rd ed.
/grestore_nopath {
  % Collect the upath with an identity CTM
    matrix setmatrix .getpath
    % Save the CTM, set identity during the uappend, then set the CTM
    grestore matrix currentmatrix matrix setmatrix
    exch newpath { exec } forall setmatrix
} bdef

/q {
  gsave //nodict begin
} bdef
% Some PDF files have excess Q operators!
/Q {
  currentdict /self .knownget {
    exec //nodict eq { end grestore_nopath false } { true } ifelse
  } {
    true	% formaterror -- not a gsave dict
  } ifelse
  { (\n   **** File has imbalanced q/Q operators \(too many Q's\) ****\n)
    pdfformaterror
  } if
} bdef

% Save PDF gstate
/qstate {       % - qstate <qstate>
  gstate
} bdef

% Set PDF gstate
/setqstate {    % <qstate> setqstate -
  { matrix setmatrix //false upath } stopped {
    pop setgstate newpath
  } {
    % Save the CTM, set identity during the uappend, then set the CTM
    exch setgstate matrix currentmatrix matrix setmatrix
    exch newpath uappend setmatrix
  } ifelse
} bdef

% ---------------- Color setting ---------------- %

/fcput		% <color> <colorspace> fcput -
 { /FillColorSpace gput /FillColor gput
 } bdef
/scput		% <color> <colorspace> scput -
 { /StrokeColorSpace gput /StrokeColor gput
 } bdef
/csput		% <colorspace> csput -
 { csset 2 copy fcput scput
 } bdef

/csdevgray [/DeviceGray] readonly def
/csdevrgb [/DeviceRGB] readonly def
/csdevcmyk [/DeviceCMYK] readonly def
/cspattern [/Pattern] readonly def
/nullpattern1 mark
   /PatternType 1 /PaintType 1 /TilingType 3 /BBox [0 0 1 1]
   /XStep 1 /YStep 1 /PaintProc { pop } bind
.dicttomark readonly def
/nullpattern2 nullpattern1 dup length dict copy readonly def

% Each entry in the color space dictionary is a procedure of the form
%	<cspace> -proc- <cspace> <initial-color>
/CSdict mark
  /DeviceGray { pop //csdevgray 0 } bind
  /DeviceRGB { pop //csdevrgb [0 0 0] cvx } bind
  /DeviceCMYK { pop //csdevcmyk [0 0 0 1] cvx } bind
  /CIEBasedA { 0 } bind
  /CIEBasedABC { [0 0 0] cvx } bind
  /ICCBased { [ 1 index 1 oget /N get { 0 } repeat ] cvx } bind
  /Separation { 1 } bind
  /DeviceN {	% What is the correct value??
    [ 1 index 1 get length { 1 } repeat ] cvx
  } bind
  /Indexed { 0 } bind
  /Pattern {
    dup type /nametype eq 1 index length 1 eq or {
      pop //cspattern //nullpattern1 matrix makepattern
    } {
      //nullpattern2 matrix makepattern 1 index 1 get csset
		% Stack: patternspace nullpattern basecolor basespace
      pop [ 3 1 roll dup type /arraytype eq { aload pop } if
      counttomark -1 roll ] cvx
    } ifelse
  } bind
.dicttomark readonly def
/csset			% <cspace> csset <color> <cspace>
 { dup dup type /nametype ne { 0 get } if //CSdict exch get exec exch
 } bdef

/g { //csdevgray fcput } bdef
/G { //csdevgray scput } bdef
/rg { 3 array astore cvx //csdevrgb fcput } bdef
/RG { 3 array astore cvx //csdevrgb scput } bdef
/k { 4 array astore cvx //csdevcmyk fcput } bdef
/K { 4 array astore cvx //csdevcmyk scput } bdef
/cs { csset fcput } bdef
/CS { csset scput } bdef
/ri { //renderingintentdict exch .knownget { .setrenderingintent } if } bdef
% We have to break up sc according to the number of operands.
/sc1 { /FillColor gput } bdef
/SC1 { /StrokeColor gput } bdef
% We have to avoid storing into a color array associated with an outer
% gsave level, so we do a kind of "copy on write".
/sc* {
  currentdict /FillColor .knownget {
    astore pop
  } {
    /FillColor load
    % FillColor may contain either a single value or an array.
    dup type /arraytype eq { length }{ pop 1 } ifelse
    array astore cvx /FillColor gput
  } ifelse
} bdef
/SC* {
  currentdict /StrokeColor .knownget {
    astore pop
  } {
    /StrokeColor load
    % StrokeColor may contain either a single value or an array.
    dup type /arraytype eq { length }{ pop 1 } ifelse
    array astore cvx /StrokeColor gput
  } ifelse
} bdef

% ---------------- Overprint/transparency setting ---------------- %

/op { /FillOverprint gput } bdef
/OP { /StrokeOverprint gput } bdef
/OPM {
  /.setoverprintmode where { pop .setoverprintmode } { pop } ifelse
} bdef
/ca { /FillConstantAlpha gput } bdef
/CA { /StrokeConstantAlpha gput } bdef
/SMask { /SoftMask gput } bdef
/AIS { /AlphaIsShape gput } bdef
/BM {
  /.setblendmode where {
    pop [ exch dup type /nametype ne { aload pop } if /Normal ] {
      { .setblendmode } .internalstopped not { exit } if pop
    } forall
  } {
    pop
  } ifelse
} bdef
/TK {
  /.settextknockout where { pop .settextknockout } { pop } ifelse
} bdef

% ---------------- Color installation ---------------- %

% Establish a given color (and color space) as current.
/.settransparencyparams {	% <alpha> <smask> .settransparencyparams -
  PDFusingtransparency {
    /.inittransparencymask where {
      pop AlphaIsShape {
        1 .setopacityalpha 0 .inittransparencymask exch .setshapealpha 1
      } {
        1 .setshapealpha 1 .inittransparencymask exch .setopacityalpha 0
      } ifelse
	% Set the soft mask by rendering the XObject.  Doing this every time
	% is obviously very inefficient; we'll improve it later.
      .settransparencymask    
    } {
      pop pop
    } ifelse
  } {
    pop pop
  } ifelse
} bdef
/.settransparencymask {		% <paramdict> <masknum> .settransparencymask -
  exch dup null eq {
    PDFusingtransparency {
      pop .inittransparencymask
    } {
      dup /Draw get exec
    } ifelse
  } {
    dup /Draw get exec
  } ifelse
} bdef
% (Non-mask) images must execute setfillblend.
/setfillblend {
  FillOverprint setoverprint
  FillConstantAlpha SoftMask .settransparencyparams
} def
/setfillstate {
  FillColor FillColorSpace setgcolor setfillblend
} def
/setstrokestate {
  StrokeColor StrokeColorSpace setgcolor StrokeOverprint setoverprint
  StrokeConstantAlpha SoftMask .settransparencyparams
} def
/Cdict 15 dict dup begin	% <color...> <colorspace> -proc- -
  /DeviceGray { pop setgray } bdef
  /DeviceRGB { pop setrgbcolor } bdef
  /DeviceCMYK { pop setcmykcolor } bdef
  /CIEBasedA { setgcolorspace setcolor } bdef
  /CIEBasedABC /CIEBasedA load def
  /CIEBasedDEF /CIEBasedA load def
  /CIEBasedDEFG /CIEBasedA load def
  /ICCBased /CIEBasedA load def
  /Separation /CIEBasedA load def
  /DeviceN /CIEBasedA load def
  /Indexed /CIEBasedA load def
  /Pattern
   { setgcolorspace

     % Since multiple patterns may share
     % same data stream, we need to ensure
     % that the stream is at 0 position.
     % Making this consistently with resolveshading,
     % which applies ReusableStreamDecode filter
     % to the PS stream, which represents the
     % PDF stream in dynamics.

     dup /Shading knownoget {
       dup /ShadingType oget 4 ge {
         /DataSource knownoget {
           dup type /filetype eq {
             0 setfileposition
           } {
             pop
           } ifelse
         } if
       } {
        pop
       } ifelse
     } if

     dup /Matrix knownoget not { matrix } if
     gsave DefaultQstate setqstate makepattern grestore setcolor
   } bdef
end def
/setgcolor	% (null | <color...>) <colorspace> setgcolor -
 { 1 index null eq
    { pop pop }
    { dup 0 get //Cdict exch get exec }
   ifelse
 } bdef
% Compare the old and new color spaces in an attempt to avoid expensive
% reloads of CIEBased color spaces.
/PCSdict 15 dict dup begin	% <colorspace> -proc- <colorspace|pdfcspace>
  /CIEBasedA { dup 1 get /PDFColorSpace .knownget { exch pop } if } bdef
  /CIEBasedABC /CIEBasedA load def
  /CIEBasedDEF /CIEBasedA load def
  /CIEBasedDEFG /CIEBasedA load def
  /Indexed {
    dup 1 get dup pdfcolorspace 2 copy ne { 3 1 roll } if pop pop
  } bdef
end def
/pdfcolorspace {	% <colorspace> pdfcolorspace <colorspace|pdfcspace>
  dup type /arraytype eq {
    //PCSdict 1 index 0 get .knownget { exec } if
  } if
} bdef
/setgcolorspace {	% <colorspace> setgcolorspace -
  dup pdfcolorspace currentcolorspace pdfcolorspace eq {
    pop
  } {
    setcolorspace
  } ifelse
} bdef
/fsexec		% <fillop|strokeop> fsexec -
 {		% Preserve the current point, if any.
    { currentpoint } stopped
    { $error /newerror false put   cvx exec }
    { 3 -1 roll cvx exec moveto }
   ifelse
 } bdef

% ---------------- Path painting and clipping ---------------- %

/S { setstrokestate /stroke fsexec } bdef
/f { setfillstate /fill fsexec } bdef
/f* { setfillstate /eofill fsexec } bdef
/n { newpath } bdef		% don't allow n to get bound in
/s { closepath S } bdef
/B { gsave setfillstate fill grestore S } bdef
/b { closepath B } bdef
/B* { gsave setfillstate eofill grestore S } bdef
/b* { closepath B* } bdef

% Clipping:

/Wdict 4 dict dup begin
/S { gsave setstrokestate stroke grestore n } bdef
/f { gsave setfillstate fill grestore n } bdef
/f* { gsave setfillstate eofill grestore n } bdef
/n { end clip newpath } bdef
end readonly def
/W { //Wdict begin } bdef
/W*dict 4 dict dup begin
Wdict { def } forall
/n { end eoclip newpath } bdef
end readonly def
/W* { //W*dict begin } bdef

% ---------------- Text control ---------------- %

/textbeginpage
 { /TextSpacing 0 def		% 0 Tc
   /TextLeading 0 def		% 0 TL
   /TextRenderingMode 0 def	% 0 Tr
   /TextRise 0 def		% 0 Ts
   /WordSpacing 0 def		% 0 Tw
   /TextHScaling 1.0 def	% 100 Tz
   /TextFont null def
   /Show { showfirst } def
 } bdef

% Contrary to the statement in the PDF manual, BT and ET *can* be nested,
% if the CharProc for a Type 3 font does a BT/ET itself.
% Since we always call the CharProc inside a q/Q, we simply ensure that
% the text state is saved and restored like the rest of the extended
% graphics state.

/settextmatrix {
  TextMatrix concat
  TextHScaling 1 ne { TextHScaling 1 scale } if
  TextRise 0 ne { 0 TextRise translate } if
  TextFont dup null eq { pop } { setfont } ifelse
} bdef
/settextstate {
	% The text state can be set even outside BT/ET.
  currentdict /TextSaveMatrix known {
    TextSaveMatrix setmatrix settextmatrix
  } if
} bdef
/settextposition {
		% Update the TextMatrix translation.
  gsave TextSaveMatrix setmatrix
  currentpoint TextRise sub TextMatrix 4 2 getinterval astore pop
		% We would like to do "grestore currentpoint translate"
		% here, but some PDF files set a singular text matrix
		% (0 0 0 0 <x> <y> Tm), so we can't do this.
  TextTempMatrix identmatrix setmatrix currentpoint
  grestore
  TextTempMatrix currentmatrix 4 2 getinterval astore pop
  TextTempMatrix setmatrix
} bdef

/BT {
  currentdict /TextLineMatrix .knownget
    { identmatrix pop TextMatrix identmatrix pop }
    { matrix /TextLineMatrix gput matrix /TextMatrix gput }
  ifelse
  { showfirst } /Show gput
  currentdict /TextSaveMatrix .knownget not {
    matrix dup /TextSaveMatrix gput
  } if currentmatrix pop settextmatrix
  matrix /TextTempMatrix gput		% see settextposition
} bdef
/ET {
  TextRenderingMode 4 ge { clip newpath } if
  TextSaveMatrix setmatrix
  currentdict /TextSaveMatrix undef
} bdef
/Tc { /TextSpacing gput { showfirst } /Show gput } bdef
/TL { /TextLeading gput } bdef
/Tr { dup .settextrenderingmode /TextRenderingMode gput { showfirst } /Show gput } bdef
/Ts { /TextRise gput settextstate } bdef
/Tw { /WordSpacing gput { showfirst } /Show gput } bdef
/Tz { 100 div /TextHScaling gput settextstate} bdef

% ---------------- Font control ---------------- %

/Tf {		% <font> <scale> Tf -
  dup 0 eq {
    (\n   **** Warning: Invalid 0.0 font scale given for Tf ****\n)
    pdfformaterror
    pop 0.00000001	% handle invalid scale by using a really small value
  } if
  1 index type /dicttype ne {
    selectfont currentfont
  } {
    dup 1 eq { pop } { scalefont } ifelse
  }
  ifelse
  /TextFont gput settextstate
} bdef

% Read a CFF font.
/FRD		% <resname> <file> FRD -
 { /FontSetInit /ProcSet findresource begin //true ReadData
 } bdef

% Copy a font, removing its FID.  If changed is true, also remove
% the UniqueID and XUID, if any.  If the original dictionary doesn't have
% the keys being removed, don't copy it.
/.copyfontdict		% <font> <changed> .copyfontdict <dict>
 { 1 index /FID known
   1 index { 2 index /UniqueID known or 2 index /XUID known or } if
    {		% We add 1 to the length just in case the original
		% didn't have a FID.
      exch dup length 1 add dict exch
       {		% Stack: changed newfont key value
	 1 index /FID eq 4 index
	  { 2 index /UniqueID eq or 2 index /XUID eq or }
	 if not { 3 copy put } if pop pop
       }
      forall exch
    }
   if pop
 } bdef

% Insert a new Encoding or Metrics into a font if necessary.
% Return a possibly updated font, and a flag to indicate whether
% the font was actually copied.
/.updatefontmetrics {	% <font> <Metrics|null> .updatefontmetrics
			%   <font'> <copied>
  dup //null ne {
    exch //true .copyfontdict dup /Metrics 4 -1 roll put //true
  } {
    pop //false
  } ifelse
} bdef

/.updatefontencoding {	% <font> <Encoding|null> .updatefontencoding
			%   <font'> <copied>
  dup //null ne { dup 2 index /Encoding get ne } { //false } ifelse {
    exch //false .copyfontdict dup /Encoding 4 -1 roll put //true
  } {
    pop //false
  } ifelse
} bdef

% Duplicate keys in CharString dictionary according to GlyphMap: <</new_glyph /old_glyph>>
% We have to do this because PDF fonts can associate multiple widths with the same glyph
% but Metrics dictionary works by the glyph name.
/.update_charstring {	% <font> <GlyphMap> .update_charstring  <font'> <copied>
  dup //null ne {
    exch //true .copyfontdict       % map font
    dup dup /CharStrings get        % map font font cstr
    dup length                      % map font font cstr len
    4 index length add              % map font font cstr len+map_len
    dict copy dup begin             % map font font cstr'
    /CharStrings exch put           % map font
    exch {                          % font /new /old
      currentdict exch .knownget {
        def
      } {
        currentdict /.notdef .knownget {
          def
        } {
          pop
          % The font has no .notdef.
          % Could not resolve the conflict,
          % but either the font is invalid or the glyph name is never used.
        } ifelse
      } ifelse
    } forall
    end //true
  } {
    pop //false
  } ifelse
} bdef

/.updatefont {	      % <font> <Encoding|null> <Metrics|null> <GlyphMap|null>
                      %        .updatefont <font'> <copied>
  4 2 roll            % <Metrics|null> <GlyphMap> <font> <Encoding|null>
  .updatefontencoding % <Metrics|null> <GlyphMap> <font> bool
  4 1 roll exch       % bool <Metrics|null> <font> <GlyphMap>
  .update_charstring  % bool <Metrics|null> <font> bool
  3 1 roll exch       % bool bool <font> <Metrics|null>
  .updatefontmetrics  % bool bool <font> bool
  4 2 roll or or      % <font> is_copied
} bdef

% ---------------- Text positioning ---------------- %

/Td {
  TextLineMatrix transform TextLineMatrix 4 2 getinterval astore pop
  TextLineMatrix TextMatrix copy pop settextstate
} bdef
/TD { dup neg /TextLeading gput Td } bdef
/T* { 0 TextLeading neg Td } bdef
/Tm {
  TextLineMatrix astore TextMatrix copy pop settextstate
} bdef

% ---------------- Text painting ---------------- %

/Vexch {
  rootfont /WMode knownoget { 1 eq { exch } if } if
} bind def

/textrenderingprocs [		% (0 is handled specially)
	% Painting-only modes
   { tf } { tS } { tB } { tn }
	% Clipping modes
   { gsave tf grestore tW }
   { gsave tS grestore tW }
   { gsave tB grestore tW }
   { tW }
] readonly def
/setshowstate
 { WordSpacing 0 eq TextSpacing 0 eq and
    { TextRenderingMode 0 eq currentdevice .devicename /pdfwrite eq or {
        { setfillstate show }
      } {
        TextRenderingMode 3 eq {
            	% Some PDF files execute 'tm' with a singular matrix,
		% and then use the text rendering mode 3.
		% The graphics library currently cannot handle text
		% operations when the CTM is singular.
		% Work around this here.
	  {	
            matrix currentmatrix dup dup
            dup 0 get 0 eq 1 index 1 get 0 eq and {
              dup dup 2 get 0 eq { 0 }{ 1 } ifelse 1 put
            } if
            dup 2 get 0 eq 1 index 3 get 0 eq and {
              dup dup 1 get 0 eq { 3 }{ 2 } ifelse 1 put
            } if
            setmatrix
            2 index setfillstate show % Tr was set to graphic state.
            setmatrix 
	    % now set the currentpoint using the original matrix
            gsave nulldevice
            setmatrix
            false charpath currentpoint newpath 
            grestore
            moveto
          }
        } {
          { false charpath textrenderingprocs TextRenderingMode get exec }
        } ifelse
      } ifelse
    }
    { TextRenderingMode 0 eq TextRenderingMode 3 eq or currentdevice .devicename /pdfwrite eq or
       % Tr was set to graphic state.
       { WordSpacing 0 eq
          { { setfillstate TextSpacing 0 Vexch 3 -1 roll ashow } }
	  { TextSpacing 0 eq
            { { setfillstate WordSpacing 0 Vexch 32 4 -1 roll widthshow } }
            { { setfillstate WordSpacing 0 Vexch 32
                 TextSpacing 0 Vexch 6 -1 roll awidthshow } }
	    ifelse
	  }
	 ifelse
       }
       { { WordSpacing TextSpacing
			% Implement the combination of t3 and false charpath.
			% Note that we must use cshow for this, because we
			% can't parse multi-byte strings any other way.
			% Stack: string xword xchar
	    { pop pop (x) dup 0 3 index put false charpath
			% Stack: xword xchar ccode
             3 copy 32 eq { add } { exch pop } ifelse 0 Vexch rmoveto pop
	    }
	   4 -1 roll cshow pop pop
	   textrenderingprocs TextRenderingMode get exec
	 }
       }
      ifelse
    }
   ifelse /Show gput
 } bdef
/showfirst { setshowstate Show } def

/Tj {
  0 0 moveto Show settextposition
} bdef
/' { T* Tj } bdef
/" { exch Tc exch Tw T* Tj } bdef
/TJ {
  0 0 moveto {
    dup type /stringtype eq {
      Show
    } { -1000 div
      currentfont /ScaleMatrix .knownget { 0 get mul } if
      0 Vexch rmoveto
    } ifelse
  } forall settextposition
} bdef

/tf { setfillstate currentpoint fill moveto } bdef
/tn { currentpoint newpath moveto } bdef % Obsolete, never used.
% For stroking characters, temporarily restore the graphics CTM so that
% the line width will be transformed properly.
/Tmatrix matrix def
/tS
 { setstrokestate
   currentpoint //Tmatrix currentmatrix TextSaveMatrix setmatrix stroke
   setmatrix moveto
 } bdef
/tB { gsave tf grestore tS } bdef
% This does the wrong thing if there have been multiple text operations
% within a single BT/ET pair, but it's a start.
/tW { } bdef

% Text formatting and painting for the AcroForm field without appearance streams.
/Tform {                % <MaxLen> (V) <Ff> <Q> Tform -
  clippath pathbbox 4 2 roll pop pop                        % MaxLen (V) Ff Q dx dy
  currentfont /ScaleMatrix .knownget { 3 get } { 1 } ifelse % MaxLen (V) Ff Q dx dy yy
  currentfont /FontBBox get dup 1 get neg exch 3 get        % MaxLen (V) Ff Q dx dy yy desc asc
  dup 0 ne { div } { pop pop 0 } ifelse                     % MaxLen (V) Ff Q dx dy yy desc/asc
  1 index mul                                               % MaxLen (V) Ff Q dx dy yy desc/asc*yy

  4 index 16#1000 and 0 ne { % multiline
    8 { pop } repeat (Multiline form fields are not yet implemented.) =
  } {
    4 index 16#1000000 and 0 ne { % comb
      8 { pop } repeat (Combed form fields are not yet implemented.) =
    } { % plain text                                       
      3 1 roll sub add 2 div             % MaxLen (V) Ff Q dx (dy-yy+desc)/2
      0 exch moveto                      % MaxLen (V) Ff Q dx
      1 index 0 ne {
        3 index stringwidth pop          % MaxLen (V) Ff Q dx w
        sub exch 1 eq { 2 div } { 2 sub } ifelse % MaxLen (V) Ff (dx-w)/2
        0 rmoveto                        % MaxLen (V) Ff
        pop                              % MaxLen (V)
      } {
        pop pop pop                      % MaxLen (V)
        2 0 rmoveto
      } ifelse
      exch pop Show                      % -
    } ifelse
  } ifelse
} bdef

end readonly put		% GS_PDF_ProcSet

.setglobal