plan9-gpl/sys/lib/ghostscript/gs_cspace.ps

%    Copyright (C) 2002 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: gs_cspace.ps,v 1.6 2003/06/26 22:42:33 dan Exp $
% basic colorspace mechanism

%
% This new implementation of color spaces extends the color space 
% formalism to all PostScript levels. Level specific features and 
% operators continue to be accessible only in the appropriate level, 
% but the colorspace concept and associated mechanisms are used 
% throughout.
%
% The color space mechanism is built around two dictionaries:
%
%   .cspace_util
%       A dictionary in global VM that is accessible in userdict only
%       during initialization. This dictionary is intended for various
%       utility procedures that are used in implementing the individual
%       color spaces.
%
%   colorspacedict
%       A dictionary of methods for each color space type. The keys
%       in this dictionary are color space type names (e.g.: /DeviceGray,
%       /Separation, etc.), and the values are dictionaries of methods.
%       The set of methods is the same for each color space type, and
%       provides a complete implementation for the corresponding color
%       space type. This dictionary is in global VM.
%
% The information specific to a color space type is created in a file
% for that type or group of types (e.g.: gs_csdev.ps, gs_csindx.ps,
% etc.). These files will generally adhere to the template:
%
%      .currentglobal true .setglobal
%      <level-specific dictionary> begin
%      ...
%      .cspace_util begin
%      colorspacedict
%      /<color space type name>
%       mark
%          /cs_validate
%            {
%               ...
%            }
%          bind
%          ...
%       .dicttomark
%      put
%      end      % .cspace_util
%      end ...  % level-specific dictionary
%      .setglobal
%
% The methods associated with a color space are listed below (along with
% their stack handling), followed by descriptions.
%
%   -   cs_potential_indexed_base   <bool>
%
%   -   cs_potential_pattern_base   <bool>
%
%   -   cs_potential_alternate   <bool>
%
%   -   cs_potential_icc_alternate   <bool>
%
%
%   <name | array>   cs_get_ncomps   <int>
%
%   <name | array>   cs_get_range   <range_array>
%
%   <name | array>   cs_get_default_color   <c1> ... <cn>
%
%
%   <c1> ... <cn>  <name | array>   cs_get_currentgray   <gray>
%
%   <c1> ... <cn>  <name | array>   cs_get_currentrgb   <red>  <green>  <blue>
%
%   <c1> ... <cn>  <name | array>   cs_get_currentcmyk 
%                                       <cyan>  <magenta>  <yellow>  <black>
%
%
%   <name | array>   cs_validate   <name | array>
%
%   <name1 | array1>    cs_substitute   <name1 | array1>  <array2>
%
%   <name1 | array1>  <array2>   cs_prepare   <name1 | array1>  <array2>
%
%   <name | array>   cs_install   -
%
%
%   <c1> ... <cn>  <array>   cs_verify_color   <c1> ... <cn>
%
%   <array>   cs_complete_color   -
%
%
% cs_potential_indexed_base, cs_potential_pattern_base,
% cs_potential_alternate, cs_potential_icc_alternate
%   These are booleans rather than procedures. They indicate if the color
%   space can be a base space of an Indexed color space (anything except
%   Indexed and Pattern), a Pattern color space (anything except Pattern),
%   the alternative color space of a Separation or DeviceN color space, or
%   the alternative color space of an ICCBased color space. The two
%   parameters are distinct only because of a Ghostscript-specific
%   implementation problem; in principle, there is nothing special about
%   ICCBased color spaces in this regard.
%
% cs_get_ncomps
%   Return the number of color components for the color spaces. For Pattern
%   color spaces, the value is -1 if there is no base space, or -(n + 1) if
%   the base space has n components.
%
% cs_get_range
%   Return the input Range array appropriate for this color space. This is
%   defined for all color spaces, though it is of interest primarily for
%   CIEBased and ICCBased color spaces. For Indexed color spaces this is
%   [ 0 hival ], where hival is the maximum support index value. For all
%   other non-CIEBased, non-ICCBased color spaces, the range is an array
%   of ncomps elements, all of which are [ 0 1 ], where ncomps is the 
%   number of color space components.
%
% cs_get_default_color
%   Generates the default color for the current color space. Under normal
%   circumstances this is done internally. It is provided in PostScript
%   only to support an optimization that doesn't change the current color
%   space more often than necessary.
%
% cs_get_currentgray, cs_get_currentrgb, cs_get_currentcmyk
%   These procedures are used to implement the currentgray, currentrgb,
%   and currentcmyk operators (which are pseudo-operators in the current
%   implementation).
%
% cs_validate
%   Validate the operand color space. Because color spaces are extensively
%   manipulated in PostScript in this implementation, error handling can
%   become burdensome. To make the code somewhat simpler, it is useful to
%   be able to validate a color space prior to manipulation, so as to
%   ensure that errors are not discovered in awkward places.
%
% cs_substitute
%   Substitute a device-independent color space for device specific color
%   space. This applies directly to the device-specific color spaces
%   (DeviceGray, DeviceRGB, DeviceCMYK), and indirectly when these color
%   spaces are used as base/alternative color spaces. The mechanism for
%   color substitution is included in all language levels, though it may
%   only be accessed for Language Level 3.
%
%   The substituted color space is the topmost of the operands pushed.
%   this may or may not be the same as the original color space, which
%   is immediately below it on the operand stack. If the two differ,
%   the substituted space will always be in local VM (and will be
%   writable).
%
%   Substitution is applied recursively to the base/alternate color
%   space of ICCBased, Indexed, Separation, DeviceN, or Pattern
%   color spaces. Because Ghostscript currently requires that any
%   base or alternative color space be the current color space when
%   the enclosing color space is set, this substitution effectively
%   occurs twice: once in the original color space, and once when the
%   base/alternative color space is made the current color space.
%   We retain the first substitution as we would eventually like to
%   remove the restriction on making the base/alternative color space
%   the current color space.
%
% cs_prepare
%   Perform any operations required on the color space for installation.
%   This method exists primarily to allow conversion of PostScript
%   procedures to functions for CIEBased color spaces. Two operands are
%   provided: the original and the substituted color space. If the two
%   differ and the latter is writable, required modifications can
%   be made "in place". Otherwise, a new instance of the second color
%   space must be built.
%
%   Currently, cs_prepare is not explicitly recursive. Because
%   Ghostscript requires a base/alternate color space to be installed
%   as the current color space prior to installing the enclosing color
%   space, the cs_prepare method will implicitly be called recursively.
%   The reason for not making this explicit is that color space
%   preparation may involve a considerable amount of work, which could
%   be avoided if, for example, an alternative color space will not
%   be used because the enclosing Separation/DeviceN color space is
%   supported in native mode by the process color model. We would
%   eventually like to remove the need to prepare color spaces that
%   will not be used.
%
% cs_install
%   This method actually installs the color space in the graphic state.
%   Only the substituted/prepared space (which may be the same as the
%   original space) is passed as an operand; the original space is handled
%   directly by the .setcolorspace operator.
%
%   The provision of a separate method for this tasks reflects the
%   historical implementation of color spaces in the Ghostscript
%   interpreter. This implementation provides a unique operator for each
%   color space type.
%
% cs_prepare_color
%   Modify a set of color operands as required by a color space. This
%   is used primarily to verify the color operands, as this is most
%   conveniently done in PostScript.
%
% cs_complete_setcolor
%   This method is invoked immediately after a (successful) invocation
%   of setcolor. Ii is provided as a separate method for compatibility
%   with Adobe implementations. These implementations invoke the lookup
%   (Indexed) or tint procedure each time setcolor is invoked (only if
%   the alternative color space is used in the case of the tint
%   transform). Because Ghostscript may convert these procedures to
%   functions (or pre-sample them), the procedures may not always be
%   called when expected. There are applications that depend on this
%   behavior (e.g.: Adobe PhotoShop 5+), so this method provides a way
%   to emulate it.
%
%   In principle, a cs_complete_setcolor procedure for an Indexed color
%   space whose base space should invoke cs_complete_setcolor on its
%   base space. Currently we don't do this, because it has not been
%   shown to be necessary. It would be simple to add if it is every
%   needed.
%
% All of these methods are procedures.
%
% For each of these methods, there is a procedure in .cspace_util with
% a dot ('.') prefix that will invoke the appropriate procedure for the
% operand array.
%

.currentglobal true .setglobal
userdict /.cspace_util 80 dict put
.cspace_util begin

%
% Colorspacedict is initially in .cspace_util; it is copied to level2dict
% in the Level 2 initialization code to retain compatibility with 
% earlier implementations.
%
/colorspacedict 20 dict def


%
%   <obj>   make_array1   <array>
%
% procedure for conditionally converting a named color space to a
% 1-element array. Since names are always global, the array will be
% as well.
%
/make_array1
  {
    dup type /nametype eq
      { currentglobal true setglobal exch 1 array astore exch setglobal }
    if
  }
bind def

%
%  <name|array>   .get_cspace_type   name
%
% Provide generic routine for retrieving the color space type.
%
/.get_cspace_type
  {
    dup type dup /arraytype eq exch /packedarraytype eq or
      { 0 get }
    if
  }
bind def

%
%   <name|array>   .get_method_dict   <dict>
%
% Get the method dictionary for a specific color space. Note that the
% color space is left on the stack.
%
/.get_method_dict
  { //colorspacedict exch //.get_cspace_type exec get }
bind def

%
%   <name|array>  <proc_name>   .get_method   <name|array>  <proc | bool>
%
% Get the named method for the operand color space.
%
/.get_method
  { exch //.get_method_dict exec exch get }
bind def


%
%   <name_array>   .cs_potential_indexed_base   <bool>
%   <name_array>   .cs_potential_pattern_base   <bool>
%   <name_array>   .cs_potential_alternate    <bool>
%   <name_array>   .cs_potential_icc_alternate   <bool>
%   <name | array>   .cs_get_ncomps   <int>
%   <name | array>   .cs_get_range   <range_array>
%   <name | array>   .cs_get_default_color   <c1>  ...  <cn>
%   <c1> ... <cn>  <name | array>   .cs_get_currentgray   <gray>
%   <c1> ... <cn>  <name | array>   .cs_get_currentrgb   <r>  <g>  <b>
%   <c1> ... <cn>  <name | array>   .cs_get_currentcmyk   <c>  <m>  <y>  <k>
%   <name | array>   .cs_validate   <name | array>
%   <name1 | array1>   .cs_substitute   <name1 | array1>  <array2>
%   <name1 | array1>  <array2>   .cs_prepare   <name1 | array1>  <array2>
%   <name | array>   .cs_install   -
%   <c1> ... <cn> <array>   .cs_prepare_color   <c1> ... <cn>
%   <array>   .cs_complete_setcolor   -
%
% These procedures provide access to the corresponding methods of the
% operand color space.
%
/.cs_potential_indexed_base
  { /cs_potential_indexed_base //.get_method exec }
bind def

/.cs_potential_pattern_base
  { /cs_potential_pattern_base //.get_method exec }
bind def

/.cs_potential_alternate
  { /cs_potential_alternate //.get_method exec }
bind def

/.cs_potential_icc_alternate
  { /cs_potential_icc_alternate //.get_method exec }
bind def

/.cs_get_ncomps
  { dup /cs_get_ncomps //.get_method exec exec }
bind def

/.cs_get_range
  { dup /cs_get_range //.get_method exec exec }
bind def

/.cs_get_default_color
  { dup /cs_get_default_color //.get_method exec exec }
bind def

/.cs_get_currentgray
  { dup /cs_get_currentgray //.get_method exec exec }
bind def

/.cs_get_currentrgb
  { dup /cs_get_currentrgb //.get_method exec exec }
bind def

/.cs_get_currentcmyk
  { dup /cs_get_currentcmyk //.get_method exec exec }
bind def

/.cs_validate
  { dup /cs_validate //.get_method exec exec }
bind def

/.cs_substitute
  { dup /cs_substitute //.get_method exec exec }
bind def

/.cs_prepare
  { dup /cs_prepare //.get_method exec exec }
bind def

/.cs_install
  { dup /cs_install //.get_method exec exec }
bind def

/.cs_prepare_color
  { dup /cs_prepare_color //.get_method exec exec }
bind def

/.cs_complete_setcolor
  { dup /cs_complete_setcolor //.get_method exec exec }
bind def


%
% Make sure we have an interpreter color space before redefining
% setcolorspace. The interpreter internal code only sets the effective
% color space; the interpreters color spaces begins as a null object.
%
% NB: This should come prior to the redefinition of setcolorspace, and
%     must use an array operand.
%
[ /DeviceGray ] setcolorspace


%
%   <c1> ... <cn>   setcolor   -
%
% As with setcolorspace, setcolor is initially placed in .cspace_util,
% and is copied to level2dict by the Level 2 initialization code. The
% internal definition of setcolor is removed from systemdict as soon
% as this procedure is defined.
%
/setcolor
  {
      {
        currentcolorspace //.cs_prepare_color exec //setcolor
        currentcolorspace //.cs_complete_setcolor exec
      }
    stopped
      { //.cspace_util /setcolor get $error /errorname get signalerror }
    if
  }
bind odef

systemdict /setcolor .undef


%
%   <name|array>  <bool>   _setcolorspace   -
%   <name|array>   _setcolorspace_nosub   -
%
%   <name|array>   setcolorspace   -
%   <name|array>   forcesetcolorspace   -
%
% setcolorspace is initially placed in .cspace_util. It is copied to
% level2dict by the Level 2 initialization code. The internal
% setcolorspace operator is removed from systemdict as soon as this
% procedure is defined.
%
% Because some jobs, in particular PDF jobs, repeatedly set the same
% color space, this procedure will check if the operand and current
% color spaces are the same. The check is absolute for parameterless
% color spaces, conservative for others. For PostScript, this
% optimization can only be employed if color space substitution is
% disabled, as otherwise there is no way to account for  possible changes
% in the /Default* instances of the ColorSpace resource category. For PDF
% jobs, resource category instances can only be changed at very specific
% times (typically page boundaries), so the "operand color space is the
% same as current color space" optimization may be used even if color
% space substitution is in effect. The optimization is also highly
% desirable in such cases, as it greatly improves performance.
%
% In certain situations, it is critical that a color space be set,
% even if it is the same as the current color space. This is the case
% when a CIEBased color space is used as a base or alternative color
% space, due to some long-standing problems with the graphics libraries
% handling of sampled information from the procedures in CIE color
% spaces and the color rendering dictionary. The forcesetcolorspace
% operator is provided for those situations.
%
% Note also that, if the current color space is not reset, at least
% the current color must be reset to its default value.
%
% Another problem arises in the case of ICCBased color spaces. These
% color spaces may be used to substitute for a DeviceGray/DeviceRGB/
% DeviceCMYK color space, and may themselves require such a color
% space as an alternate. Obviously, when this is the case the normal
% setcolorspace mechanism would encounter and infinite loop if the
% alternate colro space needed to be used. For this particular case,
% the special _setcolorspace_nosub is provided, which suppresses
% color space substitution. This routine does not bother to check if
% the operand and current color space are the same.
%
/_setcolorspace
  {
      {
        % see if the operand space is the same as the current space
        currentcolorspace dup length 1 eq
          {
            0 get
            2 index dup type dup /arraytype eq exch /packedarraytype eq or
              {
                dup length 1 eq
                  { 0 get }
                if
              }
            if
          }
          { 2 index }
        ifelse
        eq and dup
          {
            %
            % If PDFfile is defined on the dictionary stack, this is a
            % PDF job. No additional check is required in this case (see
            % comment above).
            %
            /PDFfile where
              { pop }
              { .getuseciecolor not and }   % check that UseCIEColor is off
            ifelse
          }
        if
          { //.cs_get_default_color exec setcolor }
          {
            //.cs_validate exec
            //.cs_substitute exec
            //.cs_prepare exec
            //.cs_install exec
            //make_array1 exec //setcolorspace
          }
        ifelse
      }
    stopped
      { //.cspace_util /setcolorspace get $error /errorname get signalerror }
    if
  }
bind def

/_setcolorspace_nosub
  {
      {
        //.cs_validate exec
        dup
        //.cs_prepare exec
        //.cs_install exec
        //make_array1 exec //setcolorspace
      }
    stopped
      { //.cspace_util /setcolorspace get $error /errorname get signalerror }
    if
  }
bind def

/setcolorspace { //true //_setcolorspace exec } bind odef
/forcesetcolorspace { //false //_setcolorspace exec } bind odef

%
%   -   initgraphics   -
%
% The initgraphics operator must be redefined create a real color space.
% Previously this was unnecessary, as .currentcolorspace could return
% an integer.
%
%
/initgraphics
  { initgraphics { /DeviceGray } cvlit forcesetcolorspace }
.bind systemdict begin odef end

systemdict /setcolorspace .undef


%
%   <gray>   setgray   -
%
%   <r> <g> <b>   setrgbcolor  -
%
%   <c> <m> <y> <b>   setcmykcolor   -
%
% The Level 1 color setting operators. setcmykcolor is created only if
% setcolorscreen is present. These operators are always defined in
% systemdict. 
%
/setgray
  {
      { { /DeviceGray } cvlit  //setcolorspace //setcolor }
    stopped
      { /setgray load $error /errorname get signalerror }
    if
  }
bind systemdict begin odef end

/setrgbcolor
  {
      { { /DeviceRGB } cvlit //setcolorspace //setcolor }
    stopped
      { /setrgbcolor load $error /errorname get signalerror }
    if
  }
bind systemdict begin odef end

/setcolorscreen where
  {
    pop
    /setcmykcolor
      {
          { { /DeviceCMYK } cvlit //setcolorspace //setcolor }
        stopped
          { /setcmykcolor load $error /errorname get signalerror }
        if
      }
    bind systemdict begin odef end
  }
if


%
%   -   currentgray  <gray>
%
%   -   currentrgbcolor   <r> <g> <b>
%
%   -   currentcmykcolor   <c> <m> <y> <k>
%
% Return the current color, mapped to a DeviceGray, DeviceRGB, or
% DeviceCMYK color space. The latter is only created if setcolorscreen
% is present.
/currentgray
  { currentcolor currentcolorspace //.cs_get_currentgray exec }
bind systemdict begin odef end

/currentrgbcolor
  { currentcolor currentcolorspace //.cs_get_currentrgb exec }
bind systemdict begin odef end

/setcolorscreen where
  {
    pop
    /currentcmykcolor
      { currentcolor currentcolorspace //.cs_get_currentcmyk exec }
    bind systemdict begin odef end
  }
if



%
% Add some generically useful structures and procedures to .cspace_util.
%

%
% Some common errors. The command for these errors will normally be
% overwritten by the invoking operator. We cannot "load" the secolorspace
% or setcolor operators, as they are not present in Level 1 systems.
%
/setcspace_typecheck
  { /setcolorspace cvx /typecheck signalerror }
bind def

/setcspace_rangecheck
  { /setcolorspace cvx /rangecheck signalerror }
bind def

/setcspace_invalidaccess
  { /setcolorspace cvx /invalidaccess signalerror }
bind def

/setcspace_undefined
  { /setcolorspace cvx /undefined signalerror }
bind def

/setcolor_typecheck
  { /setcolor cvx /typecheck signalerror }
bind def

/setcolor_invalidaccess
  { /setcolor cvx /invalidaccess signalerror }
bind def


%
%   <obj>   check_array   <obj>
%
% Check that an object is an array. Currently we don't check for
% readability, as a failing get or length operator should generate
% the appropriate invalidaccess error.
/check_array
  {
    dup type dup /arraytype ne exch /packedarraytype ne and
      { /setcolorspace cvx /typecheck signalerror }
    if
  }
bind def


% pre-defined procedures for cs_ncomps and cs_get_range
/ncomps_1 { pop 1 } bind def
/ncomps_3 { pop 3 } bind def
/ncomps_4 { pop 4 } bind def

/dflt_range_4 [ 0 1  0 1  0 1  0 1 ] readonly def
/dflt_range_3 dflt_range_4 0 6 getinterval def
/dflt_range_1 dflt_range_4 0 2 getinterval def

%   <obj>   get_range_[1|3|4]   <range>
/get_range_1 { pop //dflt_range_1 } bind def
/get_range_3 { pop //dflt_range_3 } bind def
/get_range_4 { pop //dflt_range_4 } bind def


%
%   <c1> ... <cn>  <name | array>  <n>
%   check_num_stack
%   <c1> ... <cn>  <array | array>
%
%   <c1>  <array>   validate_color_1   <c1>
%   <c1>  <c2>  <c3>  <arraY>   validate_color_3   <c1>  <c2>  <c3>
%   <c1>  <c2>  <c3> <c4>  <arraY>   validate_color_4   <c1>  <c2>  <c3>  <c4>
%
% check_num_stack verifies that the stack consists of a color space array and
% n numbers. This is used by most of the cs_prepare_color procedures. The
% validate_color_[1|3|4] procedures can be used as the cs_prepare_color
% procedure for Device specific, CIEBased, and Indexed color spaces.
%
% Note that the pseudo-operator that (indirectly) invokes this routine will
% handle resetting the stacks.
%
/check_num_stack
  {
    dup 2 add copy exch pop
      {
        type dup /integertype ne exch /realtype ne and
          //setcolor_typecheck
        if
      }
    repeat
    pop         % remove the extra op_count
  }
bind def

%   <c1>  <array>   validate_1   <c1>
/validate_1 { 1 //check_num_stack exec pop } bind def

%   <c1>  <c2>  <c3>   <array>   validate_3   <c1>  <c2>  <c3>
/validate_3 { 3 //check_num_stack exec pop } bind def

%   <c1>  <c2>  <c3>  <c4>  <array>   validate_4   <c1>  <c2>  <c3>  <c4>
/validate_4 { 4 //check_num_stack exec pop } bind def


%
%   <obj>   pop_1   -
%
% This is a procedure form of pop. It may be used where a procedure is
% expected, but the function of the procedure is the same as the pop
% operator.
/pop_1 { pop } bind def

%
%   <obj>   dup_1   <obj>  <obj>
%
% An analog to pop_1, this one for dup.
%
/dup_1 { dup } bind def

%
%   <obj1> ... <objn>  <n>   clear_n_objs   -
%
% Clear n objects from the operand stack.
%
/clear_n_objs { //pop_1 repeat }  bind def

%
%   <obj1> ... <objn>  <array>   clear_setcolor_operands   -
%
% Clear the setcolor operands for a color space.
%
/clear_setcolor_operands
  { //.cs_get_ncomps exec //clear_n_objs exec }
bind def

%
% Return 1, 3, or 4 zeros. These routines are used primarily for the
% CIEBased color spaces, for which currentgray and currentrgb
% should return 0 for all components, and currentcmyk should return
% 0 0 0 1.0 (this varies from Adobe's documentation but is consistent
% with their impelementations).
%
/no_currentgray { //.cs_get_ncomps exec //clear_n_objs exec 0 } bind def
/no_currentrgb { //.cs_get_ncomps exec //clear_n_objs exec 0 0 0 } bind def
/no_currentcmyk { //.cs_get_ncomps exec //clear_n_objs exec 0 0 0 1.0 } bind def


%
%   <num>   bound_0_1   <num>
%
% Bound a number to the range [0, 1]
%
/bound_0_1
  {
    dup 0 lt
      { pop 0 }
      {
        dup 1 gt
          { pop 1 }
        if
      }
    ifelse
  }
bind def


%
% Provide pseudo-operators  for sethsbcolor and currenthsbcolor. These are
% alternate versions of the setrgbcolor and currentrgbcolor operators, which
% make use of a hue/staturation/brightness color description.
%

%
%   <num_1> ...  <num_n>  n   max_n   <num>
%   <num_1> ...  <num_n>  n   min_n   <num>
%
% Find the maximum and minum of 3 color component intensities.
%
/max_n
  {
    1 sub
      { 2 copy lt { exch } if pop }
    repeat
  }
bind def

/min_n
  {
    1 sub
      { 2 copy gt { exch } if pop }
    repeat
  }
bind def


%
%   <r>  <g>  <b>   .rgb_2_hsb   <h>  <s>  <br>
%   <h>  <s>  <br>   .hsb_2_rgb   <r>  <g>  <b>
%
% Convert between RGB and HSB colors, using the hexcone approach (see
% Rogers, David, "Procedureal Elements For Computer Graphics",
% (McGraw-Hill, 1985), pp. 402 - 3).
%
% The rgb ==> hsb calculation is:
%
%   br = max(r, g, b)
%
%   if (br == 0)
%       h = 0, s = 0;
%   else {
%       v = min(r, g, b)
%       diff = br - v;
%       sat = diff / br;
%       if (r == br)
%           h = (g - b) / (6 * diff) + (b > g ? 1 : 0);
%       else if (g == br)
%           h = 1/3 + (b - r) / (6 * diff);
%       else    /* b == br */
%           h = 2/3 + (r - g) / (6 * diff);
%   }
%
% The hsb ==> rgb conversion is:
%
%    mn = (1 - s) * br, md = 6 * s * br;
%
%    switch ((int)floor(6 * h)) {
%      case 0:  /* r >= g >= b */
%        r = br;
%        g = mn + h * md;
%        b = mn;
%        break;
%
%      case 1:  /* g >= r >= b */
%        r = mn + md * (1/3 - h);
%        g = br;
%        b = mn;
%        break;
%
%      case 2:  /* g >= b >= r */
%        r = mn;
%        g = br;
%        b = mn + (h - 1/3) * md;
%        break;
%
%      case 3:  /* b >= g >= r */
%        r = mn;
%        g = mn + (2/3 - h) * md;
%        b = br;
%        break;
%
%      case 4:  /* b >= r >= g */
%        r = mn + (h - 2/3) * md;
%        g = mn;
%        b = br;
%        break;
%
%      case 5:  /* r >= b >= g */
%        r = br;
%        g = mn;
%        b = mn + (1 - h) * md;
%        break;
%
%      case 6:  /* We have wrapped around the hexcone.  Thus this case is
%      		   the same as case 0 with h = 0 */
%        h = 0;
%        r = br;
%        g = mn + h * md = mn;
%        b = mn;
%        break;
%    }
%
/.rgb_2_hsb
  {
    % find the largest and smallest components
    3 copy 3 //max_n exec dup 5 1 roll
    dup 0 eq
      { pop pop pop pop 0 0 }
      {
        4 copy pop 3 //min_n exec 1 index exch sub
        dup 2 index div 7 1 roll
        dup 0 eq
          { 5 { pop } repeat 0 3 1 roll }
          {
            6 mul 5 1 roll
            2 copy eq       % blue == brightness
              { pop pop sub exch div .666667 add }
              {
                2 index eq  % green == brightness
                  { exch pop exch sub exch div .3333333 add }
                  {
                    % red == brightness
                    sub exch pop exch div
                    dup 0 lt
                      { 1 add }
                    if
                  }
                ifelse
              }
            ifelse
            3 1 roll
          }
        ifelse
      }
    ifelse
  }
bind def


/.hsb_2_rgb
  {
    3 { 0 max 1 min 3 1 roll } repeat
    1 2 index sub 1 index mul      % (1 - s) * br
    3 -1 roll 2 index mul 6 mul    % 6 * s * br
    4 -1 roll                      % stack: <br>  <(1 - s) * br>  <6 * s * br>  <h>

    % array of procedures for the 7 hue cases
      {
        % 0 ==> r >= g >= b
        { mul 1 index add exch }

        % 1 ==> g >= r >= b
        { 0.333333 exch sub mul 1 index add 3 1 roll }

        % 2 ==> g >= b >= r
        { 0.333333 sub mul 1 index add 3 1 roll exch 3 -1 roll }

        % 3 ==> b >= g >= r
        { 0.666667 exch sub mul 1 index add 3 -1 roll }

        % 4 ==> b >= r >= g
        { 0.666667 sub mul 1 index add 3 1 roll exch }

        % 5 ==> r >= b >= g
        { 1 exch sub mul 1 index add }

        % 6 ==> r = br, g = b = mn
	% Case 6 is the same as case 0 with h = 0.  This also simplifies
	% the calculations.
        { pop pop dup }
      }
    1 index 6 mul cvi              % (int)(6 * h)
    get exec    
  }
bind def


%
%   <hue>  <saturation>  <brightness   sethsbcolor   -
%
%   - currenthsbcolor   <hue>  <saturation>  <brightness>
%
/sethsbcolor
  {
      { //.hsb_2_rgb exec setrgbcolor }
    stopped
      { /sethsbcolor load $error /errorname get signalerror }
    if
  }
bind systemdict begin odef end

/currenthsbcolor
  {
      { currentrgbcolor //.rgb_2_hsb exec }
    stopped
      { /currenthsbcolor load $error /errorname get signalerror }
    if
  }
bind systemdict begin odef end

end     % .cspace_util
.setglobal