[XeTeX] spotcolor package

[Apostolos Syropoulos]

Hello,

A few days ago someone asked me to see whether it is possible to use spot colors
in XeLaTeX.Let me say that until that moment I had no idea what spot colors are...
Now, after some search I found the spotcolor package, which of course works only
with pdfLaTeX. I tried to transform the package so to make it work with XeLaTeX.
It took my some time to understand how the original package works but in the end
I managed to create a package that works (the attached file was generated with
this package). However, one thing does not work: background color for pages.
I tried to see why it does not worked and I realized that there is a problem
with color definitions. In order to make things clear, here is how a cmyk color
is defined internally when using XeLaTeX


\def\color at cmyk#1#2{\c at lor@@cmyk#2\@@#1}
\def\c at lor@@cmyk#1,#2,#3,#4\@@#5{%
  \c at lor@arg{#4}%
  \c at lor@arg{#1}%
  \c at lor@arg{#2}%
  \c at lor@arg{#3}%
  \edef#5{cmyk #1 #2 #3 #4}%
  }

and here is how it is defined when using pdfLaTeX

\def\color at cmyk#1#2{\c at lor@@cmyk#2\@@#1}
\def\c at lor@@cmyk#1,#2,#3,#4\@@#5{%
  \c at lor@arg{#4}%
  \c at lor@arg{#1}%
  \c at lor@arg{#2}%
  \c at lor@arg{#3}%
  \edef#5{#1 #2 #3 #4 k #1 #2 #3 #4 K}%
}


You will notice that in XeLaTeX one uses the word cmyk followed by the components
that make up this color. However, in pdfLaTeX, as expected (!), the driver uses
the k and K operators directly. Package spotcolor uses the following to define
spot colors:

\def\color at spotcolor#1#2{\c at lor@@spotcolor#2\@@#1}
\def\c at lor@@spotcolor#1,#2\@@#3{%
  \c at lor@arg{#2}%
  \edef#3{/#1 cs /#1 CS #2 sc #2 SC}%
}

Here it uses four PDF operators. Unfortunately, it is impossible (?) right now
to solve this problem when using XeLaTeX. I think the reason is that in file 
spc_util.c of the dvipdfm-x source code there is the following function that
reads color specifications. 


static int
spc_read_color_pdf (struct spc_env *spe, pdf_color *colorspec, struct spc_arg *ap)
{
  ..........................................................

  nc = spc_util_read_numbers(cv, 4, spe, ap);
  switch (nc) {
  case  1:
    pdf_color_graycolor(colorspec, cv[0]);
    break;
  case  3:
    pdf_color_rgbcolor (colorspec, cv[0], cv[1], cv[2]);
    break;
  case  4:
    pdf_color_cmykcolor(colorspec, cv[0], cv[1], cv[2], cv[3]);
    break;
  default:
    /* Try to read the color names defined in dvipsname.def */
    .........................................................
  }
.............................................................

  return  error;
}


As is obvious there is no provision for reading spot color specification and
therefore I get meaningless (?) messages like the following one:

** WARNING ** No valid color specified?
** WARNING ** Interpreting special command background (color) failed.
** WARNING ** >> at page="5" position="(72, 769.89)" (in PDF)
** WARNING ** >> xxx "background /SOMECOLOR cs /SOMECOLOR CS 1.0 sc 1.0 SC"
** WARNING ** >> Reading special command stopped around >>/SOMECOLOR cs /SOMECOLOR CS 1.0 sc 1.0 SC<<
** WARNING ** No valid color specified?
** WARNING ** Interpreting special command push (color) failed.
** WARNING ** >> at page="6" position="(148.712, 702.783)" (in PDF)
** WARNING ** >> xxx "color push /SOMECOLOR cs /SOMECOLOR CS 1.0 sc 1.0 SC"
** WARNING ** >> Reading special command stopped around >>/SOMECOLOR cs /SOMECOLOR CS 1.0 sc 1.0 SC<<


Since adding support for spot color seems to me very important, I think dvipdfm-x should patched.
But since I haven't studied how dvipdfm-x works, I am not sure how to proceed. Thus, I would
like to ask for ideas and/or advice. 


Thank you,

A.S.

----------------------
Apostolos Syropoulos
Xanthi, Greece
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