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\iffalse
% This is truecols.doc, a sub-style for use with SliTeX.
% It is documented with the conventions of doc.sty; run it through a
% suitable driver file to print format the documentation.
% It is intended for use with ltugboat.sty as it stands.
% Note that with the old doc.sty you'll get extra space at the front
% of paras starting with \DescribeMacro.
% Use docstrip.tex to strip the comments to form truecols.sty.
%% Copyright D.Love, SERC Daresbury Laboratory, 1991
%% The `doc' version of this style is re-distributable and usuable
%% under conditions of the GNU copyleft, but please mark any changes,
%% list them here and report any major enhancements to the author.
\fi
\def\filedate{18/4/90}
\def\fileversion{1.2}
% \NoBlackBoxes
% \def\ps{\PS}\def\dvi{{\tt dvi}}\def\pj{Paint\-Jet}
%^^A can't use \verb in arguments:
% \def\sp{{\tt\char\escapechar special}}
% \title{Experiments in \TeX nicolour --- A \SliTeX\ Sub-style for
% Colour Printers\footnote{File version \fileversion, dated
% \filedate.}}
% \author{David Love}
% \address{SERC Daresbury Laboratory,\\Warrington WA4 4AD, UK}
% \netaddress{d.love@daresbury.ac.uk}
%
% \maketitle
%
% \begin{abstract}
% \noindent
% \SliTeX\ assumes that colour transparencies will be produced from
% layers, each printed in a single colour. This sub-style allows a
% suitable \dvi{} driver to produce multi-coloured
% slides in one go (i.e., using a single layer). It is customisable
% for \ps{} printers or simpler colour devices like the the HP \pj{}.
% \end{abstract}
%
% \section{Introduction}
% \SliTeX{}---a version of \LaTeX{} for making slides---supports colours
% in its output by producing `colour layers', one per colour \cite{slitex}.
% It is assumed that these will be copied to transparencies of the
% appropriate colour and overlapped to make a composite multi-colour
% slide. Colour is valuable on slides, but this means
% of producing it is inconvenient and inappropriate if you have
% a colour printer and a suitable \dvi{} driver for it.
%
% This sub-style for \SliTeX{} allows all the colours to be produced
% in one layer. It is designed for use with colour \ps{} printers or
% others like the HP \pj{} with suitable \dvi{} drivers, following
% experiments with these printers at Daresbury.
% It is intended to provoke discussion
% of the use of colour with \TeX{}, a subject about which little
% has been said so far in public, rather than be at all definitive.
%
% \section{Approach}
% Use of colour with \TeX{} is non-standard and has to
% be done by passing information to the \dvi{} driver. This could be
% done in one of two ways:
% \begin{itemize}
% \item using fonts whose names idenitify them to the driver to
% be printed in a particular colour but are otherwise
% identical to the black version (possibly using virtual fonts \cite{vf});
% \item using the \sp{} mechanism to tell the driver to
% change colours.
% \end{itemize}
% The second option is easier to implement with an existing driver and
% allows colour for other objects than characters i.e.,
% rules,\footnote{{\tt \char\escapechar colorslides} doesn't work
% properly with rules---they come out in each layer.}
% and has been adopted here.
% Unfortunately, existing drivers differ in their \verb+\special+
% mechanisms and few understand colour explicitly.
% However, drivers which allow you to include arbitrary \ps{} with a
% \sp{} have this ability implicitly
% since colour operators are defined in \ps{} \cite{redbook}.
% (Colour gets rendered in shades of grey on a normal laser printer,
% which can help with proofing.)
%
% There is a proposed standard for \sp{}s \cite{hosek}
% which includes colour information, but the definition of the
% \verb+textcolor+ \sp{} is inconveniently related to the \dvi{} stack.
% Working with existing \ps{} drivers, one has to make
% some assumptions about them, as detailed below.
%
% In the case of the \pj{} printer there does not appear to be an existing
% driver, so one was produced with a suitable \sp{} defined arbitrarily.
%
% \section{\pj{} Driver}
% The Hewlett-Packard \pj{} can print in colour at 180~dpi, which
% is quite adequate for making transparencies. A driver for it was
% produced using the HP Laserjet version from Beebe's family \cite{beebe}
% as a basis since this has rather similar control sequences.
% It was extended to maintain four bitmaps independently,
% allowing three colours other than black to be printed. Allowing
% more colours would make the code more complicated and slower as well
% as using more memory for the bitmaps. It supports one
% \sp{} to allow colour changes between black, red, green
% and blue. A defect is that the result of overlapping items of
% different colours is independent of their order in the \dvi{} file,
% but this simplifies the driver considerably.
%
% \section{Assumptions}
% The necessary assumptions about the driver are largely isolated in
% the macros \verb+\special@color+
% and \verb+\colormix+.\footnote{I spell the
% English way except in code names, where I reluctantly use `color'
% for consistency with existing code.}
% Suitable changes could be quite easily made to conform with an
% eventual standard for \sp{}s or use a different driver.
%
% \subsection{\ps}
% We assume that a \ps{} driver understands
% \sp{}s of the form
% \begin{center}
% \verb*+\special{ps:: +\meta{code}\verb+}+,
% \end{center}
% where \meta{code} is
% arbitrary \ps{} from which the surrounding code output by the driver is not
% protected. This is appropriate for Rokicki's
% {\tt dvips} and ArborText's DVILASER/PS\@.
\iffalse
% and
% would be for the Daresbury {\tt dvitops} if it didn't zap the
% graphics state at each font change.\footnote{This can probably be
% fixed by messing with the header.}
\fi
% We use the RGB colour model \cite[\S 4.8]{redbook}.
%
% \subsection{\pj{} or other printer}
% A non-\ps{} printer should understand a special of the form
% \verb*+{color +\meta{colour}\verb+}+, where \meta{colour} can take
% the values {\tt black\rm, \tt red\rm, \tt green\rm\ or \tt blue},
% determining the colour of all subsequent printing until the next
% change. The default is assumed to be black.
%
% \section{User interface}
% As well as re-defining some internal \SliTeX{} macros, we make some
% new ones as described below.
%
% \DescribeMacro{\psprinterfalse}
% The default is to assume the use of a \ps{} printer. Saying
% \verb+\psprinterfalse+ changes this to produce output suitable for
% the \pj{} (or similar printer). This should only be done
% in the preamble.
%
% Any colours you use {\em must\/} be declared using
% \verb+\colors+ \DescribeMacro{\colors}(even red, green, blue and black).
% \DescribeEnv{slide}
% They do not need including in the argument of \verb+\begin{slide}+ for
% use with \verb+\truecolors+, but there needs to be some argument,
% even if it's null.
%
% \DescribeMacro{\truecolors}
% Like \verb+\blackandwhite+, \verb+\truecolors+ is
% invoked from the driver file to process a batch of slides described
% in the file given as its argument. It works like
% \verb+\blackandwhite+ in that it only makes one layer, but will
% include the
% information for the printer to produce the
% colours in the \dvi{} file. Notes are not printed by
% \verb+\truecolors+.
%
% \subsection{\ps{} specifics}
% \DescribeMacro{\colormix}
% Before you use a new \ps{} colour, you have to define how it is
% mixed from red, green and blue. \verb+\colormix+ does this for you.
% It takes four arguments. The first is the name of the colour and
% the others are numeric values for the intensities of red, green and
% blue respectively in the mixture. (See the description of RGB in
% \cite{redbook}.) These values must lie in the
% range 0--1 such that 1 is most intense and 0 is no
% intensity. Thus you might define yellow by
% \[\verb+\colormix{yellow}{0}{1}{1}+\]
% You don't need to define red, green, blue or black---they are done
% already.
%
% You could put blocks of text on a coloured background either by
% setting it on top of a suitably-sized rule or using explicit \sp s.
%
% \subsection{Other printers}
% Only red, green, blue and black are available. Use of
% \verb+\colormix+ will produce a warning. Using a non-white
% background won't work very well with the \pj{}.
%
% \subsection{Problem with list environments}
% A problem occurs if you want the first text in a list environment
% item to be a different colour to the label since \verb+\special+s
% before the text appear in the \dvi{} file before the label.
% A way round this is to insert \verb+\leavevmode+ after \verb+\item+.
% This sort of problem may occur in other situtaions.
%
% \section{Code}
% \subsection{Driver-independent code}
% \begin{macrocode}
\typeout{SliTeX style option `truecols' (v. \fileversion\space of \filedate)}
% \end{macrocode}
% \DescribeMacro{\if@truecol}
% We introduce a new switch to tell us whether we can assume we have
% true colour printing capability and unset it initially.
% \begin{macrocode}
\newif \if@truecol \@truecolfalse
% \end{macrocode}
% \DescribeMacro{\the@color}
% We keep track of the current colour using \verb+\the@color+
% (to get colours right with grouping).
% Initially it's black.
% \begin{macrocode}
\def\the@color{\black}
% \end{macrocode}
% \DescribeMacro{\ifpsprinter}
% This tells us if we're dealing with a \ps{} printer (the default)
% or not.
% \begin{macrocode}
\newif \ifpsprinter \psprintertrue
% \end{macrocode}
% \DescribeMacro{\truecolors}
% A new \verb+\truecolors+ command is defined, which works like
% \verb+\blackandwhite+, printing everything in the file given as its
% argument in one layer. Thus it must set the \verb+\@bw+
% switch. This slightly unfortunate change to \verb+\@bw+'s
% meaning makes the alterations easier.
% \begin{macrocode}
\newcommand{\truecolors}[1]{\@truecoltrue \blackandwhite{#1}}
% \end{macrocode}
%\DescribeMacro{\@color}
% We modify \verb+\@color+ to take note of the \verb+@truecol+ setting
% (if \verb+@bw+ is set). If appropriate, it puts out a
% colour-changing \sp{} using \verb+\special@color+. We can omit the
% test for a colour change in math mode if we're not depending on
% invisible fonts.
% \begin{macrocode}
\def\@color#1{%
\if@truecol \else \@mmodetest \fi % change
\if@bw \@visibletrue
\if@truecol \special@color{#1}\fi % change
\else \@visiblefalse
\@for \@x@a :=#1\do{\ifx\@x@a\@currcolor\@visibletrue\fi}\fi
\@currsize \@currfont \ignorespaces}
% \end{macrocode}
% \DescribeMacro{\endslide}
% We ensure that the driver colour is
% reset to black at the end of each slide
% by setting it in \verb+\endslide+.
% \begin{macrocode}
\def\endslide{\@color{black}\par\break}
% \end{macrocode}
% \DescribeMacro{\note}
% We don't want to waste truecolour output on producing notes, which
% we will if we don't re-define \verb+\note+ (since \verb+@bw+ is set
% by \verb+\truecolors+). We just add a test on \verb+@truecol+.
% \begin{macrocode}
\def\note{%
\stepcounter{note}%
\if@bw
\if@truecol \gdef\@slidesw{F}% added
\else
\gdef\@slidesw{T}%
\if@onlynotesw\@whilenum \c@slide > \@donotehigh\relax
\do{\@setlimits\@donotelist\@donotelow\@donotehigh}\ifnum
\c@slide < \@donotelow\relax \gdef\@slidesw{F}\fi\fi\fi
\else \gdef\@slidesw{F}\fi
\if\@slidesw T\newpage\thispagestyle{note}\else
\end{note}\@gobbletoend{note}\fi }
% \end{macrocode}
% \DescribeMacro{\colors}
% We re-define \verb+\colors+ to check that we know about those
% specified. It could, perhaps, be dispensed with at the cost of
% incompatibility with standard \SliTeX{}. If we're not using \ps{}
% only the four pre-defined colours are available.
% \begin{macrocode}
\def\colors#1{%
\@for\@colortemp:=#1\do{%
\@ifundefined{\@colortemp @mix}{% change
\ifpsprinter
\errhelp{You could use I to define it now.}%
\errmessage{You need to use \noexpand\colormix to define
\@colortemp}%
\else
\errhelp{It's safe to carry on.}%
\errmessage{You can only use black, red, green and blue with
this printer, not \@colortemp}%
\expandafter\xdef\csname\@colortemp\endcsname{\relax}%
\fi
}{}
\expandafter\xdef\csname\@colortemp\endcsname
{\noexpand\@color{\@colortemp}}%
}% (do)
\ifx\@colorlist\@empty \gdef\@colorlist{#1}%
\else \xdef\@colorlist{\@colorlist,#1}\fi}
% \end{macrocode}
% \DescribeMacro{\pagestyle}
% Finally we change the default pagestyle since the alignment marks
% would only be useful with overlays.
% \begin{macrocode}
\pagestyle{plain}
% \end{macrocode}
%
% \subsection{Driver-dependent code}
% \DescribeMacro{\colormix}
% The \ps{} user can mix new colours in the RGB model using
% \verb+\colormix+. It takes four arguments, the name of the colour
% (which must then be declared with \verb+\colors+) and three real numbers
% in the range 0--1 describing respectively the intensity of red,
% green and blue in the result. The result is to define a macro of
% the form \verb+\+\meta{colour}\verb+@mix+ to be a list of arguments 2--4.
% \begin{macrocode}
\def\colormix#1#2#3#4{%
\ifpsprinter \else \typeout{Warning: \noexpand\colormix used with
\noexpand\psprinterfalse.}\fi
\color@range@check{#2}\color@range@check{#3}\color@range@check{#4}%
\expandafter\xdef\csname#1@mix\endcsname{#2 #3 #4}}
% \end{macrocode}
% \DescribeMacro{\color@range@check}
% We need to check that the numeric arguments of \verb+\colormix+ are
% in the range 0--1. Since they're real numbers we
% convert them to dimensions to test.
% \begin{macrocode}
\def\color@range@check#1{%
\def\fred{\errhelp{Carry on, but you'll get a PostScript error if
you try to print the results.}%
\errmessage{\noexpand\colormix arguments must be in the
range 0--1}}%
\ifdim#1 pt < 0pt \fred \fi \ifdim#1 pt > 1pt \fred \fi }
% \end{macrocode}
% \DescribeMacro{\special@color}
% This has to change the current colour on the output device to that
% given as its argument,
% but first has to store the current value and make sure it is
% re-instated at the end of the current group. (Coloured fonts would
% avoid the need for this.) Note the \verb+{}+ inserted at the end of
% the group to avoid spaces being gobbled afterwards as with
% \verb+{\red foo} bar+. Probably there's a better way of doing this.
% \begin{macrocode}
\def\special@color#1{%
\def\the@color{\csname#1\endcsname}\aftergroup\the@color
\aftergroup{\aftergroup}%
% \end{macrocode}
% To change colour with \ps{} we use a \sp{} which
% will emit code of the form
% \begin{center} \meta{red level}\verb*+ +\meta{green level}\verb*+ +^^A
% \meta{blue level}\verb*+ +{\tt setrgbcolor} \end{center}
% Perhaps this should be parameterised.
% The three levels are provided by a macro of the form
% \verb+\+\meta{colour}\verb+@mix+ which must be defined for each
% \meta{colour} which is used.
% It might be useful is to
% define a white font (RGB=[1~1~1]) which could be painted over a
% coloured region.
% \begin{macrocode}
\ifpsprinter \special{ps:: \csname#1@mix\endcsname\space
setrgbcolor\space}%
% \end{macrocode}
% For the \pj{} we output
% \begin{center}\verb*+\special{color +\meta{colour}\verb+}+,
% \end{center}
% where \meta{colour} can be {\tt black\rm, \tt red\rm, \tt green \rm
% or \tt blue} and we assume that \verb+#1+ is one of these.
% \begin{macrocode}
\else \special{color #1}\fi % (\ifpsprinter)
} % (\def\special@color)
% \end{macrocode}
% \DescribeMacro{\black@mix}\DescribeMacro{\red@mix}
% \DescribeMacro{\blue@mix}\DescribeMacro{\green@mix}
% Here we define the RGB mixes for the \ps{} colours we support
% initially. These macros need defining for the \pj{} too, so that we
% can check on colours the user tries to invoke.
% \begin{macrocode}
\def\black@mix{0 0 0} \def\red@mix{1 0 0}
\def\blue@mix{0 0 1} \def\green@mix{0 1 0}
% \end{macrocode}
% \begin{thebibliography}{1}
% \bibitem{slitex} Leslie Lamport. {\sl \LaTeX{}: A Document
% Preparation System}; {\tt slitex.tex} dated 10 November 1986; {\tt
% slides.sty} dated 17 January 1986.
% \bibitem{vf} Donald Knuth. \TUB, 11(1), 1990, p.~13.
% \bibitem{redbook} Adobe Systems Inc. {\sl\ps\ Language Reference Manual}.
% \bibitem{hosek} Don Hosek. Proposed \verb+DVI \special+ command
% standard. (See \TUB, 10(2), 1989, p.~188.)
%^^A \bibitem{glv&tjr} Glenn L. Vandenberg and Thomas J. Reid.
%^^A \sp{} issues. \TUB, 8(3), 1987, p.~287.
% \bibitem{beebe} Nelson H. F. Beebe. {\sl A \TeX{} DVI Driver Family}.
% \end{thebibliography}
% {\tenuit Note added:\enspace } Since doing this work I have become
% aware of two related pieces of work. One is Ken Yap's article
% ``Making 35~mm Colour Slides with \SliTeX'' in \TUB{} 11.2 (1990),
% p.~279. He also used a modified version of a Beebe driver for his
% raster device, but maintained the colour layers idea. This style
% provides the `more elegant and general solution' to the problem
% mentioned in his conclusion.
%
% The other work is concerned with specifically \PS{} printers rather
% than raster ones. It is Leslie Lamport's {\tt ps-slides.sty} which
% Sebastian Rahtz pointed out to me, available from the Aston archive.
% Since it is specific to \PS{} it can support fancier facilities. His
% approach to changing the way standard \SliTeX{} works is somewhat
% different from mine, which presumably means I was a little misguided.
% \makesignature
|