%
%From: chase@orc.olivetti.com (David Chase)
%Subject: re: Flow charts in LaTeX
%Date: Mon, 24 Oct 88 15:34:42 -0700
%
%Here is a tool that might be useful; you can use it to get lines
%which bend (90 degrees) ending in arrows, and you can study it (ha ha)
%to figure out how it might be extended to do a flow chart.
%It is included within a program to test demonstrate it.  It uses only
%the LaTeX picture macros for graphics.
%
%Note the use of dirty tricks to turn points into dimensionless
%numbers.  There may be a better way, but I couldn't find it.  My
%difficulties with this lead me to believe that either
%(1) TeX should really provide dimensionless real numbers
%or
%(2) Maybe LaTeX should use real lengths instead of dimensionless
%numbers in the picture environment.  I might get tired of always
%attaching a dimension to things, but it would be LOTS easier to write
%interesting macros.
%
%If anyone can point out to me an easier way to do this, I'd be happy
%to hear it.  People on TeXhax tried to help me a couple of years ago
%with this, but nothing seemed to work.
%
%---------------- BEGINNING OF MACROS  ----------------
% First, a dirty trick

{\catcode`p=12 \catcode`t=12 \gdef\bogusmacro#1pt{#1}}
\let\getfactor=\bogusmacro
\def\unpt#1{\expandafter\getfactor\the#1}

% A macro to get us out of the iteration.

\def\gobbleemup#1,#2,#3,{}

% TWAI does all the work, and could probably be rewritten
% to be much prettier.

\def\twai#1,#2,#3,#4,#5,{
%	\typeout{Twisty arrow increment of |#1| |#2| |#3| |#4| |#5|}

% Turn parameters into PT quantities so we can do simple arithmetic.
	\xco#1pt\relax
	\yco#2pt\relax
	\len#4pt\relax
	\advance\len -\firstshrink\relax
% We get \taoval dynamically from our caller
	\def\firstshrink{\taoval pt}\relax
% Set things up for selection and iteration
	\let\drawcommand=\line
	\def\this{#3}
	\def\xvec{0}
	\def\yvec{0}
	\let\next=\twai
% Figure out which way we're going now
	\if\this\uu
		\addtolength{\yloc}{\len}
		\def\yvec{1}
		\corner=0
		\else
	\if\this\dd
		\addtolength{\yloc}{-\len}
		\def\yvec{-1}
		\corner=1
		\else
	\if\this\ll
		\addtolength{\xloc}{-\len}
		\def\xvec{-1}
		\corner=0
		\else
	\if\this\rr
		\addtolength{\xloc}{\len}
		\def\xvec{1}
		\corner=2
		\else
	\if\this\ee
		\relax
		\else
		\typeout{Twisty Arrow Increment--arg 2 (\this) not one of {udlre}}
	\fi\fi\fi\fi\fi
        \if#5\ee
%		\typeout{Ending vector}
		\let\drawcommand=\twaiend
		\advance\len\tarad
	\fi
%        \typeout{New XL \unpt\xloc\space YL \unpt\yloc}
% Here we emit the line or ending command
	\put(\unpt\xco,\unpt\yco){\drawcommand(\xvec,\yvec){\unpt\len}}
	% Figure out the next line
	\if#5\uu
		\advance\yloc \tarad
		\advance\corner 1
		\else
	\if#5\dd
		\advance\yloc -\tarad
		\advance\corner 0
		\else
	\if#5\ll
		\advance\xloc -\tarad
		\advance\corner 2
		\else
	\if#5\rr
		\advance\xloc \tarad
		\advance\corner 0
		\else
	\if#5\ee
		\let\next=\gobbleemup
                \corner=4
		\else
	typeout{Twisty Arrow Increment--arg 5 (#5) not one of {udlre}}
	\fi\fi\fi\fi\fi
%       \typeout{Corner center XL \unpt\xloc\space YL \unpt\yloc}
	\ifcase\corner
		% case 0 TL
		\put(\unpt\xloc,\unpt\yloc){\oval(\taoval,\taoval)[tl]}
		\or
		% case 1 BL
		\put(\unpt\xloc,\unpt\yloc){\oval(\taoval,\taoval)[bl]}
		\or
		% case 2 TR
		\put(\unpt\xloc,\unpt\yloc){\oval(\taoval,\taoval)[tr]}
		\or
		% case 3 BR
		\put(\unpt\xloc,\unpt\yloc){\oval(\taoval,\taoval)[br]}
		\or
		% case 4 END
		\relax
		\fi
	\advance\xloc \xvec\tarad
	\advance\yloc \yvec\tarad
%        \typeout{Final XL \unpt\xloc\space YL \unpt\yloc}
% iterate or finish, depending upon value of 'next'
	\next\unpt\xloc,\unpt\yloc,#5,
	}
\def\twistyarrowgen(#1,#2,#3,#4)#5{{
	\def\uu{u}
	\def\dd{d}
	\def\ll{l}
	\def\rr{r}
	\def\ee{e}
	\countdef\corner=255
	\newskip{\xco}\newskip{\yco}\newskip{\len}
	\newskip{\xloc}\newskip{\yloc}
	\newskip{\tarad}\setlength{\tarad}{#3pt}
	\newskip{\dummylen}
	\let\twaiend=#4
	\setlength{\dummylen}{\tarad}
	\advance\dummylen \dummylen
	\def\taoval{\unpt\dummylen}
	\setlength{\xloc}{#1pt}\setlength{\yloc}{#2pt}
	\def\firstshrink{\tarad}\relax
	\twai #1,#2,#5,e,}}
%
\def\twistyarrow(#1,#2){\twistyarrowgen(#1,#2,2,\vector)}
\def\twistyarrowrad(#1,#2,#3){\twistyarrowgen(#1,#2,#3,\vector)}
%----------------  END OF MACROS ----------------
%\documentstyle[flowchart]{article}
%\begin{document}
%\unitlength=.1in
%\begin{center}
%\begin{picture}(30,30)
%\twistyarrowrad(0,0,1){%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11,r,11,d,10,l,10,%
%u,11}
%\end{picture}
%\end{center}
%\end{document}