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-%D \module
-%D [ file=supp-tpi,
-%D version=1997.07.05,
-%D title=\CONTEXT\ Support Macros,
-%D subtitle=\TPIC\ Conversion,
-%D author=Hans Hagen,
-%D date=\currentdate,
-%D copyright={PRAGMA / Hans Hagen \& Ton Otten}]
-%C
-%C This module is part of the \CONTEXT\ macro||package and is
-%C therefore copyrighted by \PRAGMA. Non||commercial use is
-%C granted.
-
-%D This modules implements the conversion of graphic \TPIC\
-%D specials using \METAPOST.
-%D
-%D We reimplement the \TPIC\ specials using the special
-%D mimmicking mechanism implemented in the support module
-%D \type{supp-spe} as well as the \METAPOST\ run||time support
-%D implemented in \type{supp-mps}.
-
-\ifx\undefined\writestatus \input supp-mis \relax \fi
-\ifx\undefined\mimmickspecials \input supp-spe \relax \fi
-\ifx\undefined\MPgraphicbox \input supp-mps \relax \fi
-
-\writestatus{loading}{Context Support Macros / TPIC Conversion}
-
-%D Beware: we haven't activated both mechanism yet. This is
-%D to be done in the calling module.
-
-\unprotect
-
-%D When we want to mimmick \TPIC\ specials in \PDFTEX, we need
-%D to map its graphic primitives into \PDF\ ones. The main
-%D problem in doing so is that \PDF\ does not support b-splines
-%D directly and also does not offer us something to draw arcs.
-%D Of course all this scan be implemented in \TEX, and the
-%D first implementation of this module did so, but the results
-%D were not that satisfying. Not having used these specials
-%D before, I had for instance to find out that the \TPIC\
-%D specials were not that unambiguesly defined.
-%D
-%D Then, while discussing something else, Sebastian Ratz told
-%D me that the Web2c implementation that \PDFTEX\ is base upon,
-%D offers some rather discutable, but nevertheless handy
-%D feature:
-%D
-%D \starttypen
-%D \write18{execute program with arguments}
-%D \stoptypen
-%D
-%D Knowing this, I immediatelly decided to throw away the old
-%D conversion macros and use the marvelous \METAPOST, \TEX\
-%D related, drawing program to do the conversion in as high a
-%D quality as possible.
-%D
-%D implementation we're going to present here, not only uses
-%D for drawing purposes, but also uses the more efficient
-%D \METAPOST\ features to store the path.
-%D
-%D \in{Table}[tab:TPIC specials] lists the \TPIC\ specials as
-%D mentioned in the \LATEX\ Graphics Companion and the
-%D relevant part of the \DVIPS\ source. This list shows us
-%D that we have to store the path before we can use it, simply
-%D because we don't know in advance what actions to apply on
-%D it.
-%D
-%D \plaatstabel[hier][tab:TPIC specials]{The \TPIC\ special syntax.}
-%D \starttabel[|||l|]
-%D \HL
-%D \NC \bf tag \NC \bf arguments \NC \bf meaning \NC\SR
-%D \HL
-%D \NC pn \NC $w$ \NC set linewidth \NC\FR
-%D \NC pa \NC $x$ $y$ \NC add point to path \NC\MR
-%D \NC fp \NC \NC draw/fill path \NC\MR
-%D \NC ip \NC \NC fill path \NC\MR
-%D \NC da \NC $l$ \NC draw dashed path \NC\MR
-%D \NC dt \NC $l$ \NC draw doted path \NC\MR
-%D \NC sp \NC $d$ \NC draw spline \NC\MR
-%D \NC ar \NC $x$ $y$ $r_x$ $r_y$ $b$ $e$ \NC draw (partial) arc \NC\MR
-%D \NC ia \NC $x$ $y$ $r_x$ $r_y$ $b$ $e$ \NC fill (partial) arc \NC\MR
-%D \NC sh \NC $s$ \NC fill next path \NC\LR
-%D \HL
-%D \stoptabel
-
-%D The first problem we have to take care of is the fact that
-%D there is no decent begin or end of the drawing process
-%D defined. We can however be quite sure that writers of
-%D packages using these specials will put them into a box,
-%D simply because else this is the most common used way to
-%D treat something \TEX\ as as a whole, like:
-%D
-%D \starttypen
-%D \hbox{\special{}\special{}...}
-%D \stoptypen
-%D
-%D We just start a picture as soon as the first special is
-%D encountered, so this becomes:
-%D
-%D \starttypen
-%D \hbox{\openpicture\newspecial{}\newspecial{}...
-%D \stoptypen
-
-%D The first step in opening the picture is to start a group.
-%D Now we can savely use the egroup that closes the box to also
-%D end the picture.
-
-\def\startTPICspecials%
- {\bgroup
- \let\startTPICspecials=\relax
- \aftergroup\stopTPICspecials
- \startwritingMPgraphic
- \writeMPgraphic{pair p[];}}
-
-%D As soon as we begin a picture, we inhibit nesting by
-%D relaxing the start macro. The first \METAPOST\ action we
-%D take is declaring an array of pairs named $p$.
-
-%D Ending the picture is invoked by closing the current group.
-%D Because the \TPIC\ picture comes out mirrored, we have to
-%D reflect the current \METAPOST\ picture, stored in the system
-%D variable {\it currentpicture}, around the $x$-axis.
-
-\def\stopTPICspecials%
- {\writeMPgraphic
- {currentpicture:=currentpicture reflectedabout ((0,0),(4095,0));}%
- \stopwritingMPgraphic
- \flushMPgraphics
- \loadcurrentMPgraphic{}%
- \setbox\MPgraphicbox=\hbox to \!!zeropoint
- {\kern-\wd\MPgraphicbox
- \vbox to \!!zeropoint{\box\MPgraphicbox\vss}\hss}%
- \ht\MPgraphicbox=\!!zeropoint
- \wd\MPgraphicbox=\!!zeropoint
- \dp\MPgraphicbox=\!!zeropoint
- \box\MPgraphicbox
- \egroup}
-
-%D Here the macro \type{\stopwritingMPgraphic} has to take care
-%D of executing and including the \METAPOST\ code.
-
-%D We need to keep track of the number of elements that form
-%D the path. This is needed because we don't know in advance
-%D how the points are to be connected.
-
-\newcount\TPICcounter
-
-%D When a path is draw, we can connect the points using a
-%D smooth curve of drawing straight lines. A closed path can be
-%D drawn or filled.
-
-\newif\ifTPICdraw
-\newif\ifTPICfill
-\newif\ifTPICcurve
-
-%D The \TPIC\ specials permit specifying the line and fill
-%D color as well as the linetype, which can be solid, dashed or
-%D dotted. We'll save those specifications as a \METAPOST\
-%D string, using:
-
-\let\TPIClinetype =\empty
-\let\TPICgrayscale=\empty
-
-%D The magic reduction factor $.07227$ is needed to map the
-%D \TPIC\ $1/1000$ of an inch to \POSTSCRIPT\ points. We cannot
-%D delegate this task to \METAPOST\ because this program does
-%D not accept values greater than 4095.
-
-%D I won't discuss all the specifics used in implementing
-%D the specials. The \METAPOST\ part is rather trivial. Many
-%D specials have much in common, so the amout of code is not
-%D that large.
-
-\redefinespecial pa \using#1 #2\endspecial
- {\startTPICspecials
- \bgroup
- \global\advance\TPICcounter by 1
- \dimen0=#1pt \dimen0=.07227\dimen0
- \dimen2=#2pt \dimen2=.07227\dimen2
- \writeMPgraphic{p[\the\TPICcounter]:=(\the\dimen0,\the\dimen2);}%
- \egroup}
-
-\redefinespecial pn \using#1\endspecial
- {\startTPICspecials
- \bgroup
- \dimen0=#1pt \dimen0=.07227\dimen0
- \writeMPgraphic{pickup pencircle scaled \the\dimen0;}%
- \egroup}
-
-\redefinespecial sh \using#1\endspecial
- {\startTPICspecials
- \bgroup
- \edef\g{#1}%
- \edef\g{\ifx\g\empty.5\else#1\fi}%
- \xdef\TPICgrayscale{withcolor (\g,\g,\g)}%
- \egroup}
-
-\redefinespecial wh \using#1\endspecial
- {\mimmickspecial sh \using0\endspecial}
-
-\redefinespecial bk \using#1\endspecial
- {\mimmickspecial sh \using1\endspecial}
-
-\redefinespecial da \using#1\endspecial
- {\startTPICspecials
- \bgroup
- \edef\l{#1}%
- \ifx\l\empty
- \gdef\TPIClinetype{dashed evenly}%
- \else
- \dimen0=#1in
- \ifdim\dimen0<\!!zeropoint \dimen0=-\dimen0\fi
- \edef\f{\the\dimen0 \space}%
- \dimen0=.5\dimen0
- \edef\h{\the\dimen0 \space}%
- \xdef\TPIClinetype{dashed dashpattern (on \h off \f on \h)}%
- \fi
- \egroup
- \TPICcurvefalse\TPICdrawtrue
- \drawTPICpath\using#1\endspecial}
-
-\redefinespecial dt \using#1\endspecial
- {\startTPICspecials
- \bgroup
- \edef\l{#1}%
- \xdef\TPIClinetype{dashed withdots \ifx\l\empty\else scaled #1in\fi}%
- \egroup
- \TPICcurvefalse\TPICdrawtrue
- \drawTPICpath\using#1\endspecial}
-
-\redefinespecial fp \using#1\endspecial
- {\startTPICspecials
- \TPICcurvefalse\TPICdrawtrue
- \ifdim0#1pt=\!!zeropoint
- \drawTPICpath\using#1\endspecial
- \else\ifdim0#1pt<\!!zeropoint
- \mimmickspecial dt\using#1\endspecial
- \else
- \mimmickspecial da\using#1\endspecial
- \fi\fi}
-
-\redefinespecial sp
- {\startTPICspecials\TPICdrawtrue\TPICcurvetrue\drawTPICpath}
-
-\redefinespecial ip
- {\startTPICspecials\TPICfilltrue\drawTPICpath}
-
-\redefinespecial ar
- {\startTPICspecials\TPICdrawtrue\drawTPICarc}
-
-\redefinespecial ia
- {\startTPICspecials\TPICfilltrue\drawTPICarc}
-
-%D These substitutes use two auxiliary macros that take care of
-%D actually drawing the shape or arc. Here we use the stored
-%D linetype (solid, dashed, dotted) and color (grayscale).
-
-\def\drawTPICpath\using#1\endspecial
- {\bgroup
- \ifTPICdraw
- \def\TPICgrayscale{}%
- \fi
- \writeMPgraphic
- {\ifTPICfill fill\fi\ifTPICdraw draw\fi\space
- for i:=1 upto \the\TPICcounter-1:
- p[i]\ifTPICcurve..\else--\fi
- endfor
- p[\the\TPICcounter]
- \ifTPICfill\ifTPICcurve..\else--\fi cycle \fi
- \TPIClinetype\space\TPICgrayscale;}%
- \resetTPICvariables
- \egroup}
-
-%D I have to admit that at the moment I wrote this macro, I
-%D could not write this piece of \METAPOST. Fortunately
-%D Thortsen Ohl promptly answered the question I posted to the
-%D \METAFONT\ discussion list.
-
-\def\drawTPICarc\using#1 #2 #3 #4 #5 #6\endspecial
- {\bgroup
- \ifTPICdraw
- \def\TPICgrayscale{}%
- \fi
- \dimen 0=#1pt\dimen 0=.07227\dimen 0
- \dimen 2=#2pt\dimen 2=.07227\dimen 2
- \dimen10=#3pt\dimen10=.14454\dimen10
- \dimen12=#4pt\dimen12=.14454\dimen12
- \dimen20=#5pt
- \dimen22=#6pt
- \writeMPgraphic
- {\ifTPICfill fill\fi\ifTPICdraw draw\fi \space
- \ifTPICfill\else subpath 4/3.14159*(\the\dimen20,\the\dimen22) of \fi
- fullcircle xscaled \the\dimen10 \space yscaled \the\dimen12 \space
- shifted (\the\dimen0,\the\dimen2)
- \TPIClinetype \space \TPICgrayscale;}%
- \resetTPICvariables
- \egroup}
-
-%D Resetting the variables need to be done globally because we
-%D cannot be sure if any further grouping is used by the
-%D envelopping macros.
-
-\def\resetTPICvariables%
- {\global\TPICcounter=0
- \global\TPICfillfalse
- \global\TPICdrawfalse
- \global\let\TPIClinetype=\empty
- \global\let\TPICgrayscale=\empty}
-
-%D I have to admit that by using the \METAPOST\ B‚zier cubics
-%D routines these implementation does produce better curves
-%D then most \DVI\ drivers do using the \TPIC\ prescribed
-%D b-splines. Take for instance the sequence:
-%D
-%D \starttypen
-%D \special{pa 2000 1000}
-%D \special{pa 1000 2000}
-%D \special{pa 0000 1000}
-%D \special{pa 1000 0000}
-%D \special{pa 2000 1000}
-%D \special{sp}
-%D \stoptypen
-%D
-%D One would expect that this code produced a closed circle,
-%D but the curve that comes out using b-splines is far from
-%D round. We can however savely asume that the arc producing
-%D specials will be used for drawing circle fragments, while
-%D the path specials will be used for arbitraty curves. And for
-%D b-splines to produce nice curves, one will often use many
-%D points to get the desired results. Therefore, using the
-%D \METAPOST\ B‚zier curves will certainly produce similar and
-%D even better graphics, except in those rare cases where one
-%D uses delinberately the not that accurate features of
-%D b-splines. Hereby the user is warned.
-
-\protect
-
-\endinput
- \ No newline at end of file
+%D \module
+%D [ file=supp-tpi,
+%D version=1997.07.05,
+%D title=\CONTEXT\ Support Macros,
+%D subtitle=\TPIC\ Conversion,
+%D author=Hans Hagen,
+%D date=\currentdate,
+%D copyright={PRAGMA / Hans Hagen \& Ton Otten}]
+%C
+%C This module is part of the \CONTEXT\ macro||package and is
+%C therefore copyrighted by \PRAGMA. Non||commercial use is
+%C granted.
+
+%D This modules implements the conversion of graphic \TPIC\
+%D specials using \METAPOST.
+%D
+%D We reimplement the \TPIC\ specials using the special
+%D mimmicking mechanism implemented in the support module
+%D \type{supp-spe} as well as the \METAPOST\ run||time support
+%D implemented in \type{supp-mps}.
+
+\ifx\undefined\writestatus \input supp-mis \relax \fi
+\ifx\undefined\mimmickspecials \input supp-spe \relax \fi
+\ifx\undefined\MPgraphicbox \input supp-mps \relax \fi
+\ifx\undefined\dogetEPSboundingbox \input supp-eps \relax \fi
+
+\writestatus{loading}{Context Support Macros / TPIC Conversion}
+
+%D Beware: we haven't activated both mechanism yet. This is
+%D to be done in the calling module.
+
+\unprotect
+
+%D When we want to mimmick \TPIC\ specials in \PDFTEX, we need
+%D to map its graphic primitives into \PDF\ ones. The main
+%D problem in doing so is that \PDF\ does not support b-splines
+%D directly and also does not offer us something to draw arcs.
+%D Of course all this scan be implemented in \TEX, and the
+%D first implementation of this module did so, but the results
+%D were not that satisfying. Not having used these specials
+%D before, I had for instance to find out that the \TPIC\
+%D specials were not that unambiguesly defined.
+%D
+%D Then, while discussing something else, Sebastian Ratz told
+%D me that the Web2c implementation that \PDFTEX\ is base upon,
+%D offers some rather discutable, but nevertheless handy
+%D feature:
+%D
+%D \starttypen
+%D \write18{execute program with arguments}
+%D \stoptypen
+%D
+%D Knowing this, I immediatelly decided to throw away the old
+%D conversion macros and use the marvelous \METAPOST, \TEX\
+%D related, drawing program to do the conversion in as high a
+%D quality as possible.
+%D
+%D implementation we're going to present here, not only uses
+%D for drawing purposes, but also uses the more efficient
+%D \METAPOST\ features to store the path.
+%D
+%D \in{Table}[tab:TPIC specials] lists the \TPIC\ specials as
+%D mentioned in the \LATEX\ Graphics Companion and the
+%D relevant part of the \DVIPS\ source. This list shows us
+%D that we have to store the path before we can use it, simply
+%D because we don't know in advance what actions to apply on
+%D it.
+%D
+%D \plaatstabel[hier][tab:TPIC specials]{The \TPIC\ special syntax.}
+%D \starttabel[|||l|]
+%D \HL
+%D \NC \bf tag \NC \bf arguments \NC \bf meaning \NC\SR
+%D \HL
+%D \NC pn \NC $w$ \NC set linewidth \NC\FR
+%D \NC pa \NC $x$ $y$ \NC add point to path \NC\MR
+%D \NC fp \NC \NC draw/fill path \NC\MR
+%D \NC ip \NC \NC fill path \NC\MR
+%D \NC da \NC $l$ \NC draw dashed path \NC\MR
+%D \NC dt \NC $l$ \NC draw doted path \NC\MR
+%D \NC sp \NC $d$ \NC draw spline \NC\MR
+%D \NC ar \NC $x$ $y$ $r_x$ $r_y$ $b$ $e$ \NC draw (partial) arc \NC\MR
+%D \NC ia \NC $x$ $y$ $r_x$ $r_y$ $b$ $e$ \NC fill (partial) arc \NC\MR
+%D \NC sh \NC $s$ \NC fill next path \NC\LR
+%D \HL
+%D \stoptabel
+
+%D The first problem we have to take care of is the fact that
+%D there is no decent begin or end of the drawing process
+%D defined. We can however be quite sure that writers of
+%D packages using these specials will put them into a box,
+%D simply because else this is the most common used way to
+%D treat something \TEX\ as as a whole, like:
+%D
+%D \starttypen
+%D \hbox{\special{}\special{}...}
+%D \stoptypen
+%D
+%D We just start a picture as soon as the first special is
+%D encountered, so this becomes:
+%D
+%D \starttypen
+%D \hbox{\openpicture\newspecial{}\newspecial{}...
+%D \stoptypen
+
+%D The first step in opening the picture is to start a group.
+%D Now we can savely use the egroup that closes the box to also
+%D end the picture.
+
+% BETER: check for context and include mp-tool.mp
+
+\def\startTPICspecials%
+ {\bgroup
+ \let\startTPICspecials=\relax
+ \aftergroup\stopTPICspecials
+ \startwritingMPgraphic
+ \writeMPgraphic{input mp-tool.mp;}%
+ \writeMPgraphic{pair p[];}}
+
+%D As soon as we begin a picture, we inhibit nesting by
+%D relaxing the start macro. The first \METAPOST\ action we
+%D take is declaring an array of pairs named $p$.
+
+%D Ending the picture is invoked by closing the current group.
+%D Because the \TPIC\ picture comes out mirrored, we have to
+%D reflect the current \METAPOST\ picture, stored in the system
+%D variable {\it currentpicture}, around the $x$-axis.
+
+\def\stopTPICspecials%
+ {\writeMPgraphic
+ {currentpicture:=currentpicture reflectedabout ((0,0),(4095,0));}%
+ \stopwritingMPgraphic
+ \flushMPgraphics
+ \loadcurrentMPgraphic{}%
+ \setbox\MPgraphicbox=\hbox to \!!zeropoint
+ {\kern-\wd\MPgraphicbox
+ \vbox to \!!zeropoint{\box\MPgraphicbox\vss}\hss}%
+ \ht\MPgraphicbox=\!!zeropoint
+ \wd\MPgraphicbox=\!!zeropoint
+ \dp\MPgraphicbox=\!!zeropoint
+ \box\MPgraphicbox
+ \egroup}
+
+%D Here the macro \type{\stopwritingMPgraphic} has to take care
+%D of executing and including the \METAPOST\ code.
+
+%D We need to keep track of the number of elements that form
+%D the path. This is needed because we don't know in advance
+%D how the points are to be connected.
+
+\newcount\TPICcounter
+
+%D When a path is draw, we can connect the points using a
+%D smooth curve of drawing straight lines. A closed path can be
+%D drawn or filled.
+
+\newif\ifTPICdraw
+\newif\ifTPICfill
+\newif\ifTPICcurve
+
+%D The \TPIC\ specials permit specifying the line and fill
+%D color as well as the linetype, which can be solid, dashed or
+%D dotted. We'll save those specifications as a \METAPOST\
+%D string, using:
+
+\let\TPIClinetype =\empty
+\let\TPICgrayscale=\empty
+
+%D The magic reduction factor $.07227$ is needed to map the
+%D \TPIC\ $1/1000$ of an inch to \POSTSCRIPT\ points. We cannot
+%D delegate this task to \METAPOST\ because this program does
+%D not accept values greater than 4095.
+
+%D I won't discuss all the specifics used in implementing
+%D the specials. The \METAPOST\ part is rather trivial. Many
+%D specials have much in common, so the amout of code is not
+%D that large.
+
+\redefinespecial pa \using#1 #2\endspecial
+ {\startTPICspecials
+ \bgroup
+ \global\advance\TPICcounter by 1
+ \dimen0=#1pt \dimen0=.07227\dimen0
+ \dimen2=#2pt \dimen2=.07227\dimen2
+ \writeMPgraphic{p[\the\TPICcounter]:=(\the\dimen0,\the\dimen2);}%
+ \egroup}
+
+\redefinespecial pn \using#1\endspecial
+ {\startTPICspecials
+ \bgroup
+ \dimen0=#1pt \dimen0=.07227\dimen0
+ \writeMPgraphic{pickup pencircle scaled \the\dimen0;}%
+ \egroup}
+
+\redefinespecial sh \using#1\endspecial
+ {\startTPICspecials
+ \bgroup
+ \edef\g{#1}%
+ \edef\g{\ifx\g\empty.5\else#1\fi}%
+ \xdef\TPICgrayscale{withcolor (\g,\g,\g)}%
+ \egroup}
+
+\redefinespecial wh \using#1\endspecial
+ {\mimmickspecial sh \using0\endspecial}
+
+\redefinespecial bk \using#1\endspecial
+ {\mimmickspecial sh \using1\endspecial}
+
+\redefinespecial da \using#1\endspecial
+ {\startTPICspecials
+ \bgroup
+ \edef\l{#1}%
+ \ifx\l\empty
+ \gdef\TPIClinetype{dashed evenly}%
+ \else
+ \dimen0=#1in
+ \ifdim\dimen0<\!!zeropoint \dimen0=-\dimen0\fi
+ \edef\f{\the\dimen0 \space}%
+ \dimen0=.5\dimen0
+ \edef\h{\the\dimen0 \space}%
+ \xdef\TPIClinetype{dashed dashpattern (on \h off \f on \h)}%
+ \fi
+ \egroup
+ \TPICcurvefalse\TPICdrawtrue
+ \drawTPICpath\using#1\endspecial}
+
+\redefinespecial dt \using#1\endspecial
+ {\startTPICspecials
+ \bgroup
+ \edef\l{#1}%
+ \xdef\TPIClinetype{dashed withdots \ifx\l\empty\else scaled #1in\fi}%
+ \egroup
+ \TPICcurvefalse\TPICdrawtrue
+ \drawTPICpath\using#1\endspecial}
+
+\redefinespecial fp \using#1\endspecial
+ {\startTPICspecials
+ \TPICcurvefalse\TPICdrawtrue
+ \ifdim0#1pt=\!!zeropoint
+ \drawTPICpath\using#1\endspecial
+ \else\ifdim0#1pt<\!!zeropoint
+ \mimmickspecial dt\using#1\endspecial
+ \else
+ \mimmickspecial da\using#1\endspecial
+ \fi\fi}
+
+\redefinespecial sp
+ {\startTPICspecials\TPICdrawtrue\TPICcurvetrue\drawTPICpath}
+
+\redefinespecial ip
+ {\startTPICspecials\TPICfilltrue\drawTPICpath}
+
+\redefinespecial ar
+ {\startTPICspecials\TPICdrawtrue\drawTPICarc}
+
+\redefinespecial ia
+ {\startTPICspecials\TPICfilltrue\drawTPICarc}
+
+%D These substitutes use two auxiliary macros that take care of
+%D actually drawing the shape or arc. Here we use the stored
+%D linetype (solid, dashed, dotted) and color (grayscale).
+
+\def\drawTPICpath\using#1\endspecial
+ {\bgroup
+ \ifTPICdraw
+ \def\TPICgrayscale{}%
+ \fi
+ \writeMPgraphic
+ {\ifTPICfill fill\fi\ifTPICdraw draw\fi\space
+ for i:=1 upto \the\TPICcounter-1:
+ p[i]\ifTPICcurve..\else--\fi
+ endfor
+ p[\the\TPICcounter]
+ \ifTPICfill\ifTPICcurve..\else--\fi cycle \fi
+ \TPIClinetype\space\TPICgrayscale;}%
+ \resetTPICvariables
+ \egroup}
+
+%D I have to admit that at the moment I wrote this macro, I
+%D could not write this piece of \METAPOST. Fortunately
+%D Thortsen Ohl promptly answered the question I posted to the
+%D \METAFONT\ discussion list.
+
+\def\drawTPICarc\using#1 #2 #3 #4 #5 #6\endspecial
+ {\bgroup
+ \ifTPICdraw
+ \def\TPICgrayscale{}%
+ \fi
+ \dimen 0=#1pt\dimen 0=.07227\dimen 0
+ \dimen 2=#2pt\dimen 2=.07227\dimen 2
+ \dimen10=#3pt\dimen10=.14454\dimen10
+ \dimen12=#4pt\dimen12=.14454\dimen12
+ \dimen20=#5pt
+ \dimen22=#6pt
+ \writeMPgraphic
+ {\ifTPICfill fill\fi\ifTPICdraw draw\fi \space
+ \ifTPICfill\else subpath 4/3.14159*(\the\dimen20,\the\dimen22) of \fi
+ fullcircle xscaled \the\dimen10 \space yscaled \the\dimen12 \space
+ shifted (\the\dimen0,\the\dimen2)
+ \TPIClinetype \space \TPICgrayscale;}%
+ \resetTPICvariables
+ \egroup}
+
+%D Resetting the variables need to be done globally because we
+%D cannot be sure if any further grouping is used by the
+%D envelopping macros.
+
+\def\resetTPICvariables%
+ {\global\TPICcounter=0
+ \global\TPICfillfalse
+ \global\TPICdrawfalse
+ \global\let\TPIClinetype=\empty
+ \global\let\TPICgrayscale=\empty}
+
+%D I have to admit that by using the \METAPOST\ B‚zier cubics
+%D routines these implementation does produce better curves
+%D then most \DVI\ drivers do using the \TPIC\ prescribed
+%D b-splines. Take for instance the sequence:
+%D
+%D \starttypen
+%D \special{pa 2000 1000}
+%D \special{pa 1000 2000}
+%D \special{pa 0000 1000}
+%D \special{pa 1000 0000}
+%D \special{pa 2000 1000}
+%D \special{sp}
+%D \stoptypen
+%D
+%D One would expect that this code produced a closed circle,
+%D but the curve that comes out using b-splines is far from
+%D round. We can however savely asume that the arc producing
+%D specials will be used for drawing circle fragments, while
+%D the path specials will be used for arbitraty curves. And for
+%D b-splines to produce nice curves, one will often use many
+%D points to get the desired results. Therefore, using the
+%D \METAPOST\ B‚zier curves will certainly produce similar and
+%D even better graphics, except in those rare cases where one
+%D uses delinberately the not that accurate features of
+%D b-splines. Hereby the user is warned.
+
+\protect
+
+\endinput
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