path: root/doc/context/sources/general/manuals/luametatex/luametatex-metapost.tex

% language=uk

% lua.newtable

\environment luametatex-style

\startcomponent luametatex-metapost

\startchapter[reference=metapost,title={The \METAPOST\ library \type {mplib}}]

\startsection[title={Process management}][library=mplib]

\topicindex {\METAPOST}
\topicindex {\METAPOST+mplib}
\topicindex {images+mplib}
\topicindex {images+\METAPOST}

\libindex{version}

The \METAPOST\ library interface registers itself in the table \type {mplib}. It
is based on \MPLIB\ version \ctxlua {context(mplib.version())}.

\subsection{\type {new}}

\libindex{new}

To create a new \METAPOST\ instance, call

\startfunctioncall
<mpinstance> mp = mplib.new({...})
\stopfunctioncall

This creates the \type {mp} instance object. The argument is a hash table that
can have a number of different fields, as follows:

\starttabulate[|l|l|pl|pl|]
\DB name               \BC type     \BC description                \BC default           \NC \NR
\TB
\NC \type{error_line}  \NC number   \NC error line width           \NC 79                \NC \NR
\NC \type{print_line}  \NC number   \NC line length in ps output   \NC 100               \NC \NR
\NC \type{random_seed} \NC number   \NC the initial random seed    \NC variable          \NC \NR
\NC \type{math_mode}   \NC string   \NC the number system to use:
                                        \type {scaled},
                                        \type {double} or
                                      % \type {binary} or
                                        \type {decimal}            \NC \type {scaled}    \NC \NR
\NC \type{interaction} \NC string   \NC the interaction mode:
                                        \type {batch},
                                        \type {nonstop},
                                        \type {scroll} or
                                        \type {errorstop}          \NC \type {errorstop} \NC \NR
\NC \type{job_name}    \NC string   \NC a compatibility value      \NC                   \NC \NR
\NC \type{find_file}   \NC function \NC a function to find files   \NC only local files  \NC \NR
\NC \type{utf8_mode}   \NC boolean  \NC permit characters in the
                                        range 128 upto 255 to be
                                        part of names              \NC \type {false}     \NC \NR
\NC \type{text_mode}   \NC boolean  \NC permit characters 2 and 3
                                        as fencing string literals \NC \type {false}     \NC \NR
\LL
\stoptabulate

The binary mode is no longer available in the \LUATEX\ version of \MPLIB. It
offers no real advantage and brings a ton of extra libraries with platform
specific properties that we can now avoid. We might introduce a high resolution
scaled variant at some point but only when it pays of performance wise.

The \type {find_file} function should be of this form:

\starttyping
<string> found = finder (<string> name, <string> mode, <string> type)
\stoptyping

with:

\starttabulate[|l|p|]
\DB name        \BC the requested file \NC \NR
\TB
\NC \type{mode} \NC the file mode: \type {r} or \type {w} \NC \NR
\NC \type{type} \NC the kind of file, one of: \type {mp}, \type {tfm}, \type {map},
                    \type {pfb}, \type {enc} \NC \NR
\LL
\stoptabulate

Return either the full path name of the found file, or \type {nil} if the file
cannot be found.

Note that the new version of \MPLIB\ no longer uses binary mem files, so the way
to preload a set of macros is simply to start off with an \type {input} command
in the first \type {execute} call.

When you are processing a snippet of text starting with \type {btex} or \type
{verbatimtex} and ending with \type {etex}, the \METAPOST\ \type {texscriptmode}
parameter controls how spaces and newlines get honoured. The default value is~1.
Possible values are:

\starttabulate[|l|p|]
\DB name      \BC meaning \NC \NR
\TB
\NC \type {0} \NC no newlines \NC \NR
\NC \type {1} \NC newlines in \type {verbatimtex} \NC \NR
\NC \type {2} \NC newlines in \type {verbatimtex} and \type {etex} \NC \NR
\NC \type {3} \NC no leading and trailing strip in \type {verbatimtex} \NC \NR
\NC \type {4} \NC no leading and trailing strip in \type {verbatimtex} and \type {btex} \NC \NR
\LL
\stoptabulate

That way the \LUA\ handler (assigned to \type {make_text}) can do what it likes.
An \type {etex} has to be followed by a space or \type {;} or be at the end of a
line and preceded by a space or at the beginning of a line.

\subsection{\type {statistics}}

\libindex{statistics}

You can request statistics with:

\startfunctioncall
<table> stats = mp:statistics()
\stopfunctioncall

This function returns the vital statistics for an \MPLIB\ instance. There are
four fields, giving the maximum number of used items in each of four allocated
object classes:

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{main_memory} \NC number \NC memory size \NC \NR
\NC \type{hash_size}   \NC number \NC hash size\NC \NR
\NC \type{param_size}  \NC number \NC simultaneous macro parameters\NC \NR
\NC \type{max_in_open} \NC number \NC input file nesting levels\NC \NR
\LL
\stoptabulate

Note that in the new version of \MPLIB, this is informational only. The objects
are all allocated dynamically, so there is no chance of running out of space
unless the available system memory is exhausted.

\subsection{\type {execute}}

\libindex{execute}

You can ask the \METAPOST\ interpreter to run a chunk of code by calling

\startfunctioncall
<table> rettable = execute(mp,"metapost code")
\stopfunctioncall

for various bits of \METAPOST\ language input. Be sure to check the \type
{rettable.status} (see below) because when a fatal \METAPOST\ error occurs the
\MPLIB\ instance will become unusable thereafter.

Generally speaking, it is best to keep your chunks small, but beware that all
chunks have to obey proper syntax, like each of them is a small file. For
instance, you cannot split a single statement over multiple chunks.

In contrast with the normal stand alone \type {mpost} command, there is
\notabene {no} implied \quote{input} at the start of the first chunk.

\subsection{\type {finish}}

\libindex{finish}

\startfunctioncall
<table> rettable = finish(mp)
\stopfunctioncall

If for some reason you want to stop using an \MPLIB\ instance while processing is
not yet actually done, you can call \type {finish}. Eventually, used memory
will be freed and open files will be closed by the \LUA\ garbage collector, but
an explicit \type {finish} is the only way to capture the final part of the
output streams.

\stopsection

\startsection[title={The end result}]

\libindex {fields}

The return value of \type {execute} and \type {finish} is a table with a
few possible keys (only \type {status} is always guaranteed to be present).

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{log}    \NC string \NC output to the \quote {log} stream \NC \NR
\NC \type{term}   \NC string \NC output to the \quote {term} stream \NC \NR
\NC \type{error}  \NC string \NC output to the \quote {error} stream
                                 (only used for \quote {out of memory}) \NC \NR
\NC \type{status} \NC number \NC the return value:
                                 \type {0} = good,
                                 \type {1} = warning,
                                 \type {2} = errors,
                                 \type {3} = fatal error \NC \NR
\NC \type{fig}    \NC table  \NC an array of generated figures (if any) \NC \NR
\LL
\stoptabulate

When \type {status} equals~3, you should stop using this \MPLIB\ instance
immediately, it is no longer capable of processing input.

If it is present, each of the entries in the \type {fig} array is a userdata
representing a figure object, and each of those has a number of object methods
you can call:

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{boundingbox}  \NC function \NC returns the bounding box, as an array of 4
                                         values \NC \NR
\NC \type{postscript}   \NC function \NC returns a string that is the ps output of the
                                         \type {fig}. this function accepts two optional
                                         integer arguments for specifying the values of
                                         \type {prologues} (first argument) and \type
                                         {procset} (second argument) \NC \NR
\NC \type{svg}          \NC function \NC returns a string that is the svg output of the
                                         \type {fig}. This function accepts an optional
                                         integer argument for specifying the value of
                                         \type {prologues} \NC \NR
\NC \type{objects}      \NC function \NC returns the actual array of graphic objects in
                                         this \type {fig} \NC \NR
\NC \type{copy_objects} \NC function \NC returns a deep copy of the array of graphic
                                         objects in this \type {fig} \NC \NR
\NC \type{filename}     \NC function \NC the filename this \type {fig}'s \POSTSCRIPT\
                                         output would have written to in stand alone
                                         mode \NC \NR
\NC \type{width}        \NC function \NC the \type {fontcharwd} value \NC \NR
\NC \type{height}       \NC function \NC the \type {fontcharht} value \NC \NR
\NC \type{depth}        \NC function \NC the \type {fontchardp} value \NC \NR
\NC \type{italcorr}     \NC function \NC the \type {fontcharit} value \NC \NR
\NC \type{charcode}     \NC function \NC the (rounded) \type {charcode} value \NC \NR
\LL
\stoptabulate

Note: you can call \type {fig:objects()} only once for any one \type {fig}
object!

When the boundingbox represents a \quote {negated rectangle}, i.e.\ when the
first set of coordinates is larger than the second set, the picture is empty.

Graphical objects come in various types: \type {fill}, \type {outline}, \type
{text}, \type {start_clip}, \type {stop_clip}, \type {start_bounds}, \type
{stop_bounds}, \type {special}. Each type has a different list of accessible
values.

There is a helper function (\type {mplib.fields(obj)}) to get the list of
accessible values for a particular object, but you can just as easily use the
tables given below.

All graphical objects have a field \type {type} that gives the object type as a
string value; it is not explicit mentioned in the following tables. In the
following, \type {number}s are \POSTSCRIPT\ points represented as a floating
point number, unless stated otherwise. Field values that are of type \type
{table} are explained in the next section.

\subsection{fill}

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{path}       \NC table  \NC the list of knots \NC \NR
\NC \type{htap}       \NC table  \NC the list of knots for the reversed trajectory \NC \NR
\NC \type{pen}        \NC table  \NC knots of the pen \NC \NR
\NC \type{color}      \NC table  \NC the object's color \NC \NR
\NC \type{linejoin}   \NC number \NC line join style (bare number)\NC \NR
\NC \type{miterlimit} \NC number \NC miterlimit\NC \NR
\NC \type{prescript}  \NC string \NC the prescript text \NC \NR
\NC \type{postscript} \NC string \NC the postscript text \NC \NR
\LL
\stoptabulate

The entries \type {htap} and \type {pen} are optional.

\subsection{outline}

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{path}       \NC table  \NC the list of knots \NC \NR
\NC \type{pen}        \NC table  \NC knots of the pen \NC \NR
\NC \type{color}      \NC table  \NC the object's color \NC \NR
\NC \type{linejoin}   \NC number \NC line join style (bare number) \NC \NR
\NC \type{miterlimit} \NC number \NC miterlimit \NC \NR
\NC \type{linecap}    \NC number \NC line cap style (bare number) \NC \NR
\NC \type{dash}       \NC table  \NC representation of a dash list \NC \NR
\NC \type{prescript}  \NC string \NC the prescript text \NC \NR
\NC \type{postscript} \NC string \NC the postscript text \NC \NR
\LL
\stoptabulate

The entry \type {dash} is optional.

\subsection{text}

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{text}       \NC string \NC the text \NC \NR
\NC \type{font}       \NC string \NC font tfm name \NC \NR
\NC \type{dsize}      \NC number \NC font size \NC \NR
\NC \type{color}      \NC table  \NC the object's color \NC \NR
\NC \type{width}      \NC number \NC \NC \NR
\NC \type{height}     \NC number \NC \NC \NR
\NC \type{depth}      \NC number \NC \NC \NR
\NC \type{transform}  \NC table  \NC a text transformation \NC \NR
\NC \type{prescript}  \NC string \NC the prescript text \NC \NR
\NC \type{postscript} \NC string \NC the postscript text \NC \NR
\LL
\stoptabulate

\subsection{special}

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{prescript} \NC string \NC special text \NC \NR
\LL
\stoptabulate

\subsection{start_bounds, start_clip}

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{path} \NC table \NC the list of knots \NC \NR
\LL
\stoptabulate

\subsubsection{stop_bounds, stop_clip}

Here are no fields available.

\stopsection

\startsection[title={Subsidiary table formats}]

\subsection{Paths and pens}

Paths and pens (that are really just a special type of paths as far as \MPLIB\ is
concerned) are represented by an array where each entry is a table that
represents a knot.

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{left_type}  \NC string \NC when present: endpoint, but usually absent \NC \NR
\NC \type{right_type} \NC string \NC like \type {left_type} \NC \NR
\NC \type{x_coord}    \NC number \NC X coordinate of this knot \NC \NR
\NC \type{y_coord}    \NC number \NC Y coordinate of this knot \NC \NR
\NC \type{left_x}     \NC number \NC X coordinate of the precontrol point of this knot \NC \NR
\NC \type{left_y}     \NC number \NC Y coordinate of the precontrol point of this knot \NC \NR
\NC \type{right_x}    \NC number \NC X coordinate of the postcontrol point of this knot \NC \NR
\NC \type{right_y}    \NC number \NC Y coordinate of the postcontrol point of this knot \NC \NR
\LL
\stoptabulate

There is one special case: pens that are (possibly transformed) ellipses have an
extra key \type {type} with value \type {elliptical} besides the array part
containing the knot list.

\subsection{Colors}

A color is an integer array with 0, 1, 3 or 4 values:

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{0} \NC marking only \NC no values                                                     \NC \NR
\NC \type{1} \NC greyscale    \NC one value in the range $(0,1)$, \quote {black} is $0$         \NC \NR
\NC \type{3} \NC \RGB         \NC three values in the range $(0,1)$, \quote {black} is $0,0,0$  \NC \NR
\NC \type{4} \NC \CMYK        \NC four values in the range $(0,1)$, \quote {black} is $0,0,0,1$ \NC \NR
\LL
\stoptabulate

If the color model of the internal object was \type {uninitialized}, then it was
initialized to the values representing \quote {black} in the colorspace \type
{defaultcolormodel} that was in effect at the time of the \type {shipout}.

\subsection{Transforms}

Each transform is a six|-|item array.

\starttabulate[|l|l|p|]
\DB index  \BC type \BC explanation \NC \NR
\TB
\NC \type{1} \NC number \NC represents x  \NC \NR
\NC \type{2} \NC number \NC represents y  \NC \NR
\NC \type{3} \NC number \NC represents xx \NC \NR
\NC \type{4} \NC number \NC represents yx \NC \NR
\NC \type{5} \NC number \NC represents xy \NC \NR
\NC \type{6} \NC number \NC represents yy \NC \NR
\LL
\stoptabulate

Note that the translation (index 1 and 2) comes first. This differs from the
ordering in \POSTSCRIPT, where the translation comes last.

\subsection{Dashes}

Each \type {dash} is a hash with two items. We use the same model as \POSTSCRIPT\
for the representation of the dashlist. \type {dashes} is an array of \quote {on}
and \quote {off}, values, and \type {offset} is the phase of the pattern.

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{dashes} \NC hash   \NC an array of on-off numbers \NC \NR
\NC \type{offset} \NC number \NC the starting offset value  \NC \NR
\LL
\stoptabulate

\subsection{Pens and \type {pen_info}}

\libindex{pen_info}

There is helper function (\type {pen_info(obj)}) that returns a table containing
a bunch of vital characteristics of the used pen (all values are floats):

\starttabulate[|l|l|p|]
\DB field  \BC type \BC explanation \NC \NR
\TB
\NC \type{width} \NC number \NC width of the pen \NC \NR
\NC \type{sx}    \NC number \NC $x$ scale        \NC \NR
\NC \type{rx}    \NC number \NC $xy$ multiplier  \NC \NR
\NC \type{ry}    \NC number \NC $yx$ multiplier  \NC \NR
\NC \type{sy}    \NC number \NC $y$ scale        \NC \NR
\NC \type{tx}    \NC number \NC $x$ offset       \NC \NR
\NC \type{ty}    \NC number \NC $y$ offset       \NC \NR
\LL
\stoptabulate

\subsection[title={Character size information}]

\libindex{char_width}
\libindex{char_height}
\libindex{char_depth}

These functions find the size of a glyph in a defined font. The \type {fontname}
is the same name as the argument to \type {infont}; the \type {char} is a glyph
id in the range 0 to 255; the returned \type {w} is in AFM units.

\startfunctioncall
<number> w = char_width(mp,<string> fontname, <number> char)
<number> h = char_height(mp,<string> fontname, <number> char)
<number> d = char_depth(mp,<string> fontname, <number> char)
\stopfunctioncall

\stopsection

\startsection[title=Scanners]

After a relative long period of testing the scanners are now part of the
interface. That doesn't mean that there will be no changes: depending on the
needs and experiences details might evolve. The summary below is there
still preliminary and mostly provided as reminder.

\starttabulate[|l|l|p|]
\DB scanner \BC argument \BC returns \NC \NR
\TB
\NC \type{scan_next}       \NC instance, keep         \NC token, mode, type \NC \NR
\NC \type{scan_expression} \NC instance, keep         \NC type \NC \NR
\NC \type{scan_token}      \NC instance, keep         \NC token, mode, kind \NC \NR
\NC \type{scan_symbol}     \NC instance, keep, expand \NC string \NC \NR
\NC \type{scan_numeric}    \NC instance, type         \NC number \NC \NR
\NC \type{scan_integer}    \NC instance, type         \NC integer \NC \NR
\NC \type{scan_boolean}    \NC instance, type         \NC boolean \NC \NR
\NC \type{scan_string}     \NC instance, type         \NC string \NC \NR
\NC \type{scan_pair}       \NC instance, hashed, type \NC table or two numbers \NC \NR
\NC \type{scan_color}      \NC instance, hashed, type \NC table or three numbers \NC \NR
\NC \type{scan_cmykcolor}  \NC instance, hashed, type \NC table or four numbers \NC \NR
\NC \type{scan_transform}  \NC instance, hashed, type \NC table or six numbers \NC \NR
\NC \type{scan_path}       \NC instance, hashed, type \NC table with hashes or arrays \NC \NR
\NC \type{scan_pen}        \NC instance, hashed, type \NC table with hashes or arrays \NC \NR
\LL
\stoptabulate

The types and token codes are numbers but they actually depend on the
implementation (although changes are unlikely). The types of data structures can
be queried with \type {mplib.gettypes()}:

\dontleavehmode \startluacode
    local t = mplib.gettypes()
    for i=0,#t do
        if i > 0 then
            context(", ")
        end
        context("%i: %s",i,t[i])
    end
\stopluacode .

The command codes are available with \type {mplib.getcodes()}:

\dontleavehmode \startluacode
    local t = mplib.getcodes()
    for i=0,#t do
        if i > 0 then
            context(", ")
        end
        context("%i: %s",i,t[i])
    end
\stopluacode .

Now, if you really want to use these, keep in mind that the internals of
\METAPOST\ are not trivial, especially because expression scanning can be
complex. So you need to experiment a bit. In \CONTEXT\ all is (and will be)
hidden below an abstraction layer so users are not bothered by all these
look|-|ahead and push|-|back issues that originate in the way \METAPOST\ scans
its input.

\stopsection

\startsection[title=Injectors]

It is important to know that piping code into the library is pretty fast and
efficient. Most processing time relates to memory management, calculations and
generation of output can not be neglected either. Out of curiousity I added some
functions that directly push data into the library but the gain is not that
large. \footnote {The main motivation was checking of huge paths could be
optimized. The other data structures were then added for completeness.}

\starttabulate[|l|l|]
\DB scanner \BC argument \NC \NR
\TB
\NC \type{inject_numeric}   \NC instance, number \NC \NR
\NC \type{inject_integer}   \NC instance, number \NC \NR
\NC \type{inject_boolean}   \NC instance, boolean \NC \NR
\NC \type{inject_string}    \NC instance, string \NC \NR
\NC \type{inject_pair}      \NC instance, (table with) two numbers \NC \NR
\NC \type{inject_color}     \NC instance, (table with) three numbers \NC \NR
\NC \type{inject_cmykcolor} \NC instance, (table with) four numbers \NC \NR
\NC \type{inject_transform} \NC instance, (table with) six numbers \NC \NR
\NC \type{inject_path}      \NC instance, table with hashes or arrays, cycle, variant \NC \NR
\LL
\stoptabulate

The path injector takes a table with subtables that are either hashed (like the
path solver) or arrays with two, four or six entries. When the third argument has
the value \type {true} the path is closed. When the fourth argument is \type
{true} the path is constructed out of straight lines (as with \type {--}) by
setting the \type {curl} values to~1 automatically. \footnote {This is all
experimental so future versions might provide more control.}

\stopsection

\stopchapter

\stopcomponent