% language=us

% This only works in MKIV because in LMTX we don't load the font-vir module
% any longer. No one used it anyway.

\environment mk-environment

\startcomponent mk-punk

\page[right] \start

% the opentype one:
%
% \setupbodyfont[punknova]

% the mp based runtime one:


\usemodule[m][punk]
\usetypescript[punk]
\switchtobodyfont[punk,12pt]

\StartRandomPunk

\definesymbol[1][--]
\setupsorting[logo][style=]
\setupcapitals[title=no]
\setuptype[style=\tf]
\setuptyping[style=\tf]
\logo[METAPOST] {MetaPost}
\logo[METAFONT] {MetaFont}

\chapter{How to convince Don and Hermann to use \LUATEX}

{\em The code shown here should look a bit different in versions
of \MKIV\ after March 2011. This is because the font system was
cleaned up and upgraded. The prinicples remain the same. You can
have a look at \type {m-punk.mkiv} in the \CONTEXT\ distribution.}

Odds are pretty low that Don Knuth will use \LUATEX\ for
typesetting the next update of his opus magnum, and odds are even
lower that Hermann Zapf will use \MPLIB\ for Melior Nova. However,
the next example of combining \METAFONT\ and \TEX\ may draw their
interest in this new variant: \METATEX.

The font used here is called \quote {punk} and is designed by
Donald Knuth. There is a note in the file that says: \quotation
{Font inspired by Gerard and Marjan Unger's lectures, February
1985}. If you didn't notice it yet: punk is a random font.

You may wonder why we started looking into this masterpiece of
font design. Well, there are a few reasons:

\startitemize

\item  We always liked this font, but after the rise of outline
       fonts it was not a natural candidate for using in
       documents. Fun is always a good motive.

\item  For many years we have been suggesting that special glyphs
       and/or aspects of typesetting could be realized by runtime
       generation of graphics, and we need this testbed for the
       Oriental \TEX\ project: Idris needs stretchable inter|-|glyph
       connections.

\item  Taco likes using tricky \METAPOST\ backgrounds for his
       presentations that demonstrate this programming language.

\item  Hartmut loves to tweak the backend and runtime font generation
       will demand some extensions to the font inclusion and literal
       handlers.

\item  Because Hans attends many \TEX\ conferences together with Volker
       Schaa, he has promised him to avoid repeating talk and
       presentation layouts, and so a new presentation style was needed.

\stopitemize

To this we can add an already mentioned motivation: convince Don and
Hermann to use \LUATEX\ \unknown\ who knows. And, if that fails, maybe
they can team up for an extensions to this font: more style variants,
proper math and the full range of \UNICODE\ glyphs.

The punk font is written in \METAFONT\ and there are multiple
sources. These are merged into one file which is to be processed
using the \type {mfplain} format. Definitions of characters in
this font look like:

\starttyping
beginpunkchar ("A",13,1,2) ;
    z1 = pp(1.5u,0) ; z2 = (.5w,1.1h) ; z3 = pp(w-1.5u,0) ;
    pd z1 ; pd z3 ; draw z1 -- z2 -- z3 ;
    z4 = pp .3[z1,z2] ; z5 = pp .3[z3,z2] ;
    pd z4 ; pd z5 ; draw z4 -- z5;
endchar ;
\stoptyping

When \TEX\ needs a font, i.e.\ when we have something like this:

\starttyping
\font\somefont=whatever at 12pt
\stoptyping

in \CONTEXT\ control is delegated to a font loader written in
\LUA\ that is hooked into \TEX. This loader interprets the name
and if needed filters the specification from it. Think of this:

\starttyping
\font\somefont=whatever*smallcaps at 16pt
\stoptyping

This means: load font \type {whatever} and enable the smallcaps features.
However this mechanism is mostly geared towards \TYPEONE\ and \OPENTYPE\
fonts. But punk is neither: it's a \METAFONT, and we need to treat it as
such. We will use \LUATEX's powerful virtual font technology
because that way we can smuggle the proper shapes in the final
file. And \unknown\ no bitmaps and no funny encoding.

In \CONTEXT\ \MKIV\ there is a preliminary virtual font definition
mechanism. There is no advanced \TEX\ interface yet so we need to do it in
\LUA. Fortunately we do have access to this from the font mechanism:

\starttyping
\font\somefont=mypunk@punk at 20pt
\stoptyping

This is a rather valid directive to create a font that internally
will be called \type {mypunk}. For this the virtual font creation
command \type {punk} will be used, and in a moment we will see what
this triggers.

Of course, users will never see such low level definitions. They will
use proper typescript, which set up a whole font system. For instance,
in this document we use:

\typebuffer[fontdefinition]

Now, using punk in inself is not that much of a challenge, but how about
using multiple instances of this font and then typeset the text chosing
variants of a glyph at random. Of course this will have some trade-off in
terms of runtime. In this document we use punk as the bodyfont and
therefore it comes in several sizes. On Hans's laptop generating the
glyphs takes a while:

\starttyping
7500 glyphs, 12.887 seconds runtime, 581 glyphs/second
\stoptyping

Fortunately \MKIV\ provides a caching mechanism so once the fonts
are generated, a next run will be more comfortable. This time we
get reported:

\starttyping
0.187 seconds, 60 instances, 320.856 instances/second
\stoptyping

which is not that bad for loading 60 files of 5 megabytes \PDF\
literals each. The reason why the files are large is that although
these glyphs look simple, in fact they are rather complex: each
glyph at least one paths and several knots, and since a special
pen is used, conversion results in a larger than normal description
of a shape.

Since we use the standard converter from \METAPOST\ to \PDF, we
can gain some generation time by using a dedicated converter for
glyphs. Eventually the \MPLIB\ library may even provide a proper
charstring generator so that we can construct real fonts at
runtime.

So, how does this work behind the screens? Because we can use some
of the mechanisms already present in \CONTEXT\ it is not even that complex.

\startitemize

\item The \type {punk} directive tells \CONTEXT\ to create a virtual
      font. Such a font can be made out of real fonts; we use this
      for instance in the font feature \type {combine}, where we
      add virtually composed characters that are missing by combining
      characters present. However, here we have no real font.

\item And so this virtual font is not build on top of an existing font, but
      spawns a \MPLIB\ process that will build the font, unless it is
      present in the cache on disk. The shapes are converted to \PDF\ literals
      and for each character a proper definition table is made.

\item In total 10 such fonts are made, but only one is returned to the
      font callback that asked us to provide the font. The list of
      the alternatives is stored in the \LUA\ table that represents
      the font and kept at the \LUA\ end. So, for each size used,
      a unique set of 10 variants is generated.

\item The randomizer operates on the node list. Instead of using a
      dedicated mechanism for this, we hijack one of the attribute values
      of the case swapper already present in \MKIV. After that we can selectively
      turn on and off the randomizer.

\item At some point \TEX\ will hand over the node lists to \CONTEXT. At
      that moment a lot of things can happen to the list, and one of
      them is a sequence of character handlers, of which the mentioned case
      handler is one. The handler sweeps over the nodelist
      and for each glyph node triggers a function that is bound to the
      attribute value.

\item This function is rather trivial: it looks at the font id of the
      glyph, and resolves it to the font table. If that table has a
      list of alternatives, it will randomly choose one and assign it to
      the font attribute of the glyph. That's all.

\item Eventually the backend routines will inject the \PDF\ literals that
      were collected in the commands table of the virtual glyph.

\stopitemize

It will not come as a surprise that our resulting file is larger
than what we get when using traditional outline fonts or just one
instance of punk. However, this is just an experiment, and
eventually a proper font constructor will be provided, so that the
glyph drawing is delegated to the font renderer. An intermediate
optimization can be to use so called \PDF\ xforms, but a properly
runtime generated font is best because then we can search in the
file too.

Because by now reading the punk font should go fluently we can now
move on to the code. We already have a \type {fonts} namespace,
which we now extend with an \METAPOST\ sub namespace:

\starttyping
fonts.mp = fonts.mp or { }
\stoptyping

We set a version number and define a cache on disk. When the number changes
fonts stored in the cache will be regenerated when needed. The
\type {containers} module provides the relevant function.

\starttyping
fonts.mp.version = 1.01
fonts.mp.cache = containers.define("fonts", "mp", fonts.mp.version, true)
\stoptyping

We already have a \type {metapost} namespace, and within it we define a
sub namespace:

\starttyping
metapost.characters = metapost.characters or { }
\stoptyping

Now we're ready for the real action: we define a dedicated flusher
that will be passed to the \METAPOST\ converter. A next version of
\MPLIB\ will provide the \TFM\ font information which gives better
glyph dimensions, plus additional kerning information. All this code
is defined in a closure (\type {do ... end}) which
nicely hides the local variables.

\starttyping
local characters, descriptions = { }, { }
local factor, total, variants = 100, 0, 0
local l, n, w, h, d  = { }, 0, 0, 0, 0

local flusher = {
    startfigure = function(chrnum,llx,lly,urx,ury)
        l, n = { }, chrnum
        w, h, d = urx - llx, ury, -lly
        total = total + 1
    end,
    flushfigure = function(t)
        for i=1, #t do
            l[#l+1] = t[i]
        end
    end,
    stopfigure = function()
        local cd = characters.data[n]
        descriptions[n] = {
            unicode = n,
            name = cd and cd.adobename,
            width = w*100,
            height = h*100,
            depth = d*100,
        }
        characters[i] = {
            commands = {
                { "special", "pdf: " .. table.concat(l," ") },
            }
        }
    end
}
\stoptyping

In the normal converter, the start and stop function do the
packaging in a box. The flush function is called when literals
need to be flushed. This threesome does as much as collecting
glyph information in the \type {list} table. Intermediate literals
are stored in the \type {l} table. Each glyph has a description and
(in this case) one command that defines the virtual shape. The name
is picked up from the character data table that is present in \MKIV.

As told before we generate multiple instances per requested font
and here is how it happens. We initialize the \type {mfplain}
format and reset it afterwards. The punk definition file is
adapted for multiple runs. Scaling happens here because later on
the scaler has no knowledge about what is present in the commands.
We use a few helpers for processing the \METAPOST\ code and format
the final font table in a way \CONTEXT\ \MKIV\ likes. Currently
the parameters (font dimensions) are rather hard coded, but this
will change when \MPLIB\ can provide them.

\starttyping
function metapost.characters.process(mpxformat, name, instances, scalefactor)
    statistics.starttiming(metapost.characters)
    scalefactor = scalefactor or 1
    instances = instances or 10
    local fontname = file.removesuffix(file.basename(name))
    local hash = file.robustname(string.format(
        "%s %04i %04i", fontname, scalefactor*1000, instances))
    local lists = containers.read(fonts.mp.cache, hash)
    if not lists then
        statistics.starttiming(flusher)
        local data = io.loaddata(resolvers.findfile(name))
        metapost.reset(mpxformat)
        lists = { }
        for i=1,instances do
            characters, descriptions = { }
            metapost.process(
                mpxformat,
                {
                    "randomseed := " .. i*10 .. ";",
                    "scale_factor := " .. scalefactor .. " ;",
                    data
                },
                false,
                flusher
            )
            lists[#lists+1] = {
                designsize = 655360,
                name = string.format("%s-%03i",hash,i),
                parameters = {
                    slant         =    0,
                    space         =  333   * scalefactor,
                    space_stretch =  166.5 * scalefactor,
                    space_shrink  =  111   * scalefactor,
                    x_height      =  431   * scalefactor,
                    quad          = 1000   * scalefactor,
                    extra_space   =    0
                },
                ["type"] = "virtual",
                characters = characters,
                descriptions = descriptions,
            }
        end
        metapost.reset(mpxformat) -- saves memory
        lists = containers.write(fonts.mp.cache, hash, lists)
        statistics.stoptiming(flusher)
    end
    variants = variants + #lists
    statistics.stoptiming(metapost.characters)
    return lists
end
\stoptyping

We're not yet there. This was just a font generator that returns
a list of fonts defined in a format liked by \MKIV\ and not that
far from what \TEX\ wants back from us. Next we define the
main definition function, the one that is called when the font
is defined as virtual font. The special number \type {-1000}
tells the scaler to honour the designsize, which boils down to
no scaling, but just copying to the final  table that is passed
to \TEX. The \type {define} function returns an id which we will
use later.

The scaler uses the \type {descriptions} to add dimensions (and other data
needed) in the \type {characters} table. This is something \MKIV\ specific.

\starttyping
function fonts.handlers.vf.combiner.commands.metafont(g,v)
    local size = g.specification.size
    local data = metapost.characters.process(v[2],v[3],v[4],size/655360)
    local list, t = { }, { }
    for d=1,#data do
        t = data[d]
        t = fonts.constructors.scale(t, -1000)
        t.id = font.define(t)
        list[#list+1] = t.id
    end
    for k, v in pairs(t) do
        g[k] = v -- kind of replace, when not present, make nil
    end
    g.variants = list
end
\stoptyping

We hook this into the \CONTEXT\ font handler and from now on
the \type {@punk} is recognized:

\starttyping
fonts.definers.methods.install( "punk", { { "metafont", "mfplain", "punkfont.mp", 10 } } )
\stoptyping

Now that we can define the font, we need to deal with
the randomizer. This is optional fun. The mentioned case swappers
are implemented in the \type {cases} namespace:

\starttyping
local fontdata = fonts.hashes.identifiers

cases.actions[99] = function(current)
    local c = current.char
    local used = fontdata[current.font].variants
    if used then
        local f = math.random(1,#used)
        current.font = used[f]
        return current, true
    else
        return current, false
    end
end
\stoptyping

This function is called in one of the passes over the node
list. Thanks to this framework we don't need that much code.
We didn't show two statistics functions. They are the reason why
we keep track of the total number of glyphs defined.

This leaves us defining the interface, so here we go:

\starttyping
\def\StartRandomPunk{\begingroup\setcharactercasing[99]}
\def\StopRandomPunk {\endgroup}
\stoptyping

The set command just sets the attribute that we associated
with casing (one of the many attributes). The number 99 is
rather arbitrary.

If you follow the development of \LUATEX\ and \MKIV\ (we do talks at
conferences, keep track of the development history in \type {mk.pdf},
and report on the \CONTEXT\ mailing list) you will have noticed  that
we often use somewhat extreme examples to explore and test the
functionality and this is no exception. As usual it helped us to improve
the code and extend our todo list. Can the previous code convince
the grand wizards to start using \LUATEX ? Probably not. Let's
anyway hope that they will put the addition of punk math to their todo
list. In the meantime we've already started adding missing characters:

\startlinecorrection[blank]
    \hbox to \hsize \bgroup \hss % { ' \ " }
        \dorecurse{6}{\hbox{\char123\enspace\char39\enspace\char92\enspace\char34\enspace\char125}\quad}\unskip
    \hss \egroup
\stoplinecorrection

Also, because we can be sure that Mojca Miklavec's first test will
be if her favourite characters \color [mkcolor] {\ccaron}, \color
[mkcolor] {\scaron} and \color [mkcolor] {\zcaron} are supported,
we made sure that we composed those accented characters as well.
\footnote {This is accomplished by adding \type
{composecharacters(t)} at an undisclosed location in
the previous code.}

\StopRandomPunk \page[right] \stop

\stopcomponent
