% language=us runpath=texruns:manuals/fonts

\startcomponent fonts-tricks

\environment fonts-environment

\startchapter[title=Tricks][color=middleorange]

\startsection[title=Introduction]

In this chapter topics that don't fit in the previous chapters are
collected.

\stopsection

\startsection[title=Extra characters]

In one of our projects we need a small (high) minus and here we discuss
one way of achieving this. An option is to define a new character
and use a font feature to add it, as in:

\starttyping
\startluacode
  local function addextraminus(tfmdata)
    fonts.helpers.addprivate(tfmdata, "smallminus", ... ) -- see below
    fonts.helpers.addprivate(tfmdata, "highminus",  ... ) -- see below
  end
  fonts.constructors.newfeatures.otf.register {
    name        = "extraminus",
    description = "extra minus symbols",
    default     = true,
    manipulators = {
      base = addextraminus,
      node = addextraminus,
    }
  }
\stopluacode
\stoptyping

However, why make it an option when we can just add it to any font. So,
we can end up with just:

\typebuffer[extraminus] % already defined before loading fonts

It is important to do this before fonts get loaded. Next we need to decide how to
access these characters. A straightforward way is:

\startbuffer
\def\smallminus{\privatechar{smallminus}}
\def\highminus {\privatechar{highminus}}
\stopbuffer

\typebuffer \getbuffer

An alternative is:

\starttyping
\definemathcommand [smallminus] [ord] {\privatechar{smallminus}}
\definemathcommand [highminus]  [ord] {\privatechar{highminus}}
\stoptyping

but that fails in text mode. So, we can consider:

\starttyping
\def\smallminus{\mathortext{\mathord{\privatechar{smallminus}}}{\privatechar{smallminus}}}
\def\highminus {\mathortext{\mathord{\privatechar {highminus}}}{\privatechar {highminus}}}
\stoptyping

or more compact

\starttyping
\def\smallminus{\mathortext\mathord\firstofoneargument{\privatechar{smallminus}}}
\def\highminus {\mathortext\mathord\firstofoneargument{\privatechar {highminus}}}
\stoptyping

What method you choose depends on usage. With the first, simple definitions we
get this:

\startbuffer
[\getprivateslot{smallminus}] [\getprivatechar{smallminus}] [\smallminus] $[\smallminus]$\par
[\getprivateslot {highminus}] [\getprivatechar {highminus}] [\highminus ] $[\highminus ]$\par
\stopbuffer

\typebuffer \getbuffer

Because we are fully expandable we can even use this in:

\startbuffer
\bTABLE[aligncharacter=yes,alignmentcharacter={text->\smallminus}]
  \bTR \bTD \mathminus100\smallminus00+ \eTD \eTR
  \bTR \bTD           100\smallminus00  \eTD \eTR
  \bTR \bTD \mathminus 99\smallminus00+ \eTD \eTR
  \bTR \bTD \mathminus 99\smallminus00  \eTD \eTR
  \bTR \bTD           100\highminus     \eTD \eTR
\eTABLE
\stopbuffer

\typebuffer

\startlinecorrection
\getbuffer
\stoplinecorrection

With the other definitions the alignment would not work. If you need both then
you can define different commands for text and math.

\stopsection

\startsection[title=Tabular numbers]

Some font features are meant to be used in controlled situations. An example is
the \type {tnum} feature that triggers so called \quote {tabular figures} meaning
numbers that have equal widths. Its opposite feature is \type {lnum} or lining
figures. We have two predefined \CONTEXT\ font features for this:

\starttyping
\definefontfeature [inlinenumbers]  [lnum=yes,tnum=no]
\definefontfeature [tabularnumbers] [tnum=yes,lnum=no]
\stoptyping

Some mechanisms in \CONTEXT\ had better be aware of this and one of them is the
alignment mechanism in tables.

\startbuffer[demo]
\startcombination[before=,after=]
    \startcontent
        \switchtobodyfont[pagella]\showglyphs%
        \disabledirectives[typesetters.characteralign.autofont]%
        \bTABLE[alignmentcharacter=.,aligncharacter=yes]
            \bTR \bTD  11.111 \eTD \eTR
            \bTR \bTD   2.2   \eTD \eTR
            \bTR \bTD 444.444 \eTD \eTR
        \eTABLE
        \enabledirectives[typesetters.characteralign.autofont]%
    \stopcontent
    \startcaption
        \small manual \type {tnum}
    \stopcaption
    \startcontent
        \switchtobodyfont[pagella]\showglyphs%
        \bTABLE[alignmentcharacter=.,aligncharacter=yes]
            \bTR \bTD  11.111 \eTD \eTR
            \bTR \bTD   2.2   \eTD \eTR
            \bTR \bTD 444.444 \eTD \eTR
        \eTABLE
    \stopcontent
    \startcaption
        \small auto \type {tnum}
    \stopcaption
\stopcombination
\stopbuffer

In the following examples we demonstrate how the automatic font adaption makes
sure that tabular figures are used. The table is defined as:

\typebuffer[demo]

\startbuffer
\dontleavehmode\hbox to .3\textwidth \bgroup
    \hss\getbuffer[demo]\hss
\egroup
\stopbuffer

In \in {figure}[fig:tabularnumbers] we see what the features do. We use the \type
{\feature} or \type {\addfeature} macro for this. For the moment this trickery is
controlled by a directive (beware: enabling them is global).

\startplacefigure[reference=fig:tabularnumbers,title={Tabular numbers}]
    \startcombination[nx=3,ny=2]
        {\getbuffer}                             {\tt\nohyphens default}
        {\addfeature  [inlinenumbers]\getbuffer} {\tt\nohyphens inlinenumbers}
        {\addfeature [tabularnumbers]\getbuffer} {\tt\nohyphens tabularnumbers}
        {\addfeature[oldstylenumbers]\getbuffer} {\tt\nohyphens oldstylenumbers}
        {\addfeature[oldstylenumbers]%
         \addfeature  [inlinenumbers]\getbuffer} {\tt\nohyphens oldstylenumbers\par inlinenumbers}
        {\addfeature[oldstylenumbers]%
         \addfeature [tabularnumbers]\getbuffer} {\tt\nohyphens oldstylenumbers\par tabularnumbers}
    \stopcombination
\stopplacefigure

\stopsection

\startsection[title=Symbols]

You can access glyphs by name but you need to know that name, for example:

\startbuffer
\definefontsynonym [bends] [file:manfnt.afm]

\startsymbolset [Dangerous Bends]
    \definesymbol [dbend]   [\resolvedglyphdirect{bends}{n:char_7e}]
    \definesymbol [lhdbend] [\resolvedglyphdirect{bends}{n:char_7f}]
\stopsymbolset

\setupsymbolset [Dangerous Bends]

Two dangerous bends: \symbol{dbend} and \symbol{lhdbend}.
\stopbuffer

\typebuffer

You can best save the fonts you use that way in a place that doesn't get
overwritten because names can change.

\getbuffer

\stopsection

\startsection[title=Alternative styles]

\startbuffer[demo]
    \start
        \getbuffer[setup]
        \subject{[ {\myslanted myslanted} ] [ {\it it} ] [ {\slanted slanted} ] [ $x=1$ ]}
        [ {\myslanted myslanted} ] [ {\it it} ] [ {\slanted slanted} ] [ $x=1$ ]
        \typebuffer[setup]
        \blackrule[width=\hsize,height=1pt,depth=0pt]
    \stop
\stopbuffer

In section heads we want a nested style (e.g.\ italic) to adapt to the main font.
The following definitions shows how you can influence that process. We use the
following \type {demo} buffer as sample:

\typebuffer[demo]

\startbuffer
\blackrule[width=\hsize,height=1pt,depth=0pt]

\startbuffer[setup]
\setuphead[subject][style=\tfb,before=,after=]
\definealternativestyle [myslanted] [\it] []
\stopbuffer

\getbuffer[demo]

\startbuffer[setup]
\setuphead[subject][style=\tfb,before=,after=]
\definealternativestyle [myslanted] [\it] [\bi]
\stopbuffer

\getbuffer[demo]

\startbuffer[setup]
\setuphead[subject][style=\tfb,before=,after=]
\definealternativestyle [myslanted] [\it] [\tf]
\stopbuffer

\getbuffer[demo]

\startbuffer[setup]
\definealternativestyle [myslanted] [\normalitalicface]
\setuphead[subject][style=bold,before=,after=]
\stopbuffer

\getbuffer[demo]

\startbuffer[setup]
\definealternativestyle [myslanted] [\normalitalicface]
\setuphead[subject][style=\bfd,before=,after=]
\stopbuffer

\getbuffer[demo]

\startbuffer[setup]
\definealternativestyle [myslanted] [\slantedface]
\setuphead[subject][style=boldface,before=,after=]
\stopbuffer

\getbuffer[demo]
\stopbuffer

You can influence the main method of operation with:

\starttyping
\setupalternativestyles[method=normal]
\setupalternativestyles[method=auto]
\stoptyping

\startplacefigure[title={Alternative style methods.},reference=fig:alternativestyle]
    \startcombination
        {\setupalternativestyles[method=normal]\scale[width=.45\textwidth]{\framed[width=.85\textwidth,align=normal,frame=off,offset=overlay]{\getbuffer}}} {\type{method=normal}}
        {\setupalternativestyles  [method=auto]\scale[width=.45\textwidth]{\framed[width=.85\textwidth,align=normal,frame=off,offset=overlay]{\getbuffer}}} {\type{method=auto}}
    \stopcombination
\stopplacefigure

The result is shown in \in {figure} [fig:alternativestyle]. Relevant commands are:

\starttyping
\emphasistypeface
\emphasisboldface

\normaltypeface    \typeface
\normalboldface    \boldface
\normalslantedface \slantedface
\normalitalicface  \italicface
\swaptypeface      \swapface
\stoptyping

\stopsection

\startsection[title={A virtual hack}]

Here is some virtual trickery. A virtual font is just a font but instead of a
character being a reference to a slot in a font (often via an index) it
constructs a glyph from whatever characters, rules, displacements, inline \PDF\
code, etc. We use them a lot deep down in \CONTEXT. The next example defines two
characters represented by rules. This definition is about as minimalistic as
reasonable and demonstrates how we can apply expansion (aka hz) to such a font.
\footnote {You need \LUATEX\ 1.08 or later for this.} We store the font id (a
number) in a macro. Watch how we don't refer to a glyph in a font. Because we
don't specify its type as \type {virtual} we can leave out the \type {font}
table. After all, we don't refer to real glyphs.

\startbuffer
\startluacode
local d = 400000 -- just over 6pt
local a = font.define {
    characters = {
        [string.byte("A")] =
            {
                width    = d,
                depth    = d,
                commands = { { "down", d }, { "rule", d, d } },
                expansion_factor = 1000,
            },
        [string.byte("B")] =
            {
                width    = d,
                height   = d,
                commands = { { "rule", d, d } },
                expansion_factor = 500,
            },

    },
    parameters = {
        space         = 2*d,
        space_stretch = d,
        space_shrink  = d,
    },
    stretch = 8,
    shrink  = 8,
    step    = 2,
    name    = "foo"
}

tex.count.scratchcounter = a
\stopluacode

\edef\MyFontID{\the\scratchcounter}
\stopbuffer

\typebuffer \getbuffer

% \enabletrackers[*expans*]

\startbuffer
\startoverlay
  {\vbox \bgroup
     \setuptolerance[verytolerant,stretch]
     \setfontid\MyFontID
     \dorecurse{5}{ABABABABABABABABABABABABABABABABA }
   \egroup}
  {\vbox \bgroup
     \normaladjustspacing2
     \middlegray
     \setuptolerance[verytolerant,stretch]
     \setfontid\MyFontID
     \dorecurse{5}{ABABABABABABABABABABABABABABABABA }
   \egroup}
\stopoverlay
\stopbuffer

We test this with some rather low level code and show the result in \in {figure}
[fig:virtualhack]. Of course you will never define a font this way if only
because we don't set important parameters and this version is not generic in the
sense that it scales well. You can find better examples elsewhere in the manual
and in the distribution.

\typebuffer

\startplacefigure[title={A virtual hack.},reference=fig:virtualhack]
    \getbuffer
\stopplacefigure

\stopsection

\stopchapter

\stopcomponent

