% output=pdftex engine=pdftex language=uk
%
% copyright=pragma-ade readme=readme.pdf licence=cc-by-nc-sa

\startcomponent mfun-005

\environment mfun-000

\chapter {Enhancing the layout}

\startintro

One of the most powerful and flexible commands of \CONTEXT\
is \type {\framed}. We can use the background features of
this command to invoke and position graphics that adapt
themselves to the current situation. Once understood,
overlays will become a natural part of the \CONTEXT\ users
toolkit.

\stopintro

\section {Overlays}

Many \CONTEXT\ commands support overlays. The term {\em
overlay} is a bit confusing, since such an overlay in most
cases will lay under the text. However, because there can be
many layers on top of each other, the term suits its
purpose.

When we want to put a \METAPOST\ graphic under some text, we
go through a three step process. First we define the graphic
itself:

\startbuffer
\startuniqueMPgraphic{demo circle}
  path p ;
  p := fullcircle xscaled \overlaywidth yscaled \overlayheight ;
  fill p withcolor .85white ;
  draw p withpen pencircle scaled 2pt withcolor .625red ;
\stopuniqueMPgraphic
\stopbuffer

\typebuffer

\getbuffer

This graphic will adapt itself to the width and height of
the overlay. Both \type {\overlaywidth} and \type
{\overlayheight} are macros that return a dimension
followed by a space. The next step is to register this
graphic as an overlay.

\startbuffer
\defineoverlay[demo circle][\uniqueMPgraphic{demo circle}]
\stopbuffer

\typebuffer

\getbuffer

We can now use this overlay in any command that provides
the \type {\framed} functionality. Since this graphic is
defined as unique, \CONTEXT\ will try to reuse already
calculated and embedded graphics when possible.

\startbuffer
\framed[background=demo circle]{This text is overlayed.}
\stopbuffer

\typebuffer

The background can be set to \type {color}, \type {screen},
an overlay identifier, like \typ {demo circle}, or a comma
separated list of those.

\startlinecorrection[blank]
\getbuffer
\stoplinecorrection

The \type {\framed} command automatically draws a ruled box,
which can be quite useful when debugging a graphic. However,
in this case we want to turn the frame off.

\startbuffer
\framed
  [background=demo circle,frame=off]
  {This text is overlayed.}
\stopbuffer

\typebuffer

\startlinecorrection[blank]
\getbuffer
\stoplinecorrection

In this case, it would have made sense to either set the
\type {offset} to a larger value, or to set \type
{backgroundoffset}. In the latter case, the ellipse is
positioned outside the frame.

The difference between the three offsets \type {offset},
\type {frameoffset} and \type {backgroundoffset} is
demonstrated in \in {figure} [fig:offsets]. While the \type
{offset} is added to the (natural or specified) dimensions
of the content of the box, the other two are applied to the
frame and background and don't add to the dimensions.

In the first row we only set the \type {offset}, while in
the second row, the (text) offset is set to \type {3pt}.
When not specified, the \type {offset} has a comfortable
default value of \type {.25ex} (some 25\% of the height of
an~x).

\startbuffer
\setupframed
  [width=.3\textwidth,
   background=demo circle]
\startcombination[3*3]
  {\framed[offset=none]         {\TeX}} {\tt offset=none}
  {\framed[offset=overlay]      {\TeX}} {\tt offset=overlay}
  {\framed[offset=0pt]          {\TeX}} {\tt offset=0pt}
  {\framed[offset=1pt]          {\TeX}} {\tt offset=1pt}
  {\framed[offset=2pt]          {\TeX}} {\tt offset=2pt}
  {\framed[offset=4pt]          {\TeX}} {\tt offset=4pt}
  {\framed[offset=3pt]          {\TeX}} {\tt offset=3pt}
  {\framed[frameoffset=3pt]     {\TeX}} {\tt frameoffset=3pt}
  {\framed[backgroundoffset=3pt]{\TeX}} {\tt backgroundoffset=3pt}
\stopcombination
\stopbuffer

\typebuffer

\placefigure
  [here][fig:offsets]
  {The three offsets.}
  {\getbuffer}

As the first row in \in {figure} [fig:offsets] demonstrates, instead of a value, one can
pass a keyword. The \type {overlay} keyword implies that
there is no offset at all and that the lines cover the
content. With \type {none} the frame is drawn tight around
the content. When the offset is set to \type {0pt} or more,
the text is automatically set to at least the height of a
line. You can turn this feature of by saying \type
{strut=off}. More details can be found in the \CONTEXT\
manual.

In \in {figure} [fig:all offsets] we have set {offset} to
\type {3pt}, \type {frameoffset} to \type {6pt} and \type
{backgroundoffset} to \type {9pt}. Both the frame and
background offset are sort of imaginary, since they don't
contribute to the size of the box.

\startbuffer
\ruledhbox
  {\framed
     [offset=3pt,frameoffset=6pt,backgroundoffset=9pt,
      background=screen,backgroundscreen=.85]
     {Welcome in the hall of frame!}}
\stopbuffer

\typebuffer

\placefigure
  [here][fig:all offsets]
  {The three offsets.}
  {\getbuffer}

\section {Overlay variables}

The communication between \TEX\ and embedded \METAPOST\
graphics takes place by means of some macros.

\starttabulate[|l|p|]
\HL
\NC overlay status macro    \NC meaning                        \NC \NR
\HL
\NC \tex {overlaywidth}     \NC the width of the graphic, as
                                calculated from the actual
                                width and background offset    \NC \NR
\NC \tex {overlayheight}    \NC the height of the graphic, as
                                calculated from the actual
                                height, depth and background
                                offset                         \NC \NR
\NC \tex {overlaydepth}     \NC the depth of the graphic, if
                                available                      \NC \NR
\NC \tex {overlaycolor}     \NC the background color, if given \NC \NR
\NC \tex {overlaylinecolor} \NC the color of the frame         \NC \NR
\NC \tex {overlaylinewidth} \NC the width of the frame         \NC \NR
\HL
\stoptabulate


The dimensions of the overlay are determined by dimensions of
the background, which normally is the natural size of a \type
{\framed}. When a background offset is specified, it is added
to \type {overlayheight} and \type {overlaywidth}.

Colors can be converted by \type {\MPcolor} and in addition
to the macros mentioned, you can use all macros that expand
into a dimension or dimen register prefixed by the \TEX\
primitive \type {\the} (this and other primitives are
explained in \quotation {The \TeX book}, by Donald Knuth).

\section {Stacking overlays}

A background can be a gray scale (\type {screen}), a color
(\type {color}), a previously defined overlay identifier, or
any combination of these. The next assignments are therefore
legal:

\starttyping
\framed[background=color,backgroundcolor=red]{...}
\framed[background=screen,backgroundscreen=.8]{...}
\framed[background=circle]{...}
\framed[background={color,cow},backgroundcolor=red]{...}
\framed[background={color,cow,grid},backgroundcolor=red]{...}
\stoptyping

In the last three cases of course you have to define \type
{circle}, \type {cow} and \type {grid} as overlay. These
items are packed in a comma separated list, which is to be
surrounded by \type {{}}.

\section {Foregrounds}

\startbuffer[a]
\startuniqueMPgraphic{backfore}
  draw fullcircle
    xscaled \overlaywidth yscaled \overlayheight
    withpen pencircle scaled 2pt
    withcolor .625yellow ;
\stopuniqueMPgraphic

\defineoverlay[backfore][\uniqueMPgraphic{backfore}]
\stopbuffer

\startbuffer[b]
\framed
  [background=backfore,backgroundoffset=4pt]
  {one, two, three, \unknown}
\stopbuffer

\startbuffer[c]
\framed
  [background={foreground,backfore},backgroundoffset=4pt]
  {one, two, three, \unknown}
\stopbuffer

The overlay system is actually a system of layers.
Sometimes we are confronted with a situation in which we
want the text behind another layer. This can be achieved by
explicitly placing the foreground layer, as in \in {figure}
[fig:foreground].

\getbuffer[a]

\placefigure
  [here][fig:foreground]
  {Foreground material moved backwards.}
  {\setupframed[linewidth=1pt]%
   \startcombination
     {\getbuffer[b]} {frame on top layer}
     {\getbuffer[c]} {frame on bottom layer}
   \stopcombination}

The graphic layer is defined as follows:

\typebuffer[a]

The two framed texts have a slightly different definition.
The leftmost graphic is defined as:

\typebuffer[b]

The rightmost graphic is specified as:

\typebuffer[c]

The current values of the frame color and frame width are
passed to the overlay. It often makes more sense to use
colors defined at the document level, if only to force
consistency.

\startbuffer
\startuniqueMPgraphic{super ellipse}
  path p ; p := unitsquare
    xscaled \overlaywidth yscaled \overlayheight
    superellipsed .85 ;
  pickup pencircle scaled \overlaylinewidth ;
  fill p withcolor \MPcolor{\overlaycolor} ;
  draw p withcolor \MPcolor{\overlaylinecolor} ;
\stopuniqueMPgraphic

\defineoverlay[super ellipse][\uniqueMPgraphic{super ellipse}]
\stopbuffer

\typebuffer \getbuffer

This background demonstrates that a super ellipse is rather
well suited as frame.

\startbuffer
\framed
  [background=super ellipse,
   frame=off,
   width=3cm,
   align=middle,
   framecolor=darkyellow,
   rulethickness=2pt,
   backgroundcolor=darkgray]
  {\white This is a\\Super Ellipsed\\sentence.}
\stopbuffer

\typebuffer

Such a super ellipse looks quite nice and is a good
candidate for backgrounds, for which the superness should be
at least~.85.

\startlinecorrection[blank]
\getbuffer
\stoplinecorrection

\section {Typesetting graphics}

I have run into people who consider it kind of strange when
you want to use \TEX\ for non||mathematical typesetting. If
you agree with them, you may skip this section with your
eyes closed.

One of the \CONTEXT\ presentation styles (number 15, tagged
as balls) stepwise builds screens full of sentences, quotes
or concepts, packages in balloons and typesets them as a
paragraph. We will demonstrate that \TEX\ can typeset
graphics using the following statement.

\let\processword\relax

\startbuffer[lions]
\processwords{As you may know, \TEX's ambassador is a lion,
while {\METAFONT} is represented by a lioness. It is still
unclear if they have a relationship, but if so, and if a
baby is born, may it enjoy \METAFUN.}
\stopbuffer

\startquotation
\def\processword#1{#1}\getbuffer[lions]
\stopquotation

The low level \CONTEXT\ macro \type {\processwords} provides
a mechanism to treat the individual words of its argument.
The macro is called as follows:

\typebuffer[lions]

In order to perform a task, you should also define a macro
\type {\processword}, which takes one argument. The previous
quote was typeset with the following definition in place:

\starttyping
\def\processword#1{#1}
\stoptyping

A slightly more complicated definition is the following:

\startbuffer
\def\processword#1{\noindent\framed{#1}\space}
\stopbuffer

\typebuffer \getbuffer

We now get:

\blank\getbuffer[lions]\blank

If we can use \type {\framed}, we can also use backgrounds.

\startbuffer
\def\processword#1%
  {\noindent\framed[frame=off,background=lions]{#1} }
\stopbuffer

\typebuffer \getbuffer

We can add a supperellipsed frame using the following
definition:

\startbuffer
\startuniqueMPgraphic{lions a}
  path p ; p := fullsquare
   xyscaled (\overlaywidth,\overlayheight) superellipsed .85 ;
  pickup pencircle scaled 1pt ;
  fill p withcolor .850white ; draw p withcolor .625yellow ;
\stopuniqueMPgraphic

\defineoverlay[lions][\uniqueMPgraphic{lions a}]
\stopbuffer

\typebuffer \getbuffer

\bgroup \blank \veryraggedright\getbuffer[lions]\unskip \blank \egroup

\startbuffer
\startuseMPgraphic{lions b}
  path p ; p := fullsquare
    xyscaled (\overlaywidth,\overlayheight) randomized 5pt ;
  pickup pencircle scaled 1pt ;
  fill p withcolor .850white ; draw p withcolor .625yellow ;
\stopuseMPgraphic

\defineoverlay[lions][\uniqueMPgraphic{lions b}]
\stopbuffer

\typebuffer \getbuffer

\bgroup \blank \veryraggedcenter\getbuffer[lions]\unskip \blank \egroup

\startbuffer
\startuniqueMPgraphic{lions c}
  path p ; p := fullsquare
    xyscaled (\overlaywidth,\overlayheight) squeezed 2pt ;
  pickup pencircle scaled 1pt ;
  fill p withcolor .850white ; draw p withcolor .625yellow ;
\stopuniqueMPgraphic

\defineoverlay[lions][\uniqueMPgraphic{lions c}]
\stopbuffer

\typebuffer \getbuffer

\bgroup \blank \veryraggedleft\getbuffer[lions]\unskip \blank \egroup

These paragraphs were typeset with the following settings.

\starttyping
\setupalign[broad, right]  % == \veryraggedright
\setupalign[broad, middle] % == \veryraggedcenter
\setupalign[broad, left]   % == \veryraggedleft
\stoptyping

The \type {broad} increases the raggedness. We defined three
different graphics (a, b and c) because we want some to be
unique, which saves some processing. Of course we don't
reuse the random graphics. In the definition of \type
{\processword} we have to use \type {\noindent} because
otherwise \TEX\ will put each graphic on a line of its own.
Watch the space at the end of the macro.

\section {Graphics and macros}

Because \TEX's typographic engine and \METAPOST's graphic
engine are separated, interfacing between them is not as
natural as you may expect. In \CONTEXT\ we have tried to
integrate them as much as possible, but using the interface
is not always as convenient as it should be. What method you
follow, depends on the problem at hand.

The official \METAPOST\ way to embed \TEX\ code into
graphics is to use \typ {btex ... etex}. As soon as
\CONTEXT\ writes the graphic data to the intermediate
\METAPOST\ file, it looks for these commands. When it has
encountered an \type {etex}, \CONTEXT\ will make sure that
the text that is to be typeset by \TEX\ is {\em not}
expanded. This is what you may expect, because when you
would embed those commands in a stand||alone graphic, they
would also not be expanded, if only because \METAPOST\ does
not know \TEX. With expansion we mean that \TEX\ commands
are replaced by their meaning (which can be quite
extensive).

When \METAPOST\ sees a \type {btex} command, it will consult
a so called \type {mpx} file. This file holds the \METAPOST\
representation of the text typeset by \TEX. Before
\METAPOST\ processes a graphic definition file, it first
calls another program that filters the \type {btex} commands
from the source file, and generates a \TEX\ file from them.
This file is then processed by \TEX, and after that
converted to a \type {mpx} file. In \CONTEXT\ we let
\TEXEXEC\ take care of this whole process.

Because the \typ {btex ... etex} commands are filtered from
the raw \METAPOST\ source code, they cannot be part of
macro definitions and loop constructs. When used that way,
only one instance would be found, while in practice
multiple instances may occur.

This drawback is overcome by \METAFUN's \type {textext}
command. This command still uses \typ {btex ... etex} but
writes these commands to a separate job related file each
time it is used. \footnote {It took the author a while to
find out that there is a \METAPOST\ module called \type
{tex.mp} that provides a similar feature, but with the
disadvantage that each text results in a call to \TEX. Each
text goes into a temporary file, which is then included and
results in \METAPOST\ triggering \TEX.} After the first
\METAPOST\ run, this file is merged with the original file,
and \METAPOST\ is called again. So, at the cost of an
additional run, we can use text typeset by \TEX\ in a more
versatile way. Because \METAPOST\ runs are much faster than
\TEX\ runs, the price to pay in terms of run time is
acceptable. Unlike \typ {btex ... etex}, the \TEX\ code in
\type {textext} command is expanded, but as long as
\CONTEXT\ is used this is seldom a problem, because most
commands are somewhat protected.

If we define a graphic with text to be typeset by \TEX,
there is a good chance that this text is not frozen but
passes as argument. A \TEX||like solution for passing
arbitrary content to such a graphic is the following:

\startbuffer[def]
\def\RotatedText#1#2%
  {\startuseMPgraphic{RotatedText}
     draw btex #2 etex rotated #1 ;
   \stopuseMPgraphic
   \useMPgraphic{RotatedText}}
\stopbuffer

\typebuffer[def] \getbuffer[def]

This macro takes two arguments (the \type {#} identifies an
argument):

\startbuffer[exa]
\RotatedText{15}{Some Rotated Text}
\stopbuffer

\typebuffer[exa]

The text is rotated over 15 degrees about the origin in a
counterclockwise direction.

\startlinecorrection[blank]
\getbuffer[exa]
\stoplinecorrection

In \CONTEXT\ we seldom pass settings like the angle of
rotation in this manner. You can use \type
{\setupMPvariables} to set up graphic||specific variables.
Such a variable can be accessed with \type {\MPvar}.

\startbuffer[def]
\setupMPvariables[RotatedText][rotation=90]

\startuseMPgraphic{RotatedText}
  draw btex Some Text etex rotated \MPvar{rotation} ;
\stopuseMPgraphic
\stopbuffer

\typebuffer[def] \getbuffer[def]

An example:

\startbuffer[exa]
\RotatedText{-15}{Some Rotated Text}
\stopbuffer

\typebuffer[exa]

\startlinecorrection[blank]
\getbuffer[exa]
\stoplinecorrection

In a similar fashion we can isolate the text. This permits us
to use the same graphics with different settings.

\startbuffer[def]
\setupMPvariables[RotatedText][rotation=270]

\setMPtext{RotatedText}{Some Text}

\startuseMPgraphic{RotatedText}
  draw \MPbetex{RotatedText} rotated \MPvar{rotation} ;
\stopuseMPgraphic
\stopbuffer

\typebuffer[def] \getbuffer[def]

This works as expected:

\startbuffer[exa]
\RotatedText{165}{Some Rotated Text}
\stopbuffer

\typebuffer[exa]

\startlinecorrection[blank]
\getbuffer[exa]
\stoplinecorrection

It is now a small step towards an encapsulating macro (we
assume that you are familiar with \TEX\ macro definitions).

\startbuffer[def]
\def\RotatedText[#1]#2%
  {\setupMPvariables[RotatedText][#1]%
   \setMPtext{RotatedText}{#2}%
   \useMPgraphic{RotatedText}}

\setupMPvariables[RotatedText][rotation=90]

\startuseMPgraphic{RotatedText}
  draw \MPbetex{RotatedText} rotated \MPvar{rotation} ;
\stopuseMPgraphic
\stopbuffer

\typebuffer[def] \getbuffer[def]

Again, we default to a 90 degrees rotation, and pass both the
settings and text in an indirect way. This method permits you
to build complicated graphics and still keep macros readable.

\startbuffer[exa]
\RotatedText[rotation=240]{Some Rotated Text}
\stopbuffer

\typebuffer[exa]

\startlinecorrection[blank]
\getbuffer[exa]
\stoplinecorrection

You may wonder why we don't use the variable mechanism to
pass the text. The main reason is that the text mechanism
offers a few more features, one of which is that it passes
the text straight on, without the danger of unwanted
expansion of embedded macros. Using \type {\setMPtext} also
permits you to separate \TEX\ and \METAPOST\ code and reuse
the later multiple times (imagine using the same graphic in
a section head command).

There are three ways to access a text defined with \type
{\setMPtext}. Imagine that we have the following definitions:

\startbuffer
\setMPtext {1} {Now is this \TeX\ or not?}
\setMPtext {2} {See what happens here.}
\setMPtext {3} {Text streams become pictures.}
\stopbuffer

\typebuffer \getbuffer

The \type {\MPbetex} macro returns a \typ {btex ... etex}
construct. The \type {\MPstring} returns the text as a
\METAPOST\ string, between quotes. The raw text can be
fetched with \type {\MPtext}.

\startbuffer
\startMPcode
  picture p ; p :=           \MPbetex {1}          ;
  picture q ; q :=  textext( \MPstring{2}        ) ;
  picture r ; r := thelabel("\MPtext  {3}",origin) ;

  for i=p, boundingbox p : draw i withcolor .625red    ; endfor ;
  for i=q, boundingbox q : draw i withcolor .625yellow ; endfor ;
  for i=r, boundingbox r : draw i withcolor .625white  ; endfor ;

  currentpicture := currentpicture scaled 2 ;
  draw origin withpen pencircle scaled 2.0mm withcolor white ;
  draw origin withpen pencircle scaled 1.5mm withcolor black ;
\stopMPcode
\stopbuffer

\typebuffer

The first two lines return text typeset by \TEX, while the
last line leaves this to \METAPOST.

\startlinecorrection[blank]
\getbuffer
\stoplinecorrection

If you watch closely, you will notice that the first (red)
alternative is positioned with the baseline on the origin.

\startbuffer
\startMPcode
  picture p ; p :=                  \MPbetex {1}          ;
  picture q ; q :=  textext.origin( \MPstring{2}        ) ;
  picture r ; r := thelabel.origin("\MPtext  {3}",origin) ;

  for i=p, boundingbox p : draw i withcolor .625red    ; endfor ;
  for i=q, boundingbox q : draw i withcolor .625yellow ; endfor ;
  for i=r, boundingbox r : draw i withcolor .625white  ; endfor ;

  currentpicture := currentpicture scaled 2 ;
  draw origin withpen pencircle scaled 2.0mm withcolor white ;
  draw origin withpen pencircle scaled 1.5mm withcolor black ;
\stopMPcode
\stopbuffer

\startlinecorrection[blank]
\getbuffer
\stoplinecorrection

This picture demonstrates that we can also position \type
{textext}'s and \type {label}'s on the baseline. For this
purpose the repertoire of positioning directives (\type
{top}, \type {lft}, etc.) is extended with an \type {origin}
directive. Another extra positioning directive is \type
{raw}. This one does not do any positioning at all.

\starttyping
picture q ; q :=  textext.origin( \MPstring{2}        ) ;
picture r ; r := thelabel.origin("\MPtext  {3}",origin) ;
\stoptyping

We will now apply this knowledge of text inclusion in
graphics to a more advanced example. The next definitions are
the answer to a question on the \CONTEXT\ mailinglist with
regards to framed texts with titles.

\startbuffer[a]
\defineoverlay[FunnyFrame][\useMPgraphic{FunnyFrame}]

\defineframedtext[FunnyText][frame=off,background=FunnyFrame]

\def\StartFrame{\startFunnyText}
\def\StopFrame {\stopFunnyText }

\def\FrameTitle#1%
  {\setMPtext{FunnyFrame}{\hbox spread 1em{\hss\strut#1\hss}}}

\setMPtext{FunnyFrame}{} % initialize the text variable
\stopbuffer

\startbuffer[b]
\startuseMPgraphic{FunnyFrame}
  picture p ; numeric w, h, o ;
  p := textext.rt(\MPstring{FunnyFrame}) ;
  w := OverlayWidth ; h := OverlayHeight ; o := BodyFontSize ;
  p := p shifted (2o,h-ypart center p) ; draw p ;
  drawoptions (withpen pencircle scaled 1pt withcolor .625red) ;
  draw (2o,h)--(0,h)--(0,0)--(w,0)--(w,h)--(xpart urcorner p,h) ;
  draw boundingbox p ;
  setbounds currentpicture to unitsquare xyscaled(w,h) ;
\stopuseMPgraphic
\stopbuffer[b]

\startbuffer[c1]
\FrameTitle{Zapf (1)}

\StartFrame
Coming back to the use of typefaces in electronic
publishing: many of the new typographers receive their
knowledge and information about the rules of typography from
books, from computer magazines or the instruction manuals
which they get with the purchase of a PC or software.
\StopFrame
\stopbuffer

\getbuffer[a,b,c1]

In this example, the title is positioned on top of the
frame. Title and text are entered as:

\typebuffer[c1]

The implementation is not that complicated and uses the frame
commands that are built in \CONTEXT. Instead of letting \TEX\
draw the frame, we use \METAPOST, which we also use for
handling the title. The graphic is defined as follows:

\typebuffer[b]

Because the framed title is partly positioned outside the
main frame, and because the main frame will be combined with
the text, we need to set the boundingbox explicitly. This is
a way to create so called free figures, where part of the
figure lays beyond the area that is taken into account when
positioning the graphic. The shift

\starttyping
... shifted (2o,h-ypart center p)
\stoptyping

ensures that the title is vertically centered over the top
line of the main box.

The macros that use this graphic combine some techniques of
defining macros, using predefined \CONTEXT\ classes, and
passing information to graphics.

\typebuffer[a]

There is a little bit of low level \TEX\ code involved, like
a horizontal box (\type {\hbox}) that stretches one
em||space beyond its natural size (\type {spread 1em}) with
a centered text (two times \type {\hss}). Instead of applying
this spread, we could have enlarged the frame on both sides.

\startbuffer[b]
\startuseMPgraphic{FunnyFrame}
  picture p ; numeric o ; path a, b ; pair c ;
  p := textext.rt(\MPstring{FunnyFrame}) ;
  a := unitsquare xyscaled(OverlayWidth,OverlayHeight) ;
  o := BodyFontSize ;
  p := p shifted (2o,OverlayHeight-ypart center p) ;
  drawoptions (withpen pencircle scaled 1pt withcolor .625red) ;
  b := a randomized (o/2) ;
  fill b withcolor .85white ; draw b ;
  b := (boundingbox p) randomized (o/8) ;
  fill b withcolor .85white ; draw b ;
  draw p withcolor black;
  setbounds currentpicture to a ;
 \stopuseMPgraphic
\stopbuffer

In the previous graphic we calculated the big rectangle
taking the small one into account. This was needed because
we don't use a background fill. The next definition does, so
there we can use a more straightforward approach by just
drawing (and filling) the small rectangle on top of the big
one.

\typebuffer[b] \getbuffer[b]

\startbuffer[c2]
\FrameTitle{Zapf (2)}

\StartFrame
There is not so much basic instruction, as of now, as there
was in the old days, showing the differences between good
and bad typographic design.
\StopFrame
\stopbuffer

\getbuffer[c2]

Because we use a random graphic, we cannot guarantee
beforehand that the left and right edges of the small shape
touch the horizontal lines in a nice way. The next
alternative displaces the small shape plus text so that its
center lays on the line. On the average, this looks better.

\startbuffer[b]
\startuseMPgraphic{FunnyFrame}
  picture p ; numeric o ; path a, b ; pair c ;
  p := textext.rt(\MPstring{FunnyFrame}) ;
  a := unitsquare xyscaled(OverlayWidth,OverlayHeight) ;
  o := BodyFontSize ;
  p := p shifted (2o,OverlayHeight-ypart center p) ;
  drawoptions (withpen pencircle scaled 1pt withcolor .625red) ;
  b := a randomized (o/2) ;
  fill b withcolor .85white ; draw b ;
  c := center p ;
  c := b intersectionpoint (c shifted (0,-o)--c shifted(0,o)) ;
  p := p shifted (c-center p) ;
  b := (boundingbox p) randomized (o/8) ;
  fill b withcolor .85white ; draw b ;
  draw p withcolor black;
  setbounds currentpicture to a ;
 \stopuseMPgraphic
\stopbuffer

\typebuffer[b] \getbuffer[b]

\getbuffer[c2]

Yet another definition uses super ellipsed shapes instead of
random ones. We need a high degree of superness (.95) in
order to make sure that the curves don't touch the texts.

\startbuffer[b]
\startuseMPgraphic{FunnyFrame}
  picture p ; numeric o ; path a, b ; pair c ;
  p := textext.rt(\MPstring{FunnyFrame}) ;
  o := BodyFontSize ;
  a := unitsquare xyscaled(OverlayWidth,OverlayHeight) ;
  p := p shifted (2o,OverlayHeight-ypart center p) ;
  drawoptions (withpen pencircle scaled 1pt withcolor .625red) ;
  b := a superellipsed .95 ;
  fill b withcolor .85white ; draw b ;
  b := (boundingbox p) superellipsed .95 ;
  fill b withcolor .85white ; draw b ;
  draw p withcolor black ;
  setbounds currentpicture to a ;
\stopuseMPgraphic
\stopbuffer

\typebuffer[b] \getbuffer[b]

\startbuffer[c3]
\FrameTitle{Zapf (3)}

\StartFrame
Many people are just fascinated by their PC's tricks, and
think that a widely||praised program, called up on the
screen, will make everything automatic from now on.
\StopFrame
\stopbuffer

\getbuffer[c3]

There are quite some hard coded values in these graphics,
like the linewidths, offsets and colors. Some of these can be
fetched from the \type {\framed} environment either by using
\TEX\ macros or dimensions, or by using their \METAFUN\
counterparts. In the following table we summarize both the
available \METAPOST\ variables and their \TEX\ counterparts.
They may be used interchangeably.

\starttabulate[|l|Tl|l|]
\HL
\NC \bf \METAPOST\ variable \NC \rm \bf \TEX\ command \NC \bf meaning \NC\NR
\HL
\NC OverlayWidth     \NC \string\overlaywidth
                     \NC current width \NC\NR
\NC OverlayHeight    \NC \string\overlayheight
                     \NC current height \NC\NR
\NC OverlayDepth     \NC \string\overlayheight
                     \NC current depth (often zero) \NC\NR
\NC OverlayColor     \NC \string\MPcolor\string{\string\overlaycolor\string}
                     \NC background color \NC\NR
\NC OverlayLineWidth \NC \string\overlaylinewidth
                     \NC width of the frame \NC\NR
\NC OverlayLineColor \NC \string\MPcolor\string{\overlaylinecolor\string}
                     \NC color of the frame \NC\NR
\NC BaseLineSkip     \NC \string\the\string\baselineskip
                     \NC main line distance \NC\NR
\NC LineHeight       \NC \string\the\string\baselineskip
                     \NC idem \NC\NR
\NC BodyFontSize     \NC \string\the\string\bodyfontsize
                     \NC font size of the running text \NC\NR
\NC StrutHeight      \NC \string\strutheight
                     \NC space above the baseline \NC\NR
\NC StrutDepth       \NC \string\strutdepth
                     \NC space below the baseline \NC\NR
\NC ExHeight         \NC 1ex
                     \NC height of an x \NC \NR
\NC EmWidth          \NC 1em
                     \NC width of an m-dash \NC \NR
\HL
\stoptabulate

\startbuffer[b]
\startuseMPgraphic{FunnyFrame}
  picture p ; numeric o ; path a, b ; pair c ;
  p := textext.rt(\MPstring{FunnyFrame}) ;
  o := BodyFontSize ;
  a := unitsquare xyscaled(OverlayWidth,OverlayHeight) ;
  p := p shifted (2o,OverlayHeight-ypart center p) ;
  pickup pencircle scaled OverlayLineWidth ;
  b := a superellipsed .95 ;
  fill b withcolor OverlayColor ;
  draw b withcolor OverlayLineColor ;
  b := (boundingbox p) superellipsed .95 ;
  fill b withcolor OverlayColor ;
  draw b withcolor OverlayLineColor ;
  draw p withcolor black ;
  setbounds currentpicture to a ;
\stopuseMPgraphic
\stopbuffer

\typebuffer[b] \getbuffer[b]

\startbuffer[d]
\setupframedtexts
  [FunnyText]
  [backgroundcolor=lightgray,
   framecolor=darkred,
   rulethickness=2pt,
   offset=\bodyfontsize,
   before={\blank[big,medium]},
   after={\blank[big]},
   width=\textwidth]
\stopbuffer

\getbuffer[d,c3]

We used the following command to pass the settings:

\typebuffer[d]

In a real implementation, we should also take care of some
additional spacing before the text, which is why we have
added more space before than after the framed text.

We demonstrated that when defining graphics that are part of
the layout, you need to have access to information known to
the typesetting engine. Take \in {figure} [fig:penalty]. The
line height needs to match the font and the two thin
horizontal lines should match the {\em x}||height. We also
need to position the baseline, being the lowest one of a
pair of lines, in such a way that it suits the proportions
of the line as specified by the strut. A strut is an
imaginary large character with no width. You should be aware
of the fact that while \TEX\ works its way top||down, in
\METAPOST\ the origin is in the lower left corner.

\startmode[screen]

\placefigure
  [page][fig:penalty]
  {Penalty lines.}
  {\externalfigure[mfun-999.pdf][page=12,frame=on,height=.85\textheight]}

\stopmode

\startnotmode[screen]

\placefigure
  [here][fig:penalty]
  {Penalty lines.}
  {\externalfigure[mfun-999.pdf][page=12,frame=on,height=.50\textheight]}

\stopnotmode

\typebuffer[handwrit]

This code demonstrates the use of \type {LineHeight}, \type
{ExHeight}, \type {StrutHeight} and \type {StrutDepth}. We
set the interline spacing to 1.5 so that we get a bit more
loose layout. The variables mentioned are set each time a
graphic is processed and thereby match the current font
settings.

\stopcomponent
