MetaFun - Pragma ADE

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You can of course rotate, slant and manipulate such a label picture like any other picture.
the right way
The font can be specified in the string defaultfont and the scale in defaultscale. Labels are
defined using the low level operator infont. The next statement returns a picture:
draw "this string will become a sequence of glyphs (MP)"
infont defaultfont scaled defaultscale ;
By default the infont operator is not that clever and does not apply kerning. Also, typesetting
math or accented characters are not supported. The way out of this problem is using btex ...
etex.
draw btex this string will become a sequence of glyphs (\TeX) etex ;
The difference between those two methods is shown below. The outcome of infont depends on
the current setting of the variable defaultfont.
this string will become a sequence of glyphs (MP)
this string will become a sequence of glyphs (TEX)
When you run inside CONTEXT (as we do here) there is no difference between infont and the TEX
methods. This is because we overload the infont operator and also pass its content to TEX. Both
infont and btex use the macro textext which is intercepted and redirects the task to TEX. This
happens in the current run so there is no need to pass extra information about fonts.
Instead of passing strings to infont, you can also pass characters, using char, for example
char(73). When you use infont you normally expect the font to be ASCII conforming. If this
is not the case, you must make sure that the encoding of the font that you use matches your expectations.
However, as we overload this macro it does not really matter since the string is passed
to TEX anyway. For instance, UTF encoded text should work fine as CONTEXT itself understands this
encoding.
1.16 Linear equations
In the previous sections, we used the assignment operator := to assign a value to a variable. Although
for most of the graphics that we will present in later chapters, an assignment is appropriate,
specifying a graphic in terms of expressions is not only more flexible, but also more in the spirit
of the designers of METAFONT and METAPOST.
The METAFONT book and METAPOST manual provide lots of examples, some of which involve math
that we don't consider to belong to everyones repertoire. But, even for non mathematicians using
expressions can be a rewarding challenge.
The next introduction to linear equations is based on my first experiences with METAPOST and
involves a mathematical challenge posed by a friend. I quickly ascertained that a graphical proof
was far more easy than some proof with a lot of sin(this) and cos(that) and long forgotten formulas.
I was expected to prove that the lines connecting the centers of four squares drawn upon the four
sides of a quadrilateral were perpendicular (see figure 1.2).
Welcome to MetaPost Linear equations