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Tex-Like escapes in AFNI Overlay Strings
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The function plotpak_pwritf() is used to draw strings into geometrical
overlays in the AFNI package, using a line drawing software package
written in the early 1980s to emulate a pen plotter for dot matrix
printers -- so that a lot of old pen plotter dependent code could
be recycled. This line drawing package ekes out its life, nearly
40 years later. (As the software is line drawing based, that explains
why the fonts are peculiar looking -- they are drawn by line segments,
not by antialiased curve segments as modern fonts are created -- and
there is no kerning or any other fancy typography).

The features described below can be used in the overlay label strings
used in AFNI image viewer windows, in the graph labels of program
1dplot, and probably in a few other places I've forgotten.

plotpak_pwritf() allows various TeX-like features to be embedded
in the string to be drawn. These include
  '_' is the subscript operator, as in 'a_b'
  '^' is the superscript operator, as in 'a^b'
  '{...}' is the grouping operation, as in 'a^{2b}'
  If you want actual braces in your string, you'll have to
  use the escapes '\{' and '\}'.

Various examples are given in the output of '1dplot -help'; for example:
 '\Upsilon\Phi\Chi\Psi\Omega\red\leftrightarrow\blue\partial^{2}f/\partial x^2'
Otherwise, I'm not going to teach TeX here.

Below are the TeX-like escapes that are interpreted by the
plotpak_pwritf() string drawing function in the AFNI package. They
start with the '\' character (as in TeX). In a C-language string,
you would have to do something like "\\alpha" to have the effect of
a single '\'.

Note that if you want to write something like the letter 'alpha'
next to the letter 'B', you'll have to use a space between them,
to signfify that you aren't trying to use the non-existent escape
'\alphaB' -- use '\alpha B' instead. On the other hand, you can
write '\alpha+B' since an escape's name can't have a special
character in it, so the '+' indicates the end of '\alpha'.

Greek Letters (note that '\Upsilon' is the most beautiful letter)
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  \alpha  \beta     \gamma    \delta  \epsilon  \zeta
  \eta    \theta    \iota     \kappa  \lambda   \mu
  \nu     \xi       \omicron  \pi     \rho      \sigma
  \tau    \upsilon  \phi      \chi    \psi      \omega
  \Alpha  \Beta     \Gamma    \Delta  \Epsilon  \Zeta
  \Eta    \Theta    \Iota     \Kappa  \Lambda   \Mu
  \Nu     \Xi       \Omicron  \Pi     \Rho      \Sigma
  \Tau    \Upsilon  \Phi      \Chi    \Psi      \Omega

Various Shapes
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  \Plus  \Cross  \Diamond  \Box    \FDiamond
  \FBox  \FPlus  \FCross   \Burst  \Octagon

Various Math Operators and Symbols
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  \propto \int       \times     \div        \approx         \partial
  \cap    \?         \langle    \rangle     \ddagger        \pm
  \leq    \S         \hbar      \lambar     \cup            \degree
  \nabla  \downarrow \leftarrow \rightarrow \leftrightarrow \oint
  \in     \notin     \surd      \_          \bar            \exists
  \geq    \forall    \subset    \oplus      \otimes         \dagger
  \neq    \supset    \infty     \uparrow

Some Special Characters (not often needed in AFNI)
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  \#   \$   \%   \&   \{   \}   \\\   \cents   \newline

Font Changing Operations
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  COLORS: \black  \red   \blue  \green  \yellow  \magenta  \cyan
  SIZES:  \small  \large