% Copyright 2008 by Mark Wibrow
%
% This file may be distributed and/or modified
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% 1. under the LaTeX Project Public License and/or
% 2. under the GNU Free Documentation License.
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\section{Decoration Library}
\label{section-library-decorations}



\subsection{Overview and Common Options}

The decoration libraries define a number of (more or less useful)
decorations that can be applied to paths. The usage of decorations is
not covered in the present section, please consult 
Sections~\ref{section-tikz-decorations}, which explains how
decorations are used in \tikzname, and
\ref{section-base-decorations}, which  explains how new
decorations can be defined. 

The decorations are influenced by a number of parameters that can be
set using the |decoration| option. These parameters are
typically shared between different decorations. In the following, the
general options are documented (they are defined directly in the
|decoration| module), special-purpose keys are documented
with the decoration that uses it.

Since you are encouraged to use these keys to make your own
decorations configurable, it is indicated for each key where the value
is stored (so that you can access it). Note that some values are
stored in \TeX\ dimension registers while others are stored in macros.

\begin{key}{/pgf/decoration/amplitude=\meta{dimension} (initially 2.5pt)}
  This key determines the ``desired height'' (or amplitude) of 
  decorations for which this makes sense. For instance, the initial
  value of |2.5pt| means that deforming decorations should deform a
  path by up to 2.5pt away from the original path.

  This key set the \TeX-dimension |\pgfdecorationsegmentamplitude|. 
\end{key}

\begin{key}{/pgf/decoration/meta-amplitude=\meta{dimension} (initially 2.5pt)}
  This key determines the amplitude for a meta-decoration. 

  The key set the \TeX-macro (!) |\pgfmetadecorationsegmentamplitude|.
\end{key}

\begin{key}{/pgf/decoration/segment length=\meta{dimension} (initially 10pt)}
  Many decorations are made up of small segments. This key determines
  the desired length of such segments. 

  This key set the \TeX-dimension |\pgfdecorationsegmentlength|. 
\end{key}

\begin{key}{/pgf/decoration/meta-segment length=\meta{dimension} (initially 1cm)}
  This determined the length of the meta-segments from which a
  meta-decoration is made up.

  This key set the \TeX-macro (!) |\pgfmetadecorationsegmentlength|. 
\end{key}

\begin{key}{/pgf/decoration/angle=\meta{degree} (initially 45)}
  The way some decorations look like depends on a configurable angle. For
  instance, a |wave| decoration consists of arcs and the opening angle
  of these arcs is given by the |angle|.

  This key set the \TeX-macro |\pgfdecorationsegmentangle|. 
\end{key}

\begin{key}{/pgf/decoration/aspect=\meta{factor} (initially 0.5)}
  For some decorations there is a natural aspect ratio. For instance,
  for a |brace| decoration the aspect ratio determines where the brace
  point will be.

  This key set the \TeX-macro |\pgfdecorationsegmentaspect|. 
\end{key}

\begin{key}{/pgf/decoration/start radius=\meta{dimension} (initially 2.5pt)}
  For some decorations there is a natural start radius (of some circle, presumably).

  This key stores the value directly inside the key.
\end{key}

\begin{key}{/pgf/decoration/end radius=\meta{dimension} (initially 2.5pt)}
  For some decorations there is a natural radius (of some circle, presumably).

  This key stores the value directly inside the key.
\end{key}

\begin{stylekey}{/pgf/decoration/radius=\meta{dimension}}
  Sets the start and end radius simultaneously.
\end{stylekey}


\begin{key}{/pgf/decoration/path has corners=\meta{boolean} (initially false)}
  This is a hint to the decoration code as to whether the path has
  corners or not. If a path has a sharp corner, setting this option to
  |true| may result in better rendering of the decoration because the
  joins of input segements are approached ``more carefully'' than
  when this key is set to false. However, if the path is, say, a
  smooth circle, setting this key to |true| will usually look
  worse. Most decorations ignore this key, anyway. Internally, it sets
  the \TeX-if |\ifpgfdecoratepathhascorners|.
\end{key}


\subsection{Path Morphing Decorations}

\begin{pgflibrary}{decorations.pathmorphing}
  A \emph{path morphing decorations} ``morphs'' or ``deforms'' the
  to-be-decorated path. This means that what used to be a straight
  line might afterwards be a snaking curve and have bumps. However, a
  line is still and a line and path deforming decorations do not
  change the number of subpaths. For instance, if the path used to
  consist of two circles and an open arc, the path will after the
  decoration process still consist of two closed subpath and one open
  subpath. 
\end{pgflibrary}


\subsubsection{Decorations Producing Straight Line Paths}

The following deformations use only straight lines in order to morph
the paths.

\begin{decoration}{lineto}
  This decoration replaces the path by straight lines. For each curve,
  the path simply goes directly from the start point to the end point.
  In the following example, the arc actually consist of two
  subcurves.

  This decoration is actually always defined when the decoration
  module is loaded, but it is documented here for consistency.
\begin{codeexample}[]
\begin{tikzpicture}[decoration=lineto]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{straight zigzag}
  This (meta-)decoration decorates the path by alternating between 
  |curveto| and |zigzag| decorations. It always finishes
  with the |curveto| decoration. The following parameters influence
  the decoration:
  \begin{itemize}
  \item |amplitude|
    determines how much the zig-zag lines raises above and falls below
    a straight line to the target point.
  \item |segment length|
    determines the length of a complete ``up-down'' cycle.
  \item	|meta-segment length|
    determines the length of the |curveto| and the |zigzag| decorations.
  \end{itemize}

\begin{codeexample}[]
\begin{tikzpicture}[decoration={straight zigzag,meta-segment length=1.1cm}]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{random steps}
  This decoration consists of straight line segments. The line segments
  head towards the target, but each step is randomly shifted a little
  bit. The following parameters influence the decorations:
  \begin{itemize}
  \item |segment length|
    determines the basic length of each step.
  \item |amplitude|
    The end of each step is perturbed both in $x$- and in
    $y$-direction by two values drawn uniformly from the interval
    $[-d,d]$, where $d$ is the value of |amplitude|.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}
    [decoration={random steps,segment length=2mm}]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{saw}
  This decoration looks like the blade of a saw. The following parameters
  influence the decoration:
  \begin{itemize}
  \item |amplitude|
    determines how much each spike raises above the straight line.
  \item |segment length|
    determines the length each spike.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=saw]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{zigzag}
  This decoration looks like a zig-zag line. The following parameters
  influence the decoration:
  \begin{itemize}
  \item |amplitude|
    determines how much the zig-zag lines raises above and falls below
    a straight line to the target point.
  \item |segment length|
    determines the length of a complete ``up-down'' cycle.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=zigzag]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}



\subsubsection{Decorations Producing Curved Line Paths}

\begin{decoration}{bent}
  This decoration adds a slightly bent line from the start to the
  target. The amplitude of the bent is given |amplitude|
  (an amplitude of zero gives a straight line). 
  \begin{itemize}
  \item |amplitude|
    determines the amplitude of the bent.
  \item |aspect|
    determines how tight the bent is. A good value is around |0.3|. 
  \end{itemize}
  Note that this decoration makes only little sense for curves. You
  should apply it only to straight lines.
\begin{codeexample}[]
\begin{tikzpicture}[decoration=bent]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) -- (1.5,2) -- (0,1);
\end{tikzpicture}
\end{codeexample}
\begin{codeexample}[]
\begin{tikzpicture}[decoration={bent,aspect=.3}]
  \draw [decorate,fill=examplefill] (0,0) rectangle (3.5,2);
  \node[circle,draw] (A) at (.5,.5) {A};
  \node[circle,draw] (B) at (3,1.5) {B};
  \draw[->,decorate] (A) -- (B);
  \draw[->,decorate] (B) -- (A);
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{bumps}
  This decoration replaces the path by little half ellipses. The
  following parameters influence itL
  \begin{itemize}
  \item |amplitude|
    determines the height of the half ellipse.
  \item |segment length|
    determines the width of the half ellipse.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=bumps]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{coil}
  This decoration replaces the path by a coiled line. To understand how this works,
  imagine a three-dimensional spring. The spring's axis points along
  the path toward the target. Then, we ``view'' the spring from a
  certain angle. If we look ``straight from the side'' we will see a
  perfect sine curve, if we look ``more from the front'' we will see a
  coil. The following parameters influence the decoration:  
  \begin{itemize}
  \item |amplitude|
    determines how much the coil rises above the path and falls below
    it. Thus, this is the radius of the coil.
  \item |segment length|
    determines the distance between two consecutive ``curls.'' Thus,
    when the spring is see ``from the side'' this will be the wave
    length of the sine curve. 
  \item |aspect|
    determines the ``viewing direction.'' A value of |0| means
    ``looking from the side'' and a value of |0.5|, which is the
    default, means ``look more from the front.'' 
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=coil]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\begin{codeexample}[]
\begin{tikzpicture}
    [decoration={coil,aspect=0.3,segment length=3mm,amplitude=3mm}]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}



\begin{decoration}{curveto}
  This decoration simply yields a line following the original
  path. This means that (ideally) it does not change the path and
  follows any curves in the path (hence the name). In
  reality, due to the internals of how decorations are implemented,
  this decoration actually replaces the path by numerous small
  straight lines.

  This decoration is mostly useful in conjunction with
  meta-decorations. It is also actually defined in the decoration
  module and is always available.

\begin{codeexample}[]
\begin{tikzpicture}[decoration=curveto]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}



\begin{decoration}{snake}
  This decoration replaces the path by a line that looks like a snake
  seen from above. More precisely, the snake is a sine wave with a
  ``softened'' start and ending. The following parameters influence
  the snake: 
  \begin{itemize}
  \item |amplitude|
    determines the sine wave's amplitude.
  \item |segment length|
    determines the sine wave's wave length.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=snake]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill]
    (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;
\end{tikzpicture}
\end{codeexample}
\end{decoration}



  
\subsection{Path Replacing Decorations}

\begin{pgflibrary}{decorations.pathreplacing}
  This library defines decorations that replace the to-be-decorated
  path by another path. Unlike morphing decorations, the replaced path
  might be quite different, for instance a straight line might be
  replaced by a set of circles. Note that filling a path that has been
  replaced using one of the decorations in this library typically does
  not fill the original area but, rather, the smaller area of the
  newly-created path segments.
\end{pgflibrary}

\begin{decoration}{border}
  This decoration adds straight lines the path that are at a specific
  angle to the line toward the target. The idea is to add these little
  lines to indicate the ``border'' or an area. The following
  parameters influence the decoration:  
  \begin{itemize}
  \item |segment length|
    determines the distance between consecutive ticks.
  \item |amplitude|
    determines the length of the ticks.
  \item |angle|
    determines the angle between the ticks and the line of the path. 
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=border]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate,draw,red}]
        (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{brace}
  This decoration replaces a straight line path by a long brace. The
  left and right end of the brace will be exactly on the start and
  endpoint of the decoration. The decoration really only makes sense
  for paths that are a straight line.
  \begin{itemize}
  \item |amplitude|
    determines how much the brace rises above the path.
  \item |aspect|
    determines the fraction of the total length where the ``middle
    part'' of the brace will be.  
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=brace]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}



\begin{decoration}{expanding waves}
  This decoration adds arcs to the path that get bigger along the line
  towards the target. The following parameters influence the decoration:
  \begin{itemize}
  \item |segment length|
    determines the distance between consecutive arcs.
  \item |angle|
    determines the opening angle below and above the path. Thus, the
    total opening angle is twice this angle.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration={expanding waves,angle=5}]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{moveto}
  This decoration simply jumps to the end of the path using a move-to
  path operation. It is mainly useful as |pre=moveto| or |post=moveto|
  decorations.

  This decoration is actually always defined when the decoration
  module is loaded, but it is documented here for consistency.
\end{decoration}


\begin{decoration}{ticks}
  This decoration replaces the path by straight lines that are
  orthogonal to the path. The following parameters influence the
  decoration:  
  \begin{itemize}
  \item |segment length|
    determines the distance between consecutive ticks.
  \item |amplitude|
    determines half the length of the ticks.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=ticks]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}



\begin{decoration}{waves}
  This decoration replaces the path by arcs that have a constant
  size. The following parameters influence the decoration: 
  \begin{itemize}
  \item |segment length|
    determines the distance between consecutive arcs.
  \item |angle|
    determines the opening angle below and above the path. Thus, the
    total opening angle is twice this angle.
  \item |radius|
    determines the radius of each arc.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration={waves,radius=4mm}]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}




\begin{decoration}{show path construction}
	This decoration allows ``something different'' to be done
	for each \emph{type} of input segment (i.e., moveto, lineto,
	curveto or closepath). Typically, each segment will be replaced
	with another path, but this need not necessarily be the case.
	
\begin{codeexample}[]
\begin{tikzpicture}[>=stealth, every node/.style={midway, sloped, font=\tiny},
  decoration={show path construction,
    moveto code={
      \fill [red] (\tikzinputsegmentfirst) circle (2pt) 
        node [fill=none, below] {moveto};},
    lineto code={
      \draw [blue,->] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast)
        node [above] {lineto};
    },
    curveto code={
      \draw [green!75!black,->] (\tikzinputsegmentfirst) .. controls
        (\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb) 
        ..(\tikzinputsegmentlast) node [above] {curveto};
    },
    closepath code={
      \draw [orange,->] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast)
        node [above] {closepath};}
  }]
  \draw [help lines] grid (3,2);
  \path [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle;    
\end{tikzpicture}
\end{codeexample}


  The following keys can be used to specify the code to execute
  for each type of input segment. 

\begin{key}{/pgf/decoration/moveto code=\meta{code} (initially \char`\{\char`\})}
	Set the code to be executed for every moveto input segment.
	It is important to remember that the transformations applied 
	by the decoration automaton are turned \emph{off} when \meta{code} 
	is executed.
\end{key}

\begin{key}{/pgf/decoration/lineto code=\meta{code} (initially \char`\{\char`\})}
  Set the code to be executed for every lineto input segment.
\end{key}

\begin{key}{/pgf/decoration/curveto code=\meta{code} (initially \char`\{\char`\})}
	Set the code to be executed for every curveto input segment.
\end{key}

\begin{key}{/pgf/decoration/closepath code=\meta{code} (initially \char`\{\char`\})}
  Set the code to be executed for every closepath input segment.
\end{key}

Within \meta{code} the first and last
points on the current input segment can be accessed using 
|\pgfpointdecoratedinputsegmentfirst| and 
|\pgfpointdecoratedinputsegmentlast|. For curves, the
control (support) points can be accessed using 
|\pgfpointdecoratedinputsegmentsupporta| and 
|\pgfpointdecoratedinputsegmentsupportb|.

In \tikzname, you can use the following macros
inside a \tikzname{} coordinate.

\begin{command}{\tikzinputsegmentfirst}
	The first point on the current input segment path.
\end{command}

\begin{command}{\tikzinputsegmentlast}
	The last point on the current input segment path. 
\end{command}

\begin{command}{\tikzinputsegmentsupporta}
	The first support on the curveto input segment path. 
\end{command}

\begin{command}{\tikzinputsegmentsupportb}
	The second support on the curveto input segment path. 
\end{command}

{\tikzexternaldisable
\begin{codeexample}[]
\tikzset{
  show curve controls/.style={
    decoration={
      show path construction, 
      curveto code={
      	\draw [blue, dashed] 
          (\tikzinputsegmentfirst)    -- (\tikzinputsegmentsupporta)
          node [at end, cross out, draw, solid, red, inner sep=2pt]{};
        \draw [blue, dashed] 
          (\tikzinputsegmentsupportb) -- (\tikzinputsegmentlast)
          node [at start, cross out, draw, solid, red, inner sep=2pt]{};
      }
    },decorate
  }
}

\tikzpicture
  \draw [postaction=show curve controls, thick] 
    (0,2) .. controls (2.5,1.5) and (0.5,0.5) .. (3,0);
\endtikzpicture
\end{codeexample}
}%
\end{decoration} 
 
 
 
 
\subsection{Marking Decorations}

\subsubsection{Overview}

A \emph{marking on a path} is any kind of graphic that is placed on a
specific position on a path. Markings are useful in rather diverse
situations: you can use them to, say, place little ``footsteps'' along
a path as if someone where walking along the path; to place arrow tips
on the middle of a path to indicate the ``direction'' in which
something is flowing; or you can use them to place informative
information at certain positions of a path.

For historical reasons there are three different libraries for placing
marks on a path. They differ in what kind of markings can be added to
a path. We start with the most general and most useful of these libraries.



\subsection{Arbitrary Markings}

\begin{pgflibrary}{decorations.markings}
  Markings are arbitrary ``marks'' that can be put on a path. Marks
  can be arrow tips or nodes or even whole pictures. 
\end{pgflibrary}

\begin{decoration}{markings}
  A \emph{marking} can be thought of a ``little picture'' or more
  precisely of ``some scope contents'' that is placed ``on'' a path at
  a certain position. Suppose the marking should be a simple cross. We
  can produce this with the following code:
\begin{codeexample}[code only]
\draw (-2pt,-2pt) -- (2pt,2pt);
\draw (2pt,-2pt) -- (-2pt,2pt);
\end{codeexample}
  If we use this code as a marking at position |2cm| on a path, then
  the following happens: \pgfname\ determines the position on the path
  that is 2cm along the path. Then is translates the coordiante system
  to this position and rotates it such that the positive $x$-axis is
  tangent to the path. Then a protective scope is created, inside
  which the above code is executed -- resulting in a little cross on
  the path.

  The |markings| decoration allows you to place one or more such
  markings on a path. The decoration destroys the input path (except
  in certain cases, detailed later), which means that it uses the path
  for determining positions on the path, but after the decoration is
  done this path is gone. You typically need to use a |postaction| to
  add markings. 

  Let us start with the above example in real code:
\begin{codeexample}[]
\begin{tikzpicture}[decoration={
    markings,% switch on markings
    mark=% actually add a mark
      at position 2cm
      with
      {
        \draw (-2pt,-2pt) -- (2pt,2pt);
        \draw (2pt,-2pt) -- (-2pt,2pt);
      }
    }
    ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}  

  We can also add the cross repeatedly:
\begin{codeexample}[]
\begin{tikzpicture}[decoration={
    markings,% switch on markings
    mark=% actually add a mark
      between positions 0 and 1 step 5mm
      with
      {
        \draw (-2pt,-2pt) -- (2pt,2pt);
        \draw (2pt,-2pt) -- (-2pt,2pt);
      }
    }
    ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}  

  The |mark| decoration option is used to specify a marking. It comes
  in two version:
  \begin{key}{/pgf/decoration/mark=|at position|
      \meta{pos}| with |\meta{code}}
    The options specifies that when a |marking| decoration is applied,
    there should be a marking at position \meta{pos} on the path whose
    code is given by \meta{code}.

    The \meta{pos} can have four different forms:
    \begin{enumerate}
    \item It can be a non-negative dimension like |0pt| or |2cm| or
      |5cm/2|. In this case, it refers to the position along the path
      that is this far removed from the start.
    \item It can be a negative dimesion like |-1cm-2pt| or |-1sp|. In
      this case, the position is taken from the end of the path. Thus,
      |-1cm| is the position that is $-1$cm removed from the end of
      the path.
    \item It can be a dimensionless non-negative number like |1/2| or
      |0.333+2*0.1|. In this case, the \meta{pos} is interpreted as a
      factor of the total path lenght. Thus, a \meta{pos} or |0.5|
      refers to the middle of the path, |0.1| is near the start, and
      so on.
    \item It can be a dimensionless negative number like |-0.1|. Then,
      again, the fraction of the path length counts ``from the end.''
    \end{enumerate}

    The \meta{pos} determines a position on the path. When the marking
    is applied, the (high level) coordinate system will have been
    transformed so that the origin lies at this position and the
    positive $x$-axis points along the path. For this coordinate
    system, the \meta{code} is executed. It can contains all sorts of
    graphic drawing commands, including (even named) nodes.

    If the position position lies past the end of the path (for
    instance if \meta{pos} is set to |1.2|), the marking will not be
    drawn.

    It is possible to give the |mark| option several times, which
    causes several markings to be applied. In this case, however, it
    is necessary that the positions on the path are in increasing
    order. That is, it is not allowed (and will result in chaos) to
    have a marking that lies earlier on the path to follow a marking
    that is later on the path.

\begin{codeexample}[]
\begin{tikzpicture}[decoration={
    markings,% switch on markings
    mark=at position 1cm  with \node[red]{1cm};,
    mark=at position .5   with \node[green]{mid};,
    mark=at position -1cm with {\node[blue,transform shape]{1cm from end};}}
    ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}  

    Here is an example that shows how markings can be used to place text
    on plots:
\begin{codeexample}[]
\begin{tikzpicture}[domain=0:4,label/.style={postaction={
      decorate,
      decoration={
        markings,
        mark=at position .75 with \node #1;}}}]
  \draw[very thin,color=gray] (-0.1,-1.1) grid (3.9,3.9);
  
  \draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$};
  \draw[->] (0,-1.2) -- (0,4.2) node[above] {$f(x)$};
  
  \draw[red,label={[above left]{$f(x)=x$}}]                       plot (\x,\x);
  \draw[blue,label={[below left]{$f(x)=\sin x$}}]                 plot (\x,{sin(\x r)});
  \draw[orange,label={[right]{$f(x)= \frac{1}{20} \mathrm e^x$}}] plot (\x,{0.05*exp(\x)});
\end{tikzpicture}
\end{codeexample}

    When the \meta{code} is begin executed, two special keys will have
    been setup, whose value may be of interest:
    \begin{key}{/pgf/decoration/mark info/sequence number}
      This key can only be read. Its value (which can be obtained
      using the |\pgfkeysvalueof| command) is a ``sequence number'' of
      the mark. The first mark that is added to a path has number |1|,
      the second number |2|, and so on. This key is mainly useful in
      conjunction with repeated markings (see below).
    \end{key}
    \begin{key}{/pgf/decoration/mark info/distance from start}
      This key can only be read. Its value is the distance of the
      marking from the start of the path in points. For instance, if
      the path length is 100pt and the marking is in the middle of the
      path, the value of this key would be |50.0pt|.
    \end{key}
  \end{key}

  A second way to use the |mark| key is the following:
  \begin{key}{/pgf/decoration/mark=|between positions|
      \meta{start pos} |and| \meta{end pos} |step| \meta{stepping}
      |with| \meta{code}}
    This works similarly to the |at position| versio of this option,
    only multiple marks are placed, starting at \meta{start pos} and
    then spaced apart by \meta{stepping}. The \meta{start pos}, the
    \meta{end pos}, and also the \meta{stepping} may all be specified
    in the same way as for the |at position| version, that is, either
    using units or no units and also using positive or negative
    values.

    Let us start with a simple example in which we place ten crosses
    along a path starting with the beginning of the 
    path ($\meta{start pos} = 0$) and ending at the end ($\meta{end
      pos} = 1$). 
\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    mark=between positions 0 and 1 step 0.1
         with { \draw (-2pt,-2pt) -- (2pt,2pt);
                \draw (2pt,-2pt) -- (-2pt,2pt); }} ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}      

    In the next example we place arrow shapes on the path instead of
    crosses. Note the use of the |transform shape| option to ensure
    that the nodes are actually rotated.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    mark=between positions 0 and 1 step 1cm
      with { \node [single arrow,fill=red,
                    single arrow head extend=3pt,transform shape] {};}}]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}      

    Using the key |sequence number| we can also ``number'' the nodes
    and even refer to them later on.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    mark=between positions 0 and 1 step 1cm with {
      \node [draw,
        name=mark-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number},
        transform shape]
      {\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}};}}]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
  \draw [red,->] (mark-3) -- (mark-7);
\end{tikzpicture}
\end{codeexample}      

    In the following example we use the distance info to place
    ``length information'' on a path:
\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    % Main marks
    mark=between positions 0 and 1 step 40pt with
      { \draw [help lines] (0,0) -- (0,0.5)
        node[above,font=\tiny]{
          \pgfkeysvalueof{/pgf/decoration/mark info/distance from start}}; },
    mark=at position -0.1pt with
      { \draw [help lines] (0,0) -- (0,0.5)
        node[above,font=\tiny]{
          \pgfkeysvalueof{/pgf/decoration/mark info/distance from start}}; }}] 
  \draw [help lines] grid (5,3);
  \draw [postaction={decorate}]  (0,0) .. controls (8,3) and (0,3) .. (5,0) ;
\end{tikzpicture}
\end{codeexample}      
  \end{key}

  \begin{key}{/pgf/decoration/reset marks}
    Since |mark| options accumulate, there needs to be a way to
    ``reset'' things, so that any |mark| options set in an enclosing
    scope do not interfere. This option does exactly this. Note that
    when the \meta{code} of a marking is executed, the markings are
    automatically reset.
  \end{key}

  As mentioned earlier, the decoration usually destroys the
  path. However, this is no longer the case when the following key is
  set:
  \begin{key}{/pgf/decoration/mark connection node=\meta{node name} (initially empty)}
    When this key is set to a nonempty \meta{node name} while the
    decoration is being processed, the following happens: The marking
    code should, among possibly other things, define node named
    \meta{node name}. Then, the output path of this decoration will
    contain a line-to to ``one end'' of this node, followed by a
    moveto to the ``other end'' of the node. More precisely, the first
    end is given by the position on the border of \meta{node name}
    that lies in the direction ``from which the path heads toward the
    node'' while the other end lies on the border ``where the path
    heads away from the node.'' Furthemore, this option causes the
    decoration to end with a line-to to the end instead of a move-to.

    The net effect of all this is that when you decorate a straight
    line with one or more markings that contain just a node, the line
    will effectively connect these nodes.

    Here are two examples that show how this works:
\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    mark connection node=my node,      
    mark=at position .5 with
      {\node [draw,blue,transform shape] (my node) {my node};}}]
  \draw [help lines] grid (3,2);
  \draw decorate { (0,0) -- (3,2) };
\end{tikzpicture}
\end{codeexample}      

\begin{codeexample}[]
\begin{tikzpicture}[decoration={markings,
    mark connection node=my node,      
    mark=at position .25 with
      {\node [draw,red] (my node) {my node};}}]
  \draw [help lines] grid (3,2);
  \draw decorate { (0,0) -- (3,2) };
\end{tikzpicture}
\end{codeexample}      
    
  \end{key}
\end{decoration}


\subsubsection{Arrow Tip Markings}

Frequent markings that are hard to create correctly are arrow
tips. For them, two special commands are available when the \meta{code} of
a |mark| option is execute. (They are only defined in this code):

\begin{command}{\arrow\opt{\oarg{options}}\marg{arrow end tip}}
  This command simply draws the \meta{arrow end tip} at the origin,
  pointing right. This is exactly what you need when you want to
  draw an arrow tip as a marking.

  The \meta{options} can only be given when \tikzname\ is used. In
  this case, they are executed in a scope that contains the arrow
  tip. 
\begin{codeexample}[]
\begin{tikzpicture}[decoration={
    markings,% switch on markings
    mark=at position 1cm  with {\node[red]{1cm};},
    mark=at position .75  with {\arrow[blue,line width=2mm]{>}},
    mark=at position -1cm with {\arrowreversed[black]{stealth};}}
    ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}

  Here is a more useful example:
\begin{codeexample}[]
\begin{tikzpicture}[decoration={
    markings,% switch on markings
    mark=between positions 0 and .75 step 4mm with {\arrow{stealth}},
    mark=between positions .75 and 1 step 4mm with {\arrowreversed{stealth}}}
    ]
  \draw [help lines] grid (3,2);
  \draw [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{command}

\begin{command}{\arrowreversed\opt{\oarg{options}}\marg{arrow end tip}}
  As above, only the arrow end tip is flipped and points in the
  other direction. 
\end{command}


\subsubsection{Footprint Markings}

\begin{pgflibrary}{decorations.footprints}
  The decorations of this library can be used to decorate a path with
  little footprints, as if someone had ``walked'' along the path.
\end{pgflibrary}

\begin{decoration}{footprints}
  The footprint decoration adds little footprints around the
  path. They start with the left foot.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={footprints,foot length=5pt,stride length=10pt}]
  \draw [help lines] grid (3,3);
  \fill [decorate] (0,0) -- (3,2) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
  You can influence the way this decoration looks using the following
  options:
  \begin{key}{/pgf/decoration/foot length (initially 10pt)}
    The length or size of the footprint itself. A larger value makes
    the footprint larger, but does not change the stride length.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={footprints,foot length=20pt}]
  \fill [decorate] (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}
  \begin{key}{/pgf/decoration/stride length (initially 30pt)}
    The length of strides. This is the distance between the beginnings
    of left footprints along the path.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={footprints,stride length=50pt}]
  \fill [decorate] (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}
  \begin{key}{/pgf/decoration/foot sep (initially 4pt)}
    The separation in the middle between the footprints. The
    footprints are moved away from the path by half this amount.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={footprints,foot sep=10pt}]
  \fill [decorate] (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}
  \begin{key}{/pgf/decoration/foot angle (initially 10)}
    Footprints are rotate by this much.
\begin{codeexample}[]
\begin{tikzpicture}[decoration={footprints,foot angle=60}]
  \fill [decorate] (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}
  \begin{key}{/pgf/decoration/foot of (initially human)}
    The species whose footprints are shown. Possible values are:

    \def\render#1{
      \texttt{#1} &
      \tikz [baseline,decoration={footprints,foot of=#1}]
        \fill [decorate] (0,0) -- (6,0); \\[3em]
    }
    \begin{tabular}{ll}
      \emph{Species} & \emph{Result} \\[1em]
      \render{gnome}
      \render{human}
      \render{bird}
      \render{felis silvestris}
    \end{tabular}
  \end{key}
\end{decoration}




\subsubsection{Shape Background Markings}

The third library for adding markings uses the background paths of
certains shapes. This library is included mostly for historical
reasons, using the |markings| library is usually preferable.

\begin{pgflibrary}{decorations.shapes}
  This library defines decorations that use shapes or shape-like
  drawings to decorate a path. The following options are common
  options used by the decorations in this library:
  
  \begin{key}{/pgf/decoration/shape width=\meta{dimension}  (initially 2.5pt)}
    The desired width of the shapes. For decorations that support
    varying shape sizes, this key sets both the start and end width
    (which can be overwritten using options like |shape start width|).
  \end{key}

  \begin{key}{/pgf/decoration/shape height=\meta{dimension} (initially 2.5pt)}
    Works like the previous key, only for the height.
  \end{key}

  \begin{key}{/pgf/decoration/shape size=\meta{dimension}}
    Sets the desired width and height simultaneously.
  \end{key}

  For the exact places and macros where these keys store the values,
  please consult the beginning of the code of the library.
\end{pgflibrary}



\begin{decoration}{crosses}
  This decoration replaces the path by (diagonal) crosses. The
  following parameters influence the decoration:  
  \begin{itemize}
  \item |segment length|
    determines the distance between (the centers of) consecutive crosses.
  \item |shape height|
    determines the height of each cross.
  \item |shape width|
    determines the width of each cross.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=crosses]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}

\begin{decoration}{triangles}
  This decoration replaces the path by triangles that point along the
  path. The following parameters influence the decoration: 
  \begin{itemize}
  \item |segment length|
    determines the distance between consecutive triangles.
  \item |shape height|
    determines height of the triangle side that is orthogonal
    to the path.
  \item |shape width|
    determines the width of the triangle.
  \end{itemize}
\begin{codeexample}[]
\begin{tikzpicture}[decoration=triangles]
  \draw [help lines] grid (3,2);
  \draw [decorate,fill=examplefill] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{shape backgrounds}
  This is a general decoration that replaces the to-be-decorated path by repeated
  copies of the background path of an arbitrary shape that has
  previously defined using the |\pgfdeclareshape| command (that is,
  you can use any shape in the shape libraries).

  Please note that the background path of the shapes is used, but
  \emph{no nodes are created}. This means that \emph{you cannot have
    text inside the shapes of this path, you cannot name them, or
    refer to them.} Finally, this decoration \emph{will not work with
    shapes that depend  strongly of the size of the text box (like the
    arrow shapes).}  If any of these restrictions pose a poblem, use
  the |markings| library instead.

\begin{codeexample}[]
\begin{tikzpicture}[decoration={shape backgrounds,shape=star,shape size=5pt}]
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}

\begin{codeexample}[]
\tikzset{paint/.style={ draw=#1!50!black, fill=#1!50 },
         decorate with/.style=
           {decorate,decoration={shape backgrounds,shape=#1,shape size=2mm}}}
\begin{tikzpicture}
  \draw [decorate with=dart,      paint=red]    (0,1.5) -- (3,1.5);
  \draw [decorate with=diamond,   paint=green]  (0,1)   -- (3,1);
  \draw [decorate with=rectangle, paint=blue]   (0,0.5) -- (3,0.5);
  \draw [decorate with=circle,    paint=yellow] (0,0)   -- (3,0);
\end{tikzpicture}
\end{codeexample}

  All shapes are positioned by the anchor that is specified via the
  |anchor| decoration option:

  \begin{key}{/pgf/decoration/anchor=\meta{anchor} (initially center)}
    The anchor used to position the shapes backgrounds.
  \end{key}

  A shape background path is added at the start point of the path and,
  if the distance between the shapes is appropriate, at the end point
  of the path. 
	
\begin{codeexample}[]
\begin{tikzpicture}[decoration={
      shape backgrounds,shape=regular polygon,shape size=4mm}]
  \draw [help lines] grid (3,2);
  \draw [thick] (0,0) -- (2,2) (1,0) -- (3,0);
  \draw [red, decorate, decoration={shape sep=.5cm}]  (1,0) -- (3,0);
  \draw [blue, decorate, decoration={shape sep=.5cm}] (0,0) -- (2,2);
\end{tikzpicture}
\end{codeexample}

  Keys for cusomizing specific shapes can be specified (e.g., 
  |star points|, |cloud puffs|, |kite angles|, and so on). The size of
  the shape is ``enforced'' using transformations. This means that the
  shape is typeset with an empty text box and some default size
  values, resulting in an initial shape. This shape is then rescaled
  using coordinate transformations so that it has the desired size
  (which may vary as we travel along the to-be-decorated path). This
  means that settings involving angles and distances may not appear
  entirely accurate. More general options such as |inner sep| and
  |minimum size| will be ignored,  but transformations can be applied
  to each segment as described below.
  
\begin{codeexample}[]
\tikzset{
  paint/.style={draw=#1!50!black, fill=#1!50},
  my star/.style={decorate,decoration={shape backgrounds,shape=star},
                  star points=#1}
}
\begin{tikzpicture}[decoration={shape sep=.5cm, shape size=.5cm}]
  \draw [my star=9, paint=red]                            (0,1.5) -- (3,1.5);
  \draw [my star=5, paint=blue]                           (0,.75) -- (3,.75);
  \draw [my star=5, paint=yellow, shape border rotate=30] (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}

  There are various keys to control the drawing of the shape
  decoration. 
  
  \begin{key}{/pgf/decoration/shape=\meta{shape name} (initially circle)}
    The shape whose background path is used.
  \end{key}
  
  \begin{key}{/pgf/decoration/shape sep=\meta{spacing} (initially {.25cm, between centers})}
    Set the spacing between the shapes on the decorationd path. This can be
    just a distance on its own, but the additional keywords 
    |between centers|, and |between borders| (which must be preceded by a 
    comma), specify that the distance	is between the center anchors of 
    the shapes or between the edges of the \emph{boundaries} of
    the shape borders.
	
\begin{codeexample}[]
\begin{tikzpicture}[
    decoration={shape backgrounds,shape size=.5cm,shape=signal},
    signal from=west, signal to=east,
    paint/.style={decorate, draw=#1!50!black, fill=#1!50}]
  \draw [help lines] grid (3,2);
  \draw [paint=red, decoration={shape sep=.5cm}]
    (0,2) -- (3,2);
  \draw [paint=green, decoration={shape sep={1cm, between center}}]
    (0,1) -- (3,1);
  \draw [paint=blue, decoration={shape sep={1cm, between borders}}]
    (0,0) -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}
  
  \begin{key}{/pgf/decoration/shape evenly spread=\meta{number}}
    This key overides the |shape sep| key and forces the decoration to
    fit \meta{number} shapes evenly across the path. 
    If \meta{number} is less than |1|, then no shapes will be used. 
    If \meta{number} equals |1|, then one shape is put in the middle 
    of the path. 
    The additional keywords |by centers| (the default, if no keyword is
    specified) and |by borders| can be used (both preceded by a comma), 
    to specify how the distance between shapes is determined. These
    keywords will only have a noticable effect if the shapes sizes
    differ over time.
    
\begin{codeexample}[]
\tikzset{
  paint/.style={draw=#1!50!black, fill=#1!50},
  spreading/.style={
    decorate,decoration={shape backgrounds, shape=rectangle,
    shape start size=4mm,shape end size=1mm,shape evenly spread={#1}}}
}
\begin{tikzpicture}
  \fill [paint=green,spreading={5, by borders},
         decoration={shape scaled}]            (0,2)   -- (3,2);
  \fill [paint=blue,spreading={5, by centers},
         decoration={shape scaled}]            (0,1.5) -- (3,1.5);   
  \fill [paint=red,    spreading=5]            (0,1)   -- (3,1);
  \fill [paint=orange, spreading=4]            (0,.5)  -- (3,.5);
  \fill [paint=gray,    spreading=1]            (0,0)   -- (3,0);
\end{tikzpicture}
\end{codeexample}
  \end{key}

  \begin{key}{/pgf/decoration/shape sloped=\opt{\meta{boolean}} (initially true)}
    By default, shapes are rotated to the slope of the decorationd path. If 
    \meta{boolean} is the value |false|, then this rotation is turned 
    off. Internally this sets the \TeX-if |\ifpgfshapedecorationsloped|
    appropriately.

\begin{codeexample}[]
\tikzset{
  paint/.style={draw=#1!50!black, fill=#1!50}
}
\begin{tikzpicture}[decoration={
    shape width=.65cm, shape height=.45cm,
    shape=isosceles triangle, shape sep=.75cm,
    shape backgrounds}]    
  \draw [help lines] grid (3,2);
  \draw [paint=red,decorate] (0,0) -- (2,2);
  \draw [paint=blue,decorate,decoration={shape sloped=false}]
                             (1,0) -- (3,2);
\end{tikzpicture}
\end{codeexample}
  \end{key}%

  It is possible to scale the width and height of the shapes across the
  length of the decorationd path. The shapes are scaled between the starting
  size and the ending size. The following keys customize the way the
  decoration shapes are scaled:
	
  \begin{key}{/pgf/decoration/shape scaled=\meta{boolean} (initially false)}
\begin{codeexample}[]
\tikzset{
  bigger/.style={decoration={shape start size=.125cm, shape end size=.5cm}},
  smaller/.style={decoration={shape start size=.5cm, shape end size=.125cm}},
  decoration={shape backgrounds,
              shape sep={.25cm, between borders},shape scaled}
}
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \fill [decorate, bigger, red!50]   (0,1) -- (3,2);
  \fill [decorate, smaller, blue!50] (0,0) -- (3,1);
\end{tikzpicture}
\end{codeexample}

    If this key is set to false (which is the default), then only the
    start width and height are used. Note that the keys |shape width|
    and |shape height| set the start and end height simultaneously.
  \end{key}

  \begin{key}{/pgf/decoration/shape start width=\meta{length} (initially 2.5pt)}
    The starting width of the shape.
  \end{key}%

  \begin{key}{/pgf/decoration/shape start height=\meta{length} (initially 2.5pt)}
    The starting height of the shape.
  \end{key}%
  
  \begin{stylekey}{/pgf/decoration/shape start size=\meta{length}}
    Set both the the start height and start width simultaneously.
  \end{stylekey}%

  \begin{key}{/pgf/decoration/shape end width=\meta{length} (initially 2.5pt)}
    The recommended ending width of the shape. Note, that this is the
    width that a shape will take only if it is drawn exactly at the end
    of the path.


\begin{codeexample}[]    
\tikzset{
  bigger/.style={decoration={shape start size=.25cm, shape end size=1cm}},
  smaller/.style={decoration={shape start size=1cm, shape end size=.25cm}},
  decoration={shape backgrounds,
              shape sep={.25cm, between borders},shape scaled}
}
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \fill [decorate,bigger,
         decoration={shape sep={.25cm, between borders}}, blue!50] 
    (0,1.5) -- (3,1.5);
  \fill [decorate,smaller,
         decoration={shape sep={1cm, between centers}},   red!50]  
    (0,.5)  -- (3,.5);
  \draw [gray, dotted] (0,1.625) -- (3,2)    (0,1.375) -- (3,1) 
                       (0,1)     -- (3,.625) (0,0)     -- (3,.375); 
\end{tikzpicture}
\end{codeexample}
  \end{key}%

  \begin{key}{/pgf/decoration/shape end height=\meta{length}}
    The recommended ending height of the shape.
  \end{key}%

  \begin{stylekey}{/pgf/decoration/shape end size=\meta{length}}
    Set both the the end height and end width simultaneously.
  \end{stylekey}
\end{decoration}





\subsection{Text Decorations}

\begin{pgflibrary}{decorations.text}
  The decoration in this library decorates the path with some
  text. This can be used to draw text that follows a curve.  
\end{pgflibrary}

\begin{decoration}{text along path}
  This decoration decorates the path with text. This drawing of the
  text is a ``side effect'' of the decoration. The to-be-decorated
  path is only used to determine where the characters should be put
  and it is thrown away after the decoration is done. This is why in
  the following example no line is shown.
	
\begin{codeexample}[]
\catcode`\|12
\begin{tikzpicture}[decoration={text along path,
    text={Some long text along a ridiculously long curve that}}] 
  \draw [help lines] grid (3,2);
  \draw [decorate] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\end{tikzpicture}
\end{codeexample}

  \pgfname{} ``does its best'' to typeset the text, however you
  should note the following points:
  \begin{itemize}
  \item
    Each character in the text is typeset in a separate |\hbox|. This
    means that if you want fancy things like kerning or ligatures you
    will have to manually annotate the characters in the decoration 
    text within a group, for example, |W{\kern-1ptA}TER|. 
  \item
    Each character is positioned using the center of its baseline. To
    move the text vertically (relative to the path), the additional
    transform key should be used.
  \item
    No attempt is made to ensure characters do not overlap when
    the angle between segments is considerably less than 180\textdegree{}
    (this is tricky to do in \TeX{} without a huge processing
    overhead). In general this should not be too much of a problem, 
    but, once again, kerning can be used in most cases to overcome 
    any undesirable effects.
  \item			
    It is only possible to typeset text in math mode under considerable
    restrictions. Math mode is entered and exited using any character	
    of category code 3 (e.g., in plain \TeX{} this is |$|). %$
    Math subscripts and superscripts need to be	contained within braces 
    (e.g., |{^y_i}|) as do commands like |\times| or |\cdot|. 
    However, even modestly complex mathematical	typesetting is unlikely 
    to be sucessful along a path (or even desirable).
  \item
    Some inaccuracies in positioning may be particularly apparent
    at input segment boundaries. This can (unfortunately) only be solved 
    on case by case basis by individually kerning the offending 
    characters within a group.
  \end{itemize}
  
  The following keys are used by the |text| decoration:
  \begin{key}{/pgf/decoration/text=\meta{text}
      (initially \normalfont empty)}
    Set the text to typeset along the curve. 
    Consecutive spaces are ignored, so |\ | (or |\space| in \LaTeX) 
    should be used to insert multiple spaces.	It is possible to
    format the text using normal formating commands, such as |\it|, |\bf|
    and |\color|, within customisable delimiters. Initially these
    delimiters are both {\tt\char`\|} (however, care will be needed 
    regarding	the category codes of delimiters --- see below). 

{\catcode`\|12
\begin{codeexample}[]
\catcode`\|12
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \path [decorate,decoration={text along path,
           text={a big |\color{green}|green|| juicy apple.}}] 
    (0,0) .. controls (0,2) and (3,0) .. (3,2);
\end{tikzpicture}
\end{codeexample}
}
    By following the first delimiter
    with |+|, the formatting commands are added to any exisiting 
    formatting.

{\catcode`\|12
\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \path [decorate,decoration={text along path,
           text={a |\large|big |+\bf\color{red}|red|| juicy apple.}}] 
    (0,0) .. controls (0,2) and (3,0) .. (3,2);
\end{tikzpicture}
\end{codeexample}
}
	
    Internally, the text is stored in the macro |\pgfdecorationtext|. 
    Any characters that have not been typeset when the end of the 
    path has been reached will be stored in |\pgfdecorationrestoftext|.
    
  \end{key}

{\catcode`\|12
  \begin{key}{/pgf/decoration/text format delimiters=\marg{before}\marg{after} (initially \char`\{|\char`\}\char`\{\char`\})}

    \catcode`\|13
	
    Set the characters that the text decoration will use to parse 
    formatting commands. 
    If \meta{after} is empty, then \meta{before} will be used for both
    delimiters.
    In general you should stick to characters	whose category codes are 
    |11| or |12|.
    As |+| is used to indicate that the specifed format commands 
    are added	to any exisiting ones, you should avoid using |+| as
    a delimiter. 

\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \path [decorate, decoration={text along path,text format delimiters={[}{]}, 
           text={A big [\color{red}]red[] and [\color{green}]green[] apple.}}] 
    (0,0) .. controls (0,2) and (3,0) .. (3,2);
\end{tikzpicture}
\end{codeexample}
  \end{key}
}

  \begin{key}{/pgf/decoration/text color=\meta{color}  (initially black)}
    The color of the text.
  \end{key}


\begin{key}{/pgf/decoration/reverse path=\meta{boolean} (initially false)}
  This key reverses the path. This is especially useful for typesetting
  text along different sides of curves.

\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \draw [gray, ->]
    [postaction={decoration={text along path, 
      text={a big juicy apple}, text color=red}, decorate}]
    [postaction={decoration={text along path, 
      text={a big juicy apple}, text color=blue, reverse path}, decorate}] 
    (3,0) .. controls (3,2) and (0,2) .. (0,0);
\end{tikzpicture}
\end{codeexample}
  
\end{key}

\begin{key}{/pgf/decoration/text align={\ttfamily\char`\{}\meta{alignment options}{\ttfamily\char`\}}}
  This changes the key path to |/pgf/decoration/text align| and
  executes \meta{alignment options}.
\end{key}

\begin{key}{/pgf/decoration/text align/align=\meta{alignment} (initially left)}
  Aligns the text according to \meta{alignment}, which should
  be one of |left|, |right|, or |center|.

\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \draw [red, dashed]
    [postaction={decoration={text along path, text={a big juicy apple},
      text align={align=right}}, decorate}] 
    (0,0) .. controls (0,2) and (3,2) .. (3,0);
\end{tikzpicture}
\end{codeexample}

\end{key}

\begin{stylekey}{/pgf/decoration/text align/left}
  Aligns the text to the left end of the path.

\end{stylekey}

\begin{stylekey}{/pgf/decoration/text align/right}
  Aligns the text to the right end of the path.
\end{stylekey}

\begin{stylekey}{/pgf/decoration/text align/center}
  Aligns the text to the center of the path. 
\end{stylekey}

\begin{key}{/pgf/decoration/text align/left indent=\meta{length} (initially 0pt)}
  Specifiy a distance which the automaton should move along
  before it starts typesetting the text.
\end{key}

\begin{key}{/pgf/decoration/text align/right indent=\meta{length} (initially 0pt)}
  Specifiy a distance before the end of the path, where
  the automaton should stop typesetting the text. 
\end{key}

\begin{key}{/pgf/decoration/text align/fit to path=\meta{boolean} (initially false)}
  This key makes the decoration automaton try to fit the text 
  to the length of the path. The automaton shifts forward 
  by a small amount between each character in order to fit the
  text to the path. If, however, the length of the text is longer 
  than the length of the path (i.e., the automaton would have to 
  shift \emph{backwards} between characters) this key will
  have no effect.

\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \draw [red, dashed]
    [postaction={decoration={text along path, text={a big juicy apple},
      text align=fit to path}, decorate}] 
    (0,0) .. controls (0,2) and (3,2) .. (3,0);
\end{tikzpicture}
\end{codeexample} 

\end{key}

\begin{key}{/pgf/decoration/text align/fit to path stretching spaces=\meta{boolean} (initially false)}
  This key works like the previous key except the the automaton
  shifts forward only for space characters (including |\space|, but
  \emph{excluding} |\ |).

\begin{codeexample}[]
\begin{tikzpicture}
  \draw [help lines] grid (3,2);
  \draw [red, dashed]
    [postaction={decoration={text along path, text={a big juicy apple},
      text align={fit to path stretching spaces}}, decorate}] 
    (0,0) .. controls (0,2) and (3,2) .. (3,0);
\end{tikzpicture}
\end{codeexample} 
\end{key}

\end{decoration}




\subsection{Fractal Decorations}

\begin{pgflibrary}{decorations.fractals}
  The decorations of this library can be used to create fractal
  lines. To use them, you typically have to apply the decoration
  repeatedly to an originally straight path.
\end{pgflibrary}


\begin{decoration}{Koch curve type 1}
  This decoration replaces a straight line by a ``rectangular bump.''
  By repeatedly applying this replacement, different levels of the
  Koch curve fractal can be created. Its Hausdorff dimension is $\log
  5/\log 3$.
\begin{codeexample}[]
\begin{tikzpicture}[decoration=Koch curve type 1]
  \draw decorate{ (0,0) -- (3,0) };
  \draw decorate{ decorate{ (0,-1.5) -- (3,-1.5) }};
  \draw decorate{ decorate{ decorate{ (0,-3) -- (3,-3) }}};
\end{tikzpicture}
\end{codeexample}
\end{decoration}


\begin{decoration}{Koch curve type 2}
  This decoration replaces a straight line by a ``rectangular sine.''
  Its Hausdorff dimension is $3/2$.
\begin{codeexample}[]
\begin{tikzpicture}[decoration=Koch curve type 2]
  \draw decorate{ (0,0) -- (3,0) };
  \draw decorate{ decorate{ (0,-2) -- (3,-2) }};
  \draw decorate{ decorate{ decorate{ (0,-4) -- (3,-4) }}};
\end{tikzpicture}
\end{codeexample}
\end{decoration}

\begin{decoration}{Koch snowflake}
  This decoration replaces a straight line by a ``line with a spike.''
  Koch's snowflake's Hausdorff dimension is $\log 4/\log 3$.
\begin{codeexample}[]
\begin{tikzpicture}[decoration=Koch snowflake]
  \draw decorate{ (0,0) -- (3,0) };
  \draw decorate{ decorate{ (0,-1) -- (3,-1) }};
  \draw decorate{ decorate{ decorate{ (0,-2) -- (3,-2) }}};
  \draw decorate{ decorate{ decorate{ decorate{ (0,-3) -- (3,-3) }}}};
\end{tikzpicture}
\end{codeexample}
\end{decoration}

\begin{decoration}{Cantor set}
  This decoration replaces a straight line by a ``line with a whole in
  the middle.'' The Hausdorff dimension of the Cantor set is $\log
  2/\log 3$. 
\begin{codeexample}[]
\begin{tikzpicture}[decoration=Cantor set,very thick]
  \draw decorate{ (0,0) -- (3,0) };
  \draw decorate{ decorate{ (0,-.5) -- (3,-.5) }};
  \draw decorate{ decorate{ decorate{ (0,-1) -- (3,-1) }}};
  \draw decorate{ decorate{ decorate{ decorate{ (0,-1.5) -- (3,-1.5) }}}};
\end{tikzpicture}
\end{codeexample}
\end{decoration}





\endinput



