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% Copyright 2006 by Till Tantau
%
% This file may be distributed and/or modified
%
% 1. under the LaTeX Project Public License and/or
% 2. under the GNU Free Documentation License.
%
% See the file doc/generic/pgf/licenses/LICENSE for more details.
\section{Tree Library}
\label{section-tree-library}
\begin{tikzlibrary}{trees}
This packages defines styles to be used when drawing trees.
\end{tikzlibrary}
\subsection{Growth Functions}
The package |pgflibrarytikztrees| defines two new growth
functions. They are installed using the following options:
\begin{itemize}
\itemoption{grow via three points}|=one child at (|\meta{x}%
|) and two children at (|\meta{y}|) and (|\meta{z}|)|
This option installs a growth function that works as follows: If a
parent node has just one child, this child is placed at \meta{x}. If
the parent node has two children, these are placed at \meta{y} and
\meta{z}. If the parent node has more than two children, the
children are placed at points that are linearly extrapolated from
the three points \meta{x}, \meta{y}, and \meta{z}. In detail, the
position is $x + \frac{n-1}{2}(y-x) + (c-1)(z-y)$, where $n$ is the
number of children and $c$ is the number of the current child
(starting with~$1$).
The net effect of all this is that if you have a certain ``linear
arrangement'' in mind and use this option to specify the placement
of a single child and of two children, then any number of children
will be placed correctly.
Here are some arrangements based on this growth function. We start
with a simple ``above'' arrangement:
\begin{codeexample}[]
\begin{tikzpicture}[grow via three points={%
one child at (0,1) and two children at (-.5,1) and (.5,1)}]
\node at (0,0) {one} child;
\node at (0,-1.5) {two} child child;
\node at (0,-3) {three} child child child;
\node at (0,-4.5) {four} child child child child;
\end{tikzpicture}
\end{codeexample}
The next arrangement places children above, but ``grows only to the
right.''
\begin{codeexample}[]
\begin{tikzpicture}[grow via three points={%
one child at (0,1) and two children at (0,1) and (1,1)}]
\node at (0,0) {one} child;
\node at (0,-1.5) {two} child child;
\node at (0,-3) {three} child child child;
\node at (0,-4.5) {four} child child child child;
\end{tikzpicture}
\end{codeexample}
In the final arrangement, the children are placed along a line going
down and right.
\begin{codeexample}[]
\begin{tikzpicture}[grow via three points={%
one child at (-1,-.5) and two children at (-1,-.5) and (0,-.75)}]
\node at (0,0) {one} child;
\node at (0,-1.5) {two} child child;
\node at (0,-3) {three} child child child;
\node at (0,-4.5) {four} child child child child;
\end{tikzpicture}
\end{codeexample}
These examples should make it clear how you can create new styles to
arrange your children along a line.
\itemstyle{grow cyclic}
This style causes the children to be arranged ``on a circle.'' For
this, the children are placed at distance |\tikzleveldistance| from
the parent node, but not on a straight line, but points on a
circle. Instead of a sibling distance, there is a |sibling angle|
that denotes the angle between two given children.
\begin{itemize}
\itemoption{sibling angle}|=|\meta{angle}
Sets the angle between siblings in the |grow cyclic| style.
\end{itemize}
Note that this function will rotate the coordinate system of the
children to ensure that the grandchildren will grow in the right
direction.
\begin{codeexample}[]
\begin{tikzpicture}[grow cyclic]
\tikzstyle{level 1}=[level distance=8mm,sibling angle=60]
\tikzstyle{level 2}=[level distance=4mm,sibling angle=45]
\tikzstyle{level 3}=[level distance=2mm,sibling angle=30]
\coordinate [rotate=-90] % going down
child foreach \x in {1,2,3}
{child foreach \x in {1,2,3}
{child foreach \x in {1,2,3}}};
\end{tikzpicture}
\end{codeexample}
\itemoption{clockwise from}|=|\meta{angle}
This option also cuases children to be arranged on a
circle. However, the rule for placing children is simpler thatn with
the |grow cyclic| style: The first child is placed at
\meta{angle} at a distance of |\tikzleveldistance|. The second child
is placed at the same distance from the parent, but at angle
\meta{angle}${}-{}$|\tikzsiblingangle|. The third child is displaced
by another |\tikzsiblingangle| in a clockwise fashion, and so on.
Note that this function will not rotate the coordinate system.
\begin{codeexample}[]
\begin{tikzpicture}
\node {root}
[clockwise from=30,sibling angle=30]
child {node {$30$}}
child {node {$0$}}
child {node {$-30$}}
child {node {$-60$}};
\end{tikzpicture}
\end{codeexample}
\itemoption{counterclockwise from}|=|\meta{angle}
Works the same way as |clockwise from|, but sibling angles are added
instead of subtracted.
\end{itemize}
\subsection{Edges From Parent}
The following styles can be used to modify how the edges from parents
are drawn:
\begin{itemize}
\itemstyle{edge from parent fork down}
This style will draw a line from the parent downwards (for half the
level distance) and then on to the child using only horizontal and
vertical lines.
\begin{codeexample}[]
\begin{tikzpicture}
\node {root}
[edge from parent fork down]
child {node {left}}
child {node {right}
child[child anchor=north east] {node {child}}
child {node {child}}
};
\end{tikzpicture}
\end{codeexample}
\itemstyle{edge from parent fork right}
This style behaves similarly, only it will first draw its edge to
the right.
\begin{codeexample}[]
\begin{tikzpicture}
\node {root}
[edge from parent fork right,grow=right]
child {node {left}}
child {node {right}
child {node {child}}
child {node {child}}
};
\end{tikzpicture}
\end{codeexample}
\itemstyle{edge from parent fork left}
behaves similary.
\itemstyle{edge from parent fork up}
behaves similary.
\end{itemize}
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