[Tex/LaTex] Styles in TikZ trees not working as expected

nodestikz-pgftikz-trees

I want to draw a "cut-out" region of a tree, and visually underline this by having dashed edges on top and on the bottom of my diagram (to symbolize the levels further up and further down).

I am attempting to use styles defined in the options of the \tikzpicture environment, but failing to achieve the desired result, which would look something like this:

desired result

For me, the "outermost" edges (which I want to be dashed) are just normal lines.

\documentclass{beamer}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[
  every node/.style={minimum size=4mm, inner sep=0.5mm},
  normal/.style={circle,draw},
  invis/.style={draw=none},
  border/.style={ edge from parent/.style={dashed,draw} },
  acc/.style={circle,thick,draw=green!50,fill=green!2},
  rej/.style={circle,thick,draw=red!50,fill=red!20},
  semithick]

  node[invis] (root) {}
    child[level distance=11mm] { node[border,normal] {x}
      child {node[acc] {x1}
        child {node[border,invis] {} }
        child {node[border,invis] {} }
        child {node[border,invis] {} }
      }
      child {node[rej] {x2} }
      child {node[normal] {x3}
        child {node[invis,border] {} }
        child {node[invis,border] {} }
        child {node[invis,border] {} }
      }
  }; 
\end{tikzpicture}
\end{document}

My first hunch was maybe a node could only have one style defined in its options, but even after swapping the two styles for the last tree nodes, it makes no difference. I also tried applying a style and setting an option in the same []-block, and it worked, so this doesn't seem to be the problem.

I am aware that the author of TikZ notes in the manual that "placing node options at the right place is an arcane art", but (after carefully reading) I thought basically it worked like this:

  • Options defined in a node are local in effect.
  • Options defined in a child command are inherited to all of its child nodes.

When trying to pass the border style to the child command as an alternative , I do get dashed edges which work for the bottom, but if I pass it to the first visible child node (x), all the lines in the tree are dashed (even the node outlines!) because of the inheritance mechanism.

What am I doing wrong/ should I change to achieve the desired result?

Best Answer

Just a quick demonstration with Forest. The major advantages of Forest lie in its power, flexibility and concise syntax. Regularities in content and styling can be turned into automated configuration rules and trees themselves can be specified very concisely. Since Forest is based on TikZ, the power of the host package is also available.

For example,

\begin{forest}
  bordered tree,
  [
    [x, border
      [x1, acc, for descendants=border
        [][][]
      ]
      [x2, rej]
      [x3, for children=border
        [][][]
      ]
    ]
  ]
\end{forest}

specifies the target tree:

target tree

while the following partly explains the first and partly shows one or two additional tricks,

\begin{forest}
  bordered tree,
  [
    [x, border, normal
    [x1, acc, for descendants=border, label=left:\texttt{for descendants}
        [][.,label=left:bordered children [][]][]
      ]
      [x2, rej]
      [x3, normal, for children=border, label=right:\texttt{for children}
        [][.,label=right:unbordered children [][]][, for current and ancestors={edge+=blue}]
      ]
    ]
  ]
\end{forest}

which produces:

annotated tree

Complete code:

\documentclass[border=10pt]{standalone}
\usepackage{forest}
\forestset{
  declare boolean={border}{0},
  bordered tree/.style={
    for tree={
      minimum size=4mm, 
      inner sep=0.5mm,
      edge+={semithick},
      semithick,
    },
    before typesetting nodes={
      where border={
        edge+={dashed, draw},
      }{},
      where={isodd(n_children)}{
        tempcounta/.process={
          Ow+n {n children}{(##1+1)/2}
        },
        for n={
          >  R {tempcounta} % doesn't work to plug the above in directly ??'
        }{calign with current edge},
      }{},
      where content={}{}{normal},
    },
  },
  /tikz/.cd,
  normal/.style={circle,draw},
  invis/.style={draw=none},
  acc/.style={circle,thick,draw=green!50,fill=green!2},
  rej/.style={circle,thick,draw=red!50,fill=red!20},
}
\begin{document}
\begin{forest}
  bordered tree,
  [
    [x, border
      [x1, acc, for descendants=border
        [][][]
      ]
      [x2, rej]
      [x3, for children=border
        [][][]
      ]
    ]
  ]
\end{forest}
\begin{forest}
  bordered tree,
  [
    [x, border, normal
    [x1, acc, for descendants=border, label=left:\texttt{for descendants}
        [][.,label=left:bordered children [][]][]
      ]
      [x2, rej]
      [x3, normal, for children=border, label=right:\texttt{for children}
        [][.,label=right:unbordered children [][]][, for current and ancestors={edge+=blue}]
      ]
    ]
  ]
\end{forest}
\end{document}
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