[Tex/LaTex] Fit around nodes and edges

fittikz-pgf

I know that I can use the fit library of tikz to get a fitted background behind some nodes.

How can I get the fit to be around edges as well?

My current code:

\begin{tikzpicture}[prefix=fig/,
state/.style={circle,draw,thick},
hmm/.style={draw,rectangle}]

\node[state] (a1) at (0,0) {} edge [loop above,thick] () ;
\node[state] (a2) at (1,0) {} edge [loop above,thick] () edge[<-,thick] (a1);
\node[state] (a3) at (2,0) {} edge [loop above,thick] () edge[<-,thick] (a2);

\node[hmm,fit=(a1) (a2) (a3)] (a) {};
\end{tikzpicture}

This puts the top of the background box straight through the loops. How can I fit the box nicely around the nodes and edges (so the top of the loop must be a point somehow in the fit).

Best Answer

One way to do this is to add a coordinate at the midpoint of each loop (well, in this example it's only necessary to add it to one loop since all are the same height). Then add that coordinate to the fit.

alt text

\documentclass{article}
\pagestyle{empty}
\usepackage{tikz}
\usetikzlibrary{fit}
\begin{document}

\begin{tikzpicture}[prefix=fig/,
state/.style={circle,draw,thick},
hmm/.style={draw,rectangle}]

\node[state] (a1) at (0,0) {} edge [loop above,thick] coordinate (l1) () ;
\node[state] (a2) at (1,0) {} edge [loop above,thick] coordinate (l2) () edge[<-,thick] (a1);
\node[state] (a3) at (2,0) {} edge [loop above,thick] coordinate (l3) () edge[<-,thick] (a2);

\node[hmm,fit=(a1) (a2) (a3) (l1) (l2) (l3)] (a) {};
\end{tikzpicture}
\end{document}

Note that the coordinate specification goes before the dummy target of the loop. This shows, incidentally, why that dummy target is useful. Placing the coordinate after the target puts the coordinate at the end of the loop, placing it before puts it at the midpoint.

I guess that a more elegant solution would be if it were possible to name a path and pass that name to the fit library, but I don't know if that's possible (however, last time I said something like that, someone came along and did it so I mention it just in case I can reinvoke the tikz-djinn).

Related Solutions

[Tex/LaTex] Draw edges and paths in the background of nodes in TikZ

TikZ/PGF has a concept of layers. They are described in chapter 82 “Layered Graphics” in the (v2.10) manual and can be used to have later commands be drawn below the things before them. In your example, you could write

\documentclass{article}
\usepackage{tikz}

\pgfdeclarelayer{bg}    % declare background layer
\pgfsetlayers{bg,main}  % set the order of the layers (main is the standard layer)

\begin{document}
  \begin{tikzpicture}
    \node [fill=gray!30] (foo) at (0,0) { foo };
    \node [fill=gray!30] (bar) at (2,0) { bar };
    \node [fill=gray!30] (baz) at (4,0) { baz };

    \begin{pgfonlayer}{bg}    % select the background layer
        \draw (foo) -- (baz);
    \end{pgfonlayer}
  \end{tikzpicture}
\end{document}

Actually, the backgrounds library (see chapter 25 in v2.10) already defines a background layer and a key that has to be used on a scope to select the layer:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{backgrounds}

\begin{document}
  \begin{tikzpicture}
    \node [fill=gray!30] (foo) at (0,0) { foo };
    \node [fill=gray!30] (bar) at (2,0) { bar };
    \node [fill=gray!30] (baz) at (4,0) { baz };

    \begin{scope}[on background layer]
        \draw (foo) -- (baz);
    \end{scope}
  \end{tikzpicture}
\end{document}

(The two solutions compile to the same code (except that the backgrounds library calls the layer background).)

[Tex/LaTex] Adjusting edge alignment and positioning of fitted node

This is done by setting the width of the first node, and then fitting the other two nodes to the previous nodes, using the fit library.
Same as #1.
Solved with #1.
This depends on what you want to do. If you only want two short nodes inside of the yellow, you can add two more nodes anchored there. But it depends on what you want to do

Output

Code

\documentclass[margin=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,fit}

\tikzset{
    every node/.style={draw, rectangle, align=center, text width=3cm, inner sep=0, thick, outer sep=0}
}

\begin{document}
\begin{tikzpicture}[node distance=5mm]
\node[fill=green!40, minimum height=2cm, minimum width=5cm, text width=3cm] (one) {This is\\block top left};
\node[fill=red!40,  fit={(one.west) (one.east)}, minimum height=1cm, anchor=north west, below =of one] (two) {block bottom left};
\node[fill=yellow, fit={(one)(two)},right =of two.south east, anchor=south west] (three) {This is\\block right};

\end{tikzpicture}
\end{document}