[Tex/LaTex] TikZ: How to change the path color without changing nodes alongside

tikz-arrowstikz-pgftikz-styles

It is difficult to google for this problem, as I use the to command in tikz in order to bend edges left or right.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,positioning}
\begin{document}
\newlength{\nodedist}
\setlength{\nodedist}{5cm}
\begin{tikzpicture}[
      mynode/.style={text width=4cm,draw,rounded
      corners=5pt,shape=rectangle,minimum width=1cm,text depth=2cm,inner sep=5pt},
      node distance=\nodedist,
      arrow label/.style={midway,fill=white,draw,shape=rectangle,rounded corners=3pt},
   ]
   \draw (0,0) node[mynode] (model) {
      \makebox[4cm]{Model}\\
      \hrulefill \\
   };
   \node[mynode,right=of model] (view) {
      \makebox[4cm]{View}\\
      \hrulefill \\
   };

   \node[mynode] (controller) at ($(model) !0.5! (view) + (0,-\nodedist)$) {
      \makebox[4cm]{Controller}\\
      \hrulefill \\
   };
   \draw[->] (controller.west) to[bend left,red]  node[arrow label] {Change state} (model.south);
   \draw[->] (controller.east) to[bend right]  node[arrow label] {Update display} (view.south);
   \draw[->]  (view.west) to[bend right]  node[arrow label] {Send user input} (controller.north);
   \draw[->]  (view.north) to[bend right]  node[arrow label] {Request state} (model.north);
   \draw[->]  (model.east) to[bend left] node[arrow label] {Notify of change} (view.north west);

\end{tikzpicture}
\end{document}

I want to change the arrow colour without affecting the nodes placed along it. Is this straightforwardly possible?
I could use edge from the graph library, but I wonder if it can be done with to.

Best Answer

You can use a scope with the option

every to/.style={append after command={[draw=red]}}

Example:

\begin{scope}[every to/.style={append after command={[draw=red]}}]
   \draw[->] (controller.west) to[bend left]  node[arrow label] {Change state} (model.south);
   \draw[->] (controller.east) to[bend right]  node[arrow label] {Update display} (view.south);
   \draw[->]  (view.west) to[bend right]  node[arrow label] {Send user input} (controller.north);
   \draw[->]  (view.north) to[bend right]  node[arrow label] {Request state} (model.north);
   \draw[->]  (model.east) to[bend left] node[arrow label] {Notify of change} (view.north west);
   \end{scope}

To prevent this from making the node borders red, use draw=black in

arrow label/.style={midway,fill=white,draw=black,shape=rectangle,rounded corners=3pt},

Full code:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,positioning}
\begin{document}
\newlength{\nodedist}
\setlength{\nodedist}{5cm}
\begin{tikzpicture}[
      mynode/.style={text width=4cm,draw,rounded
      corners=5pt,shape=rectangle,minimum width=1cm,text depth=2cm,inner sep=5pt},
      node distance=\nodedist,
      arrow label/.style={midway,fill=white,draw=black,shape=rectangle,rounded corners=3pt},
   ]
   \draw (0,0) node[mynode] (model) {
      \makebox[4cm]{Model}\\
      \hrulefill \\
   };
   \node[mynode,right=of model] (view) {
      \makebox[4cm]{View}\\
      \hrulefill \\
   };

   \node[mynode] (controller) at ($(model) !0.5! (view) + (0,-\nodedist)$) {
      \makebox[4cm]{Controller}\\
      \hrulefill \\
   };
   \begin{scope}[every to/.style={append after command={[draw=red]}}]
   \draw[->] (controller.west) to[bend left]  node[arrow label] {Change state} (model.south);
   \draw[->] (controller.east) to[bend right]  node[arrow label] {Update display} (view.south);
   \draw[->]  (view.west) to[bend right]  node[arrow label] {Send user input} (controller.north);
   \draw[->]  (view.north) to[bend right]  node[arrow label] {Request state} (model.north);
   \draw[->]  (model.east) to[bend left] node[arrow label] {Notify of change} (view.north west);
   \end{scope}
\end{tikzpicture}
\end{document}

Related Solutions

TikZ – How to Create a Color Changing Path in TikZ

Scoped path colour is not implemented simply because it cannot be assumed to be implemented in the final document. The lines and so forth in TikZ/PGF are written into the document using the document's method of drawing lines. Since PDF, PostScript, SVG, and so forth have native ways of drawing lines, TikZ/PGF uses those. Since TikZ/PGF tries to be backend-agnostic, it can only truly support those features that are common to all backends. My guess is that for PDF and SVG, it isn't possible to change the colour of a path halfway (pretty sure about SVG, not so sure about PDF, don't know about PostScript). So since the backends can't cope with it, neither can TikZ/PGF.

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

Best Answer

Related Solutions

TikZ – How to Create a Color Changing Path in TikZ

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

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