Parameterizing TikZ Figure

Question

I have this code that generates the process gantt chart:

\usetikzlibrary{shadows,arrows,positioning}
\begin{tikzpicture}[scale=0.75, transform shape]
      \tikzset{every node/.style={minimum height=2em},
        proc/.style={draw=black, fill=blue!15, drop shadow},
      }

      \node [draw, proc, minimum width=3em] (p2) {P2};
      \node [draw, proc, minimum width=3em, right=0em of p2.east, anchor=west] (p3) {P3};
      \node [draw, proc, minimum width=24em, right=0em of p3.east, anchor=west] (p1) {P1};


      \node [below=of p2.west] {0}  edge [draw] (p2.west);
      \node [below=of p2.east] {3} edge [draw] (p2.east);
      \node [below=of p3.east] {6} edge [draw] (p3.east);
      \node [below=of p1.east] {30} edge [draw] (p1.east);
      \end{tikzpicture}

The output:

I can see a pattern over here and I can imagine passing the parameters (e.g. p2/3,p3/3,p1/24) to some command that uses some kind of for loop to automatically generate the code. Unfortunately, my TikZ/LaTeX skills are way below that. Can anyone help me get started with automating this?

Answer 1

Try this:

\newcommand{\gantt}[1]{

    \newcounter{ganttnum}
    \setcounter{ganttnum}{0}

     \foreach \i/\j in {#1}{
         \draw (\theganttnum em,0)node [proc, minimum width=\j em, anchor=south west] (\i) {\i};
         \draw (\theganttnum em,0) -- ++(0,-0.5) node[below]{\theganttnum};
         \addtocounter{ganttnum}{\j}
     }
     \draw (\theganttnum em,0) -- ++(0,-0.5) node[below]{\theganttnum};
}

\begin{tikzpicture}[scale=0.75,transform shape]
    \gantt{P2/3,P3/3,P1/24}
\end{tikzpicture}

\begin{tikzpicture}[scale=0.75,transform shape]
    \gantt{A1/3,A2/10,A3/14,A5/3,A4/3}
\end{tikzpicture}

It creates a newcommand that takes 1 parameter, which should be a comma seperated list of the form P1/3,P2/5,P3/12. Every item has two parts: the node name (before / and the width of the node after the /).

This allows you to add an arbitrary number of nodes, with arbitrary names and widths.

A bit of explanation to the code:

Tikz' \foreach can take multiples for looping over eg. A/1, B/2, ... this comes in handy to keep the names and widths of the nodes togheter while looping over them.

I first let a counter gantt be set to 0. Each step in the loop adds the width of the node that gets added in that step be added to this counter, so the counter can be used to determine where the next node should be.

Answer 2

You can start with this code

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{shadows,arrows,positioning}

\begin{document}
\begin{tikzpicture}[scale=0.75, transform shape]
      \tikzset{every node/.style={minimum height=2em},
        proc/.style={draw=black, fill=blue!15, drop shadow},
      }

\node [draw, proc, minimum width=3em] (p2) {P2};

\foreach \i/\j/\k in {3/2/3,1/3/24}
      \node [draw, proc, minimum width=\k em, right=0em of p\j.east, anchor=west] (p\i) {P\i};


\node [below=of p2.west] {0}  edge [draw] (p2.west);
\foreach \i/\j in {2/3,3/6,1/30}
      \node [below=of p\i.east] {\j} edge [draw] (p\i.east);
\end{tikzpicture}
\end{document}

An updated version. Same loop will draw nodes and labels and a counter will take care of initial position of nodes. Once loop finishes, 0 mark is drawn.

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{shadows,arrows,positioning}

\begin{document}
\begin{tikzpicture}[scale=0.75, transform shape]
      \tikzset{every node/.style={minimum height=2em},
        proc/.style={draw=black, fill=blue!15, drop shadow},
      }

\newcounter{pos}
\setcounter{pos}{0}

\foreach \process/\width in {2/3,3/3,1/24}
{
   \node [draw, proc, minimum width=\width em,  anchor=west] (p\process) at (\thepos em,0) {P\process};
    \addtocounter{pos}{\width}
    \node [below=of p\process.east] {\thepos} edge [draw] (p\process.east);
}
\node [below=of p2.west] {0} edge [draw] (p2.west);

\end{tikzpicture}

\end{document}