Letter “p” ruining vertical alignment

Question

I have a simple diagram I have created.

\begin{figure}[t]
  \begin{center}
    \setlength{\unitlength}{10pt}
    \begin{picture}(24,4)
      \setlength\fboxsep{0pt}
      \put(0,2){$\underbrace{\strut \fcolorbox{black}{teal0}{\framebox(6,2){Preamble}}\fcolorbox{black}{purp0}{\framebox(7,2){Start code}}}_\textrm{Stage 1: estimate M}$}
      \put(13,2){$\underbrace{\strut \fcolorbox{black}{lime0}{\framebox(5,2){Data}}\fcolorbox{black}{orange0}{\framebox(6,2){Stop code}}}_\textrm{Stage 2: sample and decode}$}
    \end{picture}
    \caption{Packet format.}
    \label{fig:packet}
  \end{center}
\end{figure}

and it creates the following:

However, if you look closely you will notice the text in the last box is out of alignment with the text in the other boxes because of the "p". I would like to put it in alignment. Solution should be as close to the original image as possible, and not require additional packages like TikZ.

Answer 1

Please always post complete documents showing all packages (and colours) used. I made up some different colours.

As you are in picture mode anyway it is easier to directly control the position of the braces using \put coordinates, and you can hide the depth of the text using \raisebox.

\documentclass{article}
\usepackage{color}
\begin{document}

\begin{figure}[t]
  \begin{center}
    \setlength{\unitlength}{10pt}
    \begin{picture}(24,4)
      \setlength\fboxsep{0pt}
      \put(0,2){\fcolorbox{black}{red}{\framebox(6,2){Preamble}}%
                \fcolorbox{black}{blue}{\framebox(7,2){Start code}}%
                \fcolorbox{black}{yellow}{\framebox(5,2){Data}}%
                \fcolorbox{black}{green}{\framebox(6,2){\raisebox{0pt}[\height][0pt]{Stop code}}}}

      \put(0,0){\makebox(13.2,2){\upbracefill}\makebox(11.2,2){\upbracefill}}

      \put(0,-1){\makebox(13.2,2){Stage 1: estimate M}%
                \makebox(11.2,2){Stage 2: sample and decode}}



    \end{picture}
    \caption{Packet format.}
    \label{fig:packet}
  \end{center}
\end{figure}

\end{document}

Answer 2

It's all about the placement of the \strut:

\documentclass{article}
\usepackage{xcolor}% http://ctan.org/pkg/xcolor

\begin{document}

\begin{center}
  \setlength{\unitlength}{10pt}
  \begin{picture}(24,4)
    \setlength\fboxsep{0pt}
    \put(0,2){$\underbrace{\strut \fcolorbox{black}{red}{\framebox(6,2){Preamble}}\fcolorbox{black}{blue}{\framebox(7,2){Start code}}}_\textrm{Stage 1: estimate M}$}%
    \put(13,2){$\underbrace{\strut \fcolorbox{black}{green}{\framebox(5,2){Data}}\fcolorbox{black}{yellow}{\framebox(6,2){Stop code}}}_\textrm{Stage 2: sample and decode}$}
  \end{picture}
\end{center}

\begin{center}
  \setlength{\unitlength}{10pt}
  \begin{picture}(24,4)
    \setlength\fboxsep{0pt}
    \put(0,2){$\underbrace{\fcolorbox{black}{red}{\framebox(6,2){\strut Preamble}}\fcolorbox{black}{blue}{\framebox(7,2){\strut Start code}}}_\textrm{Stage 1: estimate M}$}%
    \put(13,2){$\underbrace{\fcolorbox{black}{green}{\framebox(5,2){\strut Data}}\fcolorbox{black}{yellow}{\framebox(6,2){\strut Stop code}}}_\textrm{Stage 2: sample and decode}$}
  \end{picture}
\end{center}

\end{document}

The upper image is the original output, while the lower one uses a \strut in each box. Since you are using \fcolorbox, you can create something like

\newcommand{\paddedbox}[4][1ex]{%
  {\setlength{\fboxsep}{#1}\fcolorbox{#2}{#3}{\strut\quad#4\quad}}}%

which creates a padded box (through setting \fboxsep; default is 1ex), vertically and horizontally (through additional placements of \quads (1em space). The code is a little cleaner

\begin{center}
  \setlength{\unitlength}{10pt}
  \begin{picture}(24,4)
    \put(0,2){$\underbrace{\paddedbox{black}{red}{Preamble}\paddedbox{black}{blue}{Start code}}_\textrm{Stage 1: estimate M}$}%
    \put(15,2){$\underbrace{\paddedbox{black}{green}{Data}\paddedbox{black}{yellow}{Stop code}}_\textrm{Stage 2: sample and decode}$}
  \end{picture}
\end{center}

and produces

Answer 3

For reference, the same problem with TikZ could be fixed as shown in Problem with TikZ and vertical alignment of text inside nodes.

Combining that hint with Connecting nodes with brace in TikZ, it is possible to build the following solution:

\documentclass{article}
\usepackage{tikz,pdftexcmds}
\usetikzlibrary{calc,shapes.arrows,decorations.pathreplacing,shadows}

% list of keys
\pgfkeys{/tikz/.cd,
  border color/.initial=black,
  border color/.get=\bordercol,
  border color/.store in=\bordercol,
  brace color/.initial=black,
  brace color/.get=\bracecol,
  brace color/.store in=\bracecol,
  brace distance/.initial=5pt,
  brace distance/.get=\bracedistance,
  brace distance/.store in=\bracedistance,
  brace position/.initial=north,
  brace position/.get=\bracepos,
  brace position/.store in=\bracepos,
  items height/.initial=1cm,
  items height/.get=\itemheight,
  items height/.store in=\itemheight,
  items width/.initial=3cm,
  items width/.get=\itemwidth,
  items width/.store in=\itemwidth,
  items distance/.initial=\itemwidth,
  items distance/.get=\itemdistance,
  items distance/.store in=\itemdistance,  
}

% list of styles
\tikzset{module/.style={
    draw=\bordercol,
    minimum height=\itemheight,
    minimum width=\itemwidth,
    text height=1.5ex,
    text depth=.25ex,
  },
  brace/.style={
    decoration={brace,raise=\bracedistance,amplitude=0.75em,#1},
    decorate,
    draw=\bracecol,
    very thick,    
  }
}

\makeatletter
\newcommand{\braceddiagram}[3][]{
  \begin{tikzpicture}[scale=0.9,transform shape,#1] % here we can pass options:
      % scale=0.9,transform shape are used to avoid overfull and underfull boxes

     % counting all the items to be displayed
     \foreach \items/\colors [count=\xi] in {#2}{\global\let\maxnumitem\xi}

     % foreach item we are going to compute at which distance it should be located
     % and then we put it with the module style and with a name <module><num-module>
     \foreach \items/\colors [count=\xi] in {#2}{%
       \path let 
         \n1={0+\xi*\itemdistance} in
         node[module,fill=\colors] (module\xi) at +(\n1,0) {\items};
     }

     % at the end we draw the brace with the comment
     \ifnum\pdf@strcmp{\bracepos}{south}=\z@
       \draw[brace=mirror] (module1.south west)--(module\maxnumitem.south east)
        node[below=3*\bracedistance, midway]{#3};
     \else
       \draw[brace] (module1.north west)--(module\maxnumitem.north east)
        node[above=3*\bracedistance, midway]{#3};
     \fi

  \end{tikzpicture}
}
\makeatother


\begin{document}

Generic examples:

\braceddiagram[brace distance=4pt]{Bla/red, Bla/blue, Bla/green}{Some comment}

\vspace{1cm}

\tikzset{my style for the diagram/.style={
    brace distance=6pt,
    brace position=south,
  }
}

\braceddiagram[my style for the diagram]{Bla/red, Bla/blue, Bla/green,Bla/yellow}{Some other comment}

\vspace{1cm}

The real example:

\begin{center}
\braceddiagram[my style for the diagram]{Preamble/red, Start code/blue}{Stage 1: estimate M}
\braceddiagram[my style for the diagram]{Data/green,Stop code/yellow}{Stage 2: sample and decode}
\end{center}

\end{document}

The result: