TIKZ: Stacking two nodes with equal width without double drawing the overlapping shapes

Question

I am trying to stack 2 Tikz nodes directly below each other with no space and without having the double-thick shape between them. Furthermore, both nodes should have the same width, either fixed or determined by the with of the bottom node. My First try is:

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\makeatletter
\pgfdeclareshape{recttop}{
  \inheritsavedanchors[from=rectangle] % this is nearly a rectangle
  \inheritanchorborder[from=rectangle]
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{north}
  \inheritanchor[from=rectangle]{south}
  \inheritanchor[from=rectangle]{west}
  \inheritanchor[from=rectangle]{east}
  \backgroundpath{% this is new
    % store lower right in xa/ya and upper right in xb/yb
    \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
    \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
    % construct main path
    \pgfsetcornersarced{\pgfpoint{5pt}{5pt}}
    \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
    \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yb}}
    \pgfsetcornersarced{\pgfpoint{0pt}{0pt}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
    \pgfpathclose
 }
}
\pgfdeclareshape{rectbottom}{
  \inheritsavedanchors[from=rectangle] % this is nearly a rectangle
  \inheritanchorborder[from=rectangle]
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{north}
  \inheritanchor[from=rectangle]{south}
  \inheritanchor[from=rectangle]{west}
  \inheritanchor[from=rectangle]{east}
  \backgroundpath{% this is new
    % store lower right in xa/ya and upper right in xb/yb
    \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
    \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
    % construct main path
    \pgfsetcornersarced{\pgfpoint{0pt}{0pt}}
    \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
    \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yb}}
    \pgfsetcornersarced{\pgfpoint{5pt}{5pt}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
    \pgfpathclose
 }
}
\makeatother



\begin{document}
\begin{tikzpicture}
%[every node/.style={fill=gray,minimum width=2cm, minimum height=1cm}]
\matrix[row sep=0pt, every node/.style={draw}]{
 \node[draw, shape=recttop, fill=red!20] (top) {CFunction};\\
 \node[draw, shape=rectbottom] (bottom) {\ttfamily func(A, E, B, Z);};\\
 }; 
\end{tikzpicture}
\end{document}

Which results in

which does not look like I want it. I need the upper node as wide as the lower one and without the double drawn line in the middle of them. Alternatively a construct which realized a similar look.

Answer 1

I need the upper node as wide as the lower one and without the double drawn line in the middle of them.

Hence, the simplest way is not to create separate shapes, but rather use the old and very useful rectangle split which automatically helps avoiding the double line and preserves the width for both parts.

A possible solution:

\documentclass[tikz,border=10pt]{standalone}

\usetikzlibrary{shapes.multipart}

\tikzset{my rect/.style={
  rectangle split, 
  rectangle split parts=2, 
  draw,
  rounded corners,
  }
}

\begin{document}

\begin{tikzpicture}
\node[my rect,rectangle split part fill={red!20,white}]{CFunction\nodepart{two}\ttfamily func(A, E, B, Z);};
\end{tikzpicture}

\end{document}

The result:

Answer 2

Set row sep=\-pgflinewidth in matrix options. It will work if all nodes have same line width.

Both nodes can have same width with every node={minimum width=4cm, draw} in matrix declaration.

\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\makeatletter
\pgfdeclareshape{recttop}{
  \inheritsavedanchors[from=rectangle] % this is nearly a rectangle
  \inheritanchorborder[from=rectangle]
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{north}
  \inheritanchor[from=rectangle]{south}
  \inheritanchor[from=rectangle]{west}
  \inheritanchor[from=rectangle]{east}
  \backgroundpath{% this is new
    % store lower right in xa/ya and upper right in xb/yb
    \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
    \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
    % construct main path
    \pgfsetcornersarced{\pgfpoint{5pt}{5pt}}
    \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
    \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yb}}
    \pgfsetcornersarced{\pgfpoint{0pt}{0pt}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
    \pgfpathclose
 }
}
\pgfdeclareshape{rectbottom}{
  \inheritsavedanchors[from=rectangle] % this is nearly a rectangle
  \inheritanchorborder[from=rectangle]
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{north}
  \inheritanchor[from=rectangle]{south}
  \inheritanchor[from=rectangle]{west}
  \inheritanchor[from=rectangle]{east}
  \backgroundpath{% this is new
    % store lower right in xa/ya and upper right in xb/yb
    \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
    \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
    % construct main path
    \pgfsetcornersarced{\pgfpoint{0pt}{0pt}}
    \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
    \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yb}}
    \pgfsetcornersarced{\pgfpoint{5pt}{5pt}}
    \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
    \pgfpathclose
 }
}
\makeatother



\begin{document}
\begin{tikzpicture}
%[every node/.style={fill=gray,minimum width=2cm, minimum height=1cm}]
\matrix[row sep=0pt, every node/.style={minimum width=4cm, draw}, row sep=-\pgflinewidth]{
 \node[draw, shape=recttop, fill=red!20] (top) {CFunction};\\
 \node[draw, shape=rectbottom] (bottom) {\ttfamily func(A, E, B, Z);};\\
 }; 
\end{tikzpicture}
\end{document}