[Tex/LaTex] Color overlap between ellipse nodes

tikz-pgf

This is very closely related to a question about highlighting the overlap between circular nodes at Highlight overlap between nodes and draw arrow from node edge. But there is a new angle: how to generalize this to ellipses (and I suppose other shapes, but I care about ellipses for the moment).

You might expect that the following code would fill in the overlap between the ellipses with green:

\documentclass{article}

\usepackage{tikz}

\newcommand*{\MyRadius}{7cm}

\begin{document}

\def\A{(0,0) ellipse [minimum width = 2*\MyRadius, minimum height = \MyRadius]}
\def\B{(8,0) ellipse [minimum width = 2*\MyRadius, minimum height = \MyRadius]}

\begin{tikzpicture}

\node[draw, shape=ellipse, minimum width=2*\MyRadius, minimum height=\MyRadius, ultra thick] (A) at (0,0) {};
\node[draw, shape=ellipse, minimum width=2*\MyRadius, minimum height=\MyRadius, ultra thick] (B) at (8,0) {};

\begin{scope}
\clip \A;
\fill[green, opacity=0.2] \B;
\end{scope}

\end{tikzpicture}

\end{document}

But it doesn't. I also tried specifiying the height and width of the ellipses in (x, y) format, instead of in square brackets, but that is even worse (produces an error).

ellipses without color in overlap

Best Answer

Note that there is a difference between the path ellipse, which has parameters x radius and y radius, and the shape ellipse, which is not predefined but to be found in the shapes.geometric library and for which minimum width is an "x diameter". Once this is taken into account you can use the same type of code as you used for circles:

Sample output

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes.geometric}

\newcommand*{\MyRadius}{2cm}

\begin{document}

\def\A{(0,0) ellipse [x radius = 2*\MyRadius, y radius = \MyRadius]}
\def\B{(4,0) ellipse [x radius = 2*\MyRadius, y radius = \MyRadius]}

\begin{tikzpicture}
  \node[draw, shape=ellipse, minimum width=4*\MyRadius, minimum height=2*\MyRadius, ultra thick] (A) at (0,0) {};
\node[draw, shape=ellipse, minimum width=4*\MyRadius, minimum height=2*\MyRadius, ultra thick] (B) at (4,0) {};

\begin{scope}
\clip \A;
\fill[green, opacity=0.2] \B;
\end{scope}

\end{tikzpicture}

\end{document}

Adding your node connecting like operations as your circle case now works as expected too:

Second sample

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes.geometric}

\newcommand*{\MyRadius}{2cm}

\begin{document}

\def\A{(0,0) ellipse [x radius = 2*\MyRadius, y radius = \MyRadius]}
\def\B{(4,0) ellipse [x radius = 2*\MyRadius, y radius = \MyRadius]}

\begin{tikzpicture}
  \node[draw, shape=ellipse, minimum width=4*\MyRadius, minimum height=2*\MyRadius, ultra thick] (A) at (0,0) {};
\node[draw, shape=ellipse, minimum width=4*\MyRadius, minimum height=2*\MyRadius, ultra thick] (B) at (4,0) {};

\begin{scope}
\clip \A;
\fill[green, opacity=0.2] \B;
\end{scope}

\node(nom) at (0,-3) {[A]}; 
\node(gen) at (4,-3) {[B]}; 

\draw[->]  (A) -- (nom);
\draw[->]  (B) -- (gen);
\end{tikzpicture}

\end{document}

Related Solutions

[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)

[Tex/LaTex] How to define the default vertical distance between nodes

I don't really get the question so I hope this is what you wanted. If you include a full document (such that we copy paste and see the problem on our systems) things are much more easier.

Here, you can change the default setting within a scope but your block style had a node distance which was resetting every time it is issued. I've made it 2mm such that we can see the difference easier.

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows,shapes.geometric,positioning}

\begin{document}
\begin{tikzpicture}[decision/.style={diamond, draw, text width=4.5em, text badly centered, node distance=3.5cm, inner sep=0pt},
                    block/.style   ={rectangle, draw, text width=6em, text centered, rounded corners, minimum height=4em, minimum height=2em},
                    cloud/.style   ={draw, ellipse, minimum height=2em},
                    line/.style    ={draw,-latex'},
                    node distance = 1cm, 
                    auto]
    \node [block] (1st) {1st};
    \node [block, right= of 1st]  (2nd1) {2nd1};
\begin{scope}[node distance=2mm and 10mm]%Here we change it for everything inside this scope
    \node [block, above= of 2nd1] (2nd2) {2nd2};
    \node [block, below= of 2nd1] (2nd3) {2nd3};
    \node [block, right= of 2nd1] (3rd1) {3rd1};
    \node [block, above= of 3rd1] (3rd2) {3rd2};
    \node [block, above= of 3rd2] (3rd3) {3rd3};
\end{scope}
    \node [block, below= of 3rd1] (3rd4) {3rd4};
    \node [block, below= of 3rd4] (3rd5) {3rd5};

    \path [line] (1st) -- (2nd1);
    \path [line] (2nd1) -- (2nd2);
    \path [line] (2nd1) -- (2nd3);
    \path [line] (2nd2) -- (3rd3);
    \path [line] (2nd1) -- (3rd1);
    \path [line] (1st) -- (2nd1);
\end{tikzpicture}
\end{document}

enter image description here

Best Answer

Related Solutions

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

[Tex/LaTex] How to define the default vertical distance between nodes

Related Question