[Tex/LaTex] How to color a region

colortikz-pgf

The following code

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{intersections,positioning}

\begin{document}

\begin{tikzpicture}[radius=5]
\draw (0,0) rectangle (5,5);
\draw[name path=c1] (0,0) arc[start angle=-90,end angle=0] -- (5,5);
\draw[name path=c2] (5,0) arc[start angle=0,end angle=90] -- (0,5);
\draw[name path=c3] (5,5) arc[start angle=90,end angle=180] -- (0,5);
\draw[name path=c4] (0,5) arc[start angle=180,end angle=270] -- (5,0);
\begin{scope}
\fill [name intersections={of=c1 and c2}]
  (intersection-1) circle (2pt) node[label=right:$A$] {};
\fill [name intersections={of=c2 and c3}]
  (intersection-1) circle (2pt) node[label=above:$B$] {};
\fill [name intersections={of=c3 and c4}]
  (intersection-1) circle (2pt) node[label=left:$C$] {};
\fill [name intersections={of=c4 and c1}]
  (intersection-1) circle (2pt) node[label=below:$D$] {};
\end{scope}
\end{tikzpicture}

\end{document}

produces

How can I apply color only to the central region limited by the arcs crossing at A, B, C and D?

Best Answer

If you don't mind to have the paths twice in your picture you can use clipping to only draw the inner area. Clipping is local to the scope and accumulates. So you can take the figure as two overlapping "leaves" and clip to both, then fill the whole rectangle.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{intersections,positioning}

\begin{document}

\begin{tikzpicture}[radius=5]
\begin{scope}
\clip (0,0) arc[start angle=-90,end angle=0]   -- (5,5)
            arc[start angle=90,end angle=180]  -- (0,0);
\clip (0,5) arc[start angle=180,end angle=270] -- (5,0)
            arc[start angle=0,end angle=90]    -- (0,5);
\fill [red] (0,0) rectangle (5,5);
\end{scope}
\draw (0,0) rectangle (5,5);
\draw[name path=c1] (0,0) arc[start angle=-90,end angle=0] -- (5,5);
\draw[name path=c2] (5,0) arc[start angle=0,end angle=90] -- (0,5);
\draw[name path=c3] (5,5) arc[start angle=90,end angle=180] -- (0,5);
\draw[name path=c4] (0,5) arc[start angle=180,end angle=270] -- (5,0);
\begin{scope}
\fill [name intersections={of=c1 and c2}]
  (intersection-1) circle (2pt) node[label=right:$A$] {};
\fill [name intersections={of=c2 and c3}]
  (intersection-1) circle (2pt) node[label=above:$B$] {};
\fill [name intersections={of=c3 and c4}]
  (intersection-1) circle (2pt) node[label=left:$C$] {};
\fill [name intersections={of=c4 and c1}]
  (intersection-1) circle (2pt) node[label=below:$D$] {};
\end{scope}
\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] Numerical conditional within tikz keys

I am definitely unfamiliar with both beamer and tikz (do not quite get what the \only are supposed to do) but perhaps this could go in the direction you want:

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{chains}
\newcounter{count}

% helper macro:
\long\def\GobToSemiColon #1;{}

\newcommand\myPicture{
\begin{tikzpicture}
  \begin{scope}[start chain = going below]
  \ifnum\value{count}<1 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>3 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is between
    1 and 3};

  \ifnum\value{count}>-1 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is
    negative}; 

  \ifnum\value{count}<100 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>200 \expandafter\GobToSemiColon\fi  
  \node[draw, rectangle, on chain] {display only if counter is between
    100 and 200};

  \ifnum\value{count}<3 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>20 \expandafter\GobToSemiColon\fi
  \node[draw, circle, on chain] {only when counter is in the range 3 to 20};
  \end{scope}
\end{tikzpicture}
}

\begin{document}
\begin{frame}
\only{\setcounter{count}{-3}\myPicture}
\only{\setcounter{count}{105}\myPicture}
\only{\setcounter{count}{39}\myPicture}
\only{\setcounter{count}{2}\myPicture}
\only{\setcounter{count}{5}\myPicture}
\end{frame}
\end{document}

beamer

Best Answer

Related Solutions

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

[Tex/LaTex] Numerical conditional within tikz keys

Related Question