[Tex/LaTex] How to align a “double arrow” with a tikz arc shape

tikz-pgf

I want to align the double arrow shape in the tikz package with an arc, like this one:

\documentclass[landscape]{article}
\usepackage[a2paper]{geometry}
\usepackage{tikz}
\usetikzlibrary{fadings,shapes.arrows,shadows,arrows,positioning,shapes}
\pagenumbering{gobble}

\begin{document}
\begin{tikzpicture}[scale=2,node distance=1cm, auto,baseline=-.5ex]

\node (dummy) at (-5,-8) {}; 

\begin{scope}[remember picture,overlay,shift={(dummy.center)}]
\draw (8.75,4.75) arc (440:160:7.5); % I'm trying to align my double arrow shape with this arc.
\end{scope}

\end{tikzpicture}
\end{document}

By popular demand – a picture:

Preferrably I want the arrow tips to be unaffected by the bending of the shape. This would probably require a different shape than double arrow, though.

Best Answer

Workaround (version 1)

I have only a workaround for you. I draw two arrows on each other, the arrowheads are shifted, so I manually move them slightly back. The first arrowhead's position is controlled by an extra point, the second arrowhead's position is controlled by an angle and a distance. Please try it if it fits your needs.

%! *latex mal-doublearrow.tex
\documentclass[landscape]{article}
\usepackage[a2paper]{geometry}
\usepackage{tikz}
\usetikzlibrary{shapes.arrows}
%\usetikzlibrary{fadings,shadows,arrows,positioning,shapes}
\pagenumbering{gobble}
\begin{document}
\tikzset{mal/.style={<->, >=stealth, 
double arrow, line width=8mm,
 draw=black, double arrow head extend=1.5cm, double arrow head indent=1.25cm}}
\begin{tikzpicture}%[scale=2,node distance=1cm, auto,baseline=-.5ex]
\node (dummy) at (-5,15) {}; 
\begin{scope}[remember picture,overlay,at={(dummy)}]
\def\malpath{(7,5)-- (8.75,4.75) arc (440:160:7.5)--+(65:2)}
\draw[mal] \malpath; % I'm trying to align my double arrow shape with this arc.
\def\malpath{(7.2,5)--(8.75,4.75) arc (440:160:7.5)--+(65:1.8)}
\draw[mal, line width=6mm, draw=yellow] \malpath;
\end{scope}
\end{tikzpicture}
\end{document}

mwe

Edit (version 2)

%! *latex mal-doublearrow.tex
\documentclass[landscape]{article}
\usepackage[a2paper]{geometry}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,shapes}
\pagenumbering{gobble}
\begin{document}
\tikzset{mal/.style={<->, >={Stealth[length=40mm,sep=-5mm]},
 double distance=6mm, line width=5mm,
 draw=black, double=yellow}}
\begin{tikzpicture}
\begin{scope}
\draw[mal](6.5,5)--(8.75,4.75) arc (440:160:7.5)--+(70:2);
\end{scope}
\end{tikzpicture}
\end{document}

mwe

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