[Tex/LaTex] Reversing a path in TikZ

gnuplottikz-pgf

When I use \path plot function {x^2}; in tikz, it plots it left-to-right (the default domain is -5:5). This is annoying, because, for example, one cannot pile on -- plot function {x^2 + 1} -- cycle; and then fill the whole thing; it doesn't fill the obvious cycle, but rather the self-intersecting one going between opposite corners as it "returns carriage", so to speak.

Is there some way to get plot function to generate points in the reverse order? Alternatively, is there some way of getting tikz to draw a path in the reverse order the points were specified? (This last one is of more general utility, since the orientation of a path is used a lot.)

Best Answer

If you use PGFplots for plotting your functions, the paths will be reversed and connected appropriately by using stack plots=y in the axis options and issuing \closedcycle after the second plot:

\documentclass{article}

\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    stack plots=y,
    hide axis
]
\addplot [draw=orange,thick]{x^2};
\addplot [draw=orange, thick, fill=yellow] {1} \closedcycle;
\end{axis}
\end{tikzpicture}

\end{document}

If all you want is the filled path, you can disable the axes by using hide axis.

Related Solutions

[Tex/LaTex] way to draw TikZ lines on the “inside” or “outside” of a path

I was idling thinking how one might go about this, when I came up with a very simple solution. I wouldn't be surprised to learn that this is what Illustrator does. Looking at the diagrams, it would seem that way.

My initial plan was to figure out some sort of decoration that would "shift" a path to the left or right, but that just seemed fraught with difficulties. But I couldn't think of a way to get TikZ to treat the two halves of a path in a different manner. Then I realised that there is such a way: clipping.

When TikZ clips against a path then the two sides of that path are treated in a different manner. So that can be used to get it to only draw one side. Sort of. You draw a path, but clip it against itself. Since the clipping path has no width, this means that half the path gets drawn. The "Sort of" is because the decision about which half depends on the region that is being enclosed, not the actual side of the path. This, I think, leads to the funny look on the Illustrator images in the question.

A general solution to this would involve a command to draw and clip in the same breath. That could be done with my spath library (still in development, but available from the TeX-SX site on launchpad), and one would have to use the "reverse" clip method from somewhere around here for dealing with the other side. But to demonstrate the concept, we can just do it by hand. Here's the cube:

Cube with clipping

and here's the code:

\documentclass{article}
%\url{http://tex.stackexchange.com/q/29991/86}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[scale=5,line width=2mm]
\draw (0,0,0) -- (1,0,0) -- (1,1,0) -- (0,1,0) -- cycle;
\draw (1,0,0) -- (1,0,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\draw (0,1,0) -- (0,1,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\begin{scope}[yshift=-2cm,line width=4mm]
\begin{scope}
\clip (0,0,0) -- (1,0,0) -- (1,1,0) -- (0,1,0) -- cycle;
\draw (0,0,0) -- (1,0,0) -- (1,1,0) -- (0,1,0) -- cycle;
\end{scope}
\begin{scope}
\clip (1,0,0) -- (1,0,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\draw (1,0,0) -- (1,0,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\end{scope}
\begin{scope}
\clip (0,1,0) -- (0,1,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\draw (0,1,0) -- (0,1,-1) -- (1,1,-1) -- (1,1,0) -- cycle;
\end{scope}
\end{scope}
\end{tikzpicture}
\end{document}

Note the scopes to limit the clips, and the doubled line width, since we lose half of it in the clip.

[Tex/LaTex] Drawing arrows along a function in pgfplots

As you didn't answer my comment yet, I will just post my solution to the problem I think you are trying to solve.

You may just use the code, given in my answer to this question: Add arrows to a smooth tikz function Next you will need to remove the smooth statement, because it will interfere with decorate and give you nice errors like ? Dimension too large. This won't have an effect on the smoothness of your drawing, because you already use sufficiently many samples.

Implementation

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\tikzset{
  set arrow inside/.code={\pgfqkeys{/tikz/arrow inside}{#1}},
  set arrow inside={end/.initial=>, opt/.initial=},
  /pgf/decoration/Mark/.style={
    mark/.expanded=at position #1 with
    {
      \noexpand\arrow[\pgfkeysvalueof{/tikz/arrow inside/opt}]{\pgfkeysvalueof{/tikz/arrow inside/end}}
    }
  },
  arrow inside/.style 2 args={
    set arrow inside={#1},
    postaction={
      decorate,decoration={
        markings,Mark/.list={#2}
      }
    }
  },
}
\begin{document}
\begin{tikzpicture}
  \draw node [circle] at (-1,0) {$z_0$};
  \begin{scope}[very thick,rotate=45]
    \draw[domain=0:6.28,samples=200] plot (xy polar cs:angle=\x r,radius={1-sin(2*\x r)}) [arrow inside={}{0.25,0.5,0.75}];
  \end{scope}
\end{tikzpicture} 
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] way to draw TikZ lines on the “inside” or “outside” of a path

[Tex/LaTex] Drawing arrows along a function in pgfplots

Implementation

Output

Related Question