改变箭头方向

Question

我试图在 tikz 中绘制一条路径，使用 Paul Gaborit 的解决方案TikZ：如何在线中间画箭头？我设法得到了这个，其中路径是环的一半。

但我希望左下角的箭头和内侧半圆箭头向右移动（因此，在遍历路径时所有箭头都具有相同的方向，并且环的内部位于左侧）。

我在绘画中糟糕的编辑

我正在使用的代码

 \usepackage{tikz}
 \usetikzlibrary{positioning, calc, arrows, decorations.markings, decorations.pathreplacing}

\tikzset{
  % style to apply some styles to each segment of a path
  on each segment/.style={
    decorate,
    decoration={
      show path construction,
      moveto code={},
      lineto code={
        \path [#1]
        (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);
      },
      curveto code={
        \path [#1] (\tikzinputsegmentfirst)
        .. controls
        (\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb)
        ..
        (\tikzinputsegmentlast);
      },
      closepath code={
        \path [#1]
        (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);
      },
    },
  },
  % style to add an arrow in the middle of a path
  mid arrow/.style={postaction={decorate,decoration={
        markings,
        mark=at position .5 with {\arrow[#1]{stealth}}
      }}},
}


\begin{center}
\begin{tikzpicture}[domain=0:4]
\draw [<->, very thick] (0,4) node (yaxis) [above] {$y$}
    |- (-4,0) node (zaxis) [left] {}
    |- (4,0) node (xaxis) [right] {$x$}
    ;
   \path [draw=black, ultra thick, postaction={on each segment={mid arrow=black}}] (3,0) arc (0:180:3cm)
    (1,0) -> (3,0)
    (1,0) arc (0:180:1cm)
    (-1,0) -> (-3,0) ;
\end{tikzpicture}
\end{center}

任何帮助，将不胜感激 ：）

Answer 1

将来，请考虑发布完整的最小工作示例（MWE）。这让其他人更容易开始帮助你。:-)

Paul Gaborit 的代码将箭头应用于路径遍历的方向。因此在这种情况下，只需更改有问题的路径段的方向即可。

我只需要更改环境中的两行代码tikzpicture；这两行更改都在下面代码的注释行中详细说明。

\documentclass[border=5pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{positioning, calc, arrows, decorations.markings, decorations.pathreplacing}

\tikzset{
  % style to apply some styles to each segment of a path
  on each segment/.style={
    decorate,
    decoration={
      show path construction,
      moveto code={},
      lineto code={
        \path [#1]
        (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);
      },
      curveto code={
        \path [#1] (\tikzinputsegmentfirst)
        .. controls
        (\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb)
        ..
        (\tikzinputsegmentlast);
      },
      closepath code={
        \path [#1]
        (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);
      },
    },
  },
  % style to add an arrow in the middle of a path
  mid arrow/.style={postaction={decorate,decoration={
        markings,
        mark=at position .5 with {\arrow[#1]{stealth}}
      }}},
}

\begin{document}
\begin{tikzpicture}[domain=0:4]
\draw [<->, very thick] (0,4) node (yaxis) [above] {$y$}
    |- (-4,0) node (zaxis) [left] {}
    |- (4,0) node (xaxis) [right] {$x$}
    ;
   \path [draw=black, ultra thick, postaction={on each segment={mid arrow=black}}] (3,0) arc (0:180:3cm)
    (1,0) -> (3,0)
    (-1,0) arc (180:0:1cm) % changed starting point and swapped arc bounding angles
    (-3,0) -> (-1,0) ; % swapped coordinates here
\end{tikzpicture}
\end{document}