TikZ：使用decorations.markings來裝飾剪切路徑

Question

我沿著線剪了一個圓圈atan(2/3)。我想在圓圈被剪掉的地方放一個箭。我認為這就像(atan(2/3) + 180)/360獲取其沿路徑的百分比位置一樣簡單。不幸的是，事實並非如此。32.5由於反覆試驗，我最終減少了學位。不過，我想做一個更精確的位置。

\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.markings}

\begin{document}
\begin{tikzpicture}
  \pgfmathsetmacro{\angle}{atan(2/3)};
  \pgfmathsetmacro{\ppi}{\angle + 180};
  \pgfmathsetmacro{\percent}{(\ppi - 32.5)/360};

  \begin{scope}[rotate = \angle, decoration = {
      markings,
      mark = at position \percent with {\arrow{stealth}}
    }]
    \clip (0, .4) rectangle (-.45, 0);

    \draw[postaction = decorate] (cylinder) circle[radius = .395cm];
  \end{scope}
\end{tikzpicture}
\end{document}

Answer 1

我們來分析一下。沒有\clip，沒有旋轉和繪製的矩形，這就是你的圓：

這表明該\percent值應該是50。和

\pgfmathsetmacro{\ppi}{\angle + 180};
\pgfmathsetmacro{\percent}{(\ppi)/360};

你當然不是在給予，50%而是更多。準確地說，你付出atan(2/3)的更多\ppi。如果我們使\ppi= 180，那麼\percent將是50。

\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.markings}

\begin{document}
\begin{tikzpicture}
  \pgfmathsetmacro{\angle}{atan(2/3)};
  \pgfmathsetmacro{\ppi}{180};
  \pgfmathsetmacro{\percent}{(\ppi)/360};

  \begin{scope}[rotate = 0, decoration = {%     % change rotate to \angle
      markings,
      mark = at position \percent with {\arrow{stealth}}
    }]
    %\clip (0, .4) rectangle (-.45, 0);
    \draw (0, .4) rectangle (-.45, 0);

    \draw[postaction = decorate] (0,0) circle[radius = .395cm];
  \end{scope}
\end{tikzpicture}
\end{document}

現在您可以旋轉和剪輯以獲得：

\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.markings}

\begin{document}
\begin{tikzpicture}
  \pgfmathsetmacro{\angle}{atan(2/3)};
  \pgfmathsetmacro{\ppi}{180};
  \pgfmathsetmacro{\percent}{(\ppi)/360};

  \begin{scope}[rotate = \angle, decoration = {
      markings,
      mark = at position \percent with {\arrow{stealth}}
    }]
    \clip (0, .4) rectangle (-.45, 0);
    %\draw (0, .4) rectangle (-.45, 0);

    \draw[postaction = decorate] (0,0) circle[radius = .395cm];
  \end{scope}
\end{tikzpicture}
\end{document}