Tikz，foreach 循环中的 pgfmathtruncatemacro 不起作用

Question

在下面的代码中，循环中的最后一行（在代码的末尾）似乎没有执行它应该做的事情：分配\angB给\angA：

\begin{tikzpicture}[scale=1]

  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (p1);
   \path (o)+(90:1.2) coordinate (p2);
  \draw[dotted] (p2) -- (p1);
   \path (o)+(270:1) coordinate (q1);
   \path (o)+(30:1) coordinate (q2);
   \path (o)+(150:1) coordinate (q3);
  \draw[] (q1) -- (q2);
  \draw[] (q2) -- (q3);
  \draw[] (q3) -- (q1);
   \path (q1)+(90:0.8) coordinate (z);
  \draw[->] (z) arc (90:60:0.8);
  \path[above right] (z) node{$\theta$};
  \path[below] (q1) node{$\theta=30^\circ$};
  
  \begin{scope}[shift={(3,0)}]

  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (q1);

  \pgfmathtruncatemacro{\angA}{270}
  \pgfmathtruncatemacro{\t}{25}
  \foreach \n in {0,...,100}
  {
    \pgfmathtruncatemacro{\angB}{\angA+180-2*\t}
    \path (o)+({\angA}:1) coordinate (q1);
    \path (o)+({\angB}:1) coordinate (q2);
    \draw[] (q1) -- (q2);
    \pgfmathtruncatemacro{\angA}{\angB}
  } 

  \path[below] (q1) node{$\theta=\t^\circ$};

  \end{scope}

\end{tikzpicture}

结果：右边的图片应该有更多的线条：

编辑是否存在某种“步骤变量范围”？我注意到，q1尽管在循环中对其进行了大量重新定义，但它仍保持了其值。

Answer 1

常见的问题：每次循环都是一组执行，所以忘记了\foreach的设置。\angA

使其成为全局的（确保使用不会干扰其他任何内容的命令名称）。

\documentclass{article}
\usepackage{tikz}

\newcommand{\pgfmathtruncategmacro}[2]{%
  \pgfmathtruncatemacro\pgfmathresult{#2}%
  \global\let#1\pgfmathresult
}

\begin{document}

\begin{tikzpicture}[scale=1]

  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (p1);
   \path (o)+(90:1.2) coordinate (p2);
  \draw[dotted] (p2) -- (p1);
   \path (o)+(270:1) coordinate (q1);
   \path (o)+(30:1) coordinate (q2);
   \path (o)+(150:1) coordinate (q3);
  \draw[] (q1) -- (q2);
  \draw[] (q2) -- (q3);
  \draw[] (q3) -- (q1);
   \path (q1)+(90:0.8) coordinate (z);
  \draw[->] (z) arc (90:60:0.8);
  \path[above right] (z) node{$\theta$};
  \path[below] (q1) node{$\theta=30^\circ$};
  
  \begin{scope}[shift={(3,0)}]

  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (q1);

  \pgfmathtruncategmacro{\angA}{270}
  \pgfmathtruncatemacro{\t}{25}
  \foreach \n [remember=\n as \prevn (initially -1)] in {0,...,100}
  {
    \pgfmathtruncatemacro{\angB}{\angA+180-2*\t}
    \path (o)+({\angA}:1) coordinate (q\prevn);
    \path (o)+({\angB}:1) coordinate (q\n);
    \draw[] (q\prevn) -- (q\n);
    \pgfmathtruncategmacro{\angA}{\angB}
  } 

  \path[below] (q-1) node{$\theta=\t^\circ$};

  \end{scope}

\end{tikzpicture}

\end{document}

Answer 2

不需要全局宏。pgffor有用remember于此目的的关键。

\documentclass[tikz,border=3mm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=1]
 \begin{scope}[local bounding box=L]
  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (p1);
   \path (o)+(90:1.2) coordinate (p2);
  \draw[dotted] (p2) -- (p1);
   \path (o)+(270:1) coordinate (q1);
   \path (o)+(30:1) coordinate (q2);
   \path (o)+(150:1) coordinate (q3);
  \draw[] (q1) -- (q2);
  \draw[] (q2) -- (q3);
  \draw[] (q3) -- (q1);
   \path (q1)+(90:0.8) coordinate (z);
  \draw[->] (z) arc (90:60:0.8);
  \path[above right] (z) node{$\theta$};
  \path (L.south) node[below]{$\theta=30^\circ$};
 \end{scope} 
 % 
 \begin{scope}[shift={(3,0)},local bounding box=R]
  \coordinate (o) at (0,0);
  \draw[thick] (o) circle(1);
   \path (o)+(270:1) coordinate (q1);

  \pgfmathtruncatemacro{\angA}{270}
  \pgfmathtruncatemacro{\t}{25}
  \foreach \n [remember=\angA as \angA] in {0,...,100}
  {
    \pgfmathtruncatemacro{\angB}{\angA+180-2*\t}
    \path (o)+({\angA}:1) coordinate (q1);
    \path (o)+({\angB}:1) coordinate (q2);
    \draw (q1) -- (q2);
    \pgfmathtruncatemacro{\angA}{\angB}
  } 

  \path (R.south) node[below]{$\theta=\t^\circ$};
 \end{scope}
\end{tikzpicture}
\end{document}