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TikZ 锚点和坐标有什么区别

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TikZ 锚点和坐标有什么区别

在他的回答中访问 TikZ 坐标的逻辑值，Jake提出了一个代码来获取TikZ坐标的值。

今天我尝试用它来回答根据坐标自动标记节点，制作多边形 我想打印一些坐标值node anchors

\documentclass[tikz, margin=5pt]{standalone}

\makeatletter
\newcommand\xcoord[2][center]{{%
    \pgfpointanchor{#2}{#1}%
    \pgfmathparse{\pgf@x/\pgf@xx}%
    \pgfmathprintnumber{\pgfmathresult}%
}}
\newcommand\ycoord[2][center]{{%
    \pgfpointanchor{#2}{#1}%
    \pgfmathparse{\pgf@y/\pgf@yy}%
    \pgfmathprintnumber{\pgfmathresult}%
}}
\makeatother

\pgfkeys{/pgf/number format/.cd,fixed,fixed zerofill,precision=2}

\begin{document}
\begin{tikzpicture}
\node[draw, minimum size=2cm] (A) {A};
\node[above right] at (A.north east) {(\xcoord{A.north east},\ycoord{A.north east})};
\end{tikzpicture}
\end{document}

但编译因下一条错误消息而停止

! Package pgf Error: No shape named A.north east is known.

See the pgf package documentation for explanation. 
Type  H <return> for immediate help.  
...                                              
l.22 ... at (A.north east) {(\xcoord{A.north east}
                                 ,\ycoord{A.north east})};

然后我尝试真实的 coordinate

\coordinate (aux) at (A.north east);
\node[above right] at (A.north east) {(\xcoord{aux},\ycoord{aux})};

并且成功了。你能解释一下为什么吗？

答案1

如果你看一下 Jake 的代码，它有一个可选参数，默认情况下为center，用于\pgfpointanchor。手册中的引文：

\pgfpointanchor{ node }{ anchor }

anchor此命令是另一个“点命令”，类似于第 97 节中描述的命令。它返回给定的坐标node。

因此，您确实应该使用这些宏作为

\node[above right] at (A.north east) {(\xcoord[north east]{A}, ycoord[north east]{A})};

正如您使用它们一样，\pgfpointanchor查找一个名为的节点A.north east，但该节点的名称是A。

这与 a 一起工作的原因coordinate是 acoordinate实际上是 a node。

\documentclass[tikz, margin=5pt]{standalone}

\makeatletter
\newcommand\xcoord[2][center]{{%
    \pgfpointanchor{#2}{#1}%
    \pgfmathparse{\pgf@x/\pgf@xx}%
    \pgfmathprintnumber{\pgfmathresult}%
}}
\newcommand\ycoord[2][center]{{%
    \pgfpointanchor{#2}{#1}%
    \pgfmathparse{\pgf@y/\pgf@yy}%
    \pgfmathprintnumber{\pgfmathresult}%
}}
\makeatother

\pgfkeys{/pgf/number format/.cd,fixed,fixed zerofill,precision=2}

\begin{document}
\begin{tikzpicture}
\node[draw, minimum size=2cm] (A) {A};
\node[above right] at (A.north east) {(\xcoord[north east]{A},\ycoord[north east]{A})};
\end{tikzpicture}
\end{document}

在此处输入图片描述

答案2

如果您不介意使用内部宏，\tikz@scan@one@point将允许使用 TikZ 坐标。它还将处理默认center锚点：

\documentclass[tikz, margin=5pt]{standalone}

\makeatletter
\def\xcoord#1{%
    % \tikz@scan@one@point takes an argument before the
    % coordinate which is the command to be executed after
    % the coordinate is parsed. \pgf@process just keeps
    % the coordinate calculation local and globally
    % sets \pgf@x and \pgf@y to the appropriate value.
    %
    % NB. Must use \nullfont to prevent naughty spaces.
    %
    {\nullfont\tikz@scan@one@point\pgf@process(#1)}%
    \pgfmathparse{\pgf@x/\pgf@xx}%
    \pgfmathprintnumber{\pgfmathresult}%
}
\def\ycoord#1{%
   {\nullfont\tikz@scan@one@point\pgf@process(#1)}%
   \pgfmathparse{\pgf@y/\pgf@yy}%
   \pgfmathprintnumber{\pgfmathresult}%
}
\makeatother

\pgfkeys{/pgf/number format/.cd,fixed,fixed zerofill,precision=2}
\tikzset{mark cross at/.pic={
  \draw [red, shift={(#1)}, scale=1/20] (1,1) -- (-1,-1) (1,-1) -- (-1,1);
  \node [above=5pt,fill=blue!20, fill opacity=0.75, node font=\tiny\tt]
     at (#1) {(\xcoord{#1},\ycoord{#1})};
}}
\begin{document}

\begin{tikzpicture}

\node[draw, minimum size=4cm, outer sep=0pt] (A) {A};

\path (A) pic {mark cross at={A}}; 
\foreach \a in {north, south, east, west, north west, south west, south east, north east}
  \path pic {mark cross at={A.\a}}; 
\end{tikzpicture}
\end{document}

在此处输入图片描述

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