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比较 Tikz 中的节点坐标

tag-icon • tag-icon tikz-pgf etoolbox
比较 Tikz 中的节点坐标

我正在尝试根据节点坐标自动生成图纸。构造过程本身非常简单：从节点 i 到节点 i+1 画一个箭头（i 和 i+1 为节点名称，事先已修复，我不想修改）。棘手的部分是节点可以以任何顺序排列在一条线上，我希望所有圆弧都绘制在水平线上方。我曾尝试提取x节点的坐标并使用以下方法进行比较，但没有成功\ifnumcomp：

\documentclass{article}
\usepackage{etoolbox}
\usepackage{tikz}

\begin{document}

This is fine:
\begin{tikzpicture}
% node placement
\node[circle,draw,inner sep=2pt] (0) at (0, 0) [label=below:0] {};
\node[circle,draw,inner sep=2pt] (1) at (1, 0) [label=below:1] {};
\node[circle,draw,inner sep=2pt] (2) at (2, 0) [label=below:2] {};
\foreach [count=\q from 0] \p in {1, 2}
    \draw[->,>=stealth] (\q) to [bend left=60] (\p);
% arcs
\end{tikzpicture}

This is not fine:
\begin{tikzpicture}
% node placement
\node[circle,draw,inner sep=2pt] (0) at (0, 0) [label=below:0] {};
\node[circle,draw,inner sep=2pt] (2) at (1, 0) [label=below:2] {};
\node[circle,draw,inner sep=2pt] (1) at (2, 0) [label=below:1] {};
\foreach [count=\q from 0] \p in {1, 2}
    \draw[->,>=stealth] (\q) to [bend left=60] (\p);
% arcs
\end{tikzpicture}, I want it to look like this: \begin{tikzpicture}
% node placement
\node[circle,draw,inner sep=2pt] (0) at (0, 0) [label=below:0] {};
\node[circle,draw,inner sep=2pt] (2) at (1, 0) [label=below:2] {};
\node[circle,draw,inner sep=2pt] (1) at (2, 0) [label=below:1] {};
% \foreach [count=\q from 0] \p in {1, 2}
    \draw[->,>=stealth] (0) to [bend left=60] (1);
    \draw[->,>=stealth] (1) to [bend right=60] (2);
% arcs
\end{tikzpicture}

This attempt at combining \verb|\ifnumcomp| and \verb|\pgfextractx| fails:
\begin{tikzpicture}
% node placement
\node[circle,draw,inner sep=2pt] (0) at (0, 0) [label=below:0] {};
\node[circle,draw,inner sep=2pt] (2) at (1, 0) [label=below:2] {};
\node[circle,draw,inner sep=2pt] (1) at (2, 0) [label=below:1] {};
\foreach [count=\q from 0] \p in {1, 2} {
    \newdimen\px
    \newdimen\qx
    \pgfextractx{\px}{\p}
    \pgfextractx{\qx}{\q}
    \ifnumcomp{\qx}{<}{\px}{
    \draw[->,>=stealth] (\q) to [bend left=60] (\p);
    }{
    \draw[->,>=stealth] (\q) to [bend right=60] (\p);
    }
}
% arcs
\end{tikzpicture}

\end{document}

该文件内容如下：

在此处输入图片描述

我该如何修复我尝试的解决方案？（或者有人知道“更好”/“更简单”/......的解决方案？）

（为了使图纸看起来更好，弯曲角度应该与节点之间的距离成比例，但我想这应该是一个单独的问题）。

答案1

使用Andrew Stacey 的回答到相关问题允许我获得想要的结果。这是一个完整的工作示例：

\documentclass{article}

\usepackage{etoolbox}
\usepackage{tikz}
% Andrew Stacey's code:
\makeatletter
\newcommand{\gettikzxy}[3]{%
\tikz@scan@one@point\pgfutil@firstofone#1\relax
\edef#2{\the\pgf@x}%
\edef#3{\the\pgf@y}%
}
\makeatother

\begin{document}

\begin{tikzpicture}
    % node placement
    \node[circle,draw,inner sep=2pt] (0) at (0, 0) [label=below:0] {};
    \node[circle,draw,inner sep=2pt] (2) at (1, 0) [label=below:2] {};
    \node[circle,draw,inner sep=2pt] (1) at (2, 0) [label=below:1] {};

    % arcs
    \foreach [count=\q from 0] \p in {1, 2} {
        \gettikzxy{(\p)}{\px}{\py}
        \gettikzxy{(\q)}{\qx}{\qy}
        \ifdimcomp{\qx}{<}{\px}{
            \draw[->,>=stealth] (\q) to [bend left=60] (\p);
        }{
            \draw[->,>=stealth] (\q) to [bend right=60] (\p);
        }
    }
\end{tikzpicture}

\end{document}

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