TikZ 中的半圆使用起点和终点而不是角度

Question

我需要在 TikX 中画一个半圆，起始于 (x1, y1)，结束于 (x2, y2)，假设该圆以 (cx, cy) 为中心，半径为 r。

例如：

（x1，y1）=（0.25598，0.8256）

（x2，y2）=（0.3870，0.7221）

（cx，cy）=（0.5，1）

r = 0.3

大多数例子都使用角度而不是点。

Answer 1

借助海科·奥伯迪克：

\documentclass{standalone}
\usepackage[french]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
  \coordinate (A) at (2.5598,8.256);
  \coordinate (B) at (3.870,7.221);

  \coordinate (C) at ($(A)!.5!(B)$);

  \draw[fill=red] (A) circle [radius=2pt];
  \draw[fill=blue] (B) circle [radius=2pt];
  \draw (A) -- (B);
  \pgfmathanglebetweenpoints{\pgfpointanchor{C}{center}}{\pgfpointanchor{A}{center}}
  \let\StartAngle\pgfmathresult
  \pgfmathanglebetweenpoints{\pgfpointanchor{C}{center}}{\pgfpointanchor{B}{center}}
  \let\EndAngle\pgfmathresult

  \draw[fill=green] (C) circle [radius=2pt];

  \draw (A) let \p1 = ($(C) - (A)$),
  \n1 = {veclen(\x1, \y1)}
  in 
  arc [start angle=\StartAngle, end angle=\EndAngle, radius=\n1];

\end{tikzpicture}

\end{document}

Answer 2

角度可以通过以下方式计算\pgfmathanglebetweenpoints：

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \coordinate (c) at (.5, 1);
  \coordinate (p1) at (.25598, .8256);
  \coordinate (p2) at (.3870, .7221);
  \pgfmathanglebetweenpoints{\pgfpointanchor{c}{center}}{\pgfpointanchor{p1}{center}}
  \let\StartAngle\pgfmathresult
  \pgfmathanglebetweenpoints{\pgfpointanchor{c}{center}}{\pgfpointanchor{p2}{center}}
  \let\EndAngle\pgfmathresult
  \draw (p1) arc[start angle=\StartAngle, end angle=\EndAngle, radius=.3];
  \fill[radius=.5pt, red] (p2) circle[] (p1) circle[] (c) circle[];
\end{tikzpicture}
\end{document}