在 tikz 中填充圆圈

Question

我想使用 tikz 填充两个半圆之间的区域。以下是我尝试过但失败了的方法。

\documentclass[a4paper,12pt]{article}
\begin{tikzpicture}
\draw [-, ] (-3,0) --(-0.4,0);
\draw [-, ] (0.4,0) --(3,0);
\fill[gray!15]  ( -3,-3) |- (-0.4,0) arc (-180:0:4mm)-- (3,0) -| 
 (3,-3);
\draw [blue,thick,domain=180:360] plot ({.4*cos(\x)}, {.4*sin(\x)});
\draw [blue,thick,domain=180:360] plot ({3*cos(\x)}, {3*sin(\x)});
\end{tikzpicture}
\end{document}

Answer 1

像这样？

\documentclass[tikz,margin=3mm]{standalone}

\begin{document}
\begin{tikzpicture}
\draw [-]  ( -3,0) -- (-0.4,0)
           (0.4,0) -- (3,0);
\fill[gray!15]  (-3,0)  -- (-0.4,0) arc (-180:0: 4mm) 
                        -- (3,0)    arc (0:-180:30mm); % <-- changed
\draw [blue,thick,domain=180:360] plot ({.4*cos(\x)}, {.4*sin(\x)});
\draw [blue,thick,domain=180:360] plot ({ 3*cos(\x)}, { 3*sin(\x)});
\end{tikzpicture}
\end{document}

附录：考虑保罗·加博利在下面发表评论，您的 MWE 可以简化和改进，arc而是使用绘制plot函数：

\documentclass[tikz,margin=3mm]{standalone}

\begin{document}
\begin{tikzpicture}
\draw [-]   ( -3,0) -- (-0.4,0)
            (0.4,0) -- (3,0);
\fill[gray!15]      (-3,0) -- (-0.4,0) arc (-180:0: 4mm)
                           -- (3,0)    arc (0:-180:30mm); 
\draw[blue,thick]   (.4,0) arc (0:-180: 4mm); % <-- changed
\draw[blue,thick]   ( 3,0) arc (0:-180:30mm); % <-- changed
\end{tikzpicture}
\end{document}