使用 tikz 绘制维恩图：擦除弧线

Question

考虑以下 MWE，它生成下面的维恩图：

\documentclass[12pt]{article}

\usepackage{tikz,pstricks,pst-jtree}
% pst-jtree enables the \multiline \cr \endmultiline syntax
\usetikzlibrary{shapes,backgrounds}

\begin{document}

\begin{center}
\begin{center}
  \def\first{(0,0) ellipse (6em and 4em)}
  \def\second{(2.7,0) ellipse (6em and 4em)}
  \def\third{(1.45,1.5) ellipse (6em and 4em)}
  \begin{tikzpicture}
    \draw \first node [below] { };
    \draw \second node [below] { };
    \draw \third node [above] { };

    % first coordinate control x axis, second controls y axis
    \node at (-1.1,-.3) (A) {first};
    \node at (3.8,-.5) (B) {second};
    \node at (2.1,.8) (C) {\multiline we care\cr about this\endmultiline};
    \node at (1.5,2.5) (C) {third};

    \begin{scope}[fill opacity = .5]
      \clip \third;
      \fill[light-gray] \second;
    \end{scope}
  \end{tikzpicture}
\end{center}

\end{center}

\end{document}

出于美观原因，我不希望椭圆的线条first干扰we care about this图例。是否可以消除first阴影区域中的圆弧？

Answer 1

只需改变绘制顺序：

1. 第一个椭圆
2. 灰色地带
3. 第二和第三个省略号和文本节点。

进一步说明：

• 通过节点选项启用多行文本align。

• light-gray由于连字符，颜色名称有点不令人满意。当\fill[light-gray]使用简写符号时，如果颜色未定义（如问题示例中所示），TikZ 会将连字符误解为箭头规范。TikZ 会抱怨未知的箭头尖，light而不是未定义的颜色错误fill=light-gray或未知的键。

示例文件：

\documentclass[12pt]{article}

\usepackage{tikz}
\usetikzlibrary{shapes}

\begin{document}
\begin{center}
  \def\first{(0,0) ellipse (6em and 4em)}
  \def\second{(2.7,0) ellipse (6em and 4em)}
  \def\third{(1.45,1.5) ellipse (6em and 4em)}
  \begin{tikzpicture}
    \draw \first node [below] { };
    \begin{scope}
      \clip \third;
      \fill[lightgray] \second;
    \end{scope}
    \draw \second node [below] { };
    \draw \third node [above] { };

    % first coordinate control x axis, second controls y axis
    \node at (-1.1,-.3) (A) {first};
    \node at (3.8,-.5) (B) {second};
    \node[align=center] at (2.1,.8) (C) {we care\\ about this};
    \node at (1.5,2.5) (C) {third};
  \end{tikzpicture}
\end{center}
\end{document}