如何在 beamer 中使用 TikZ 制作矩形聚光灯？

Question

我正在尝试改变下面突出显示区域的形状MWE（基于这是@BambOo 的解决方案）。

\documentclass{beamer}
\usepackage{tikz}

\tikzset{
    use page relative coordinates/.style={
        shift={(current page.south west)},
        x={(current page.south east)},
        y={(current page.north west)}
    },
}

\begin{document}
    
    \begin{frame}{title}{subtitle}
    \begin{block}{Block title}
        Some content
    \end{block}
    \includegraphics[width=0.5\textwidth]{example-image-a}
    \begin{tikzpicture}[remember picture,overlay,use page relative coordinates]
    \fill[opacity=0.5,black] (0,0) rectangle (1,1) (0.25,0.5) circle (2cm);
    \end{tikzpicture}
\end{frame}
\end{document}

两者都不

\begin{tikzpicture}[remember picture,overlay,use page relative coordinates]
    \fill[opacity=0.5,black] (0,0) rectangle (1,1) (0.15,0.15) rectangle (0.2,0.2);
    \end{tikzpicture}

也不

\begin{tikzpicture}[remember picture,overlay,use page relative coordinates]
    \fill[opacity=0.5,black] (0,0) rectangle (1,1); 
    \fill[opacity=0,black] (0.15,0.15) rectangle (0.2,0.2);
    \end{tikzpicture}

完成工作。

我怎样才能让它工作？

Answer 1

如果你添加even odd rule选项，它就会起作用。为什么？我不知道，似乎将矩形与圆形组合不需要明确修复规则

\documentclass{beamer}
\usepackage{tikz}

\tikzset{
    use page relative coordinates/.style={
        shift={(current page.south west)},
        x={(current page.south east)},
        y={(current page.north west)}
    },
}

\begin{document}
    
    \begin{frame}{title}{subtitle}
    \begin{block}{Block title}
        Some content
    \end{block}
    \includegraphics[width=0.5\textwidth]{example-image-a}
    \begin{tikzpicture}[remember picture,overlay,use page relative coordinates]
    \filldraw[opacity=0.5, black, even odd rule] (0,0) rectangle (1,1) (0.2,0.2) rectangle (0.38,0.6);
    \end{tikzpicture}
\end{frame}
\end{document}