为什么贝塞尔曲线中的坐标会增加 TikZ 中的填充？

Question

我用贝塞尔曲线画了一点tikzpicture，用于文本中。我注意到它有异常多的水平空白，比圆形还要多：

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \draw (0,0) .. controls (a) and ($2*(a -| 0,0)-(a)$) .. (0,0);
    \end{tikzpicture}
    ipsum

    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \draw (0,0) circle [radius=0.4cm];
    \end{tikzpicture}
    ipsum
\end{document}

我认为白色空间来自controls贝塞尔曲线语法中使用的坐标：

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \draw (0,0) .. controls (a) and ($2*(a -| 0,0)-(a)$) .. (0,0);
        \node[red] at (a)                  {$\cdot$};
        \node[red] at ($2*(a -| 0,0)-(a)$) {$\cdot$};
    \end{tikzpicture}
    ipsum
\end{document}

但是，仅向圆形图片添加坐标并不能提供额外的空白！这是怎么回事？我该如何避免这种情况？

Answer 1

基于当我“弯曲”边缘时，Tikz 使用哪种类型的曲线？，您的示例代码可以更改为：

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,decorations.pathreplacing,shapes.misc}
\tikzset{
    show control points/.style={
        decoration={show path construction, curveto code={
                \draw [blue, dashed]
                    (\tikzinputsegmentfirst) -- (\tikzinputsegmentsupporta)
                    node [at end, cross out, draw, solid, red, inner sep=2pt]{};
                \draw [blue, dashed]
                    (\tikzinputsegmentsupportb) -- (\tikzinputsegmentlast)
                    node [at start, cross out, draw, solid, red, inner sep=2pt]{};
            }
        },
        postaction=decorate
    },
}
\begin{document}
    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \draw[show control points] (0,0) .. controls (a) and ($2*(a -| 0,0)-(a)$) .. (0,0);
    \end{tikzpicture}
    ipsum

    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \draw[show control points] (0,0) circle [radius=0.4cm];
    \end{tikzpicture}
    ipsum
\end{document}

这表明贝塞尔控制点如下：

请注意，TikZ 图形的边界框包含所有控制点。您可以使用以下方法\useasboundingbox修复此问题：

    Lorem
    \begin{tikzpicture}
        \coordinate (a) at (-1,2);
        \useasboundingbox (-.2,0) rectangle (.2,1.5);
        \draw[show control points] (0,0) .. controls (a) and ($2*(a -| 0,0)-(a)$) .. (0,0);
    \end{tikzpicture}
    ipsum

得出的结果是：