如何让文字修饰的周长自动等于文字的长度？

Question

我想要一些用文字装饰的圆圈，其周长自动等于文字的长度。

这有点像我的 MWE，但不需要通过反复试验手动计算半径。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations.text}
\begin{document}
    \begin{tikzpicture}
        \path[draw, 
            postaction={decorate,decoration={%
                text={egreg~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (0,0) circle [radius=.46em];
        \path[draw, 
            postaction={decorate,decoration={%
                text={David Carlisle~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (2,0) circle [radius=1.05em];   
        \path[draw, 
            postaction={decorate,decoration={%
                text={Herr Prof.\ Paulinho van Duck~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (1,-2) circle [radius=2.2em];   
    \end{tikzpicture}
\end{document}

Answer 1

将文本放入新的长度寄存器，例如，

\newlength\circl
\settowidth\circl{Herr Prof.\ Paulinho van Duck duck duck~}

这应该是圆的周长，然后进行计算。要从周长得到半径，r = circumference/2pi，或者这样说radius=.1591549\circl，其中.1591549 = 1/2pi。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations.text}
\begin{document}
\newlength\circl
\settowidth\circl{Herr Prof.\ Paulinho van Duck duck duck~}
    \begin{tikzpicture}
        \path[draw, 
            postaction={decorate,decoration={%
                text={egreg~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (0,0) circle [radius=.46em];
        \path[draw, 
            postaction={decorate,decoration={%
                text={David Carlisle~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (2,0) circle [radius=1.05em];   
        \path[draw, 
            postaction={decorate,decoration={%
                text={Herr Prof.\ Paulinho van Duck duck duck~}, 
                text along path,
                text align=right,
                raise=-10pt,
                }}
            ]
            (1,-3) circle [radius=.1591549\circl];   
    \end{tikzpicture}
\end{document}