如何在 Tikz 中向 Halo 添加箭头和文字？

Question

我想知道如何添加一个从圆圈区域出来的箭头，如 Tikz 所示，并在箭头末端添加一些文字。以下是我目前所得到的

\usetikzlibrary{backgrounds}
\begin{document}

\begin{tikzpicture}[halo/.style={line join=round,
 double,line cap=round,double distance=#1,shorten >=-#1/2,shorten <=-#1/2},
 halo/.default=7mm]
    \node[circle,draw,fill=gray](s){s}
        child{node[circle,draw,fill=white]{}
             child{node[circle,draw,fill=gray]{}}
        }
        child{node[circle,draw,fill=white]{}
             child{node[circle,draw,fill=gray]{}}
        }
        child{node[circle,draw,fill=white](R1){}
            child{node[circle,draw,fill=gray](R2){}}
        };
 \begin{scope}[on background layer]     
  \draw[halo] (s) -- (R1.center) -- (R2);       
 \end{scope}
 \path (R2.south) ++ (0,-3.5mm); % shorten does not get taken into account by the bounding box
\end{tikzpicture}
\end{document}

Answer 1

像这样？

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{backgrounds,calc}
\begin{document}

\begin{tikzpicture}[halo/.style={line join=round,
 double,line cap=round,double distance=#1,shorten >=-#1/2,shorten <=-#1/2},
 halo/.default=7mm]
    \node[circle,draw,fill=gray](s){s}
        child{node[circle,draw,fill=white]{}
             child{node[circle,draw,fill=gray]{}}
        }
        child{node[circle,draw,fill=white]{}
             child{node[circle,draw,fill=gray]{}}
        }
        child{node[circle,draw,fill=white](R1){}
            child{node[circle,draw,fill=gray](R2){}}
        };
 \begin{scope}[on background layer]     
  \draw[halo] (s) -- (R1.center) coordinate[pos=0.8] (tip) -- (R2);       
 \end{scope}
 \path (R2.south) ++ (0,-3.5mm); % shorten does not get taken into account by the bounding box
 \draw[stealth-] ($ (tip)!3.5mm!-90:(s) $) to[bend right=20]
 ($ (tip)!1.2cm!-90:(s) $) node[above]{text};
\end{tikzpicture}
\end{document}