我正在合并两个不同问题的解决方案，但遇到了兼容性问题：
第一个来自Tikz：箭头位于中心，允许箭头上的装饰在中间有一个箭头
第二个来自tikz 边界框/裁剪：曲线空间太大使用曲线的控制点时限制边界框。
我实际上是在尝试创建一个有向图，其中两个循环来自一个边，所以如果有人找到更好的解决方案，那就太好了。
我可以创建我想要的图形，但是由于控制点的原因，边界框（棕色）太大：
由代码创建：
\documentclass{scrarticle}
\usepackage{tikz}
\usepackage{lipsum}
\usetikzlibrary{decorations.markings}
\begin{document}
\usetikzlibrary{arrows,positioning}
% arrows with middlearrow arrow head in middle
\tikzset{middlearrow/.style={
decoration={markings,
mark= at position 0.5 with {\arrow{#1}} ,
},
postaction={decorate}
}
% middlearrow/.default={>}
}
\lipsum[66]
\begin{center}
\begin{tikzpicture}
\node[circle,fill=black,inner sep=2pt,label=b] (b) at (0,0) {};
\draw[middlearrow={>}] (b) .. controls (2,2) and (2,-2) .. (b);
\draw[middlearrow={>}] (b) .. controls (-2,-2) and (-2,2) .. (b);
\draw [brown] (current bounding box.south west) rectangle (current bounding box.north east);
\end{tikzpicture}
\end{center}
\lipsum[66]
\end{document}
我尝试添加边界框解决方案来删除多余的空间：
\documentclass{scrarticle}
\usepackage{tikz}
\usepackage{lipsum}
%limit boundary box: from https://tex.stackexchange.com/questions/290357/tikz-bounding-box-cropping-too-much-space-for-curves
\usetikzlibrary{calc,decorations.pathreplacing}
\tikzset{
bezier/controls/.code args={(#1) and (#2)}{
\def\mystartcontrol{#1}
\def\mytargetcontrol{#2}
},
bezier/limit/.store in=\mylimit,
bezier/limit=1cm,
bezier/.code={
\tikzset{bezier/.cd,#1}
\tikzset{
to path={
let
\p0=(\tikztostart), \p1=(\mystartcontrol),
\p2=(\mytargetcontrol), \p3=(\tikztotarget),
\n0={veclen(\x1-\x0,\y1-\y0)},
\n1={veclen(\x3-\x2,\y3-\y2)},
\n2={\mylimit}
in \pgfextra{
\pgfmathtruncatemacro\ok{max((\n0>\n2),(\n1>\n2))}
}
\ifnum\ok=1 %
let
\p{01}=($(\p0)!.5!(\p1)$), \p{12}=($(\p1)!.5!(\p2)$), \p{23}=($(\p2)!.5!(\p3)$),
\p{0112}=($(\p{01})!.5!(\p{12})$), \p{1223}=($(\p{12})!.5!(\p{23})$),
\p{01121223}=($(\p{0112})!.5!(\p{1223})$)
in
to[bezier={controls={(\p{01}) and (\p{0112})}}]
(\p{01121223})
to[bezier={controls={(\p{1223}) and (\p{23})}}]
(\p3)
\else
[overlay=false] .. controls (\p1) and (\p2) .. (\p3) [overlay=true]
\fi
},
}%, <-- Comma here results in "Missing character: There is no , in font nullfont!"
},
limit bb/.style n args={2}{
overlay,
decorate,
decoration={
show path construction,
moveto code={},
lineto code={\path[#2] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);},
curveto code={
\path[#2]
(\tikzinputsegmentfirst)
to[bezier={limit=#1,controls={(\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb)}}]
(\tikzinputsegmentlast);
},
closepath code={\path[#2] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast);},
},
},
limit bb/.default={1mm}{draw},
}
\usetikzlibrary{decorations.markings}
\begin{document}
\usetikzlibrary{arrows,positioning}
% arrows with middlearrow arrow head in middle
\tikzset{middlearrow/.style={
decoration={markings,
mark= at position 0.5 with {\arrow{#1}} ,
},
postaction={decorate}
}
% middlearrow/.default={>}
}
\lipsum[66]
\begin{center}
\begin{tikzpicture}
\node[circle,fill=black,inner sep=2pt,label=b] (b) at (0,0) {};
\draw[middlearrow={>},limit bb] (b) .. controls (2,2) and (2,-2) .. (b);
\draw[middlearrow={>},limit bb] (b) .. controls (-2,-2) and (-2,2) .. (b);
\end{tikzpicture}
\end{center}
\lipsum[66]
\end{document}
返回错误“我无法修饰空路径”。（第二段代码按预期工作，只需从两个箭头的选项中删除其中一个middlearrow={>}或即可）limit bb
我想我正在寻找一种不太技术性的方法来限制边界框大小，手动是一种我乐意使用的选项。
答案1
您的问题可以通过使用该bbox库来解决：
\documentclass{scrarticle}
\usepackage{tikz}
\usetikzlibrary{arrows,
bbox, % <----
decorations.markings,
positioning}
\usepackage{lipsum}
\begin{document}
\lipsum[66]
\begin{center}
\begin{tikzpicture}[bezier bounding box, % <----
middlearrow/.style={decoration={markings,
mark=at position 0.5 with {\arrow{#1}} ,
},
postaction={decorate}
}
]
\node[circle,fill=black,inner sep=2pt,label=b] (b) at (0,0) {};
\draw[middlearrow={>}] (b) .. controls (2,2) and (2,-2) .. (b);
\draw[middlearrow={>}] (b) .. controls (-2,-2) and (-2,2) .. (b);
\draw [brown] (current bounding box.south west) rectangle (current bounding box.north east);
\end{tikzpicture}
\end{center}
\lipsum[66]
\end{document}
笔记：应在文档前言中加载库。