如何在 TikZ 中正确绘制这张图片？

Question

这是我想要制作的图片：

这是由以下极其丑陋的代码生成的：

\documentclass[tikz]{standalone}

\usetikzlibrary{decorations.markings}
\usetikzlibrary{hobby}

\definecolor{col1}{RGB}{127,127,127}
\definecolor{col2}{RGB}{240,240,240}

\begin{document}

\begin{tikzpicture}[use Hobby shortcut]
    \clip (0,0) rectangle (1,1);
    \path[yshift=10,
    postaction={
        decorate,
        decoration={
            markings,
            mark=between positions 0 and \pgfdecoratedpathlength step .01cm with {
                \pgfmathsetmacro\myval{multiply(divide(
                    \pgfkeysvalueof{/pgf/decoration/mark info/distance from start}, \pgfdecoratedpathlength),100)};
                \pgfsetfillcolor{col2!\myval!col1};
                \pgfpathcircle{\pgfpointorigin}{1.5};
                \pgfusepath{fill};}
    }}] 
    (.075,.2)..([closed].2,.4)..(.8,0)..(.925,.2)..(.8,.4)..(.2,0);
    \fill[col1] (.075,.55) circle (0.052cm);
\end{tikzpicture}

\end{document}

该代码无法编译，因为会出现许多类似这样的错误：

Dimension too large. (...2,.4)..(.8,0)..(.925,.2)..(.8,.4)..(.2,0); ...)

但是我能够获得结果 pdf，从而得到上面的图片。

我的问题是：如何正确绘制这幅图？提前感谢任何即将到来的建议〜

Answer 1

您pgfplots可以使用它point meta来改变图表的颜色。

\documentclass[tikz,border=3mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.17}
\begin{document}
\begin{tikzpicture}
\begin{axis}[hide axis,width=8cm,height=4cm,clip=false] 
\addplot[domain=0:360,samples=720,line cap=round,        
colormap={}{ 
            color(0cm)=(gray!10);
            color(16cm)=(gray);
        },
        line width=5mm, variable=t,point meta=t,mesh]
        ({-cos(t)},{-sin(2*t)});
\end{axis}
\end{tikzpicture}
\end{document}

为了获得适当的边界框，您可以将线宽存储在宏中。

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.17}
\begin{document}
\begin{tikzpicture}
\begin{axis}[hide axis,width=8cm,height=4cm,clip=false]
\def\mylw{5mm} %<- line width 
\addplot[domain=0:360,samples=720,line cap=round,        
colormap={}{ 
            color(0cm)=(gray!10);
            color(16cm)=(gray);
        },
        line width=\mylw, variable=t,point meta=t,mesh]
        ({-cos(t)},{-sin(2*t)});
% add points to have an appropriat bounding box     
\path ([xshift=-\mylw/2,yshift=-\mylw/2]-1,-1)
 ([xshift=\mylw/2,yshift=\mylw/2]1,1);      
\end{axis}
\end{tikzpicture}
\end{document}