如何在背景图像上制作径向褪色？

Question

我有三个想要相互叠加的对象：背景图片上的一些文本，使用圆圈创建从白色到透明的径向渐变，以便可以阅读文本。

我不确定是否是因为我的 TeX 引擎（sharelatex.com 中的 PdfLaTeX 和 LaTeX），但由于某种原因，我无法让圆圈与背景图像一起淡出为透明。

这是代码：

\documentclass[margin=10pt]{standalone}
\usepackage{tikz}
\usepackage{graphics}
\usetikzlibrary{arrows,positioning,trees,fadings} 



\pgfdeclareradialshading{myshading}{\pgfpointorigin}{%
color(0mm)=(white);
% color(5mm)=(pgftransparent!10);
% color(8mm)=(pgftransparent!20);
color(15mm)=(pgftransparent!100)
}

\pgfdeclarefading{myfading}{\pgfuseshading{myshading}}


\tikzset{
    >=stealth',
  punkt2/.style={
         rectangle,
         rounded corners,
         dashed,
         draw=black, thick,
         text width=7em,
         minimum height=2em,
         text centered},
    level 1/.style={sibling angle=45, level distance=3.5cm},
    edge from parent/.style= {draw=none},
}

\begin{document}
\begin{tikzpicture}
\node[opacity=0.5] (img2) at (0,7.5) {\includegraphics[height=18cm]{greenelephant}};
\shade[shading=myshading] (0,7.5) circle (5.5);

\coordinate (main2) at (0,7.5) [counterclockwise from=90]
    child { node[punkt2, text width=10em, solid] (a1) {State 0}}
    child { node[punkt2] (a2) {State 1}}
    child { node[punkt2] (a3) {State 2}}
    child { node[punkt2] (a4) {State 3}}
    child { node[punkt2, text width=10em, solid] (a5) {State 4}}
    child { node[punkt2] (a6) {State 5}}
    child { node[punkt2] (a7) {State 6}}
    child { node[punkt2] (a8) {State 7}};


\draw[->] (a1) edge[bend right=10] (a2);
\draw[->] (a2) edge[bend right=10] (a3);
\draw[->] (a3) edge[bend right=10] (a4);
\draw[->] (a4) edge[bend right=10] (a5);
\draw[->] (a5) edge[bend right=10] (a6);
\draw[->] (a6) edge[bend right=10] (a7);
\draw[->] (a7) edge[bend right=10] (a8);
\draw[->] (a8) edge[bend right=10] (a1);

\node at (0,7.5) (label2) {\textsc{Cycle}};

\end{tikzpicture}
\end{document}

而不是命令

\shade[shading=myshading] (0,7.5) circle (5.5);

我也尝试过这个

 \pgfsetfading{myfading}{} \fill[white] (0,7.5) circle (5);

但是这个命令似乎中断了其余的处理，因为我甚至没有得到圆圈或文本。

Answer 1

类似这样的？我怕我没有大象，所以我用老虎代替了。

或者 （编辑） 像这样？

\documentclass[margin=10pt,tikz,multi]{standalone}
\usetikzlibrary{arrows.meta,positioning,trees,fadings}
\pgfdeclareradialshading[radialcolour1,radialcolour2,radialcolour3]{myshading}{\pgfpointorigin}{%
  color(0)=(radialcolour1);
  color(15bp)=(radialcolour2);
  color(50bp)=(radialcolour3)
}
\tikzset{%
  radial inner colour/.code={
    \colorlet{radialcolour1}{#1}
  },
  radial mid colour/.code={
    \colorlet{radialcolour2}{#1}
  },
  radial outer colour/.code={
    \colorlet{radialcolour3}{#1}
  },
  radial inner colour=white,
  radial mid colour=white!50!black,
  radial outer colour=black,
  my inner shading/.style={
    radial inner colour=#1,
    shading=myshading,
  },
  my mid shading/.style={
    radial mid colour=#1,
    shading=myshading,
  },
  my outer shading/.style={
    radial outer colour=#1,
    shading=myshading,
  },
  >={Stealth[]},
  punkt2/.style={
    rectangle,
    rounded corners,
    dashed,
    draw=black,
    thick,
    text width=7em,
    minimum height=2em,
    text centered},
  level 1/.style={sibling angle=45, level distance=3.5cm},
  edge from parent/.style={draw=none},
}
\tikzfading[name=myfading, my inner shading=transparent!100, my outer shading=transparent!0, my mid shading=transparent!0]
\tikzfading[name=myfading2, my inner shading=transparent!0, my mid shading=transparent!25, my outer shading=transparent!100]
\begin{document}
\begin{tikzpicture}
  \node [opacity=0.5] (img2) at (0,7.5) {\includegraphics[height=18cm]{tiger}};
  \fill [path fading=myfading, fill=white] (0,7.5) circle (5.5);
  \coordinate (main2) at (0,7.5) [counterclockwise from=90]
  child { node[punkt2, text width=10em, solid] (a1) {State 0}}
  child { node[punkt2] (a2) {State 1}}
  child { node[punkt2] (a3) {State 2}}
  child { node[punkt2] (a4) {State 3}}
  child { node[punkt2, text width=10em, solid] (a5) {State 4}}
  child { node[punkt2] (a6) {State 5}}
  child { node[punkt2] (a7) {State 6}}
  child { node[punkt2] (a8) {State 7}};
  \draw[->] (a1) edge[bend right=10] (a2);
  \draw[->] (a2) edge[bend right=10] (a3);
  \draw[->] (a3) edge[bend right=10] (a4);
  \draw[->] (a4) edge[bend right=10] (a5);
  \draw[->] (a5) edge[bend right=10] (a6);
  \draw[->] (a6) edge[bend right=10] (a7);
  \draw[->] (a7) edge[bend right=10] (a8);
  \draw[->] (a8) edge[bend right=10] (a1);
  \node at (0,7.5) (label2) {\textsc{Cycle}};
\end{tikzpicture}
\begin{tikzpicture}
  \node [opacity=0.5] (img2) at (0,7.5) {\includegraphics[height=18cm]{tiger}};
  \fill [path fading=myfading2, fill=white] (0,7.5) circle (5.5);
  \coordinate (main2) at (0,7.5) [counterclockwise from=90]
  child { node[punkt2, text width=10em, solid] (a1) {State 0}}
  child { node[punkt2] (a2) {State 1}}
  child { node[punkt2] (a3) {State 2}}
  child { node[punkt2] (a4) {State 3}}
  child { node[punkt2, text width=10em, solid] (a5) {State 4}}
  child { node[punkt2] (a6) {State 5}}
  child { node[punkt2] (a7) {State 6}}
  child { node[punkt2] (a8) {State 7}};
  \draw[->] (a1) edge[bend right=10] (a2);
  \draw[->] (a2) edge[bend right=10] (a3);
  \draw[->] (a3) edge[bend right=10] (a4);
  \draw[->] (a4) edge[bend right=10] (a5);
  \draw[->] (a5) edge[bend right=10] (a6);
  \draw[->] (a6) edge[bend right=10] (a7);
  \draw[->] (a7) edge[bend right=10] (a8);
  \draw[->] (a8) edge[bend right=10] (a1);
  \node at (0,7.5) (label2) {\textsc{Cycle}};
\end{tikzpicture}
\end{document}