TikZ：为节点的边框添加阴影

Question

我想遮蔽一个节点和节点的边界。

以下代码可以工作，但我不太喜欢必须在背景层上的节点后绘制一些东西。我更喜欢可以在样式中使用并直接在节点上使用的解决方案。有人有什么好主意吗？

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage{tikz}
\usetikzlibrary{backgrounds}
\usetikzlibrary{calc}

\tikzset{
 shrink inner sep/.code={
   \pgfkeysgetvalue{/pgf/inner xsep}{\currentinnerxsep}
   \pgfkeysgetvalue{/pgf/inner ysep}{\currentinnerysep}
   \pgfkeyssetvalue{/pgf/inner xsep}{\currentinnerxsep - 0.5\pgflinewidth}
   \pgfkeyssetvalue{/pgf/inner ysep}{\currentinnerysep - 0.5\pgflinewidth}
   }}
\begin{document}
\begin{tikzpicture}
\draw (0,0) node[rectangle,
      rounded corners,
      shading=axis,
      thick,
      outer sep=0pt,
      shrink inner sep,
      left color=red!50!white,
      right color=green!50!white
       ](A){abcabc abc};
 \begin{scope}[on background layer]
 \shade[rectangle,
        left color = red,
        right color= green,
        thick,
        rounded corners=4pt+\pgflinewidth]
       ($(A.south west)+(-\pgflinewidth,-\pgflinewidth)$) rectangle
       ($(A.north east)+(\pgflinewidth,\pgflinewidth)$)
        ;
\end{scope};
\end{tikzpicture}

\begin{tikzpicture}
\draw (0,0) node[rectangle,
       rounded corners,
       fill=red!50!white,
       draw=red,
       thick
       ](A){abcabc abc};
\end{tikzpicture}      

\begin{tikzpicture}
\draw (0,0) node[rectangle,
       rounded corners,
       shading=axis,
       left color=red!50!white,
       right color=green!50!white,
       draw=red,
       thick
       ](A){abcabc abc};
\end{tikzpicture}       
\end{document}

Answer 1

这可能是一种可行的方法；已经定义了两种样式：

• horizontal shaded border接收左颜色和右颜色作为参数：horizontal shaded border=red and green
• vertical shaded border接收顶部和底部颜色作为参数：vertical shaded border=blue and orange

代码：

\documentclass[tikz,border=10pt,png]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\tikzset{
 shrink inner sep/.code={
   \pgfkeysgetvalue{/pgf/inner xsep}{\currentinnerxsep}
   \pgfkeysgetvalue{/pgf/inner ysep}{\currentinnerysep}
   \pgfkeyssetvalue{/pgf/inner xsep}{\currentinnerxsep - 0.5\pgflinewidth}
   \pgfkeyssetvalue{/pgf/inner ysep}{\currentinnerysep - 0.5\pgflinewidth}
   }
}

\tikzset{horizontal shaded border/.style args={#1 and #2}{
    append after command={
       \pgfextra{%                 
          \begin{pgfinterruptpath}
                \path[rounded corners,left color=#1,right color=#2]
                ($(\tikzlastnode.south west)+(-\pgflinewidth,-\pgflinewidth)$) 
                rectangle
                ($(\tikzlastnode.north east)+(\pgflinewidth,\pgflinewidth)$);        
           \end{pgfinterruptpath}
        } 
    }
  },
  vertical shaded border/.style args={#1 and #2}{
    append after command={
       \pgfextra{%                 
          \begin{pgfinterruptpath}
                \path[rounded corners,top color=#1,bottom color=#2]
                ($(\tikzlastnode.south west)+(-\pgflinewidth,-\pgflinewidth)$) 
                rectangle
                ($(\tikzlastnode.north east)+(\pgflinewidth,\pgflinewidth)$);        
           \end{pgfinterruptpath}
        } 
    }
  }
}
\begin{tikzpicture}
\draw (0,0) node[rectangle,
      rounded corners,
      thick,
      outer sep=0pt,
      shrink inner sep,
      left color=red!50!white,
      right color=green!50!white,
      horizontal shaded border=red and green
      ](A){abcabc abc};
\draw (2.5,0) node[rectangle,
      rounded corners,
      thick,
      outer sep=0pt,
      shrink inner sep,
      top color=cyan!50,
      bottom color=orange!50,
      vertical shaded border=blue and orange
      ](A){abcabc abc};
\end{tikzpicture}
\end{document}

结果：

代码注释

边框在节点之后绘制，方法是：append after command；要访问节点的锚点，宏\tikzlastnode很有用：事情非常类似于 如何修改 TikZ 中的节点以自动在其顶部添加一条线？

Answer 2

我不知道这算不算一个“好”主意。它有一个很大的缺陷，（我在 Ubuntu 上）我无法在 evince 中正确查看它（褪色不显示），但可以在 okular 中查看它。我无法在 gimp 中对生成的 PDF 进行任何操作，因为褪色没有保留/尊重。我不得不对 okular 进行屏幕截图以获取此图像。这真是令人讨厌。

所以，这不是一个可移植的解决方案。我怀疑是处理/渲染 PDF 的底层库导致了 Linux 上的问题（大概是libpoppler）。因此，这不太可能成为 Windows 上的问题。

除此之外，我们的想法是使用可以与preaction样式一起应用的淡入淡出。

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{fadings}

\tikzset{
    shade border west to east/.style args={#1 to #2}{
        preaction={draw, very thick, path fading=east, #1},
        preaction={draw, very thick, path fading=west, #2}
    },
    shade fill west to east/.style args={#1 to #2}{
        left color=#1,
        right color=#2
    }
}
\begin{document}

\begin{tikzpicture}
\node [rounded corners=1ex, 
    shade fill west to east=red!50 to green!50,
    shade border west to east=red to green] {abcabc abc};
\end{tikzpicture}

\end{document}