为什么 pgf 只为我绘制一条路径？

Question

这是我的一个或多或少最简单的示例，我在其中绘制了一个带有小折角的“文档”形状。值是硬编码的，以减小示例的大小。

我的问题是，在 中beforebackgroundpath，我明确给出命令绘制一条粗红色线条，然后向下移动一点并绘制另一条更细的黑色线条。但是，只绘制了粗红线。

\documentclass[tikz,border=1mm]{standalone}

\makeatletter
\pgfdeclareshape{document}{
    \inheritsavedanchors[from=rectangle]
    \inheritanchorborder[from=rectangle]
    \inheritanchor[from=rectangle]{center}
    \inheritanchor[from=rectangle]{north}
    \inheritanchor[from=rectangle]{north east}
    \inheritanchor[from=rectangle]{east}
    \inheritanchor[from=rectangle]{south east}
    \inheritanchor[from=rectangle]{south}
    \inheritanchor[from=rectangle]{south west}
    \inheritanchor[from=rectangle]{west}
    \inheritanchor[from=rectangle]{north west}
    \backgroundpath{
        \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
        \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
        % main shape
        \pgf@xc=\pgf@xb
        \advance\pgf@xc by-10pt
        \pgf@yc=\pgf@yb
        \advance\pgf@yc by-5pt
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
        \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yb}}
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
        \pgfpathclose
        % fold
        \pgfpathmoveto{\pgfpoint{\pgf@xb}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yb}}
    }
    \beforebackgroundpath{
        \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
        \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
        % lines
        \advance\pgf@xa by+5pt
        \advance\pgf@xb by-5pt
        \pgfmathsetlength\pgf@yc{(\pgf@yb-\pgf@ya)/8}
        \pgf@ya=\pgf@yb
        \advance\pgf@ya by-10pt
        \pgf@xc=.3\pgf@xb
        \pgfsetstrokecolor{red}
        \pgfsetlinewidth{4pt}
        \advance\pgf@ya by-\pgf@yc
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@ya}}
        \pgfusepath{stroke}
        \pgfsetstrokecolor{black}
        \pgfsetlinewidth{2pt}
        \advance\pgf@ya by-\pgf@yc
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
        \pgfusepath{stroke}
    }
}
\makeatother

\begin{document}

\begin{tikzpicture}
    \node[document,draw,text width=3cm,minimum height=5cm] {};
\end{tikzpicture}

\end{document}

Answer 1

问题是\pgf@xb被 覆盖\pgfusepath{stroke}，所以你画了一条长度为 0pt 的线。你需要\pgf@xb随后设置，例如

\documentclass[tikz,border=1mm]{standalone}

\makeatletter
\pgfdeclareshape{document}{
    \inheritsavedanchors[from=rectangle]
    \inheritanchorborder[from=rectangle]
    \inheritanchor[from=rectangle]{center}
    \inheritanchor[from=rectangle]{north}
    \inheritanchor[from=rectangle]{north east}
    \inheritanchor[from=rectangle]{east}
    \inheritanchor[from=rectangle]{south east}
    \inheritanchor[from=rectangle]{south}
    \inheritanchor[from=rectangle]{south west}
    \inheritanchor[from=rectangle]{west}
    \inheritanchor[from=rectangle]{north west}
    \backgroundpath{
        \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
        \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
        % main shape
        \pgf@xc=\pgf@xb
        \advance\pgf@xc by-10pt
        \pgf@yc=\pgf@yb
        \advance\pgf@yc by-5pt
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}
        \pgfpathlineto{\pgfpoint{\pgf@xa}{\pgf@yb}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yb}}
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}
        \pgfpathclose
        % fold
        \pgfpathmoveto{\pgfpoint{\pgf@xb}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yc}}
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@yb}}
    }
    \beforebackgroundpath{
        \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
        \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
        % lines
        \advance\pgf@xa by+5pt
        \advance\pgf@xb by-5pt
        \pgfmathsetlength\pgf@yc{(\pgf@yb-\pgf@ya)/8}%
        \pgf@ya=\pgf@yb
        \advance\pgf@ya by-10pt
        \pgf@xc=.3\pgf@xb
        \pgfsetstrokecolor{red}%
        \pgfsetlinewidth{4pt}
        \advance\pgf@ya by-\pgf@yc
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}%
        \pgfpathlineto{\pgfpoint{\pgf@xc}{\pgf@ya}}%
        \typeout{before pgfusepath: xb=\the\pgf@xb}%
        \pgfusepath{stroke}%
        \typeout{after pgfusepath: xb=\the\pgf@xb}%
        \pgfsetstrokecolor{black}%
        \pgfsetlinewidth{2pt}
        \advance\pgf@ya by-\pgf@yc
        \pgf@xb=2\pgf@xc
        \pgfpathmoveto{\pgfpoint{\pgf@xa}{\pgf@ya}}%
        \pgfpathlineto{\pgfpoint{\pgf@xb}{\pgf@ya}}%
        \pgfusepath{stroke}%
    }
}
\makeatother

\begin{document}

\begin{tikzpicture}
    \node[document,draw,text width=3cm,minimum height=5cm] {};
\end{tikzpicture}

\end{document}