在 pdftex 中将 pdf 页面设置为 tikz 图片尺寸

Question

我尝试使用 pdftex (Plain TeX) (一种独立程序) 根据图片尺寸设置 pdf 页面。这样的图片应该显示在文档的中心。但我失败了。

\input tikz

\def\fitpagetothebox0%
{%

   \ifdim\pagetotal>0pt
      \errmessage{page must be clear to call the command \string\fitpagetothebox0 macro}
   \fi

   \hoffset=-1in
   \voffset=-1in

   \pdfpagewidth=\wd0
   \pdfpageheight=\ht0
   \advance \pdfpageheight by \dp0
   \hsize=\wd0
   \vsize=\ht0

   \output{\shipout
           \vbox
           {\noindent
            \vfil
            \hbox{\hfil\box255\hfil}
            \vfil}}
}

\setbox0=\hbox
{%
\tikzpicture
\tikzstyle{every node}=[draw, double, line width=1pt,
                        circle, text width=1.2cm, text centered]

\node[double=red!30, fill=white!90] (eletron) at (-3,0) {$e^-$};
\node[double=blue!50, fill=white!90] (proton) at (3,0) {$p^+$};

\foreach \i in {0,12,...,360}
   \draw[<-<,overlay,out=\i] (eletron) to [in=180-\i](proton);

\endtikzpicture
}%


\fitpagetothebox0
\hbox to \hsize{\hfil\box0\hfil}

\end

我究竟做错了什么？