\documentclass{article}
\usepackage[pdftex,a3paper,margin=1pt,landscape]{geometry}
%% draw macros
\newcount\mlength
\newcount\cstate
\newdimen\mandelunit
\mandelunit=0.5pt
\def\wp{%
  \ifnum\cstate=1 \global\advance\mlength1
  \else\ifnum\cstate=-1 \vrule width \mlength\mandelunit height \mandelunit depth 0pt \global\mlength1 \fi\fi
  \global\cstate1}
\def\bp{%
  \ifnum\cstate=-1 \global\advance\mlength1
  \else\ifnum\cstate=1 \hspace*{\mlength\mandelunit}\global\mlength1 \fi\fi
  \global\cstate-1}
\def\r{%
  \ifnum\cstate=1\hspace*{\mlength\mandelunit}\else\vrule width \mlength\mandelunit height \mandelunit depth 0pt \fi
  \global\cstate0 \global\mlength0}

% Mandelbrot
\newskip\x
\newskip\y
\newskip\a
\newskip\b
\newskip\xx
\newskip\yy
\newskip\tmp
\newcount\k
\def\maxloop{20}
\def\scale{0.002}

\def\loopMandel{%
  \ifdim\b<-1.0pt\relax
    \let\next\relax
  \else
    \drawMandel
    \let\next\loopMandel
    \ifdim\a>0.5pt\relax
      \r\\
      \a=-1.5pt\relax
      \advance\b-\scale pt\relax
    \else
      \advance\a\scale pt\relax
    \fi
  \fi
  \next}
\def\drawMandel{%
  \x=0pt\relax
  \y=0pt\relax
  \k=0\relax
  \checkMandel
  \ifnum\k>\maxloop\relax
    \bp
  \else
    \wp
  \fi
}
\makeatletter
\def\checkMandel{%
  \ifnum\k>\maxloop
    \let\checkNext\relax
  \else
    \xx=\strip@pt\x\x
    \yy=\strip@pt\y\y
    \tmp\xx \advance\tmp\yy
    \ifdim\tmp>4.0pt\relax
      \let\checkNext\relax
    \else
      \let\checkNext\checkMandel
      \advance\k1\relax
      \tmp=\strip@pt\x\y
      \multiply\tmp2\relax
      \advance\tmp\b
      \y\tmp
      \x\a
      \advance\x\xx
      \advance\x-\yy
    \fi
  \fi
  \checkNext
}
\makeatother

\begin{document}
\thispagestyle{empty}\noindent
\leavevmode\baselineskip=\mandelunit
\a=-1.5pt\relax
\b=1.0pt\relax
\loopMandel
\end{document}