% ---------------------------------------------------------------------------- %
%% \file illusion.tex
%% \author Sebastien Beaugrand
%% \sa http://beaugrand.chez.com/
%% \copyright CeCILL 2.1 Free Software license
% ---------------------------------------------------------------------------- %
\documentclass[a4paper]{article}
\usepackage{vmargin}
\setmarginsrb{2cm}{2cm}{2cm}{2cm}{0cm}{0cm}{0cm}{0cm}
\pagestyle{empty}
\usepackage{multido}
\usepackage{pstricks}

\begin{document}
\newrgbcolor{grey}{0.71 0.71 0.71}
\def\w{0.45}
\def\h{0.3}
\rput(8,-12.35){%
  \psframe[linestyle=none,fillstyle=solid,fillcolor=grey](-8.5,-8.5)(8.5,8.5)
  \SpecialCoor
  \degrees[360]
  \qdisk(0,0){0.7mm}
  \multido{\i=0+12}{30}{%
    \rput{\i}(5.00;\i){%
      \rput{ -56.31}(0,0){% 45+11.31 ou arctan(w/h)
        \psline[linecolor=white](0, \h)(\w,0)
        \psline[linecolor=black](-\w,0)(0,-\h)
        \psline[linecolor=white](-\w,0)(0, \h)
        \psline[linecolor=black](0,-\h)(\w,0)
      }
    }
  }
  \multido{\i=0+10}{36}{%
    \rput{\i}(6.25;\i){%
      \rput{-123.69}(0,0){% 90+45-11.31 ou 180-arctan(w/h)
        \psline[linecolor=white](0, \h)(\w,0)
        \psline[linecolor=black](-\w,0)(0,-\h)
        \psline[linecolor=white](-\w,0)(0, \h)
        \psline[linecolor=black](0,-\h)(\w,0)
      }
    }
  }
}
\end{document}