\documentclass{standalone}

\usepackage{tikz}
\begin{document}


 
 
 \begin{tikzpicture}[xscale=1,yscale=1]
\draw[clip] (0,0)--(pi, 0)--(pi,pi)--(0,0);
    \draw [blue] plot[id=curve, raw gnuplot] function{
  f(x,y) = sin (8*x)* sin (3*y)- sin (8*y)* sin (3*x)+
  -sin (7*x)* sin (4*y)+sin (7*y)* sin (4*x);
    set xrange [0:pi];
      set yrange [0:pi];
      set view 0,0;
      set isosample 3000,3000;
      %set size square;
      set cont base;
      set cntrparam levels incre 0,0.1,0;
      unset surface;
      splot f(x,y)
    };
    
    
     
       \end{tikzpicture}

\end{document}
