600 setwidth
400 setheight

-7 8 setxrange
-5 5 setyrange

%% la source d'eclairage
/src {-3 -3 7} def
/kp 8 def

/f {
   /y exch def
   /x exch def
   3 x mul 
   2 y mul add
   1 add
   x dup mul y dup mul add neg Exp 1.8 mul
   mul
} def

/vect_J {.7 .4} def
/vect_I {1 0} def
/vect_K {0 1} def

%% syntaxe : nx ny (f) src_pt [color] kp x_min x_max y_min y_max surfz
100 100 (f) src [1 .65 0] kp -4 4 2 copy surfz