% --- start of displayed preamble in the book ---

% --- start of displayed preamble in the book ---
vardef star(expr n) =
for i_:=0 upto 2n-1:
if odd i_: 1/2 fi (right rotated (180*(i_/n))) --
endfor cycle
enddef;

vardef blur(expr p,w,col)=
for i:=10 downto 1:
pickup pencircle scaled ((i*i/100)*w);
draw p withcolor ((i/10)[col,white]);
endfor;
enddef;

% --- end of displayed preamble in the book ---
defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
blur (unitsquare scaled 3cm,.5mm,red);
blur (fullcircle scaled 4cm,1mm,blue);
blur (star(10) xscaled 30mm yscaled 20mm
rotated 20,2mm,black);
endfig;
end;