///withoutPrompt 
function play(T,X,XI)
  scf(1);clf();h=gcf();
  h.pixmap = "on";
  h.figure_size = [1400 600];
  h.children.axes_visible=['off','off','off'] ;
  h.children.isoview='on';
  h.children.tight_limits = "on"
  h.children.margins = [0,0,0,0];
  
  XXX=[-XI-l2:0.2:3*XI+l2];
  FY=[];XC=[];
  for x=XXX,
    th=atan(Fx(x));
    XC=[XC,x+sin(th)*r2]
    FY=[FY,F(x)-cos(th)*r2];
  end
  h.children.data_bounds=[min(XC),min(FY);max(XC),max(FY)+d];
  
  xfpoly([XC(1),XC,XC($)],[min(FY)-d,FY,min(FY)-d]); hfp = gce();
  hfp.foreground = 5;
  drawlater()
  
  h.pixel_drawing_mode='xor'
  
  l3=1.15*l2; // car body length (half) for animation
  realtimeinit(1); // intialize real time operation
  for i=1:size(T,'*')
    t=T(i);
    X=XX(:,i);
    x=X(1);xd=X(2);y=X(3);yd=X(4);th=X(5);thd=X(6);xsi=X(7);eta=X(8);
    x0=x+xsi*sin(th)-l2*cos(th);
    x1=x+eta*sin(th)+l2*cos(th);
    y0=y-xsi*cos(th)-l2*sin(th);
    y1=y-eta*cos(th)+l2*sin(th);
    xp=[x0,x-l2*cos(th);x+l2*cos(th),x1]';
    yp=[y0,y-l2*sin(th);y+l2*sin(th),y1]';
    xpp=[x-l3*cos(th);x+l3*cos(th)];
    ypp=[y-l3*sin(th);y+l3*sin(th)];
    W1=[x0-r2,y0+r2,2*r2,2*r2,0,360*64];
    W2=[x1-r2,y1+r2,2*r2,2*r2,0,360*64];
    
    if i==1 then
      xpoly(xpp,ypp); hp1 = gce();
      hp1.thickness=10;
      xpolys(xp,yp); hp2 = gce();hp21=hp2.children(1);hp22=hp2.children(2)
      xfarcs([W1',W2']); ha = gce();ha1=ha.children(1);ha2=ha.children(2)
      realtime(t);
      draw([hp1,hp2,ha])//draw car
    else
      draw([hp1,hp2,ha])//erase car
      hp1.data=[xpp,ypp];
      hp21.data=[xp(:,1),yp(:,1)];
      hp22.data=[xp(:,2),yp(:,2)];
      ha1.data=W1;
      ha2.data=W2;
      realtime(t);  
      draw([hp1,hp2,ha])//draw car
    end
    show_pixmap()
  end
  h.pixel_drawing_mode='copy'
  drawnow() 
  show_pixmap()
endfunction ///\withPrompt{}