\ shows crosshair on the canvas
begin
  while 1=1 do
    begin
      call wait(10);
      call cvclear;
      if cvx>-1 then
        begin
          call cvline(cvx,0,cvx,300);
          call cvline(0,cvy,500,cvy);
          call cvline(0,0,cvx,cvy);
          call cvline(0,300,cvx,cvy);
          call cvline(500,0,cvx,cvy);
          call cvline(500,300,cvx,cvy);
          call cvball(cvx,cvy,20);
        end
    end
end.