light_source(0,0,10);
my $r = 0.6;
my $sphere = sphere(1)->translate(-$r,-$r,0);
animate {
    $dx = -0.03 + 0.08*rand();
    $dy = -0.03 + 0.08*rand();
    $sphere->translate($dx,$dy,0);
    return ($sphere->center->@*)[0] < 0.6;
};