has glut => sub {
    my $self = shift;
    my $system = $self->load_system('GLUT');
    $self->opengl->on(render => sub { $system->swap_buffers });
    return $system;
};

has opengl => sub {
    my $self = shift;
    my $system = $self->load_system('OpenGL');
    $self->glut->on(resize=> sub { shift; $system->resize(@_) });
    return $self;
};