UAV::Pilot v0.3 Released

2013-06-17

Version 0.3 of UAV::Pilot has been released on CPAN. The major change in this version is an improved event loop based on AnyEvent.

AnyEvent is a very nice framework overall, but unfortunately doesn’t have quite the right syntax for UAV::Pilot’s purposes. Consider this plain-English description of a UAV flight:

Takeoff, wait 5 seconds, then pitch forward for 2 seconds, then pitch backwards for 2 seconds, then land

In AnyEvent’s standard interface, things would work out something like this:

my $timer; $timer = AnyEvent->timer(
    after => 5,
    cb => sub {
        $uav->pitch( -1.0 );
        my $timer2; $timer2 = AnyEvent->timer(
            after => 2, 
            cb => sub {
                $uav->pitch( 1.0 );
                my $timer3; $timer3 = AnyEvent->timer(
                    after => 2,
                    cb => sub {
                        $uav->land;
                        $cv->send;
                    },
                );
                $timer2;
            },
        );
        $timer;
    },
);

$uav->takeoff;
$cv->recv;

All that indentation gets hairy. So I created an interface on top of AnyEvent, UAV::Pilot::EasyEvent, which is based on the Node.js event interface used by NodeCopter. Here’s how you’d write the same problem using EasyEvent:

my $cv = AnyEvent->condvar;
my $event = UAV::Pilot::EasyEvent->new({
    condvar => $cv,
});

$event
    ->add_timer(
        duration => 2000,
        duration_units => $event->UNITS_MILLISECOND,
        cb => sub { $uav->pitch( -1.0 ) },
    )->add_timer(
        duration => 2000,
        duration_units => $event->UNITS_MILLISECOND,
        cb => sub { $uav->pitch( 1.0 ) },
    )->add_timer(
        duration => 2000,
        duration_units => $event->UNITS_MILLISECOND,
        cb => sub { 
            $uav->land;
            $cv->send;
        },
    );

$event->activate_events;
$uav->takeoff;
$cv->recv;

Much better.

As an added bonus, having a good event interface means we can also support controlling UAVs through SDL joysticks. See bin/uav_joysticks in the distribution for details.