Repliconz - dev log 1, Enemies, Collision Detection

So what's changed since part 0?

Youtube linky, Repliconz gameplay so far

The green things chasing the Guy are instances of the Baddie class. Since Baddies are Things, many methods have been moved from Guy to Game::Repliconz::Thing which are common to Baddies, including move, constrain_velocity_xy and shoot. Bullets are also Things, so now technically bullets can shoot bullets, but we won't be doing that... yet. Anyone like the idea of cluster bullets?

The movement of baddies is somewhere between a bullet and the guy. A vector is calculated from current baddie position and guy position, so the baddies pursue the guy. Converting this to a unit vector using the bullet's Pythagoras square method would allow the baddies to travel in any arbitrary direction. This results in them converging rather quickly, giving the appearance of a single, super-strong enemy.

It turns out that constrain_velocity_xy, which was created to limit the guy's speed, can also be used to limit the baddies' movement to 45 degree angles. They eventually converge using this method too, but hopefully you'll have shot a good few of them by the time that happens. Anyway, now Game::Repliconz::Baddie::move is pretty simple:

sub move {
    my ( $self, $target_x, $target_y, $dt, $app ) = @_;

    my $v_y = $target_y - $self->{y};
    my $v_x = $target_x - $self->{x};

    ($v_x, $v_y) = $self->constrain_velocity_xy($v_x, $v_y);

    $self->{x} += $v_x * $self->{velocity} * $dt;
    $self->{y} += $v_y * $self->{velocity} * $dt;

    ($self->{x} > 0 || $self->{x} < ($app->w - $self->{w})) &&
    ($self->{y} > 0 || $self->{y} < ($app->h - $self->{h})) &&
    ($self->{on_screen} = 1);
}

The on_screen property will be used later in decisions about collision detection, since bullets continue off screen and enemies spawn there.

Baddies are pushed onto a queue in the main move callback, with more being spawned when the queue goes below a certain size.

Our collision detection is currently very simple, using Collision::Util to check overlapping rectangles. I need to check out how accurate this is, as the framerate / app delay will have an effect... a bullet might be rendered on either side of a target without ever "passing through" it. The video above appears to show some baddies being "hit", yet surviving.

The last change you might have noticed is the cursor is now a sprite, which is achieved simply by hiding the cursor and rendering a png file sprite at the mouse X/Y position.

As always, comments, criticism and contributions welcome.

Code for Repliconz is on Github.

Comments

fuzzix
Mon, 27 Jan 2014 00:19

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