movement.pl

use strict;
use warnings;
use SDL;
use SDLx::App;
use SDLx::Rect;
use SDL::Events;
use SDL::Event;


my $app=SDLx::App->new(w=>800,h=>600,title=>"Movement!",d=>32,exit_on_quit=>1);

#The rectangle that we'll be moving around.
my $rect=SDLx::Rect->new(200,200,40,40);

#x and y velocities.
#For simplicity's sake, we'll have zero acceleration.
my $v_x=0;
my $v_y=0;

#Basic rendering handler.
$app->add_show_handler(sub{
    $app->draw_rect([0,0,$app->width,$app->height],[0,0,0,255]);
    $app->draw_rect($rect,[0,0,255,255]);
    $app->update;
    }
);


$app->add_event_handler(sub{
    my ($event,$app)=@_;

    #Set velocity equal to plus or minus 2 depending on ASWD direction.
    if($event->type == SDL_KEYDOWN)
    {
        my $key= lc(SDL::Events::get_key_name($event->key_sym));

        if($key eq 'a')
        {
            $v_x=-2;
        }
        elsif($key eq 'd')
        {
            $v_x=2;
        }
        elsif($key eq 'w')
        {
            $v_y=2;
        }
        elsif($key eq 's')
        {
            $v_y=-2;
        }
    }
    elsif($event->type == SDL_KEYUP) #Reset velocity if key is released.
    {
        my $key= lc(SDL::Events::get_key_name($event->key_sym));
        if($key eq 'a' or $key eq 'd')
        {
            $v_x=0;
        }
        elsif($key eq 'w' or $key eq 's')
        {
            $v_y=0;
        }
    }
});

#Quit when "q" is pressed.
$app->add_event_handler(sub{
    my $event=shift;
    if($event->type == SDL_KEYDOWN)
    {
        if(lc(SDL::Events::get_key_name($event->key_sym)) eq 'q')
        {
            $app->stop;
        }
    }
});


$app->add_move_handler(\&move);

sub move
{
    my ($step,$app,$t)=@_;
    return unless $step;

    #Gather x and y coordinates of rectangle.
    my $x=$rect->x;
    my $y=$rect->y;

    #Adjust positions accordingly.
    $x+=$v_x * $step;
    $y-=$v_y * $step;

    #Set new coordinates.
    $rect->x($x);
    $rect->y($y);

    #Debugging, to figure out WTF is going on.
    #print "$v_x,$v_y,$t\n";
}

$app->run();