Hi, i have put together a working version of the pong game, where two paddles play the ball to each other, using the SDL module. I have found this code in a manual and everything seems fine. There is just one problem: the paddles, that move only vertically, are faster moving up then moving downwards, while they are given the same speed. This is where it happens:

 $app->add_event_handler(sub {
        my $event= shift;
        if($event->type == SDL_KEYDOWN){
            if($event-> key_sym == SDLK_UP){
                $player1->{v_y} = -2;
            }        
            elsif($event->key_sym == SDLK_DOWN){                      
+                      
                $player1->{v_y} = 2;
            }
        }
        elsif($event->type == SDL_KEYUP){
            if($event->key_sym == SDLK_DOWN  || $event->key_sym == SDL
+K_UP){
            $player1->{v_y} = 0;
            }
        }
});
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This code looks alright to me. I have added the entire code so you can see for yourself, it's slower when moving down. I hate to solve this problem with given different speeds. Hope you can help.

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

my $app = SDLx::App->new(w =>500,h=>500,t=>"Pong",exit_on_quit=>1,dt=>
+0.02);
my $player1={paddle=>SDLx::Rect->new(10,$app->h/2,10,40),v_y=>0,score=
+>0};
my $player2={paddle=>SDLx::Rect->new($app->w-20,$app->h/2,10,40),v_y=>
+0,score=>0};
my $ball = {rect => SDLx::Rect->new($app->w / 2, $app->h / 2, 10, 10),
+v_x=>-3,v_y=>1.5}; 
my $score = SDLx::Text->new(x=>240);

$app->add_show_handler(sub{
    $app->draw_rect([0,0,$app->w,$app->h],[0,0,0,0]);
    $app->draw_rect($ball->{rect},[255,0,0,0]);
    $app->draw_rect($player1->{paddle},[255,0,0,0]);
    $app->draw_rect($player2->{paddle},[255,0,0,0]);
    $score->write_to($app,$player1->{score}.'x'.$player2->{score});
    $app->update;
});

$app->add_move_handler(sub {
    my $step = shift;
    my $paddle = $player1->{paddle};
    my $v_y = $player1->{v_y};
    $paddle->y($paddle->y + ($step * $v_y));
    if($paddle->y >= $app->h){
        $paddle->y(0);
    }
    elsif($paddle->y + 40 <= 0){
        $paddle->y(500);
    }        
});

$app->add_move_handler(sub {
    my $step = shift;
    my $paddle = $player2->{paddle};
    my $v_y = $player2->{v_y};
    if($ball->{rect}->y > $paddle->y){
        $v_y = 2;
    }
    elsif($ball->{rect}->y < $paddle->y){
        $v_y = -2;
    }
    else{
        $v_y = 0;
    }
    $paddle->y($paddle->y + ($step * $v_y));
});

$app->add_move_handler(sub{
     my $step = shift;
     my $ball_rect = $ball->{rect};
     $ball_rect->x( $ball_rect->x + ($ball->{v_x} * $step) );
     $ball_rect->y( $ball_rect->y + ($ball->{v_y} * $step) ); 
     if($ball_rect->bottom >= $app->h){
        $ball_rect->bottom($app->h);
        $ball->{v_y}*=-1;
     }
     elsif($ball_rect->top<=0){
        $ball_rect->top(0);
        $ball->{v_y}*=-1;
     }
     elsif($ball_rect->right>=$app->w){
        $player1->{score}++;
        reset_game();
        return
        }    
     elsif($ball_rect->left<=0){
        $player2->{score}++;
        reset_game();
        return;
     }
     elsif(check_collision($ball_rect,$player1->{paddle})){
        $ball_rect->left($player1->{paddle}->right);
        $ball->{v_x} *= -1;
     }
     elsif(check_collision($ball_rect,$player2->{paddle})){
        $ball_rect->right($player2->{paddle}->left);
        $ball->{v_x} *= -1;
     }
});    

$app->add_event_handler(sub {
        my $event= shift;
        if($event->type == SDL_KEYDOWN){
            if($event-> key_sym == SDLK_UP){
                $player1->{v_y} = -2;
            }        
            elsif($event->key_sym == SDLK_DOWN){                      
+                      
                $player1->{v_y} = 2;
            }
        }
        elsif($event->type == SDL_KEYUP){
            if($event->key_sym == SDLK_DOWN  || $event->key_sym == SDL
+K_UP){
            $player1->{v_y} = 0;
            }
        }
});
    
$app->run;


sub check_collision{
    my($A,$B) = @_;
    return if $A->bottom < $B->top;
    return if $A->top > $B->bottom;
    return if $A->right < $B->left;
    return if $A->left > $B->right;
    return 1;
}

sub reset_game{
    $player1->{paddle}->y($app->h/2);
    $player2->{paddle}->y($app->h/2);
    $ball->{rect}->x($app->w/2);
    $ball->{rect}->y($app->h/2);
    $ball->{v_x} = (4 + rand(2)) * (rand (2) > 1 ? 1 : -1);
    $ball->{v_y} = (1.5 + rand(1)) * (rand (2) > 1 ? 1 : -1);        
}
[download]