Here is an OO-way (perhaps more readable):

#!/usr/bin/perl
use strict;
use warnings;
#=====================================================================
+=====
{package point;

  sub new {return bless {x=>$_[1], y=>$_[2]}, __PACKAGE__;}
  sub Print {
     my ($self) = @_;
     return "(" . $self->{x} . "," . $self->{y} . ")";
  }

1;
}
#=====================================================================
+=====
{package rect;

    sub new {
       # Takes 2 'point's 
       return bless {p1=>$_[1], p2=>$_[2]}, __PACKAGE__;
    }

1;
}
#=====================================================================
+=====

my @rect_x = (3,2,4,0,3,0,4,0,3,2,0,4);
my @rect_y = (0,0,0,1,1,0,3,3,3,3,2,2);
my @rectangles;
# Create the 'rect' objects, and collect in @rectangles
for my $idx(0..$#rect_x){
  push @rectangles, rect::->new(point::->new($rect_x[$idx], $rect_y[$i
+dx]), undef);
}

@rectangles = sort {
                        $b->{p1}{x} <=> $a->{p1}{x} ||
                        $a->{p1}{y} <=> $b->{p1}{y}
                   } @rectangles;

for (0..$#rectangles){
    my $r = $rectangles[$_];
    print "Rectangle ", ($_+1) , " -> ",
      $r->{p1}->Print(), "\n";
}
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