use List::Util qw(min max);
sub x1{0} sub y1{1} sub x2{2} sub y2{3}

sub rect_overlap_1 {
    my($r1,$r2) = @_;
    return max($$r1[x1],$$r2[x1]) <= min($$r1[x2],$$r2[x2])
        && max($$r1[y1],$$r2[y1]) <= min($$r1[y2],$$r2[y2]);
}

# some tests:
use Test::Simple 'no_plan';
ok  rect_overlap_1 [10, 10, 30, 30], [20, 20, 40, 60];  # do
ok !rect_overlap_1 [10, 10, 30, 30], [20, 40, 40, 60];  # don't
ok  rect_overlap_1 [10, 10, 30, 30], [15, 15, 20, 20];  # inside
ok  rect_overlap_1 [10, 10, 30, 30], [40, 20, 20, 60];  # do

sub rect_overlap_2 {
    my($r1,$r2) = @_;
    return max(min(@$r1[x1,x2]),min(@$r2[x1,x2]))
        <= min(max(@$r1[x1,x2]),max(@$r2[x1,x2]))
        && max(min(@$r1[y1,y2]),min(@$r2[y1,y2]))
        <= min(max(@$r1[y1,y2]),max(@$r2[y1,y2]));
}

ok  rect_overlap_2 [10, 10, 30, 30], [20, 20, 40, 60];  # do
ok !rect_overlap_2 [10, 10, 30, 30], [20, 40, 40, 60];  # don't
ok  rect_overlap_2 [10, 10, 30, 30], [15, 15, 20, 20];  # inside
ok  rect_overlap_2 [10, 10, 30, 30], [40, 20, 20, 60];  # do

sub rect_overlap_3 {
    my($r1,$r2) = @_;
    return max(map{min(@$_[x1,x2])}($r1,$r2))
        <= min(map{max(@$_[x1,x2])}($r1,$r2))
        && max(map{min(@$_[y1,y2])}($r1,$r2))
        <= min(map{max(@$_[y1,y2])}($r1,$r2));
}

ok  rect_overlap_3 [10, 10, 30, 30], [20, 20, 40, 60];  # do
ok !rect_overlap_3 [10, 10, 30, 30], [20, 40, 40, 60];  # don't
ok  rect_overlap_3 [10, 10, 30, 30], [15, 15, 20, 20];  # inside
ok  rect_overlap_3 [10, 10, 30, 30], [40, 20, 20, 60];  # do

sub rect_overlap {
    return max(map{min(@$_[x1,x2])}@_) <= min(map{max(@$_[x1,x2])}@_)
        && max(map{min(@$_[y1,y2])}@_) <= min(map{max(@$_[y1,y2])}@_);
}

ok  rect_overlap [10, 10, 30, 30], [20, 20, 40, 60];  # do
ok !rect_overlap [10, 10, 30, 30], [20, 40, 40, 60];  # don't
ok  rect_overlap [10, 10, 30, 30], [15, 15, 20, 20];  # inside
ok  rect_overlap [10, 10, 30, 30], [40, 20, 20, 60];  # do
ok  rect_overlap [10, 10, 30, 30], [15, 15, 20, 20], [20, 20, 40, 60];  # (20,20)