hilbert.p6

sub rot($n, int $x is rw, int $y is rw, $rx, $ry) {
    if $ry == 0 {
        if $rx == 1 {
            $x = $n - 1 - $x;
            $x = $n - 1 - $y;
        }

        my int $t = $x;
        $x = $y;
        $y = $t;
    }
}

sub d2xy($n, $d, int $x is rw, int $y is rw) {
    my $t = $d;
    $x = 0;
    $y = 0;
    for 1, 2, 4 ... $n -> int $s {
        my $rx = 1 +& ($t div 2);
        my $ry = 1 & ($t +^ $rx);
        rot($s, $x, $y, $rx, $ry);
        $x += $s * $rx;
        $y += $s * $ry;
        $t div= 4;
    }
}

sub frame($_, $t, $dt) {
    .rgb(1, 0.75, 0.1);
    my int $x;
    my int $y;
    for ^128 {
        d2xy(8, $_, $x, $y);
        .line_to($x, $y);
    }
    .stroke();
}