As a first approximation you can loop over the characters, and add 0 for combining characters, 1 for "normal" one and 2 for characters in the Han script block. 
sub visual_length {
    my $s = shift;
    my $l = 0;
    while ($s =~ m/(.)/g){
        my $c = $1;
        if ($c =~ m/\p{M}){
            # do nothing
        } elsif ($c =~ m/\p{Han}) {
            $l += 2;
        } else {
            $l++;
        }
    }
    return $l;
}

[download]

That could use much more tweaking, but maybe it's a start for you.

In reply to Re: The “real length" of UTF8 strings by moritz
in thread The “real length" of UTF8 strings by Anonymous Monk

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