use strict;
use warnings;
use Font::TTFMetrics;

my $pointsize  = 16;
my $resolution = 72;

my $metrics = Font::TTFMetrics-> new( "Arial.ttf" );
my $c = $pointsize * $resolution / 72 / $metrics-> get_units_per_em;

my $str = "\x{0628}\x{0644}\x{062D}\x{0629}";

printf "Wrong answer: %.0f\n", $metrics-> string_width( $str ) * $c;
printf "Right answer: %.0f\n", $metrics-> string_width( render_arabic( $str )) * $c;

sub render_arabic {
    my $word = shift;
    
    return $word if length $word == 1;  # isolated
    
    my %LUT = ( 
        "\x{0628}" => [ "\x{FE90}", "\x{FE92}", "\x{FE91}" ],
        "\x{0644}" => [ "\x{FEDE}", "\x{FEE0}", "\x{FEDF}" ],
        "\x{062D}" => [ "\x{FEA2}", "\x{FEA4}", "\x{FEA3}" ],
        "\x{0629}" => [ "\x{FE94}" ],
    );
    
    $word =~ s/^.          /$LUT{ $& }[ 2 ]/x;
    $word =~ s/(?<=.).(?=.)/$LUT{ $& }[ 1 ]/xg;
    $word =~ s/          .$/$LUT{ $& }[ 0 ]/x;
    
    return $word
}