What unit is “advanced” stored in for True Type fonts table “hmtx”?

问题

I am running a very simple script that I wrote to get the "advance" of True Type fonts. The font in specific is New Times Roman. This is the kind of values that I'm getting back,

{
   "A" : 1479
   "a" : 909,
   "B" : 1366,
   "b" : 1024
   "C" : 1366,
   "c" : 909,
   "N" : 1479,
   "n" : 1024,
   "M" : 1821,
   "m" : 1593,
   "." : 512,
}

I'm using the Perl library Font::TTF, you can find the manual here. And, here is my script,

use strict;
use warnings;
use autodie;
use Font::TTF::Font;

my $f = Font::TTF::Font->open('/usr/share/fonts/truetype/msttcorefonts/Times_New_Roman.ttf')
  || die $!;

my $json = JSON::XS->new->ascii->pretty->allow_nonref;

my @chars = ( '.', '-', 'a'...'z', 'A'...'Z', 0..9 );

my %db;
foreach my $char ( @chars ) {
  my $ord = ord($char);
  my $snum = $f->{'cmap'}->ms_lookup($ord);
  $f->{'hmtx'}->read;
  my $sadv = $f->{'hmtx'}{'advance'}[$snum];
  $db{$char} = $sadv;
}

use JSON::XS qw(encode_json);
print $json->encode( \%db );

回答1:

It's in "units-per-em" [1]. It is a grid of glyph design space with side of size defined in HEAD tag under "unitsPerEm". TrueType usually has it 2048, .otf with Postscript outlines 1000. So if you want to get anything useful, take the size of font, multiply by the advance and divide by unitsPerEm.

[1] http://en.wikipedia.org/wiki/Em_(typography)

来源：https://stackoverflow.com/questions/22904518/what-unit-is-advanced-stored-in-for-true-type-fonts-table-hmtx