Font

OpenType

OpenType is the specification behind every container the package reads: the sfnt structure, the table set, layout features, and variations. In file names, .otf usually means an OpenType font with CFF or CFF2 outlines, whose signature is OTTO. Those outlines are not supported, and loading such a file raises UnsupportedFontException:

<?php

use Alto\Font\Exception\UnsupportedFontException;
use Alto\Font\Font;

try {
    $font = Font::fromFile(__DIR__.'/fonts/SourceSerif-Regular.otf');
} catch (UnsupportedFontException $error) {
    echo $error->getMessage(); // CFF/OpenType outlines are not supported.
}

Which .otf files work

Only the outlines matter. A font sold as .otf but built with TrueType glyf outlines has the 0x00010000 signature, loads normally, and is reported as FontFormat::TrueType. FontFormat::fromPath() maps .otf to FontFormat::OpenType because that is the usual case, but loading trusts the signature.

Everything else in the OpenType specification applies equally to both outline flavors and is supported where documented: the required tables, GSUB, GPOS, GDEF, kern, and the variation tables. See Tables.

Writing and subsetting

The package never produces CFF outlines. Writing and subsetting start from a loaded glyf font and produce glyf output; see TrueType.

Requirements and limits

  • An OTTO signature raises UnsupportedFontException on load.
  • A 0x00010000 signature with an .otf extension loads as TrueType.
  • In an OTC collection with CFF faces, the selected face fails with UnsupportedFontException.
  • Converting CFF to TrueType is not available; use a glyf build of the font.