Other varieites of sfnt-housed font may not have them. The "required" tables listed in Table 2 are only required for TrueType fonts. Informally, people often refer to any sfnt-housed font as a "TrueType font," but this is strictly speaking inaccurate. This is an important distinction, because Apple supports other varieties of sfnt-housed font on OS X and iOS, most notably bitmap-only fonts and OpenType fonts. The required tables and their tag names are shown in Table 2.Īpple makes a distinction between a "TrueType font" (which refers to a particular font outline definition technology) and an "sfnt-housed font," which refers to any font which uses the same packaging format as a TrueType font: that is, it uses the same directory structure and the same table format and meaning for any tables present. Tables that are required must appear in any valid TrueType font file. When tag names are shown in text they are enclosed in straight quotes. Tag names with less than four characters have trailing spaces. Currently defined tag names consist of four characters. Others are optional depending upon the functionality expected of a particular font. Certain tables are required for all fonts. The directory is followed by a sequence of tables containing the font data. The first of the tables is the font directory, a special table that facilitates access to the other tables in the font. Each table must be long aligned and padded with zeroes if necessary. TrueType Font files: an overviewĪ TrueType font file consists of a sequence of concatenated tables. This means it can represent numbers between 1.999 (0x7fff) and -2.0 (0x8000). NOTE: A shortFrac is an int16_t with a bias of 14. It is represented as a signed 64-bit integer. The long internal format of a date in seconds since 12:00 midnight, January 1, 1904. Table 1 : The 'sfnt' data types Data typeġ6-bit signed integer that describes a quantity in FUnits, the smallest measurable distance in em space.ġ6-bit unsigned integer that describes a quantity in FUnits, the smallest measurable distance in em space.ġ6-bit signed fixed number with the low 14 bits representing fraction. In addition to standard integer data types, the TrueType font format uses the following: For convenience in accessing the information presented in this chapter, tables are described in alphabetical order. With the exception of the font directory which must appear first in the font file, the tables that make up a font can appear in any order. Table 1 describes the data types used in TrueType font files on all platforms. This chapter documents the tables that make up a TrueType font file, including AAT extensions to the core TrueType specification.ĝocumentation is not included for OpenType-specific tables, even those supported on OS X and iOS.ğor further information on those tables, see the OpenType specification.
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