post — PostScript Table (OpenType 1.8)
This table contains additional information needed to use TrueType or OpenType™ fonts on PostScript printers. This includes data for the FontInfo dictionary entry and the PostScript names of all the glyphs. For more information about PostScript names, see the Adobe document Unicode and Glyph Names.
Versions 1.0, 2.0, and 2.5 refer to TrueType fonts and OpenType fonts with TrueType data. OpenType fonts with TrueType data may also use Version 3.0. OpenType fonts with CFF data use Version 3.0 only.
Header
The table begins as follows:
| Type | Name | Description |
|---|---|---|
| Fixed | Version | 0x00010000 for version 1.0 0x00020000 for version 2.0 0x00025000 for version 2.5 (deprecated) 0x00030000 for version 3.0 |
| Fixed | italicAngle | Italic angle in counter-clockwise degrees from the vertical. Zero for upright text, negative for text that leans to the right (forward). |
| FWord | underlinePosition | This is the suggested distance of the top of the underline from the baseline (negative values indicate below baseline). The PostScript definition of this FontInfo dictionary key (the y coordinate of the center of the stroke) is not used for historical reasons. The value of the PostScript key may be calculated by subtracting half the underlineThickness from the value of this field. |
| FWord | underlineThickness | Suggested values for the underline thickness. |
| ULONG | isFixedPitch | Set to 0 if the font is proportionally spaced, non-zero if the font is not proportionally spaced (i.e. monospaced). |
| ULONG | minMemType42 | Minimum memory usage when an OpenType font is downloaded. |
| ULONG | maxMemType42 | Maximum memory usage when an OpenType font is downloaded. |
| ULONG | minMemType1 | Minimum memory usage when an OpenType font is downloaded as a Type 1 font. |
| ULONG | maxMemType1 | Maximum memory usage when an OpenType font is downloaded as a Type 1 font. |
The last four entries in the table are present because PostScript drivers can do better memory management if the virtual memory (VM) requirements of a downloadable OpenType font are known before the font is downloaded. This information should be supplied if known. If it is not known, set the value to zero. The driver will still work but will be less efficient.
Maximum memory usage is minimum memory usage plus maximum runtime memory use. Maximum runtime memory use depends on the maximum band size of any bitmap potentially rasterized by the font scaler. Runtime memory usage could be calculated by rendering characters at different point sizes and comparing memory use.
If the version is 1.0 or 3.0, the table ends here. The additional entries for versions 2.0 and 2.5 are shown below. Apple has defined a version 4.0 for use with Apple Advanced Typography (AAT), which is described in their documentation.
Version 1.0
This version is used in order to supply PostScript glyph names when the font file contains exactly the 258 glyphs in the standard Macintosh TrueType font file (see 'post' Format 1 in Apple’s specification for a list of the 258 Macintosh glyph names), and the font does not otherwise supply glyph names. As a result, the glyph names are taken from the system with no storage required by the font.
Version 2.0
This is the version required in order to supply PostScript glyph names for fonts which do not supply them elsewhere. A version 2.0 'post' table can be used in fonts with TrueType or CFF version 2 outlines.
| Type | Name | Description |
|---|---|---|
| USHORT | numberOfGlyphs | Number of glyphs (this should be the same as numGlyphs in 'maxp' table). |
| USHORT | glyphNameIndex[numGlyphs]. | This is not an offset, but is the ordinal number of the glyph in 'post' string tables. |
| CHAR | names[numberNewGlyphs] | Glyph names with length bytes [variable] (a Pascal string). |
This font file contains glyphs not in the standard Macintosh set, or the ordering of the glyphs in the font file differs from the standard Macintosh set. The glyph name array maps the glyphs in this font to name index. If the name index is between 0 and 257, treat the name index as a glyph index in the Macintosh standard order. If the name index is between 258 and 65535, then subtract 258 and use that to index into the list of Pascal strings at the end of the table. Thus a given font may map some of its glyphs to the standard glyph names, and some to its own names.
If you do not want to associate a PostScript name with a particular glyph, use index number 0 which points to the name .notdef.
Version 2.5
This version of the 'post' table has been deprecated as of OpenType Specification v1.3.
This version provides a space-saving table for TrueType-based fonts which contain a pure subset of, or a simple reordering of, the standard Macintosh glyph set.
| Type | Name | Description |
|---|---|---|
| USHORT | numberOfGlyphs | Number of glyphs |
| CHAR | offset[numGlyphs] | Difference between graphic index and standard order of glyph |
This version is useful for TrueType-based font files that contain only glyphs in the standard Macintosh glyph set but which have those glyphs arranged in a non-standard order or which are missing some glyphs. The table contains one byte for each glyph in the font file. The byte is treated as a signed offset that maps the glyph index used in this font into the standard glyph index. In other words, assuming that the font contains the three glyphs A, B, and C which are the 37th, 38th, and 39th glyphs in the standard ordering, the 'post' table would contain the bytes +36, +36, +36. This format has been deprecated by Apple, as of February 2000.
Version 3.0
The version makes it possible to create a font that is not burdened with a large 'post' table set of glyph names. A version 3.0 'post' table can be used by OpenType fonts with TrueType or CFF (version 1 or 2) data.
This version specifies that no PostScript name information is provided for the glyphs in this font file. The printing behavior of this version on PostScript printers is unspecified, except that it should not result in a fatal or unrecoverable error. Some drivers may print nothing; other drivers may attempt to print using a default naming scheme.
Windows makes use of the italic angle value in the 'post' table but does not actually require any glyph names to be stored as Pascal strings.
'post' Table and OpenType Font Variations
In a variable font, various font-metric values within the 'post' table may need to be adjusted for different variation instances. Variation data for 'post' entries can be provided in the metrics variations ('MVAR') table. Different 'post' entries are associated with particular variation data in the 'MVAR' table using value tags, as follows:
| 'post' entry | Tag |
|---|---|
| underlinePosition | 'undo' |
| underlineThickness | 'unds' |
Note: The italicAngle value is not adjusted by variation data since this corresponds to the 'slnt' variation axis that can be used to define a font’s variation space. Appropriate post.italicAngle values for a variation instance can be derived from the 'slnt' user coordinates that are used to select a particular variation instance. See the discussion of the 'slnt' axis in the Variation Axis Tags section of the 'fvar' table chapter for details on the relationship between italicAngle and the 'slnt' axis.
For general information on OpenType Font Variations, see the chapter, OpenType Font Variations Overview.