The 'fvar' table

General table information

Apple Advanced Typography variations allow the font designer to build high quality styles into the typeface itself. This reduces the dependence on algorithmic styling in the graphics system. To include variations in your font, you must include the font variations table. If you are building a TrueType font, you will also need a glyph variations table.

The font variations table (tag name: 'fvar') defines the global information concerning which variation axes are included in your font and any named coordinates in the variation space, called instances. An instance provides the application with a short list of "pre-chosen" coordinates to offer the user.

The next figure shows a capital 'Q' glyph drawn at various points along the 'wght' axis. Since the minimum and maximum values have been defined as +0.7 and +1.3, respectively, the specification of a style coordinate of 1.0 refers to the style of the center 'Q.'

Multiple axes can be combined. For example, you may want to create a 'wght' axis and a 'wdth' axis. The user can then select any combination of weight and width, such as 75% bold and 50% condensed. The next figure shows an example of a two-axis font variation in which the weight axis has a minimum value of 1.0 and maximum of 1.5 and the width axis has a minimum of 0.6 and a maximum of 1.0.

Variation Axis Tags

A set of "standard" axis tags has been defined by Apple. Other tags may be defined, but should be registered with Apple DTS (Developer Technical Support).

Tag
Name
Default
Description
'wght' Weight 1.0 Used for making a font range from light to black.
'wdth' Width 1.0 Used for fonts ranging from narrow to wide.
'slnt' Slant 0.0 Specifies the angle (in degrees) of italic slant.
'opsz' Optical Size 12.0 Specifies the optical point size.

All real numbers like 1.0 and 12.0 are actually stored as 16.16 fixed point numbers, so 1.0 is really 0x10000 and 12.0 is really 0xC0000.

Font Variations Table Format

The font variations table consists of a font variations table header, followed by the list of variations axis records, followed by the list of instance records. The overall structure of this table is shown in the following figure:

The format of the font variations table header is shown in the following table:

Type
Name
Description
fixed version Set to 1.0 (0x10000).
uint16 offsetToData Offset in bytes from the beginning of the table to the beginning of the first axis data.
uint16 countSizePairs Axis + instance = 2.
uint16 axisCount The number of style axes in this font.
uint16 axisSize The number of bytes in each gxFontVariationAxis record. Set to 20 bytes.
uint16 instanceCount The number of named instances for the font found in the sfntInstance array.
uint16 instanceSize The number of bytes in each gxFontInstance array. InstanceSize = axisCount * sizeof(gxShortFrac).
sfntVariationAxis axis[axisCount] The font variation axis array.
sfntInstance instance[instanceCount] The instance array.

Note: The countSizePairs is currently 2 to indicate two count-size pairs follow: the axis count-size pair, and the offset count-size pair. Future versions of the "fvar" table may increase this number.

The format for the sfntVariationAxis array is as follows:

Type
Name
Description
uint32 axisTag Axis name.
fixed32 minValue The minimum style coordinate for the axis.
fixed32 defaultValue The default style coordinate for the axis.
fixed32 maxValue The maximum style coordinate for the axis.
uint16 flags Set to zero.
uint16 nameID The designation in the 'name' table.

Each axis contains a tag with a registered name. Each axis is defined by its minimum value and maximum value. This is the dynamic range of the axis. A default value is also defined. The nameID specifies the name to be used in application style menus and font pickers. The nameID must be greater than 255 and less than 32768.

The sfntInstance array is a list of named coordinates. For example, it may be desirable to define and name specific coordinates for bold, demi, condense, demi condense, radical, or other appropriate styles.

The format of the sfntInstance array is shown in the following table:

Type
Name
Description
uint16 nameID The name of the defined instance coordinate. Similar to the nameID in the variation axis record, this identifies a name in the font's 'name' table.
uint16 flags Set to zero.
fixed32 coord[axisCount] This is the coordinate of the defined instance.

Font Variations Table Example

This example font has two variation axes. This table summarizes the font variation data to be included for this font:

Axis Tag
Min Value
Default Value
Maximum Value
NameID
'wght' 0.5 1.0 2.0 256
'wdth' 0.5 1.0 2.0 257

The font variation table for this example font is given in the following table. The flags for both axes are 0.

Offset/
length
Value
Name
Comment
0/4 0x00010000 version Version number of the font variation table, in fixed-point format.
4/2 20 offsetToData Offset from the beginning of the table to the beginning of the first axis data is 20 bytes.
6/2 2 countSizePairs Set to 2.
8/2 2 axisCount There are two axes in this font variation.
10/2 20 axisSize Each gxFontVariation axis description requires 20 bytes.
12/2 3 instanceCount There are three named instances.
14/2 12 instanceSize Each sfntInstance requires 12 bytes.
(The first sfntVariationAxis follows)
16/4 0x77676874 axisTag The axis tag in ASCII is 'wght'.
20/4 0x00008000 minValue The minimum coordinate value defined for this axis is 0.5.
24/4 0x00010000 defaultValue The default instance coordinate value defined for this axis is 1.0.
28/4 0x00020000 maxValue The maximum value defined for this axis is 2.0.
32/2 0x0000 flag No flag is set.
34/2 256 nameID The nameID value in the name table.
(The second sfntVariationAxis follows)
36/4 0x77647468 axisTag The axis tag in ASCII is 'wdth'.
40/4 0x00008000 minValue The minimum coordinate value defined for this axis is 0.5.
44/4 0x00010000 defaultValue The default instance coordinate value defined for this axis is 1.0.
48/4 0x00020000 maxValue The maximum value defined for this axis is 2.0.
52/2 0x0000 flag No flag is set.
54/2 257 nameID The nameID designation in the name table.
(The sfntInstance array follows)
56/2 258 nameID[1] The nameID designation in the name table for the first instance.
58/2 0 flags Set to zero.
60/4 0x00008000 coordinate[1] Coordinate of the first instance along the first axis.
64/4 0x00010000 coordinate[1] Coordinate of the first instance along the second axis.
68/2 259 nameID[2] The nameID designation in the name table for the second instance.
70/2 0 flags Set to zero.
72/4 0x00020000 coordinate[2] Coordinate of the second instance along the first axis.
76/4 0x00018000 coordinate[2] Coordinate of the second instance along the second axis.
80/2 260 nameID[3] The nameID designation in the name table for the first instance.
82/2 0 flags Set to zero.
84/4 0x00020000 coordinate[3] Coordinate of the third instance along the first axis.
88/4 0x00008000 coordinate[3] Coordinate of the third instance along the second axis.

Mac OS-specific information

The 'fvar' table is supported on Mac OS only via QuickDraw GX or ATSUI. Applications which do not take advantage of these technologies directly or indirectly may not use style variations within fonts.

Newton-specific information

The 'fvar' table is not supported on the Newton OS.

Dependencies

The 'fvar' table should have the same number of axes as the 'gvar' table. The name references should correspond do the correct entries in the 'name' table.

Tools

The only tool currently supported for editing 'fvar' tables is ftxdumperfuser. Note that ftxdumperfuser does not have a specific XML format for 'fvar' tables; you must use the generic table format.


Change Log

12 December 2002
Corrected the explanation of the instanceCount field.
18 November 1999
Removed reference to QuickDraw GX.
30 September 1996
Switched to use the <TABLE> tag.
3 May 1995
Introduction and Variation Axis Tags sections rewritten.
29 April 1995
Initial conversion to HTML format.
applefonts@apple.com

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Last updated: JHJ