avar table

Maps axis coordinates to modified values, enabling non-linear interpolation for variable fonts.

Scope

• Format family: Shared SFNT
• Table tag in JSON: avar

Specs

• https://learn.microsoft.com/en-us/typography/opentype/spec/avar
• OpenType table registry: https://learn.microsoft.com/en-us/typography/opentype/spec/otff#font-tables

JSON Skeleton

This skeleton reflects fields currently parsed/written by Font Flux JS for this table.

{
  "tables": {
    "avar": {
      "majorVersion": 0,
      "minorVersion": 0,
      "reserved": 0,
      "segmentMaps": null,
      "_checksum": 0
    }
  }
}

Top-level Fields

• majorVersion - number (0..65535)
• minorVersion - number (0..65535)
• reserved - number (0..65535)
• segmentMaps - implementation-defined

Validation Constraints

• segmentMaps.length should match axis count from fvar.
• Each segment map should include monotonic axisValueMaps pairs from normalized fromCoordinate to toCoordinate values.
• Coordinates are F2DOT14 values in normalized axis space.
• reserved is typically 0.

Authoring Example

{
	"tables": {
		"avar": {
			"majorVersion": 1,
			"minorVersion": 0,
			"reserved": 0,
			"segmentMaps": [
				{
					"axisValueMaps": [
						{ "fromCoordinate": -1.0, "toCoordinate": -1.0 },
						{ "fromCoordinate": 0.0, "toCoordinate": 0.0 },
						{ "fromCoordinate": 1.0, "toCoordinate": 1.0 }
					]
				}
			],
			"_checksum": 0
		}
	}
}

Additional Nested Keys Seen In Implementation

• fromCoordinate
• toCoordinate

Notes

• Preserve _checksum for stable round-tripping.
• If a table is only partially understood, prefer keeping unknown bytes in _raw instead of dropping data.
• Validate with .validate() after edits.