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GDEF table ​

Classifies glyphs (base, ligature, mark, component) and provides attachment and ligature caret data for layout.

Scope ​

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

Specs ​

JSON Skeleton ​

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

json
{
	"tables": {
		"GDEF": {
			"majorVersion": 0,
			"minorVersion": 0,
			"glyphClassDef": null,
			"attachList": null,
			"ligCaretList": null,
			"markAttachClassDef": null,
			"markGlyphSetsDef": null,
			"itemVariationStore": null,
			"_checksum": 0
		}
	}
}

Top-level Fields ​

  • majorVersion - number (0..65535)
  • minorVersion - number (0..65535)
  • glyphClassDef - implementation-defined
  • attachList - implementation-defined
  • ligCaretList - implementation-defined
  • markAttachClassDef - implementation-defined
  • markGlyphSetsDef - implementation-defined
  • itemVariationStore - structured ItemVariationStore (parsed via shared parser)

Nested JSON Structure ​

Common parsed shape (optional blocks appear only when present in source data):

json
{
	"majorVersion": 1,
	"minorVersion": 3,
	"glyphClassDef": {
		"format": 1,
		"startGlyphID": 0,
		"classValueArray": [1, 2]
	},
	"attachList": {
		"coverage": { "format": 1, "glyphArray": [10, 11] },
		"attachPoints": [[12, 45], [20]]
	},
	"ligCaretList": {
		"coverage": { "format": 1, "glyphArray": [50] },
		"ligGlyphs": [
			[
				{ "format": 1, "coordinate": 320 },
				{ "format": 2, "caretValuePointIndex": 7 },
				{
					"format": 3,
					"coordinate": 400,
					"device": { "format": 1, "deltaFormat": 2, "deltaValues": [0] }
				}
			]
		]
	},
	"markAttachClassDef": {
		"format": 2,
		"classRangeRecords": [{ "start": 100, "end": 120, "class": 1 }]
	},
	"markGlyphSetsDef": {
		"format": 1,
		"coverages": [{ "format": 1, "glyphArray": [200, 201] }]
	},
	"itemVarStoreOffset": 1234,
	"itemVariationStore": {
		"format": 1,
		"variationRegionList": {
			"axisCount": 1,
			"regions": [
				{ "regionAxes": [{ "startCoord": 0, "peakCoord": 1, "endCoord": 1 }] }
			]
		},
		"itemVariationData": []
	}
}

Notes:

  • itemVariationStore is a fully parsed ItemVariationStore matching the format used by HVAR/VVAR/MVAR/COLR.
  • ClassDef/Coverage/Device object formats are shared OpenType Layout structures.

Validation Constraints ​

  • Requires OpenType Layout context: usually authored together with GPOS and/or GSUB.
  • minorVersion >= 2 enables markGlyphSetsDef.
  • minorVersion >= 3 enables itemVarStoreOffset / itemVariationStore.
  • For attachment/caret/glyph-set blocks, coverage sizes should align with corresponding arrays.

Authoring Example ​

json
{
	"tables": {
		"GDEF": {
			"majorVersion": 1,
			"minorVersion": 2,
			"glyphClassDef": {
				"format": 1,
				"startGlyphID": 0,
				"classValues": [1, 2, 3]
			},
			"_checksum": 0
		}
	}
}

Additional Nested Keys Seen In Implementation ​

  • glyphClassDef
  • attachList
  • ligCaretList
  • markAttachClassDef
  • markGlyphSetsDef
  • itemVarStoreOffset
  • itemVariationStore

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.