Common Table Examples

The rest of this chapter describes and illustrates examples of all the common table formats. All the examples reflect unique parameters, but the samples provide a useful reference for building tables specific to other situations.

The examples have three columns showing hex data, source, and comments.

Example 1: ScriptList Table and ScriptRecords

Example 1 illustrates a ScriptList table and ScriptRecord definitions for a Japanese font with multiple scripts: Han Ideographic, Kana, and Latin. Each script has script-specific behavior.

Example 1

Hex Data	Source	Comments
0003 68616E69 0014 6B616E61 0018 6C61746E 001C	ScriptList TheScriptList 3 "hani" HanIScriptTable "kana" KanaScriptTable "latn" LatinScriptTable	;ScriptList table definition ;ScriptCount ;ScriptRecord[0] ; in alphabetical order by ; ScriptTag ;ScriptTag ; Han Ideographic script ;offset to Script table ;ScriptRecord[1] ;ScriptTag ; Hiragana and Katakana scripts ;offset to Script table ;ScriptRecord[2] ;ScriptTag ; Latin script ;offset to Script table

Example 2: Script Table, LangSysRecord, and LangSys Table

Example 2 illustrates the Script table, LangSysRecord, and LangSys table definitions for the Arabic script and the Urdu language system. The default LangSys table defines three default Arabic script features used to replace certain glyphs in words with their proper initial, medial, and final glyph forms. These contextual substitutions are invariant and occur in all language systems that use the Arabic script.

Many alternative glyphs in the Arabic script have language-specific uses. For instance, the Arabic, Farsi, and Urdu language systems use different glyphs for numerals. To maintain character-set compatibility, the Unicode standard includes separate character codes for the Arabic and Farsi numeral glyphs. However, the standard uses the same character codes for Farsi and Urdu numerals, even though three of the Urdu glyphs (4, 6, and 7) differ from the Farsi glyphs. To access and display the proper glyphs for the Urdu numerals, users of the text-processing client must enter the character codes for the Farsi numerals. Then the text-processing client uses a required TrueType Open glyph substitution feature, defined in the Urdu LangSys table, to access the correct Urdu glyphs for the 4, 6, and 7 numerals.

Note that the Urdu LangSys table repeats the default script features. This repetition is necessary because the Urdu language system also uses alternative glyphs in the initial, medial, and final glyph positions in words.

Example 2

Hex Data	Source	Comments
	Script
	ArabicScriptTable	;Script table definition
000A	DefLangSys	;offset to DefaultLangSys table
0001	1	;LangSysCount
		;LangSysRecord[0]
		; in alphabetical order by
		; LangSysTag
55524420	"URD "	;LangSysTag
		; Urdu language
0016	UrduLangSys	;offset to LangSys table for
		; Urdu
	LangSys
	DefLangSys	;default LangSys table
		; definition
0000	NULL	;LookupOrder
		; reserved, null
FFFF	0xFFFF	;ReqFeatureIndex
		; no required features
0003	3	;FeatureCount
0000	0	;FeatureIndex[0]
		; in arbitrary order
		; "init" feature (initial
		; glyph)
0001	1	;FeatureIndex[1]
		; "fina" feature (final glyph)
0002	2	;FeatureIndex[2]
		; for "medi" feature (medial
		; glyph)
	LangSys
	UrduLangSys	;LangSys table definition
0000	NULL	;LookupOrder
		; reserved, null
0003	3	;ReqFeatureIndex
		; numeral subsitution in Urdu
0003	3	;FeatureCount
0000	0	;FeatureIndex[0]
		; in arbitrary order
		; "init" feature (initial
		; glyph)
0001	1	;FeatureIndex[1]
		; "fina" feature (final glyph)
0002	2	;FeatureIndex[2]
		; "medi" feature (medial glyph)

Example 3: FeatureList Table and Feature Table

Example 3 shows the FeatureList and Feature table definitions for ligatures in the Latin script. The FeatureList has three features, all optional and named "liga." One feature, also a default, implements ligatures in Latin if no language-specific feature specifies other ligatures. Two other features implement ligatures in the Turkish and German languages, respectively.

Three lookups define glyph substitutions for rendering ligatures in this font. The first lookup produces the "ffl," "fl," and "ff" ligatures; the second produces the "ffi" and "fi" ligatures; and the third produces the eszet ligature.

The ligatures that begin with an "f" are separated into two sets because Turkish has a dotless "i" glyph and so does not use "ffi" and "fi" ligatures. However, Turkish does use the "ffl," "fl," and "ff" ligatures, and the TurkishLigatures feature table lists this one lookup.

Only the German language system uses the eszet ligature, so the GermanLigatures feature table includes a lookup for rendering that ligature.

Because the Latin script can use both sets of ligatures, the DefaultLigatures feature table defines two LookupList indices: one for the "ffl," "fl," and "ff" ligatures, and one for the "ffi" and "fi" ligatures. If the text-processing client selects this feature, then the font applies both lookups.

Note that the TurkishLigatures and DefaultLigatures feature tables both list a LookupListIndex of zero (0) for the "ffl," "fl," and "ff" ligatures lookup. This is because language-specific lookups override all default language-system lookups, and a language-system feature table must explicitly list all lookups that apply to the language.

Example 3

Hex Data	Source	Comments
	FeatureList
	TheFeatureList	;FeatureList table definition
0003	3	;FeatureCount
		;FeatureRecord[0]
6C696761	"liga"	;FeatureTag
0014	TurkishLigatures	;offset to Feature table
		; FflFfFlLiga
		;FeatureRecord[1]
6C696761	"liga"	;FeatureTag
001A	DefaultLigatures	;offset to Feature table
		; FfiFiLiga, FflFfFlLiga
		;FeatureRecord[2]
6C696761	"liga"	;FeatureTag
0022	GermanLigatures	;offset to Feature table
		; EszetLiga
	Feature
	TurkishLigatures	;Feature table definition
0000	NULL	;FeatureParams
		; reserved, null
0001	1	;LookupCount
0000	0	;LookupListIndex[0]
		; ffl, fl, ff ligature
		; substitution Lookup
	Feature
	DefaultLigatures	;Feature table definition
0000	NULL	;FeatureParams - reserved, null
0002	2	;LookupCount
0000	0	;LookupListIndex[0]
		; in arbitrary order
		; ffl, fl, ff ligatures
0001	1	;LookupListIndex[1]
		; ffi, fi ligature substitution
		; Lookup
	Feature
	GermanLigatures	;Feature table definition
0000	NULL	;FeatureParams - reserved, null
0001	3	;LookupCount
0000	0	;LookupListIndex[0]
		; in arbitrary order
		; ffl, fl, ff ligatures
0001	1	;LookupListIndex[1]
		; ffi, fi ligature substitution
		; Lookup
0002	2	;LookupListIndex[0]
		; eszet ligature substitution
		; Lookup

Example 4: LookupList Table and Lookup Table

A continuation of Example 3, Example 4 shows three ligature lookups in the LookupList table. The first generates the "ffl," "fl," and "ff" ligatures; the second produces the "ffi" and "fi" ligatures; and the third generates the eszet ligature. Each lookup table defines an offset to a subtable that contains data for the ligature substitution.

Example 4

Hex Data	Source	Comments
	LookupList
	TheLookupList	;LookupList table definition
0003	3	;LookupCount
0008	FflFlFfLookup	;offset to Lookup[0] table
		; in design order
0010	FfiFiLookup	;offset to Lookup[1] table
0018	EszetLookup	;offset to Lookup[2] table
	Lookup
	FflFlFfLookup	;Lookup[0] table definition
0004	4	;LookupType
		; ligature subst
000C	0x000C	;LookupFlag
		; IgnoreLigatures, IgnoreMarks
0001	1	;SubTableCount
0018	FflFlFfSubtable	;offset to FflFlFf ligature
		; substitution subtable
	Lookup
	FfiFiLookup	;Lookup[1] table definition
0004	4	;LookupType
		; ligature subst
000C	0x000C	;LookupFlag
		; IgnoreLigatures, IgnoreMarks
0001	1	;SubTableCount
0028	FfiFiSubtable	;offset to FfiFi ligature
		; substitution subtable

	Lookup
	EszetLookup	;Lookup[2] table definition
0004	4	;LookupType
		; ligature subst
000C	0x000C	;LookupFlag
		; IgnoreLigatures, IgnoreMarks
0001	1	;SubTableCount
0038	EszetSubtable	;offset to Eszet ligature
		; substitution subtable

Example 5: CoverageFormat1 Table (GlyphID List)

Example 5 illustrates a Coverage table that lists the GlyphIDs of all lowercase descender glyphs in a font. The table uses the list format instead of the range format because the GlyphIDs for the descender glyphs are not consecutively ordered.

Example 5

Hex Data	Source	Comments
	CoverageFormat1
	DescenderCoverage	;Coverage table definition
0001	1	;CoverageFormat
		; lists
0005	5	;GlyphCount
0038	gGlyphID	;GlyphArray[0]
		; in GlyphID order
003B	jGlyphID	;GlyphArray[1]
0041	pGlyphID	;GlyphArray[2]
0042	qGlyphID	;GlyphArray[3]
004A	yGlyphID	;GlyphArray[4]

Example 6: CoverageFormat2 Table (GlyphID Ranges)

Example 6 shows a Coverage table that defines ten numeral glyphs (0 through 9). The table uses the range format instead of the list format because the GlyphIDs are ordered consecutively in the font. The StartCoverageIndex of zero (0) indicates that the first GlyphID, for the zero glyph, returns a Coverage Index of 0. The second GlyphID, for the numeral one (1) glyph, returns a Coverage Index of 1, and so on.

Example 6

Hex Data	Source	Comments
	CoverageFormat2
	NumeralCoverage	;Coverage table definition
0002	2	;CoverageFormat
		; GlyphID ranges
0001	1	;RangeCount
		;RangeRecord[0]
004E	0glyphID	;Start GlyphID

0057	9glyphID	;End GlyphID

0000	0	;StartCoverageIndex
		; first CoverageIndex = 0

Example 7: ClassDefFormat1 Table (Class Array)

The ClassDef table in Example 7 assigns class values to the lowercase glyphs in a font. The x-height glyphs are in Class 0, the ascender glyphs are in Class 1, and the descender glyphs are in Class 2. The array begins with the index for the lowercase "a" glyph.

Example 7

Hex Data	Source	Comments
	ClassDefFormat1
	LowercaseClassDef	;ClassDef table definition
0001	1	;ClassFormat
0032	aGlyphID	;StartGlyph

001A	26	;GlyphCount
0000	0	;aGlyph, Xheight Class 0
0001	1	;bGlyph, Ascender Class 1
0000	0	;cGlyph, Xheight Class 0
0001	1	;dGlyph, Ascender Class 1
0000	0	;eGlyph, Xheight Class 0
0001	1	;fGlyph, Ascender Class 1
0002	2	;gGlyph, Descender Class 2
0001	1	;hGlyph, Ascender Class 1
0000	0	;iGlyph, Ascender Class 1
0002	2	;jGlyph, Descender Class 2
0001	1	;kGlyph, Ascender Class 1
0001	1	;lGlyph, Ascender Class 1
0000	0	;mGlyph, Xheight Class 0
0000	0	;nGlyph, Xheight Class 0
0000	0	;oGlyph, Xheight Class 0
0002	2	;pGlyph, Descender Class 2
0002	2	;qGlyph, Descender Class 2
0000	0	;rGlyph, Xheight Class 0
0000	0	;sGlyph, Xheight Class 0
0001	1	;tGlyph, Ascender Class 1
0000	0	;uGlyph, Xheight Class 0
0000	0	;vGlyph, Xheight Class 0
0000	0	;wGlyph, Xheight Class 0
0000	0	;xGlyph, Xheight Class 0
0002	2	;yGlyph, Descender Class 2
0000	0	;zGlyph, Xheight Class 0

Example 8: ClassDefFormat2 Table (Class Ranges)

In Example 8, the ClassDef table assigns class values to four types of glyphs in the Arabic script: medium-height base glyphs, high base glyphs, very high base glyphs, and default mark glyphs. The table lists only Class 1, Class 2, and Class 3; all glyphs not explicitly assigned a class fall into Class 0.

The table uses the range format because the GlyphIDs in each class are ordered consecutively in the font. In the ClassRange array, ClassRange definitions are ordered by the Start glyph index in each range. The indices of the high base glyphs, defined in ClassRange[0], are first in the font and have a class value of 2. ClassRange[1] defines all the very high base glyphs and assigns a class value of 3. ClassRange[2] contains all default mark glyphs; the class value is 1. Class 0 consists of all the medium-height base glyphs, which are not explicitly assigned a class value.

Example 8

Hex Data	Source	Comments
	ClassDefFormat2
	GlyphHeightClassDef	;Class table definition
0002	2	;Class Format
		; ranges
0003	3	;ClassRangeCount
		;ClassRange[0]
		; ordered by StartGlyphID
0030	tahGlyphID	;Start
		; first GlyphID in the range
0031	dhahGlyphID	;End
		; Last GlyphID in the range
0002	2	;Class
		; high base glyphs
		;ClassRange[1]
0040	cafGlyphID	;Start
		;first GlyphID in the range
0041	gafGlyphID	;End
		; Last GlyphID in the range
0003	3	;Class
		; very high base glyphs
		;ClassRange[2]
00D2	fathatanDefaultGlyphID	;Start
		; first GlyphID in the range


00D3	dammatanDefaultGlyphID	;End
		; Last GlyphID in the range


0001	1	;Class
		; default marks

Example 9: Device Table

Example 9 defines the minimum extent value for a math script, using a Device table to adjust the value according to the size of the output font. Here, the Device table defines single-pixel adjustments for font sizes from 11 ppem to 15 ppem. The DeltaFormat is 1, which signifies a packed array of signed 2-bit values, eight values per uint16.

Example 9