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OpenType tables used by Windows

Required Tables
cmap	Character to glyph mapping	Required
head	Font header	Required
hhea	Horizontal headerRequired
hmtx	Horizontal metrics	Required
maxp	Maximum profile	Required
name	Naming table	Required
OS/2	Windows specific metrics	Required
post	PostScript information	Required
TrueType Tables
cvt	Control Value Table	Ignored
fpgm	Font program	Ignored
glyf	Glyph data	Ignored
loca	Index to location	Ignored
prep	CVT Program	Ignored
PostScript Tables
CFF	Compact font format	Required
Advanced Typographic Tables
BASE	Baseline data	Ignored
GDEF	Glyph definition data	Ignored
GPOS	Glyph positioning data	For "kern" feature
GSUB	Glyph substitution data	For "vrt2" feature
JSTF	Justification data	Ignored
Bitmap Tables
EBDT	Embedded bitmap data	Ignored
EBLC	Embedded bitmap location data	Ignored
EBSC	Embedded bitmap scaling data	Ignored
Other OpenType Tables
DSIG	Digital signature	Ignored
gasp	Grid-fitting/Scan-conversion	Ignored
hdmx	Horizontal device metrics	Ignored
kern	Kerning	Ignored
LTSH	Linear threshold data	Ignored
PCLT	PCL 5 data	Ignored
VDMX	Vertical device metrics	Ignored
vhea	Vertical metrics header	For vertical mode
vmtx	Vertical metrics	For vertical mode

Following is a discussion of ATM's treatment of individual OpenType tables. Reviewers should be familiar with the v.1.2 OpenType Specification.

cmap

The cmap table version must be >= 0 (equivalent to ignoring it).

The OpenType specificationstrongly recommends, but ATM requires a cmap with PlatformID 3 (Microsoft) and EncodingID 1 (Unicode). This cmap must be in format 4 (Microsoft Standard).

ATM uses an optional cmap with PlatformID 4 (Custom) and EncodingID less than 256. This provides a "compatibility" cmap that contains the original font encoding for converted non-StandardEncoded Adobe fonts. The compatibility cmap must be in either format 0 (Apple Standard) or format 6 (Trimmed). Note: PlatformID 4 is not defined in the current OpenType specification.

All other cmaps are ignored. In particular, ATM does not use:

• PlatformID 1 EncodingID 0 (Macintosh)
• PlatformID 3 EncodingID 0 (Symbol)
• PlatformID 3 EncodingID 2-6 (Far East)

Note: contrary to the current OpenType specification, ATM does not support PlatformID 3 EncodingID 0 for Symbol fonts, even for the font "Symbol".

The cmap table checksum must be correct.

head

ATM uses the following fields from the head table.

• version (must be >= 1.0 and < 2.0)
• fontRevision
• magicNumber (must be 0x5F0F3CF5)
• flags
• unitsPerEm
• lowestRecPPEM
• xMin,yMin,xMax,yMax (for single master fonts only)
• macStyle

If the OS/2.achVendID is 'ADBE' then fontRevision must be >= 1.0 (0.9 during beta).

When bit 12 of the flags field is set, it indicates a converted font, and ATM does the following:

• Enable Non-linear external leading.
• Disable support for multiple 'kern' subtables, for class kerning and for kern filtering.
• Force OS/2.usWeightClass to either Regular (400) or Bold (700). Force panose.bWeight to either Book (5) or Bold (8), respectively.
• Enable the algorithmic calculation of OS/2.sTypoAscender, OS/2.sTypoDescender and OS/2.sTypoLineGap for multiple master fonts.

All other bits in the flags field are ignored.

All other fields are ignored.

The head table checksum (and the checkSumAdjustment field) are currently ignored.

hhea

ATM uses the following fields from the hhea table.

• version (must be >= 1.0 and < 2.0)
• advanceWidthMax (for single master fonts only)
• Ascender (for single master fonts only)
• Descender (for single master fonts only)
• caretSlopeRise
• caretSlopeRun
• numberOfHMetrics

All other fields are ignored.

The hhea table checksum must be correct.

hmtx

ATM uses the hMetrics array to obtain advance widths for single master fonts. This includes an implicit advance width when numberOfHMetrics is less than numGlyphs. ATM ignores leftSideBearing. The hmtx table is required but is actually ignored for Multiple Master fonts.

The hmtx table checksum must be correct.

maxp

ATM requires the maxp table and obtains numGlyphs from it. The version must be >= 0.5 (hexadecimal) and < 2.0. All other fields are ignored.

The maxp table checksum must be correct.

name

ATM requires a format 0 name table. Names must be defined for PlatformID 3 (Microsoft) and EncodingID 1 (Unicode). ATM requires the following NameIDs.

• 1 Font Family
• 2 Font Subfamily
• 3 Unique font identifier
• 6 PostScript

The following NameID is optional:

• 17 Preferred Subfamily

All other names are ignored.

The name table checksum must be correct.

OS/2

ATM uses the following fields:

• version (must be >= 2)
• xAvgCharWidth (for single master only)
• usWeightClass (for non-converted fonts only)
• fsType
• ySubscriptXSize
• ySubscriptYSize
• ySubscriptXOffset
• ySubscriptYOffset
• ySuperscriptXSize
• ySuperscriptYSize
• ySuperscriptXOffset
• ySuperscriptYOffset
• yStrikeOutSize
• yStrikeOutPosition
• panose
• ulUnicodeRange1
• ulUnicodeRange2
• ulUnicodeRange3
• ulUnicodeRange4
• achVendID
• sTypoAscender(except converted multiple master)
• sTypoDescender(except converted multiple master)
• sTypoLineGap(except converted multiple master)
• usWinAscent(for single master only)
• usWinDescent (for single master only)
• ulCodePageRange1
• ulCodePageRange2
• sXHeight (for single master only)
• sCapHeight (for single master only)
• usDefaultChar
• usBreakChar

The following fields are ignored.

• xAvgCharWidth (for multiple master only)
• usWeightClass (for converted fonts only)
• usWidthClass
• sFamilyClass
• fsSelection
• sTypoAscender (for converted multiple master only)
• sTypoDescender (for converted multiple master only)
• sTypoLineGap (for converted multiple master only)
• usWinAscent (for multiple master only)
• usWinDescent (for multiple master only)
• sXHeight (for multiple master only)
• sCapHeight (for multiple master only)
• usFirstCharIndex
• usLastCharIndex
• usMaxLookups

The OS/2 table checksum must be correct.

post

ATM uses the following fields from the post table.

• version (must be >= 3.0 and < 4.0)
• underlineThickness
• underlinePosition
• italicAngle

All other fields are ignored.

The post table checksum must be correct.

CFF

ATM requires this table.

The CFF table checksum is currently ignored.

GPOS

If the GPOS table is present, ATM requires the version to be >= 1.0 and < 2.0.

The GPOS table is used only for the 'kern' feature. See ATM Kerning Spec.

The GPOS table checksum must be correct.

GSUB

ATM looks for a GSUB table in every OpenType font to determine if vertical mode is supported (see description below). The requirements stated in thi s section are necessary for ATM to support vertical mode for the font. If any of these requirements are not met, then ATM loads the font but disables vertical mode.

If the GSUB table is present, ATM requires the version to be >= 1.0 and < 2.0. The ScriptList is ignored. If the FeatureList does not contain a 'vrt2' feature, the rest of the GSUB table is ignored. The vrt2 feature must include a single lookup of LookupType 1 (Single Substitution Subtable). The predecessor feature, 'vert', is ignored.

The lookup must contain a single subtable of format 1 (delta) or format 2 (general Single Substitution). The LookupFlag must be zero.

The coverage table must be format 1 (index array) or format 2 (index ranges).

The Windows menuname (name ID FontFamily (1)) must <= 30 characters long (to allow for '@').

The GSUB table checksum must be correct.

EBDT, EBLC, EBSC

ATM does not support bitmaps in OpenType fonts.

vhea

This table is required for fonts that support vertical mode. ATM uses the following fields from the vhea table.

• version (must be >= 1.0 and < 2.0)
• numOfLongVerMetrics

All other fields are ignored.

The vhea table checksum must be correct.

vmtx

This table is required for fonts that support vertical mode.

ATM uses the vMetrics array to obtain advance widths in vertical mode. This includes an implicit advance width when numOfLongVerMetrics is less than numGlyphs. ATM ignores rightSideBearing.

The vmtx table checksum must be correct.

vertical mode

ATM reports a second "face" to the system for fonts that support vertical mode:

The Windows menuname of this face is formed by appending '@' with the normal font menuname.

The font bounding box is rotated 90 degrees counter-clockwise. The metrics derived from the bounding box are recalculated:

• sTypoAscender
• sTypoDescender
• sTypoLineGap
• usWinAscent
• usWinDescent

The Unicode encoding from the cmap is recalculated, using the one-to-one glyph substitution specified by GSUB 'vrt2'.

When producing glyph data for the @facename, ATM does the following:

• Rotates each glyph 90 degrees counter-clockwise.
• Uses advance widths from vmtx instead of hmtx.