'avar' correction in OpenType 1.8, OpenType 1.8.1

[Peter Constable]

An error in the 'avar' table chapter of the OT spec was just pointed out: the axisCount field was defined in OT as uint16, which matches what is used for the corresponding field in the 'fvar' and 'gvar' tables in both OT and Apple's TrueType spec. However, Apple's 'avar' table spec used int32 for the axisCount field - I assume this was done to provide four-byte alignment of header fields. This was not noticed when the 'avar' chapter for the OT spec was drafted. But clearly compatibility with Apple's 'avar' spec is necessary.

We've published errata for OT 1.8 and OT 1.8.1 with a correction for this issue.

https://www.microsoft.com/typography/otspec/errata.htm
https://www.microsoft.com/typography/otspec180/errata.htm

The 'avar' header is now documented as follows:

Axis variation table:
Type

Name

Description

uint16

majorVersion

Major version number of the axis variations table - set to 1.

uint16

minorVersion

Minor version number of the axis variations table - set to 0.

uint16

<reserved>

Permanently reserved; set to zero.

uint16

axisCount

The number of variation axes for this font. This must be the same number as axisCount in the 'fvar' table.

SegmentMaps

axisSegmentMaps[axisCount]

The segment maps array - one segment map for each axis, in the order of axes specified in the 'fvar' table.



Peter

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