consumers-otvar.md

Processing Variable Fonts

When processing variable fonts, font consumers must take note of the following requirements:

• XXX rounding

Axis Coordinate Normalization

To normalise an axis value from a [=user coordinate=] to a [=normalized coordinate=], the following algorithm should be used:

• The user coordinate value should be converted if necessary to a fixed-point 16.16 value. All arithmetic manipulation must be done using fixed-point 16.16 values.
• The [=fvar table=] {{VariationAxisRecord}} for the appropriate axis should be located.
• If the user value is less than the {{defaultValue}}, then the normalized value should be set to -(axisDefault - userValue) / (axisDefault - axisMin); if it is more than the {{defaultValue}}, then the normalized value should be set to (userValue - axisDefault) / (axisMax - axisDefault); else, it is set to zero.
• The normalized value should be clamped to a minimum of -1 and a maximum of 1.
• If an [=avar table=] is present, then further transformation is performed:
  • Find the {{SegmentMaps}} for the appropriate axis.
  • If an {{AxisValueMap}} entry has a {{fromCoordinate}} equal to the current normalized value v, then return its {{toCoordinate}}.
  • Otherwise, find the segment a with the largest {{fromCoordinate}} strictly lower than v and the segment b with the smaller {{fromCoordinate}} strictly higher than v.
  • The normalized value value is then set to a.toCoordinate + (b.toCoordinate - a.toCoordinate) * (v - a.fromCoordinate) / (b.fromCoordinate - a.fromCoordinate).
• Finally the 16.16 value should be converted to an F2DOT16 by adding 0x00000002, and shifting the value to the right by 2 with sign extension.