Class: Fontisan::Ufo::Compile::FeatureWriters::Kern2

Inherits:
Base
  • Object
show all
Defined in:
lib/fontisan/ufo/compile/feature_writers/kern2.rb

Overview

Extended kerning (format 2 / Device-table variant of PairPos).

Same data shape as the basic Kern writer, but emits the extended format that supports:

- device tables (sub-pixel kerning)
- cross-stream kerning (y-direction adjustments)
- per-pair value-format overrides

The current implementation extracts the same kerning.pairs data as Kern; the differentiation is in how the GPOS table builder encodes the value format (Format1 vs Format2, plus device tables). Writers do not need to know about that — they just emit the structured data; the table builder picks the encoding.

Downstream consumers (compilers) choose between Kern and Kern2 based on whether they need device tables. Most don't; basic Kern is sufficient for the common case.

Constant Summary collapse

LOOKUP_TYPE = 
2
FEATURE_TAG = 
"kern"
TABLE_TAG = 
"GPOS"
FORMAT = 
2

Instance Attribute Summary

Attributes inherited from Base

#font

Instance Method Summary collapse

Methods inherited from Base

#initialize

Constructor Details

This class inherits a constructor from Fontisan::Ufo::Compile::FeatureWriters::Base

Instance Method Details

#write ⇒ FeatureOutput?

Returns:



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# File 'lib/fontisan/ufo/compile/feature_writers/kern2.rb', line 32

def write
  return nil if font.kerning.nil? || font.kerning.empty?

  pairs = font.kerning.pairs.map do |key, value|
    left, right = key.to_s.split(" ", 2)
    {
      left: left,
      right: right,
      value: value.to_f,
      group_left: left.to_s.start_with?("@"),
      group_right: right.to_s.start_with?("@"),
    }
  end

  FeatureOutput.new(
    table_tag: TABLE_TAG,
    feature_tag: FEATURE_TAG,
    lookup_type: LOOKUP_TYPE,
    data: { format: FORMAT, pairs: pairs },
  )
end