Class: Fontisan::Variable::MetricDeltaProcessor

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/variable/metric_delta_processor.rb

Overview

Applies metric deltas from HVAR, VVAR, and MVAR tables

Processes variation data for font metrics including:

  • Horizontal metrics (advance widths, LSB, RSB) via HVAR
  • Vertical metrics (advance heights, TSB, BSB) via VVAR
  • Font-level metrics (ascent, descent, line gap, etc.) via MVAR

Uses ItemVariationStore and region scalars to calculate accumulated deltas which are then applied to original metric values.

Examples:

Apply metric deltas

processor = MetricDeltaProcessor.new(hvar, vvar, mvar)
deltas = processor.apply_deltas(glyph_id, region_scalars)
# => { advance_width: 10, lsb: -2, ... }

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(hvar: nil, vvar: nil, mvar: nil, config: {}) ⇒ MetricDeltaProcessor

Initialize the processor

Parameters:



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 31

def initialize(hvar: nil, vvar: nil, mvar: nil, config: {})
  @hvar = hvar
  @vvar = vvar
  @mvar = mvar
  @config = load_config.merge(config)
end

Instance Attribute Details

#config ⇒ Hash (readonly)

Returns Configuration settings.

Returns:

  • (Hash) —

    Configuration settings



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 23

def config
  @config
end

Instance Method Details

#advance_width_delta(glyph_id, region_scalars) ⇒ Integer

Get advance width delta for a glyph

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • region_scalars (Array<Float>) —

    Region scalars

Returns:

  • (Integer) —

    Advance width delta



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 86

def advance_width_delta(glyph_id, region_scalars)
  return 0 unless @hvar

  delta_set = @hvar.advance_width_delta_set(glyph_id)
  return 0 unless delta_set

  accumulated = calculate_accumulated_delta(delta_set, region_scalars)
  apply_rounding(accumulated)
end

#apply_deltas(glyph_id, region_scalars) ⇒ Hash

Apply all metric deltas for a glyph

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • region_scalars (Array<Float>) —

    Scalar for each region

Returns:

  • (Hash) —

    Metric deltas



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 43

def apply_deltas(glyph_id, region_scalars)
  result = {}

  # Apply horizontal metric deltas if HVAR present
  if @hvar && @config.dig(:metric_deltas, :apply_hvar)
    result[:horizontal] = apply_hvar_deltas(glyph_id, region_scalars)
  end

  # Apply vertical metric deltas if VVAR present
  if @vvar && @config.dig(:metric_deltas, :apply_vvar)
    result[:vertical] = apply_vvar_deltas(glyph_id, region_scalars)
  end

  result
end

#apply_font_metrics(region_scalars) ⇒ Hash

Apply font-level metric deltas

Parameters:

  • region_scalars (Array<Float>) —

    Scalar for each region

Returns:

  • (Hash) —

    Font-level metric deltas



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 63

def apply_font_metrics(region_scalars)
  return {} unless @mvar && @config.dig(:metric_deltas, :apply_mvar)

  result = {}

  # Process each metric tag in MVAR
  @mvar.metric_tags.each do |tag|
    delta_set = @mvar.metric_delta_set(tag)
    next unless delta_set

    # Calculate accumulated delta
    accumulated = calculate_accumulated_delta(delta_set, region_scalars)
    result[tag] = apply_rounding(accumulated)
  end

  result
end

#has_hvar? ⇒ Boolean

Check if horizontal variations are present

Returns:

  • (Boolean) —

    True if HVAR present



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 129

def has_hvar?
  !@hvar.nil?
end

#has_mvar? ⇒ Boolean

Check if font metric variations are present

Returns:

  • (Boolean) —

    True if MVAR present



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 143

def has_mvar?
  !@mvar.nil?
end

#has_vvar? ⇒ Boolean

Check if vertical variations are present

Returns:

  • (Boolean) —

    True if VVAR present



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 136

def has_vvar?
  !@vvar.nil?
end

#lsb_delta(glyph_id, region_scalars) ⇒ Integer

Get LSB delta for a glyph

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • region_scalars (Array<Float>) —

    Region scalars

Returns:

  • (Integer) —

    LSB delta



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 101

def lsb_delta(glyph_id, region_scalars)
  return 0 unless @hvar

  delta_set = @hvar.lsb_delta_set(glyph_id)
  return 0 unless delta_set

  accumulated = calculate_accumulated_delta(delta_set, region_scalars)
  apply_rounding(accumulated)
end

#rsb_delta(glyph_id, region_scalars) ⇒ Integer

Get RSB delta for a glyph

Parameters:

  • glyph_id (Integer) —

    Glyph ID

  • region_scalars (Array<Float>) —

    Region scalars

Returns:

  • (Integer) —

    RSB delta



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# File 'lib/fontisan/variable/metric_delta_processor.rb', line 116

def rsb_delta(glyph_id, region_scalars)
  return 0 unless @hvar

  delta_set = @hvar.rsb_delta_set(glyph_id)
  return 0 unless delta_set

  accumulated = calculate_accumulated_delta(delta_set, region_scalars)
  apply_rounding(accumulated)
end