Class: HeadMusic::Style::Guidelines::NoParallelPerfectAcrossBarline

Inherits:
Annotation
  • Object
show all
Defined in:
lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb

Overview

A counterpoint guideline

Constant Summary collapse

MESSAGE = 
"Avoid parallel perfect consonances from weak beat to the following downbeat."

Instance Method Summary collapse

Constructor Details

This class inherits a constructor from HeadMusic::Style::Annotation

Instance Method Details

#cantus_firmus_positions ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 46

def cantus_firmus_positions
  @cantus_firmus_positions ||= Set.new(cantus_firmus.notes.map { |n| n.position.to_s })
end

#downbeat_position?(position) ⇒ Boolean (private)

Returns:

  • (Boolean) 


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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 42

def downbeat_position?(position)
  cantus_firmus_positions.include?(position.to_s)
end

#marks ⇒ Object 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 8

def marks
  parallel_perfect_across_barline_pairs.map do |pair|
    HeadMusic::Style::Mark.for_all(pair.flat_map(&:notes))
  end
end

#next_downbeat_interval(weak_interval) ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 50

def next_downbeat_interval(weak_interval)
  next_cf_note = cantus_firmus.notes.detect { |n| n.position > weak_interval.position }
  return unless next_cf_note

  interval = HeadMusic::Analysis::HarmonicInterval.new(cantus_firmus, voice, next_cf_note.position)
  interval if interval.notes.length == 2
end

#parallel_perfect_across_barline_pairs ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 16

def parallel_perfect_across_barline_pairs
  weak_strong_interval_pairs.select do |weak, strong|
    weak.perfect_consonance?(:two_part_harmony) &&
      strong.perfect_consonance?(:two_part_harmony) &&
      same_simple_type?(weak, strong)
  end
end

#same_simple_type?(first, second) ⇒ Boolean (private)

Returns:

  • (Boolean) 


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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 58

def same_simple_type?(first, second)
  first.simple_number == second.simple_number
end

#weak_beat_harmonic_intervals ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 31

def weak_beat_harmonic_intervals
  weak_beat_positions.filter_map do |position|
    interval = HeadMusic::Analysis::HarmonicInterval.new(cantus_firmus, voice, position)
    interval if interval.notes.length == 2
  end
end

#weak_beat_positions ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 38

def weak_beat_positions
  notes.map(&:position).reject { |pos| downbeat_position?(pos) }
end

#weak_strong_interval_pairs ⇒ Object (private) 



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# File 'lib/head_music/style/guidelines/no_parallel_perfect_across_barline.rb', line 24

def weak_strong_interval_pairs
  weak_beat_harmonic_intervals.filter_map do |weak_interval|
    next_downbeat = next_downbeat_interval(weak_interval)
    [weak_interval, next_downbeat] if next_downbeat
  end
end