guitar.rb

# Guitar Strumming - by Emlyn
# This tries to work out the guitar (or ukulele etc.) fingering for arbitrary chords (and tuning).
# It seems to work reasonably well for basic chords, but is quite naive and probably makes many mistakes.
# Ideas, bug reports, fixes etc. gratefully received, just comment below, or tweet @emlyn77.
# Feel free to make use of this code as you like (with attribution if you feel like it, but you don't have to).
# Thanks to @Project_Hell_CK for fixing the tuning, and spotting that it gets chord(:f, :major) not quite right.

# Return ring representing the chord chrd, as played on a guitar with given tuning
def guitar(tonic, name=nil, tuning: :guitar, debug: false)
  tunings = {
    :ukulele => [:g, :c, :e, :a],
    :guitar => [:e2, :a2, :d3, :g3, :b3, :e4]
  }
  tuning = tunings[tuning] || tuning

  # Next note higher or equal to base note n, that is in the chord c
  def next_note(n, c)
    # Make sure n is a number
    n = note(n)
    # Get distances to each note in chord, add smallest to base note
    n + (c.map {|x| (note(x) - n) % 12}).min
  end

  if tonic.respond_to?(:each) and name==nil then
    chrd = tonic
  else
    chrd = (chord tonic, name || :M)
  end

  # For each string, get the next higher note that is in the chord
  c = tuning.map {|n| next_note(n, chrd)}

  # We want the lowest note to be the root of the chord
  root = note(chrd[0])
  first_root = c.take_while {|n| (n - root) % 12 != 0}.count

  # Drop up to half the lowest strings to make that the case if possible
  if first_root > 0 and first_root < tuning.count / 2
    c = (ring :r) * first_root + c.drop(first_root)
  end

  # Display chord fingering
  if debug
    puts c.zip(tuning).map {|n, s| if n == :r then 'x' else (n - note(s)) end}.to_a.join, c
  end
  c
end

# Strum a chord with a certain delay between strings
def guitar_strum(chrd, dt)
  in_thread do
    play_pattern_timed chrd.drop_while{|n| [nil,:r].include? n}, dt
  end
end

def strum(chrd, pattern: nil, t: 0.25, dt: 0.025)
  if pattern == nil then
    guitar_strum(chrd, dt)
  else
    pattern.split(//).each do |shape|
      case shape
      when 'D'
        guitar_strum chrd, dt
      when 'd'
        with_fx :level, amp: 0.7 do
          guitar_strum chrd, dt
        end
      when 'U'
        with_fx :level, amp: 0.8 do
          guitar_strum chrd.reverse, dt*0.9
        end
      when 'u'
        with_fx :level, amp: 0.6 do
          guitar_strum chrd.reverse, dt*0.9
        end
      else
        # nothing
      end
      sleep t
    end
  end
end