melodies.lua

-- melody generator

engine.name="PolyPerc"
musicutil=require("musicutil")

function init()
  engine.release(2)
  engine.amp(0.3)
  local chords={"I","vi","IV","iii"} -- change to any chords
  local movement_left=6 -- change to 0-12
  local movement_right=6 -- change to 0-12
  local stay_on_chord=0.95 -- change to 0-1
  play(chords,1,movement_left,movement_right,stay_on_chord)
end

function play(chord_structure,factor,move_left,move_right,stay_scale)
  stay_scale=util.clamp(stay_scale,0,1)
  -- notes to play
  local notes_to_play={}

  -- generate chords
  local chords={}
  for i,v in ipairs(chord_structure) do
    local scale=musicutil.generate_scale(12,1,8)
    local chord_notes=musicutil.generate_chord_roman(12,1,v)
    local notes_in_chord={}
    for _,u in ipairs(chord_notes) do
      notes_in_chord[u]=true
      for j=1,8 do
        notes_in_chord[u+(12*j)]=true
      end
    end
    local note_start=72
    for jj=1,4*factor do
      -- find note_start in scale
      local notes_to_choose={}
      for _,note in ipairs(scale) do
        if note>note_start-move_left and note<note_start+move_right then
          table.insert(notes_to_choose,note)
        end
      end
      local weights={}
      local scale_size=#notes_to_choose
      for i,note in ipairs(notes_to_choose) do
        weights[i]=notes_in_chord[note]~=nil and scale_size or scale_size*(1-stay_scale)
        -- weights[i]=weights[i]+(scale_size-i)
      end
      local note_next=choose_with_weights(notes_to_choose,weights)
      table.insert(notes_to_play,note_next)
      note_start=note_next
    end
  end

  local notei=0
  local note_last=0
  clock.run(function()
    while true do
      clock.sync(1/factor)
      notei=(notei)%#notes_to_play+1
      local note_next=notes_to_play[notei]
      if note_next~=note_last then
        engine.hz(musicutil.note_num_to_freq(note_next))
      end
      note_last=note_next
    end
  end)
end

function choose_with_weights(choices,weights)
  local totalWeight=0
  for _,weight in pairs(weights) do
    totalWeight=totalWeight+weight
  end

  local rand=math.random()*totalWeight
  local choice=nil
  for i,weight in pairs(weights) do
    if rand<weight then
      choice=choices[i]
      break
    else
      rand=rand-weight
    end
  end
  return choice
end