protoplug LUA Midi Mono Mode (Monoplay)

plugin.lua

require "include/protoplug"

local TARGET_CH = 1
local RETRIGGER_VELOCITY = nil

local held = {}
local currentOut = -1

local function isNoteOn(ev)
  return ev:isNoteOn() and ev:getVel() > 0
end

local function isNoteOff(ev)
  return ev:isNoteOff() or (ev:isNoteOn() and ev:getVel() == 0)
end

local function highestHeldNote()
  for n = 127, 0, -1 do
    if held[n] ~= nil then
      return n
    end
  end
  return -1
end

function plugin.processBlock(samples, smax, midiBuf)
  local out = {}

  for ev in midiBuf:eachEvent() do
    if not (ev:isNoteOn() or ev:isNoteOff()) then
      table.insert(out, ev)

    elseif ev:getChannel() ~= TARGET_CH then
      table.insert(out, ev)

    else
      local t = ev.time or 0
      local note = ev:getNote()
      local vel = ev:getVel()

      if isNoteOn(ev) then
        held[note] = vel

        if currentOut == -1 then
          currentOut = note
          table.insert(out, midi.Event.noteOn(TARGET_CH, note, vel, t))

        elseif note > currentOut then
          table.insert(out, midi.Event.noteOff(TARGET_CH, currentOut, 0, t))
          currentOut = note
          table.insert(out, midi.Event.noteOn(TARGET_CH, note, vel, t))
        end

      elseif isNoteOff(ev) then
        held[note] = nil

        if note == currentOut then
          table.insert(out, midi.Event.noteOff(TARGET_CH, currentOut, 0, t))
          currentOut = -1

          local nextNote = highestHeldNote()
          if nextNote ~= -1 then
            local nextVel = held[nextNote]
            if RETRIGGER_VELOCITY ~= nil then
              nextVel = RETRIGGER_VELOCITY
            end
            currentOut = nextNote
            table.insert(out, midi.Event.noteOn(TARGET_CH, nextNote, nextVel, t))
          end
        end
      end
    end
  end

  midiBuf:clear()

  for i = 1, #out do
    midiBuf:addEvent(out[i])
  end
end