Monostep Sequencer

• A list of hit or no-hits
• On a step check if there is a hit; if yes then trigger the sound.

This is the most basic kind of sequencer you can make.

type
    Monostep* = object
        steps: seq[bool]
        at: int
        note: MidiNote
        channel: MidiChannel

proc step*(self: var Monostep; feed: var seq[MidiMessage]) =
    # we always turn the note off
    feed.add(MidiMessage(kind: Note, note: self.note, channel: self.channel, velocity: 0))

    # advance the play head
    self.at = (self.at + 1) mod self.steps.len.int

    # we might trigger the note
    if self.steps[self.at]:
        feed.add(MidiMessage(kind: Note, note: self.note, channel: self.channel, velocity: 127))

To behave more like a traditional tracker, add a hot bit to Monostep:

hot: bool

Now we only emit a note ON on a beat, an OFF on a rest, and nothing otherwise:

proc step*(self: var Monostep; feed: var seq[MidiMessage]) =
    # advance the play head
    self.at = (self.at + 1) mod self.steps.len.int

    # we might trigger the note
    if self.steps[self.at]:
        feed.add(MidiMessage(kind: Note, note: self.note, channel: self.channel, velocity: 127))
        self.hot = true
    else:
        if self.hot:
            feed.add(MidiMessage(kind: Note, note: self.note, channel: self.channel, velocity: 0))
        self.hot = false