musicxml2fmf.py

#!/usr/bin/env python3

import click
from lxml import etree

downsteps = {
    "C": ("B", -1),
    "D": ("C", 0),
    "E": ("D", 0),
    "F": ("E", 0),
    "G": ("F", 0),
    "A": ("G", 0),
    "B": ("A", 0),
}


def getNoteValue(duration, divisions):
    """Convert MusicXML durations to note values.

    This method takes as input the MusicXML duration and the current divisions.
    The divisions define in how many divisions a measure is seperated.
    Division 1 separates a measure in 4 units, division 2 in 8 units and so on.

    Accordingly with divisons 2 the smalest note value is an 8th, i.e. duration 1 is an 8th note.
    with divisons 1 the duration 1 is a 4th note.

    Returns a tuple of the noteValue, a string of dots and the duration that is left over due to rounding error.

    for divisions 2 the output is as follows:
    durations = {
        1: (8, "", None),
        2: (4, "", None),
        3: (4, ".", None),
        4: (2, "", None),
        5: (2, "", 1),  # rounded
        6: (2, ".", None),
        7: (2, "..", None),
        8: (1, "", None),
    }
    """
    v = duration
    msb = 1  # most significant bit
    msb_pos = 1
    while (v := v >> 1):
        msb = msb << 1
        msb_pos += 1
    noteValue = int(format(msb, 'b').zfill(2 + divisions)[::-1], base=2)
    rest = format(duration - msb, 'b').zfill(msb_pos - 1)
    dots = ""
    i = 0
    while i < len(rest) and int(rest[i]):
        i += 1
        dots += "."
    correction = 0
    if rest[i:]:
        correction = int(rest[i:], base=2)
    return (noteValue, dots, correction)


filetypeHeader = """Filetype: Flipper Music Format
Version: 0
BPM: {bpm}
Duration: {duration}
Octave: {octave}
Notes: """


def noteFactory(divisons):
    class Note:
        def __init__(self, duration=1, step="C", sharp="", octave=5):
            self.duration = int(duration)
            self.step = step
            self.sharp = sharp
            self.octave = int(octave)

        def __str__(self):
            noteValue, dot, correction = getNoteValue(self.duration, divisons)
            correctionStr = ""
            if correction:
                correctionStr = ", " + str(Rest(correction))
            return f"{noteValue}{self.step}{self.sharp}{self.octave}{dot}" + correctionStr

        def __repr__(self):
            return f"<{self.duration}, {self.step}, {self.sharp}, {self.octave}>"

        def __add__(self, other):
            if (
                isinstance(other, Note)
                and self.step == other.step
                and self.octave == other.octave
                and self.sharp == other.sharp
            ):

                return [
                    Note(self.duration + other.duration, self.step, self.sharp, self.octave)
                ]
            return [self, other]

    class Rest:
        def __init__(self, duration=1):
            self.duration = int(duration)

        def __str__(self):
            noteValue, dot, correction = getNoteValue(self.duration, divisons)
            correctionStr = ""
            if correction:
                correctionStr = ", " + str(Rest(correction))
            return f"{noteValue}P{dot}" + correctionStr
    return Note, Rest


@click.command()
@click.option("--input", help="File to read the MusicXML from (suffix: '.musicxml').")
@click.option("--output", help="File to write the Flipper Music to (suffix: '.fmf').")
@click.option(
    "--bpm", default=120, help="Beats per minute for the piece (default: 120)."
)
@click.option("--duration", default=8, help="Default duration of a tone (default: 8).")
@click.option("--octave", default=5, help="Default octave of a note (default: 5).")
def convert(input, output, bpm, duration, octave):
    defaultDuration = duration
    defaultOctave = octave
    flipperNotes = []
    overTie = False
    tree = etree.parse(input)
    divisions = int(tree.xpath("//score-partwise/part/measure/attributes/divisions")[0].text)
    Note, Rest = noteFactory(divisions)
    musicXmlNotes = tree.xpath("//score-partwise/part/measure/note")
    for noteTag in musicXmlNotes:
        duration = noteTag.xpath("duration")[0].text
        if noteTag.xpath("rest"):
            flipperNotes.append(Rest(duration))
            continue
        alter = False
        if noteTag.xpath("pitch/alter"):
            alter = int(noteTag.xpath("pitch/alter")[0].text)
        step = noteTag.xpath("pitch/step")[0].text
        octave = int(noteTag.xpath("pitch/octave")[0].text)
        sharp = ""
        if alter:
            if alter < 0:
                step, octaveShift = downsteps[step]
                octave = octave + octaveShift
            sharp = "#"
        note = Note(duration, step, sharp, octave)
        if overTie:
            tiedNotes = flipperNotes[-1] + note
            flipperNotes = flipperNotes[:-1] + tiedNotes
        else:
            flipperNotes.append(note)
        if noteTag.xpath("notations/tied") or noteTag.xpath("notations/slur"):
            tieStart = False
            tieStop = False
            for tied in noteTag.xpath("notations/tied") + noteTag.xpath("notations/slur"):
                tieStart = tied.attrib["type"] in "start"
                tieStop = tied.attrib["type"] in "stop"
            if tieStart:
                overTie = True
            elif tieStop:
                overTie = False

    with open(output, "w") as o:
        o.write(
            filetypeHeader.format(
                bpm=bpm, duration=defaultDuration, octave=defaultOctave
            )
        )
        o.write(", ".join(str(n) for n in flipperNotes))