Issue with ScoreVariant

[leleogere]

Following #380, @sildater suggested opening an issue for that, even if the ScoreVariant class does not seem public looking at its doc.

I was trying to manually split a score into multiple chunks of a few measures, which was in good progress, but I was suggested the object ScoreVariant that would do exactly what I wanted to do.

However, while it does work for some measures, some others seem to cause issues, like the measure 9 of a Rachmaninoff piece:

Manual extraction of measure 9 (working):

Automatic extraction of measure 9 using ScoreVariant (bugged):

After some investigations, I managed to track down what the issue was. When creating the new part with this score, it seems that the ScoreVariant objects creates it with part._quarter_durations set to [1] by default, while the original part has it set to [120]. Setting it manually using the part.quarter_duration_map method seems to fix the problem.

It's weird that the ScoreVariant does not take care of this by itself, as it seems that its create_variant_part method does play with the quarter durations (although I did not investigate further).

You can generate both versions with the following script:

from pathlib import Path

import partitura as pt
import partitura.score

SCORE_PATH = Path('/home/user/nasap-dataset/Rachmaninoff/Preludes_op_32/5/xml_score.musicxml')
START_MEASURE = 8
END_MEASURE = 10
OUT_DIR = Path("/tmp") / SCORE_PATH.name

score = pt.load_musicxml(SCORE_PATH)
assert len(score.parts) == 1
part = score.parts[0]

OUT_DIR.mkdir(exist_ok=True)

# Get the asked measures
start_measure: pt.score.Measure = part.measures[START_MEASURE - 1]
end_measure: pt.score.Measure = part.measures[END_MEASURE - 1]
print(f"Start measure: {start_measure}")
print(f"End measure: {end_measure}")

# Create a new ScoreVariant
sv = pt.score.ScoreVariant(part)
sv.add_segment(start_measure.start, end_measure.end)
new_part = sv.create_variant_part()

# See the difference between the quarter durations of the original and new part
print(f"{part._quarter_durations = }")
print(f"{new_part._quarter_durations = }")

# Save the new part without adapting the quarter durations
pt.save_musicxml(new_part, OUT_DIR / f"M{START_MEASURE}-{END_MEASURE}_naive.musicxml")

# Manually fix the quarter durations and save the new version
new_part.set_quarter_duration(0, part.quarter_duration_map(start_measure.start.t))
pt.save_musicxml(new_part, OUT_DIR / f"M{START_MEASURE}-{END_MEASURE}_fixed.musicxml")

EDIT: You can find another example of this issue in measure 26 of Bach/Fugue/bwv_857 in the ASAP dataset.

[sildater]

Thanks for submitting this issue and the detailed tests! I'll look into this.