incorrect beaming in pickup measure

[mattblo]

Issue type

Engraving bug (incorrect score rendering)

Bug description

If you have a score with a pickup maesure on an unaccented beat the auto beaming is wrong.

Steps to reproduce

1. Create a new 6/8 score with a pickup measure 4/8
2. Write 4 eight Notes
   Wrong:
   
   

Right:

Screenshots/Screen recordings

No response

MuseScore Version

OS: Windows 10 Version 2009 or later, Arch.: x86_64, MuseScore version (64-bit): 4.2.1-240230937, revision: github-musescore-musescore-d757433

Regression

No.

Operating system

Windows 11

Additional context

This also happens in a 3/4 measure with an 3/8 Pickup measure.

[MarcSabatella]

Definitely not a regression - MuseScore has never had an algorithm to try to decide if a given incomplete measure should be treated as the first or second half of a full measure in terms of beaming. Note the same applies when splitting a measure for the purpose of adding mid-measure repeats or system breaks, or indeed any incomplete measure.

I was pretty sure there was already an issue here on GitHub regarding this but I'm not finding it. So I'll just repeat something I know I've observed before - there does exist a simple heuristic for deciding this in the swing playback code:

MuseScore/src/engraving/dom/swing.cpp

Lines 62 to 73 in 5087c42

	// adjust for anacrusis
	const Measure* cm = chord->measure();
	const MeasureBase* pm = cm->prev();
	ElementType pt = pm ? pm->type() : ElementType::INVALID;
	if (!pm || pm->lineBreak() || pm->pageBreak() || pm->sectionBreak()
	|| pt == ElementType::VBOX || pt == ElementType::HBOX
	|| pt == ElementType::FBOX || pt == ElementType::TBOX) {
	Fraction offset = cm->timesig() - cm->ticks();
	if (offset > Fraction(0, 1)) {
	tick += offset;
	}
	}

It doesn't handle split measures on the same system well, though - so, split measures for the purpose of repeats don't play well in swing.

It could be nice to have one function to make this determination consistently for both beaming and for swing.

[XiaoMigros]

I'd be happy to work on this!