center one-line staff

[sammik]

(For some context see comments to #19086)

One line staff looks better, if it is centered. It can be done manually by setting y - offset.
This PR just makes it happen automagically, whenever user changes number of lines to one, or move it back, if user increase number of lines.

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[XiaoMigros]

Shouldnt line 143 be m_staffType->setYoffset(yOffset + Spatium((linesOld - 1) / 2))? That way it will be centered when changing from non-5 line staves too. Also, it's perhaps worth considering to center all staves and not just 1-line ones?

[sammik]

Shouldnt line 143 be m_staffType->setYoffset(yOffset + Spatium((linesOld - 1) / 2))? That way it will be centered when changing from non-5 line staves too. Also, it's perhaps worth considering to center all staves and not just 1-line ones?

Yes, that is the question, what is intended behaviour.

Relation between 5-lines and 1-line staff is clear, because of barlines height.

Anything else (5 : 2 : 3 : 1) is questionable (in my opinion).

[mike-spa]

1. Spatium(2) is not the correct variable to use, because it returns the score-wide value of spatium. If this staff is scaled, spatium is different. Better to do something like double yCenteringOffset = 2 * spatium(); (spatium() function always returns the local spatium).
2. The distance between staff lines can be changed too, so it's not always equal to the spatium, so even better would be double yCenteringOffset = 2 * staff()->lineDist(tick()) * spatium();
3. You are applying the 2-space offset on top of the already existing offset. Could this lead to strange results if the user has already applied some manual offset? I think it would be safer in this case to override the user offset and just set offset = 2sp for the single line and offset = 0 for all the other cases.

[sammik]

@mike-spa thank You. Couple notes:

1. Spatium(2) is not the correct variable to use, because it returns the score-wide value of spatium. If this staff is scaled, spatium is different. Better to do something like double yCenteringOffset = 2 * spatium(); (spatium() function always returns the local spatium).

• I think, here no, as it is in Spatium units, so it is magnitude independent.

2. The distance between staff lines can be changed too, so it's not always equal to the spatium, so even better would be double yCenteringOffset = 2 * staff()->lineDist(tick()) * spatium();

• great idea! But if so, also line distance change on one line staff should recenter it, otherways something like this would happen:

LineHeight.mp4

So I fixed that too in last commit.

3. You are applying the 2-space offset on top of the already existing offset. Could this lead to strange results if the user has already applied some manual offset? I think it would be safer in this case to override the user offset and just set offset = 2sp for the single line and offset = 0 for all the other cases.

• Yes, I was thinking of this too, but in some situations, results may be even worse, I think.

Lets say, I have staff with offset set and want to create staff change to oneline staff . With Your proposal, offset is lost and staff is not centered. Than If I change back to 5 line staff, still wrongly offsetted. see:

New1.mp4

Oroginally, it behaves, I think better:

Old1.mp4

But Yes, in other situations, your proposal may be bit better (if previous offset is not meant as "general offset, but just like ad-hoc offset)

Changing to oneline in this situation seems to be more logical. But I am not sure, if change back is:

New2.mp4

In original, change to one line is worse, but change back may is really back to previous state:

Old2.mp4

I am not sure, if new one is better, but I aplied Your proposal, so it is done new way.
I can chage it, of course.

P.S. it seems, selection on offset staff needs improvement too :)

Have a nice day!