Hi all, Sharing here some extremely rough ideas on ways to potentially improve spacing for MetronomeMarks, RehearsalMarks, etc. Please pardon the very long message and rough code. Since I'm unsure how consistently I will be able to work on this, I wanted to share my proof of concept/work in progress.
Idea 1: A custom grob MarkAlignSpanner, created by Mark_align_engraver. This is based very closely on DynamicLineSpanner and the example engraver here: https://extending-lilypond.gitlab.io/en/extending/translation.html#example-for-setting-bounds-align-all-dynamics-engraver . Currently one issue is that when ledger lines or tall marks push the MarkAlignSpanner upward, the vertical extent of the system is not calculated correctly. I'm assuming this can be remedied by something in the grob definition. The nice thing about using a spanner rather than a custom MarkLine context is that, similar to DynamicLineSpanner, multiple MarkAlignSpanners could be created and broken allowing for multiple baselines, rather than just a single one for the entire score. Not sure exactly what criteria to use for breaking MarkAlignSpanners automatically – ideally I'd like for marks to align on the same axis spanner until a mark would require a different vertical offset beyond a threshold value, at which point the axis spanner would be broken. But that might require spacing information not available during translation. Maybe there is a clever solution? Idea 2: A custom grob MarkSpaceSpanner, created by Mark_space_engraver (code included in the same attached file, despite the file name). The idea here is to create a spanner connecting each consecutive mark, and to avoid horizontal overlapping marks by setting spacing-rods and minimum length. This could avoid the issues with music spacing caused by just setting extra-spacing-width and extra-spacing-height as in markLengthOn; also markLengthOn does not guarantee that marks will not be stacked vertically, particularly in situations with longer tempo markings over compressed MMRs. The proof-of-concept basically works, though it currently does not account for marks with horizontal extent to the left of the anchor point. I'm assuming that is a solvable problem. The more significant issue is that when I tried using this engraver in the context of a real world instrumental part, I still saw places where long marks over multi-measure rests were allowed to become stacked vertically, like this: [image: Screenshot 2023-07-12 at 5.39.44 PM.png] I'm not sure why this happens even with minimum-length and spacing rods set, and I haven't yet replicated the issue in a minimal test case. Perhaps a bug that prevents the spanner from being created/attached to bounds in certain cases? This is the first time I've attempted to create a custom grob or mess around with spanners like this, so I'm not sure exactly how to troubleshoot or what to look for. This proof-of-concept also doesn't currently work for spacing marks that occur at the same moment. I'm assuming this has to do with something fundamental in how spanners work, but I'm not sure. Not a showstopper, since Jean posted a very handy engraver to handle alignment and spacing of RehearsalMark + MetronomeMark at the same moment ( https://www.mail-archive.com/lilypond-user@gnu.org/msg146068.html). Another minor issue with this idea is that MarkSpaceSpanner should only affect spacing when it is unbroken. The commented out after-line-breaking callback in the grob definition was my attempt at resolving this, but it doesn't appear to work. I'm guessing because by the time grob-suicide is called, it has already affected the spacing? I'm assuming this is probably solvable though.
mark-align-spanner.ily
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