#5951 Calculate skylines only once.

[Han-Wen Nienhuys]

Before, Axis_group_interface::skyline_spacing() would call the
function add_interior_skylines(), which recursed into
VerticalAxisGroups. This caused staff-skylines to be computed twice:
once as part of the Staff's VerticalAxisGroup, and once to compute
the skyline for System.

Instead, in Axis_group_interface::skyline_spacing(), compute the
vertical-skylines for all constituent elements. Since the property is
subject to caching, the Staff skyline is only computed once.

To make this work

• Add flags to the NoteColumn using Axis_group_interface::add_element

• add vertical-skylines callbacks for NoteColumn and
  NoteCollision, which are also X,Y Axis groups.

• declare add-stem-support for bass figures (or the digits are meshed
  in with stems that stick out of the staff.)

• calculate a skyline for BassFigureAlignment, otherwise, the skyline
  is computed from the extent of the alignment, which is inaccurate if
  some bass figures have accidentals.

Formatting impact:

• ottava-edge.ly - the ottava bracket meshes better with the stem,
  leading to tighter spacing.

Timing impact

ac49229cdf - Calculate skylines only once.
baseline: eaf40071f5 Use vectors rather than lists for skylines.
args: -I carver MSDM
memory: med diff 1916 (stddevs 103 135, n=5)
memory: med diff 0.2 % (ac49229cdf is fatter)
time: med diff -0.37 (stddevs 0.08 0.14, n=5)
time: med diff -0.8 % (ac49229cdf is faster)

https://codereview.appspot.com/553980043

[Han-Wen Nienhuys]

fix snafu

https://codereview.appspot.com/553980043

[Anonymous]

Passes make, make check and a full make doc.

Reg test diffs attached

[Anonymous]

diffs

[Anonymous]

Patch on countdown for May 6th

[Anonymous]

Patch counted down - please push

[Jonas Hahnfeld]

commit 750d6a547567409b6aa2d49bcb34912774aae4bc
Author:     Han-Wen Nienhuys <hanwen@lilypond.org>
AuthorDate: Sun Apr 26 15:39:01 2020 +0200
Commit:     Han-Wen Nienhuys <hanwen@lilypond.org>
CommitDate: Fri May 8 09:14:16 2020 +0200

    Calculate skylines only once.

    Before, Axis_group_interface::skyline_spacing() would call the
    function add_interior_skylines(), which recursed into
    VerticalAxisGroups.  This caused staff-skylines to be computed twice:
    once as part of the Staff's VerticalAxisGroup, and once to compute
    the skyline for System.

    Instead, in Axis_group_interface::skyline_spacing(), compute the
    vertical-skylines for all constituent elements.  Since the property is
    subject to caching, the Staff skyline is only computed once.

    To make this work

    * Add flags to the NoteColumn using Axis_group_interface::add_element

    * add vertical-skylines callbacks for NoteColumn and
      NoteCollision, which are also X,Y Axis groups.

    * declare add-stem-support for bass figures (or the digits are meshed
      in with stems that stick out of the staff.)

    * calculate a skyline for BassFigureAlignment, otherwise, the skyline
      is computed from the extent of the alignment, which is inaccurate if
      some bass figures have accidentals.

    Formatting impact:

    * ottava-edge.ly - the ottava bracket meshes better with the stem,
      leading to tighter spacing.

    Timing impact

    ac49229cdf - Calculate skylines only once.
      baseline: eaf40071f5 Use vectors rather than lists for skylines.
      args: -I carver MSDM
      memory: med diff 1916 (stddevs 103 135, n=5)
      memory: med diff 0.2 % (ac49229cdf is fatter)
      time: med diff -0.37 (stddevs 0.08 0.14, n=5)
      time: med diff -0.8 % (ac49229cdf is faster)