#5938 Thread skyline construction through stencil interpretation

[Han-Wen Nienhuys]

Before, we'd convert stencils to a combination of boxes and buildings,
and afterwards convert those to skylines.

The new approach has the following advantages:

• We can convert stencils to line segments directly, allowing for more
  precise outlines, and reduced memory overhead

• We can treat line thicknesses much more simply: we just extend line
  segments by 0.5 thicknesses on either side, and add them .5
  thickness up and down.

A next improvement is to thread Lazy_skyline_pair through to the glyph
outline generation. This would let us cut back on memory use for path
storage, and reduce the number of paths by 2x (the orientation of the
outline segments tells us if they are for the up or down skyline.)

Formatting impact:

The regtest shows 114 differences. The improved skylines lead to
slightly denser formatting, both horizontally and vertically. In
particular, some accidental configurations become very cramped (eg
accidental-placement.ly)

Timing impact: TODO

https://codereview.appspot.com/581960043

[Han-Wen Nienhuys]

separate header file, pass in transform.

https://codereview.appspot.com/581960043

[Han-Wen Nienhuys]

split functions into scm arg and rest

https://codereview.appspot.com/581960043

[Han-Wen Nienhuys]

tweaks; timings.

https://codereview.appspot.com/581960043

[Anonymous]

Passes make, make check and a full make doc

reg test diffs here (5.7MB)

https://cloud-u8zj2dc4b.yourownnet.eu/s/PzkGrdM36mA3qBf

[Han-Wen Nienhuys]

jonas, dak.

https://codereview.appspot.com/581960043

[Anonymous]

Passes make, make check and a full make doc

reg test diffs (patch set 5) here (~5.7MB):

https://cloud-u8zj2dc4b.yourownnet.eu/s/RAYGMaSKjTCKxmb

[Anonymous]

Patch on countdown for May 2nd

[Han-Wen Nienhuys]

update commit msg; no functional changes

https://codereview.appspot.com/581960043

[Anonymous]

I'll set to review and update tomorrow on the next countdown

[Han-Wen Nienhuys]

why does this need to go through another round? There are no code changes; it's just a rebase and update of the commit msg.

[Anonymous]

Patch counted down - please push

(@Hanwen, what I meant was that by using, I assume git-cl, the issue was set back to 'New', so all i was saying was that i'll review it on the next countdown as 'not new' - i.e. you can now push it).

[Jonas Hahnfeld]

commit 267e894e79fe5ce238c4db40f2a760511eead001
Author:     Han-Wen Nienhuys <hanwen@lilypond.org>
AuthorDate: Sat Apr 25 12:10:59 2020 +0200
Commit:     Han-Wen Nienhuys <hanwen@lilypond.org>
CommitDate: Sat May 2 09:26:21 2020 +0200

    Thread skyline construction through stencil interpretation