11.3.4 Optimal page turning

Often it is necessary to find a page breaking configuration so that there is a rest at the end of every second page. This way, the musician can turn the page without having to miss notes. The ly:page-turn-breaking function attempts to find a page breaking minimizing cramping and stretching, but with the additional restriction that it is only allowed to introduce page turns in specified places.

There are two steps to using this page breaking function. First, you must enable it in the \paper block. Then, you must tell the function where you would like to allow page breaks.

There are two ways to achieve the second step. First, you can specify each potential page turn manually, by inserting \allowPageTurn into your input file at the appropriate places.

If this is too tedious, you can add a Page_turn_engraver to a Staff or Voice context. The Page_turn_engraver will scan the context for sections without notes (note that it does not scan for rests; it scans for the absence of notes. This is so that single-staff polyphony with rests in one of the parts does not throw off the Page_turn_engraver). When it finds a sufficiently long section without notes, the Page_turn_engraver will insert an \allowPageTurn at the final barline in that section, unless there is a ‘special’ barline (such as a double bar), in which case the \allowPageTurn will be inserted at the final ‘special’ barline in the section.

The Page_turn_engraver reads the context property minimumPageTurnLength to determine how long a note-free section must be before a page turn is considered. The default value for minimumPageTurnLength is #(ly:make-moment 1 1). If you want to disable page turns, you can set it to something very large.

\new Staff \with { \consists "Page_turn_engraver" }
{
  a4 b c d |
  R1 | % a page turn will be allowed here
  a4 b c d |
  \set Staff.minimumPageTurnLength = #(ly:make-moment 5 2)
  R1 | % a page turn will not be allowed here
  a4 b r2 |
  R1*2 | % a page turn will be allowed here
  a1
}

The Page_turn_engraver detects volta repeats. It will only allow a page turn during the repeat if there is enough time at the beginning and end of the repeat to turn the page back. The Page_turn_engraver can also disable page turns if the repeat is very short. If you set the context property minimumRepeatLengthForPageTurn then the Page_turn_engraver will only allow turns in repeats whose duration is longer than this value.

Bugs

There should only be one Page_turn_engraver in a score. If there is more than one, they will interfere with each other.