magnifyStaff and key signature padding.

[Pierre Perol-Schneider]

Hi bug squad,

magnifyStaff uses the same key signature padding as a full size staff (0).
Actually, 100% of the chamber music scores facsimiles found on IMSLP have a
larger padding on smaller staves.
So here's a workaround proposal:

\version "2.19.83"

scaleStaff = #(define-music-function (scaleFac) (number?)
                 #{
                   \magnifyStaff #scaleFac
                   \override KeySignature.padding = #(* 2/3 (- 1 scaleFac))
                 #})

sizeTest = #5/7
keyTest = { \key cis\major s4*4 \bar "" }

\markup\italic "Default output:"
<<
  \new Staff \with { \magnifyStaff #sizeTest } \keyTest
  \new Staff \keyTest
>>

\markup\italic "Regular output:"
<<
  \new Staff \with { \scaleStaff #sizeTest } \keyTest
  \new Staff \keyTest
>>

See also: https://notat.io/viewtopic.php?f=2&t=470

Cheers,
Pierre