* scm/layout-page-layout.scm (page-breaking-wrapper): new

function. Call the page breaking function selected in the
`page-breaking' \paper variable, then the post processing function
chosen using the `page-post-process' \paper variable.
(line-height): new function. Return the height of a system.
(line-minimum-position-on-page): new function. Return the position
of a system on page (using the previous line position), only
considering between system padding.
(stretchable-line?): new function. Says whether a line can be
stretched (ie. is not a title nor a single staff system).
(page-maximum-space-left): new function. Computes space left on a
page, when all systems are separated by their padding.

* lily/page-breaking.cc (breaking::make_pages): Move page post
processing function call to page breaking wrapper (common to all
page breakers).

* lily/paper-book.cc (book::pages): call the page breaking
wrapper, instead of the page breaker directly

* ly/paper-defaults.ly: Add \paper variables for page breaking
wrapper and page post processing function. Make
`write-page-layout' value depend on the 'dump-tweaks option. Add a
`system-maximum-stretch-procedure' variable for holding a function
computing the maximum stretch a system allows.

* scm/layout-page-dump.scm (write-page-breaks): computes the
stretch to apply to systems on a page to minimize left
space. Dump this stretch length.

* ly/music-functions-init.ly (spacingTweaks): implement it. Read
the system-stretch property of the tweak data to stretch the
system.
(includePageLayoutFile): Void function which includes the
generated page-layout file if it exists and if the page layout
dumping is not asked.
(scoreTweak): if the score tweak named by the argument exists,
return it.

2 files changed, 50 insertions, 3 deletions

diff --git a/ly/music-functions-init.ly b/ly/music-functions-init.ly
index 02519f5361..b910223f68 100644
--- a/ly/music-functions-init.ly
+++ b/ly/music-functions-init.ly
@@ -370,6 +370,9 @@ parenthesize =
    (set! (ly:music-property arg 'parenthesize) #t)
    arg)
 
+%% for lambda*
+#(use-modules (ice-9 optargs))
+
 parallelMusic =
 #(define-music-function (parser location voice-ids music) (list? ly:music?)
   "Define parallel music sequences, separated by '|' (bar check signs),
@@ -439,7 +442,7 @@ Example:
               voices)
     ;;
     ;; check sequence length
-    (apply for-each (lambda (. seqs)
+    (apply for-each (lambda* (#:rest seqs)
                       (let ((moment-reference (ly:music-length (car seqs))))
                         (for-each (lambda (seq moment)
                                     (if (not (equal? moment moment-reference))
@@ -500,12 +503,45 @@ shiftDurations =
     (lambda (x)
       (shift-one-duration-log x dur dots)) arg))
 
-
-%% this is a stub. Write your own to suit the spacing tweak output.
 spacingTweaks =
 #(define-music-function (parser location parameters) (list?)
+   "Set the system stretch, by reading the 'system-stretch property of
+   the `parameters' assoc list."
+   #{
+      \overrideProperty #"Score.NonMusicalPaperColumn"
+        #'line-break-system-details
+        #$(list (cons 'alignment-extra-space (cdr (assoc 'system-stretch parameters))))
+   #})
+
+%% Parser used to read page-layout file, and then retreive score tweaks.
+#(define page-layout-parser #f)
+
+includePageLayoutFile = 
+#(define-music-function (parser location) ()
+   "If page breaks and tweak dump is not asked, and the file
+   <basename>-page-layout.ly exists, include it."
+   (if (not (ly:get-option 'dump-tweaks))
+       (let ((tweak-filename (format #f "~a-page-layout.ly"
+				     (ly:parser-output-name parser))))
+	 (if (access? tweak-filename R_OK)
+	     (begin
+	       (ly:message "Including tweak file ~a" tweak-filename)
+               (set! page-layout-parser (ly:clone-parser parser))
+	       (ly:parser-parse-string page-layout-parser
+                                       (format #f "\\include \"~a\""
+                                               tweak-filename))))))
    (make-music 'SequentialMusic 'void #t))
 
+scoreTweak =
+#(define-music-function (parser location name) (string?)
+   "Include the score tweak, if exists."
+   (if (and page-layout-parser (not (ly:get-option 'dump-tweaks)))
+       (let ((tweak-music (ly:parser-lookup page-layout-parser
+                                            (string->symbol name))))
+         (if (ly:music? tweak-music)
+             tweak-music
+             (make-music 'SequentialMusic)))
+       (make-music 'SequentialMusic)))
 
 transposedCueDuring =
 #(define-music-function
diff --git a/ly/paper-defaults.ly b/ly/paper-defaults.ly
index 2e265c7ab1..44ec0b961e 100644
--- a/ly/paper-defaults.ly
+++ b/ly/paper-defaults.ly
@@ -97,6 +97,17 @@
 	(word-space . 0.6)))
 
     #(define page-breaking ly:optimal-breaking)
+    #(define page-breaking-wrapper page-breaking-wrapper)
+    #(define page-post-process post-process-pages)
+
+    #(define write-page-layout (ly:get-option 'dump-tweaks))
+    #(define system-maximum-stretch-procedure
+       (lambda (line)
+	 (if (stretchable-line? line)
+	     (let ((height (line-height line)))
+	       (/ (* height height) 80.0))
+	     0.0)))
+
 %    #(define page-music-height default-page-music-height )
 %    #(define page-make-stencil default-page-make-stencil )