]> git.donarmstrong.com Git - lilypond.git/blobdiff - scm/layout-page-layout.scm
* python/convertrules.py (conv): warning on \tempo{}
[lilypond.git] / scm / layout-page-layout.scm
index 96b1265d4a2348e39c1faa12555a5cf285369317..215b5003d02e074ed9521a66e581888a53f379b1 100644 (file)
-;;;; page-layout.scm -- page breaking and page layout
+;;;; layout-page-layout.scm -- page breaking and page layout
 ;;;;
 ;;;;  source file of the GNU LilyPond music typesetter
 ;;;;
 ;;;; (c) 2004--2006 Jan Nieuwenhuizen <janneke@gnu.org>
 ;;;;          Han-Wen Nienhuys <hanwen@cs.uu.nl>
 
-(use-modules (oop goops describe)
-            (oop goops)
-            (scm paper-system)
-            (scm page)
-            )
-
-(define (write-page-breaks pages) 
-  "Dump page breaks"
-
-  
-  (define tweaks '())
-
-  (define (record when property-pairs)
-    (set! tweaks
-         (acons when property-pairs
-                tweaks)))
-  (define (graceless-moment mom)
-    (ly:make-moment
-     (ly:moment-main-numerator mom)
-     (ly:moment-main-denominator mom)
-     0 0))
-     
-  (define (moment->skip mom)
-    (let*
-       ((main (if (> (ly:moment-main-numerator mom) 0)
-                  (format "\\skip 1*~a/~a"
-                          (ly:moment-main-numerator mom)
-                          (ly:moment-main-denominator mom))
-                  ""))
-        (grace (if (< (ly:moment-grace-numerator mom) 0)
-                   (format "\\grace { \\skip 1*~a/~a }"
-                           (- (ly:moment-grace-numerator mom))
-                           (ly:moment-grace-denominator mom))
-                   "")))
-
-      (format "~a~a" main grace)))
-    
-  (define (dump-tweaks out-port tweak-list last-moment)
-    (if (not (null? tweak-list))
-       (let*
-           ((now (caar tweak-list))
-            (diff (ly:moment-sub now last-moment))
-            (these-tweaks (cdar tweak-list))
-            (skip (moment->skip diff))
-            (line-break-str (if (assoc-get 'line-break these-tweaks #f)
-                                "\\break\n"
-                                ""))
-            (page-break-str (if (assoc-get 'page-break these-tweaks #f)
-                                "\\pageBreak\n"
-                                ""))
-            (space-tweaks (format "\\spacingTweaks #'~a\n"
-                                  (with-output-to-string
-                                    (lambda ()
-                                      (pretty-print
-                                  
-                                       (assoc-get 'spacing-parameters these-tweaks '()))))
-                                    ))
-            (base (format "~a~a~a"
-                          line-break-str
-                          page-break-str
-                          space-tweaks))
-            )
-
-         (format out-port "~a\n~a\n" skip base)
-         (dump-tweaks out-port (cdr tweak-list) (graceless-moment now))
-       )))
-  
-  (define (handle-page page)
-    (define index 0)
-    (define (handle-system sys)
-      (let*
-         ((props `((line-break . #t)
-                   (spacing-parameters
-                    . ((system-Y-extent . ,(paper-system-extent sys Y))
-                       (system-refpoint-Y-extent . ,(paper-system-staff-extents sys))
-                       (system-index . ,index)
-                       (page-system-count . ,(length (page-lines page)))
-                       (page-printable-height . ,(page-printable-height page)) 
-                       (page-space-left . ,(page-property page 'space-left))))
-                   )))
-
-       (if (equal? (car (page-lines page)) sys)
-           (set! props (cons '(page-break . #t)
-                             props)))
-       (if (not (ly:prob-property? sys 'is-title))
-           (record (ly:grob-property (ly:spanner-bound (ly:prob-property sys 'system-grob) LEFT) 'when)
-                 props))
-
-       (set! index (1+ index))
-       ))
-    (for-each handle-system (page-lines page)))
-  
-  
-  (for-each handle-page pages)
-
-  (let*
-      ((out-port (open-output-file "breaks.ly")))
-
-    (display "{" out-port)
-    (dump-tweaks out-port (reverse tweaks) (ly:make-moment 0 1))
-    (display "}" out-port)
-  ))
-
-
+(define-module (scm layout-page-layout)
+  #:use-module (srfi srfi-1)
+  #:use-module (oop goops describe)
+  #:use-module (oop goops)
+  #:use-module (scm paper-system)
+  #:use-module (scm page)
+  #:use-module (scm layout-page-dump)
+  #:use-module (lily)
+  #:export (post-process-pages optimal-page-breaks make-page-from-systems))
 
 (define (post-process-pages layout pages)
-  (if (ly:get-option 'write-page-layout)
+  (if (ly:output-def-lookup layout 'write-page-layout #f)
       (write-page-breaks pages)))
 
-
-
-;;; optimal page breaking
-
-;;; This is not optimal page breaking, this is optimal distribution of
-;;; lines over pages; line breaks are a given.
+;;;
+;;; Utilities for computing line distances and positions
+;;;
+(define (line-next-space line next-line layout)
+  "Return space to use between `line' and `next-line'.
+  `next-line' can be #f, meaning that `line' is the last line."
+  (let* ((title? (paper-system-title? line))
+         (next-title? (and next-line (paper-system-title? next-line))))
+    (cond ((and title? next-title?)
+           (ly:output-def-lookup layout 'between-title-space))
+          (title?
+           (ly:output-def-lookup layout 'after-title-space))
+          (next-title?
+           (ly:output-def-lookup layout 'before-title-space))
+          (else
+           (ly:prob-property
+            line 'next-space
+            (ly:output-def-lookup layout 'between-system-space))))))
+
+(define (line-next-padding line next-line layout)
+  "Return padding to use between `line' and `next-line'.
+  `next-line' can be #f, meaning that `line' is the last line."
+  (ly:prob-property
+   line 'next-padding
+   (ly:output-def-lookup layout 'between-system-padding)))
+
+
+(define (line-minimum-distance line next-line layout)
+  "Minimum distance between `line' reference position and `next-line'
+ reference position. If next-line is #f, return #f."
+  (and next-line
+       (max 0 (- (+ (interval-end (paper-system-extent next-line Y))
+                    (line-next-padding line next-line layout))
+                 (interval-start (paper-system-extent line Y))))))
+
+(define (line-ideal-distance line next-line layout)
+  "Ideal distance between `line' reference position and `next-line'
+ reference position. If next-line is #f, return #f."
+  (and next-line
+       (+ (max 0 (- (+ (interval-end (paper-system-staff-extents next-line))
+                       (line-next-padding line next-line layout))
+                    (interval-start (paper-system-staff-extents line))))
+          (line-next-space line next-line layout))))
+
+(define (first-line-position line layout)
+  "Position of the first line on page"
+  (max (+ (ly:output-def-lookup layout 'page-top-space)
+          (interval-end (paper-system-staff-extents line)))
+       (interval-end (paper-system-extent line Y))))
+
+(define (line-ideal-relative-position line prev-line layout)
+  "Return ideal position of `line', relative to `prev-line' position.
+  `prev-line' can be #f, meaning that `line' is the first line."
+  (if (not prev-line)
+      ;; first line on page
+      (first-line-position line layout)
+      ;; not the first line on page
+      (max (line-minimum-distance prev-line line layout)
+           (line-ideal-distance prev-line line layout))))
+
+(define (line-minimum-relative-position line prev-line layout)
+  "Return position of `line', relative to `prev-line' position.
+  `prev-line' can be #f, meaning that `line' is the first line."
+  (if (not prev-line)
+      ;; first line on page
+      (first-line-position line layout)
+      ;; not the first line on page
+      (line-minimum-distance prev-line line layout)))
+
+;;;
+;;; Page breaking functions
+;;;
+
+;; Optimal distribution of
+;; lines over pages; line breaks are a given.
 
 ;; TODO:
 ;;
 ;; - density scoring
 ;; - separate function for word-wrap style breaking?
-;; - raggedbottom? raggedlastbottom?
-
-(define-public (optimal-page-breaks lines paper-book)
-  "Return pages as a list starting with 1st page. Each page is a 'page Prob."
-
-  (define MAXPENALTY 1e9)
-  (define paper (ly:paper-book-paper paper-book))
+;; - ragged-bottom? ragged-last-bottom?
 
-  ;; ugh.
-  (define page-alist (layout->page-init (ly:paper-book-paper paper-book))) 
-  (define scopes (ly:paper-book-scopes paper-book))
-  (define force-equalization-factor #f)
-  (define (get-path node done)
-    "Follow NODE.PREV, and return as an ascending list of pages. DONE
+(define (get-path node done)
+  "Follow NODE.PREV, and return as an ascending list of pages. DONE
 is what have collected so far, and has ascending page numbers."
-
-    (if (page? node)
-       (get-path (page-prev node) (cons node done))
-       done))
-
-  (define (combine-penalties force user best-paths)
-    (let* ((prev-force (if (null? best-paths)
-                          0.0
-                          (page-force (car best-paths))))
-          (prev-penalty (if (null? best-paths)
-                            0.0
-                            (page-penalty (car best-paths))))
-        (inter-system-space (ly:output-def-lookup paper 'betweensystemspace))
+  (if (page? node)
+      (get-path (page-prev node) (cons node done))
+      done))
+
+(define (combine-penalties force user best-paths
+                           inter-system-space force-equalization-factor)
+  (let* ((prev-force (if (null? best-paths)
+                         0.0
+                         (page-force (car best-paths))))
+         (prev-penalty (if (null? best-paths)
+                           0.0
+                           (page-penalty (car best-paths))))
         (relative-force (/ force inter-system-space))
         (abs-relative-force (abs relative-force)))
-
-      (+ (* abs-relative-force (+ abs-relative-force 1))
-        prev-penalty
-        (* force-equalization-factor (/ (abs (- prev-force force))
-                                        inter-system-space))
-        user)))
-
-  (define (space-systems page-height lines ragged?)
-    (let* ((global-inter-system-space
-           (ly:output-def-lookup paper 'betweensystemspace))
-          (top-space
-           (ly:output-def-lookup paper 'pagetopspace))
-          (global-fixed-dist (ly:output-def-lookup paper 'betweensystempadding))
-          
-          (system-vector (list->vector
-                          (append lines
-                                  (if (= (length lines) 1)
-                                      '(#f)
-                                      '()))))
-          (staff-extents
-           (list->vector
-            (append (map paper-system-staff-extents lines)
-                    (if (= (length lines) 1)
-                        '((0 . 0))
-                        '()))))
-
-          (real-extents
-           (list->vector
-            (append
-             (map
-              (lambda (sys) (paper-system-extent sys Y)) lines)
-             (if (= (length lines) 1)
-                 '((0 .  0))
-                 '()))))
-          
-          (system-count (vector-length real-extents))
-          (topskip (max
-                    (+
-                     top-space
-                     (interval-end (vector-ref staff-extents 0)))
-                    (interval-end (vector-ref real-extents 0))
-                    ))
-          (last-system (vector-ref system-vector (1- system-count)))
-          (bottom-space (if (ly:prob? last-system)
-                            (ly:prob-property last-system 'bottom-space 0.0)
-                            0.0))
-          (space-left (- page-height
-                         bottom-space
-                         (apply + (map interval-length
-                                       (vector->list real-extents)))))
-
-          (space (- page-height
-                    topskip
-                    bottom-space
-                    (-  (interval-start
-                         (vector-ref real-extents (1- system-count))))))
-
-          (calc-spring
-           (lambda (idx)
-             (let* (
-                    (upper-system (vector-ref system-vector idx))
-                    (between-space (ly:prob-property upper-system 'next-space
-                                                             global-inter-system-space))
-                    (fixed-dist (ly:prob-property upper-system 'next-padding
-                                                          global-fixed-dist))
-                    
-                    (this-system-ext (vector-ref staff-extents idx))
-                    (next-system-ext (vector-ref staff-extents (1+ idx)))
-                    (fixed (max 0 (- (+ (interval-end next-system-ext)
-                                        fixed-dist)
-                                     (interval-start this-system-ext))))
-                    (title1? (and (vector-ref system-vector idx)
-                                  (paper-system-title? (vector-ref system-vector idx)
-                                                            )))
-                    (title2? (and
-                              (vector-ref system-vector (1+ idx))
-                              (paper-system-title? (vector-ref system-vector (1+ idx)))))
-                    (ideal (+
-                            (cond
-                             ((and title2? title1?)
-                              (ly:output-def-lookup paper 'betweentitlespace))
-                             (title1?
-                              (ly:output-def-lookup paper 'aftertitlespace))
-                             (title2?
-                              (ly:output-def-lookup paper 'beforetitlespace))
-                             (else between-space))
-                            fixed))
-                    (hooke (/ 1 (- ideal fixed))))
-               (list ideal hooke))))
-
-          (springs (map calc-spring (iota (1- system-count))))
-          (calc-rod
-           (lambda (idx)
-             (let* (
-                    (upper-system (vector-ref system-vector idx))
-                    (fixed-dist (ly:prob-property upper-system 'next-padding
-                                                          global-fixed-dist))
-                    (this-system-ext (vector-ref real-extents idx))
-                    (next-system-ext (vector-ref real-extents (1+ idx)))
-                    
-                    (distance (max  (- (+ (interval-end next-system-ext)
-                                          fixed-dist)
-                                       (interval-start this-system-ext)
-                                       ) 0))
-                    (entry (list idx (1+ idx) distance)))
-               entry)))
-          (rods (map calc-rod (iota (1- system-count))))
-
-          ;; we don't set ragged based on amount space left.
-          ;; raggedbottomlast = ##T is much more predictable
-          (result (ly:solve-spring-rod-problem
-                   springs rods space
-                   ragged?))
-
-          (force (car result))
-          (positions
-           (map (lambda (y)
-                  (+ y topskip))
-                (cdr  result))))
-
-      (if #f ;; debug.
-         (begin
-           (display (list "\n# systems: " system-count
-                          "\nreal-ext" real-extents "\nstaff-ext" staff-extents
-                          "\ninterscore" global-inter-system-space
-                          "\nspace-left" space-left
-                          "\nspring,rod" springs rods
-                          "\ntopskip " topskip
-                          " space " space
-                          "\npage-height" page-height
-                          "\nragged" ragged?
-                          "\nforce" force
-                          "\nres" (cdr result)
-                          "\npositions" positions "\n"))))
-
-      (cons force positions)))
-
-  (define (walk-paths done-lines best-paths current-lines  last? current-best)
-    "Return the best optimal-page-break-node that contains
+    (+ (* abs-relative-force (+ abs-relative-force 1))
+       prev-penalty
+       (* force-equalization-factor (/ (abs (- prev-force force))
+                                       inter-system-space))
+       user)))
+
+(define (space-systems page-height lines ragged? paper)
+  "Compute lines positions on page: return force and line positions as a pair.
+ force is #f if lines do not fit on page."
+  (let* ((empty-stencil (ly:make-stencil '() '(0 . 0) '(0 . 0)))
+        (empty-prob (ly:make-prob 'paper-system (list `(stencil . ,empty-stencil))))
+        (cdr-lines (append (cdr lines)
+                           (if (<= (length lines) 1)
+                               (list empty-prob)
+                               '())))
+        (springs (map (lambda (prev-line line)
+                         (list (line-ideal-distance prev-line line paper)
+                               (/ 1.0 (line-next-space prev-line line paper))))
+                       lines
+                       cdr-lines))
+         (rods (map (let ((i -1))
+                      (lambda (prev-line line)
+                        (set! i (1+ i))
+                        (list i (1+ i)
+                              (line-minimum-distance prev-line line paper))))
+                       lines
+                       cdr-lines))
+         (last-line (car (last-pair lines)))
+         (topskip (first-line-position (first lines) paper))
+         (space-to-fill (- page-height
+                           topskip
+                           (ly:prob-property last-line
+                                             'bottom-space 0.0)
+                           (- (interval-start (paper-system-extent
+                                               last-line Y)))))
+         (space-result
+          (ly:solve-spring-rod-problem springs rods space-to-fill ragged?)))
+    (cons (car space-result)
+          (map (lambda (y)
+                 (+ y topskip))
+               (cdr space-result)))))
+
+(define (make-page-from-systems paper-book lines page-number ragged? last?)
+  (let*
+    ((page (make-page
+            paper-book
+            'lines lines
+            'page-number page-number
+            'is-last last?))
+     (height (page-printable-height page))
+     (posns (if (> (length lines) 0)
+               (cdr (space-systems height lines ragged? (ly:paper-book-paper paper-book)))
+               '())))
+    (page-set-property! page 'configuration posns)
+    page))
+
+(define (walk-paths done-lines best-paths current-lines last? current-best
+                    paper-book page-alist)
+  "Return the best optimal-page-break-node that contains
 CURRENT-LINES.  DONE-LINES.reversed ++ CURRENT-LINES is a consecutive
 ascending range of lines, and BEST-PATHS contains the optimal breaks
 corresponding to DONE-LINES.
 
 CURRENT-BEST is the best result sofar, or #f."
-
-
-    (let* ((this-page-num (if (null? best-paths)
-                              (ly:output-def-lookup paper 'firstpagenumber)
-                              (1+ (page-page-number (car best-paths)))))
-
-          (this-page (make-page
-                      page-alist
-                      'paper-book paper-book
-                      'is-last last?
-                      'page-number this-page-num))
-
-          (ragged-all? (eq? #t (ly:output-def-lookup paper 'raggedbottom)))
-          (ragged-last? (eq? #t (ly:output-def-lookup paper 'raggedlastbottom)))
-          (ragged? (or ragged-all?
-                       (and ragged-last?
-                            last?)))
-           (height (page-printable-height this-page))
-          (vertical-spacing (space-systems height current-lines ragged?))
-          (satisfied-constraints (car vertical-spacing))
-           (force (if satisfied-constraints
-                     (if (and last? ragged-last?)
-                         0.0
-                         satisfied-constraints)
-                     10000))
-          (positions (cdr vertical-spacing))
-          (get-break-penalty (lambda (sys)
-                               (ly:prob-property sys 'penalty 0.0)))
-          (user-nobreak-penalties
-           (-
-            (apply + (filter negative?
-                             (map get-break-penalty
-                                  (cdr current-lines))))))
-           (user-penalty
-           (+
-            (max (get-break-penalty (car current-lines)) 0.0)
-            user-nobreak-penalties))
-          
-           (total-penalty (combine-penalties
-                           force user-penalty
-                          best-paths))
-
-           (better? (or
-                     (not current-best)
-                     (< total-penalty (page-penalty current-best))))
-           (new-best (if better?
-                        (begin
-                          (map
-                           (lambda (x)
-                             (page-set-property! this-page
-                                                 (car x)
-                                                 (cdr x)))
-                           (list
-                            (cons 'prev (if (null? best-paths)
-                                            #f
-                                            (car best-paths)))
-                            (cons 'lines current-lines)
-                            (cons 'force force)
-                            (cons 'configuration positions)
-                            (cons 'penalty total-penalty)))
-                          this-page)
-                         current-best)))
-
-;;      (display total-penalty) (newline)
-      (if #f ;; debug
-          (display
-           (list
-            "\nuser pen " user-penalty
-           "\nsatisfied-constraints" satisfied-constraints
-           "\nlast? " last? "ragged?" ragged?
-            "\nbetter? " better? " total-penalty " total-penalty "\n"
-           "\nconfig " positions
-            "\nforce " force
-           "\nlines: " current-lines "\n")))
-
-      (if #f ; debug
-         (display (list "\nnew-best is " (page-lines new-best)
-                        "\ncontinuation of "
-                        (if (null? best-paths)
-                            "start"
-                            (page-lines (car best-paths))))))
-
-      (if (and (pair? done-lines)
-               ;; if this page is too full, adding another line won't help
-               satisfied-constraints)
-          (walk-paths (cdr done-lines) (cdr best-paths)
-                      (cons (car done-lines) current-lines)
-                      last? new-best)
-         new-best)))
-
-  (define (walk-lines done best-paths todo)
-    "Return the best page breaking as a single
+  (let* ((paper (ly:paper-book-paper paper-book))
+         (this-page (make-page
+                     paper-book
+                     'is-last last?
+                     'page-number (if (null? best-paths)
+                                      (ly:output-def-lookup paper 'first-page-number)
+                                      (1+ (page-page-number (first best-paths))))))
+         (ragged-all? (eq? #t (ly:output-def-lookup paper 'ragged-bottom)))
+         (ragged-last? (eq? #t (ly:output-def-lookup paper 'ragged-last-bottom)))
+         (ragged? (or ragged-all? (and ragged-last? last?)))
+         (height (page-printable-height this-page))
+         (vertical-spacing (space-systems height current-lines ragged? paper))
+         (satisfied-constraints (car vertical-spacing))
+         (force (if satisfied-constraints
+                    (if (and last? ragged-last?)
+                        0.0
+                        satisfied-constraints)
+                    10000))
+         (positions (cdr vertical-spacing))
+         (get-break-penalty (lambda (sys)
+                              (ly:prob-property sys 'penalty 0.0)))
+         (user-nobreak-penalties (- (apply + (filter negative?
+                                                     (map get-break-penalty
+                                                          (cdr current-lines))))))
+         (user-penalty (+ (max (get-break-penalty (car current-lines)) 0.0)
+                          user-nobreak-penalties))
+         (total-penalty (combine-penalties
+                         force user-penalty best-paths
+                         (ly:output-def-lookup paper 'between-system-space)
+                         (ly:output-def-lookup paper 'verticalequalizationfactor 0.3)))
+         (new-best (if (or (not current-best)
+                           (and satisfied-constraints
+                                (< total-penalty (page-penalty current-best))))
+                       (begin
+                         (map (lambda (x)
+                                (page-set-property! this-page
+                                                    (car x)
+                                                    (cdr x)))
+                              (list (cons 'prev (if (null? best-paths)
+                                                    #f
+                                                    (car best-paths)))
+                                    (cons 'lines current-lines)
+                                    (cons 'force force)
+                                    (cons 'configuration positions)
+                                    (cons 'penalty total-penalty)))
+                         this-page)
+                       current-best)))
+    (if #f ;; debug
+        (display
+         (list
+          "\nuser pen " user-penalty
+          "\nsatisfied-constraints" satisfied-constraints
+          "\nlast? " last? "ragged?" ragged?
+          "\nis-better " is-better " total-penalty " total-penalty "\n"
+          "\nconfig " positions
+          "\nforce " force
+          "\nlines: " current-lines "\n")))
+    (if #f ; debug
+        (display (list "\nnew-best is " (page-lines new-best)
+                       "\ncontinuation of "
+                       (if (null? best-paths)
+                           "start"
+                           (page-lines (car best-paths))))))
+    (if (and (pair? done-lines)
+             ;; if this page is too full, adding another line won't help
+             satisfied-constraints)
+        (walk-paths (cdr done-lines) (cdr best-paths)
+                    (cons (car done-lines) current-lines)
+                    last? new-best
+                    paper-book page-alist)
+        new-best)))
+
+(define (walk-lines done best-paths todo paper-book page-alist)
+  "Return the best page breaking as a single
 page node for optimally breaking TODO ++
 DONE.reversed. BEST-PATHS is a list of break nodes corresponding to
 DONE."
-    
-    (if (null? todo)
-       (car best-paths)
-       (let* ((this-line (car todo))
-              (last? (null? (cdr todo)))
-              (next (walk-paths done best-paths (list this-line) last? #f)))
-
-         ;; (display "\n***************")
-         (walk-lines (cons this-line done)
-                     (cons next best-paths)
-                     (cdr todo)))))
-
-  (define (line-number node)
-    (ly:prob-property (car (page-lines node)) 'number))
-  
-  (ly:message (_ "Calculating page breaks..."))
-  (set! force-equalization-factor
-       (ly:output-def-lookup paper 'verticalequalizationfactor 0.3))
-  
-  (let* ((best-break-node (walk-lines '() '() lines))
-        (break-nodes (get-path best-break-node '()))
-        )
-
-    (page-set-property! (car (last-pair break-nodes)) 'is-last #t)
-    (if #f; (ly:get-option 'verbose)
-       (begin
-         (display (list
-                   "\nbreaks: " (map line-number break-nodes))
-                  "\nsystems " (map page-lines break-nodes)
-                  "\npenalties " (map page-penalty break-nodes)
-                  "\nconfigs " (map page-configuration break-nodes))))
-
-    ;; construct page stencils.
-    (for-each page-stencil break-nodes)
-    (post-process-pages paper break-nodes)
-    
-    break-nodes))
+  (if (null? todo)
+      (car best-paths)
+      (let* ((this-line (car todo))
+             (last? (null? (cdr todo)))
+             (next (walk-paths done best-paths (list this-line) last? #f
+                               paper-book page-alist)))
+        (walk-lines (cons this-line done)
+                    (cons next best-paths)
+                    (cdr todo)
+                    paper-book
+                    page-alist))))
+
+(define-public (optimal-page-breaks paper-book)
+  "Return pages as a list starting with 1st page. Each page is a 'page Prob."
+  (let* ((paper (ly:paper-book-paper paper-book))
+        (lines (ly:paper-book-systems paper-book))
+         (page-alist (layout->page-init paper)) 
+         (force-equalization-factor (ly:output-def-lookup
+                                     paper 'verticalequalizationfactor 0.3)))
+    (ly:message (_ "Calculating page breaks..."))
+    (let* ((best-break-node (walk-lines '() '() lines paper-book page-alist))
+           (break-nodes (get-path best-break-node '())))
+      (page-set-property! (car (last-pair break-nodes)) 'is-last #t)
+      (if #f; (ly:get-option 'verbose)
+          (begin
+            (display (list
+                      "\nbreaks: " (map (lambda (node)
+                                          (ly:prob-property (car (page-lines node))
+                                                            'number))
+                                        break-nodes)
+                      "\nsystems " (map page-lines break-nodes)
+                      "\npenalties " (map page-penalty break-nodes)
+                      "\nconfigs " (map page-configuration break-nodes)))))
+      ;; construct page stencils.
+      (for-each page-stencil break-nodes)
+      (post-process-pages paper break-nodes)
+      break-nodes)))