Account for title spacing in page breaking.

[lilypond.git] / lily / page-spacing.cc

diff --git a/lily/page-spacing.cc b/lily/page-spacing.cc
index b556c1c3053273ac565396087b87a80843f787fd..76ef484b14daf04c23f9e424b203ed186f935c2a 100644 (file)
--- a/lily/page-spacing.cc
+++ b/lily/page-spacing.cc
@@ -57,7 +57,14 @@ Page_spacing::append_system (const Line_details &line)
       first_line_ = line;
     }
 
-  spring_len_ += line.space_;
+  // line.space_ measures the spring which goes from the bottom refpoint
+  // of one system to the top refpoint of the next. spring_len_ measures
+  // how much of that is stretchable.
+  Real refpoint_dist = last_line_.tallness_
+    + last_line_.refpoint_extent_[DOWN]
+    - line.refpoint_extent_[UP];
+  Real space = line.title_ ? last_line_.title_space_ : last_line_.space_;
+  spring_len_ += max (0.0, space - refpoint_dist);
   inverse_spring_k_ += line.inverse_hooke_;
 
   last_line_ = line;
@@ -74,7 +81,12 @@ Page_spacing::prepend_system (const Line_details &line)
   rod_height_ -= first_line_.full_height ();
   rod_height_ += first_line_.tallness_;
   rod_height_ += line.full_height();
-  spring_len_ += line.space_;
+
+  Real refpoint_dist = line.tallness_
+    + line.refpoint_extent_[DOWN]
+    - first_line_.refpoint_extent_[UP];
+  Real space = first_line_.title_ ? line.title_space_ : line.space_;
+  spring_len_ += max (0.0, space - refpoint_dist);
   inverse_spring_k_ += line.inverse_hooke_;
 
   first_line_ = line;
@@ -247,10 +259,13 @@ Page_spacer::calc_subproblem (vsize page, vsize line)
   bool last = line == lines_.size () - 1;
 
   // Note: if page == VPOS then we don't actually know yet which page number we're
-  // working on, so we have to recalculate the page height in the loop.  In that case,
-  // the algorithm may not be optimal: if our page has a very large header then perhaps
-  // we need to look ahead a few systems in order to find the best solution.  But
-  // we won't, because we stop once we overfill the page with the large header.
+  // working on, so we have to recalculate the page height in the loop.  Therefore
+  // our early-exit condition from the loop depends on paper_height rather than
+  // page_height (ie. we break only if we would overfill a page without margins
+  // or headers/footers).  Otherwise, the algorithm would not be optimal:
+  // if our page has a very large header then perhaps
+  // we should look ahead a few systems in order to find the best solution.  A
+  // good example of this is input/regression/page-spacing-tall-headfoot.ly
   vsize page_num = page == VPOS ? 0 : page;
   Real paper_height = breaker_->paper_height ();
   Page_spacing space (breaker_->page_height (page_num + first_page_num_, last),