Fix breathing sign Y-offset when using line-positions. (issue4620051)

[n . puttock]

Reviewers: ,

Message:
This fixes issue #1696, ensuring breathing signs are always positioned
on extremal staff lines.

Description:
Fix breathing sign Y-offset when using line-positions.

* input/regression/breathing-sign-custom-staff.ly

  new regtest

* lily/breathing-sign.cc (offset_callback):

  use Staff_symbol::line_span () to calculate offset instead of
  Staff_symbol_referencer::line_count (): the latter is only useful for
  symmetrical staves

  tidy code; remove obsolete TODO

Please review this at http://codereview.appspot.com/4620051/

Affected files:
  A input/regression/breathing-sign-custom-staff.ly
  M lily/breathing-sign.cc


Index: input/regression/breathing-sign-custom-staff.ly
diff --git a/input/regression/breathing-sign-custom-staff.ly  
b/input/regression/breathing-sign-custom-staff.ly
new file mode 100644
index  
0000000000000000000000000000000000000000..98305b0510b574dffe2a4e2d7d15d83a9b22d60b
--- /dev/null
+++ b/input/regression/breathing-sign-custom-staff.ly
@@ -0,0 +1,13 @@
+\version "2.15.2"
+
+\header {
+  texidoc = "Breathing signs are positioned correctly on custom staves
+which use @code{line-positions}."
+}
+
+\relative c' {
+  \override Staff.StaffSymbol #'line-positions = #'(-7 -5 -3 -1)
+  b2 \breathe b
+  \override BreathingSign #'direction = #DOWN
+  \breathe
+}
Index: lily/breathing-sign.cc
diff --git a/lily/breathing-sign.cc b/lily/breathing-sign.cc
index  
09fd1d7c516e7b35cd1ce85f1e944d7b9869ebd1..a59bd650703fe2aafc2ea40e58b2e85492c78a6b  
100644
--- a/lily/breathing-sign.cc
+++ b/lily/breathing-sign.cc
@@ -20,20 +20,16 @@

 #include "breathing-sign.hh"

-#include "staff-symbol-referencer.hh"
-#include "directional-element-interface.hh"
-#include "output-def.hh"
-#include "lookup.hh"
 #include "dimensions.hh"
 #include "direction.hh"
-#include "text-interface.hh"
+#include "directional-element-interface.hh"
 #include "font-interface.hh"
 #include "grob.hh"
-
-/*
-  TODO: thickness should be a grob property (unit: linethickness)
-  rather than hardwired to (staff_space / 6).
-*/
+#include "lookup.hh"
+#include "output-def.hh"
+#include "staff-symbol.hh"
+#include "staff-symbol-referencer.hh"
+#include "text-interface.hh"

 /*
   UGH : this is full of C&P code. Consolidate!  --hwn
@@ -177,14 +173,20 @@ Breathing_sign::offset_callback (SCM smob)
       set_grob_direction (me, d);
     }

-  Real inter = Staff_symbol_referencer::staff_space (me) / 2;
-  int sz = Staff_symbol_referencer::line_count (me) - 1;
-  return scm_from_double (inter * sz * d);
+  Grob *staff = Staff_symbol_referencer::get_staff_symbol (me);
+  if (staff)
+    {
+      Interval iv = Staff_symbol::line_span (staff);
+      Real inter = Staff_symbol::staff_space (me) / 2;
+      return scm_from_double (inter * iv[d]);
+    }
+
+  return scm_from_double (0.0);
 }

 ADD_INTERFACE (Breathing_sign,
               "A breathing sign.",
-       
+
               /* properties */
               "direction "
               );