Fixes cross staff issue with beam collision avoidance.

Beam collision avoidance is now turned off for "fake" cross staff beams
(those that are registered as cross staff because of auto-beaming but
are in fact not).  Additionally, beams no longer process other
cross-staff beams as covered grobs.

This fix closes issue 1632 on the tracker.

3 files changed, 26 insertions, 5 deletions

diff --git a/input/regression/beam-collision-cross-staff.ly b/input/regression/beam-collision-cross-staff.ly
index d546aafa18..450c167ad7 100644
--- a/input/regression/beam-collision-cross-staff.ly
+++ b/input/regression/beam-collision-cross-staff.ly
@@ -2,11 +2,25 @@
   texidoc = "cross staff beams work with collisions."
 }
 
-\version "2.13.55"
+\version "2.13.61"
 
-<< 
+<<
  \new Staff = "PianoRH" s4.
  \new Staff = "PianoLH" {
    d''8 [b''! \change Staff = "PianoRH"  d'' ]
  }
 >>
+
+<<
+  \new Staff = up \relative c' {
+    c8 c c c
+    c c c c
+    b' b b b
+  }
+  \new Staff = down \relative c' {
+    s8 c c \change Staff = up c
+    \change Staff = down c [ c s16 \change Staff = up a'16 s16 a16 ]
+    \stemUp
+    \change Staff = down b8 b b b \change Staff = up
+  }
+>>
diff --git a/lily/beam-collision-engraver.cc b/lily/beam-collision-engraver.cc
index 19e9b82caf..cdb4be6270 100644
--- a/lily/beam-collision-engraver.cc
+++ b/lily/beam-collision-engraver.cc
@@ -76,8 +76,6 @@ Beam_collision_engraver::finalize ()
   for (vsize i = 0; i < beams_.size (); i++)
     {
       Grob *beam_grob = beams_[i].grob ();
-      if (Beam::is_cross_staff (beam_grob))
-        continue;
 
       Context *beam_context = beams_[i].context ();
 
diff --git a/lily/beam.cc b/lily/beam.cc
index 1ae30fb5f8..938567984e 100644
--- a/lily/beam.cc
+++ b/lily/beam.cc
@@ -37,6 +37,7 @@
 
 #include "beam.hh"
 
+#include "align-interface.hh"
 #include "beam-scoring-problem.hh"
 #include "beaming-pattern.hh"
 #include "directional-element-interface.hh"
@@ -1204,7 +1205,15 @@ Beam::shift_region_to_valid (SCM grob, SCM posns)
     {
       if (!covered[i]->is_live())
         continue;
-      
+
+      // TODO - use this logic in is_cross_staff.
+      if (is_cross_staff (me)
+          && Align_interface::has_interface (common_refpoint_of_array (stems, me, Y_AXIS)))
+        continue;
+
+      if (Beam::has_interface (covered[i]) && is_cross_staff (covered[i]))
+        continue;
+
       Box b;
       for (Axis a = X_AXIS; a < NO_AXES; incr (a))
         b[a] = covered[i]->extent (common[a], a);