From 982d3cb1b1745b5de6443779adc6cd4a0c15a119 Mon Sep 17 00:00:00 2001
From: Trevor Daniels <t.daniels@treda.co.uk>
Date: Thu, 3 Dec 2009 15:26:13 +0000
Subject: [PATCH] Add 'whiteout as a Grob interface property

 - If true, the grob will be printed on a white
   background which overlays grobs in lower
   layers.  As the order of printing grobs in the
   same layer is generally unpredictable this
   should always be used in conjunction with
   explicit layer settings.
---
 input/regression/whiteout-lower-layers.ly | 21 +++++++++++++++++++++
 lily/grob.cc                              | 10 ++++++++++
 scm/define-grob-properties.scm            |  2 ++
 scm/define-grobs.scm                      |  1 +
 4 files changed, 34 insertions(+)
 create mode 100644 input/regression/whiteout-lower-layers.ly

diff --git a/input/regression/whiteout-lower-layers.ly b/input/regression/whiteout-lower-layers.ly
new file mode 100644
index 0000000000..75dbd96dc6
--- /dev/null
+++ b/input/regression/whiteout-lower-layers.ly
@@ -0,0 +1,21 @@
+\version "2.13.9"
+
+\header { texidoc = "If the 'whiteout property of a
+grob is set to #t, that part of all objects in lower
+layers which falls under the extent of the grob is
+whited out.  Here the TimeSignature whites out the
+Tie but not the StaffSymbol.
+"
+}
+
+\relative c' {
+  \time 3/4
+  \override Staff.StaffSymbol #'layer = #4
+  \once \override Tie #'layer = #2
+  b'2.~
+  \once \override Staff.TimeSignature #'whiteout = ##t
+  \once \override Staff.TimeSignature #'layer = #3
+  \time 5/4
+  b4
+}
+
diff --git a/lily/grob.cc b/lily/grob.cc
index a6e715d206..b27350b929 100644
--- a/lily/grob.cc
+++ b/lily/grob.cc
@@ -155,6 +155,15 @@ Grob::get_print_stencil () const
 	  retval = Stencil (retval.extent_box (), expr);
 	}
 
+      /* process whiteout */
+      if (to_boolean (get_property ("whiteout")))
+        {
+          /* Call the scheme procedure stencil-whiteout in scm/stencils.scm */
+          /* to add a round-filled-box stencil to the stencil list */
+          retval
+            = *unsmob_stencil (scm_call_1 (ly_lily_module_constant ("stencil-whiteout"),
+                                           retval.smobbed_copy()));
+        }
     }
 
   return retval;
@@ -662,6 +671,7 @@ ADD_INTERFACE (Grob,
 	       "staff-symbol "
 	       "stencil "
 	       "transparent "
+	       "whiteout "
 	       );
 
 /****************************************************************
diff --git a/scm/define-grob-properties.scm b/scm/define-grob-properties.scm
index b3a10bd53a..e7b67b0528 100644
--- a/scm/define-grob-properties.scm
+++ b/scm/define-grob-properties.scm
@@ -845,6 +845,8 @@ one below this grob.")
 ;;
      (when ,ly:moment? "Global time step associated with this column
 happen?")
+     (whiteout ,boolean? "If true, the grob is printed over a white
+background to white-out underlying material.  Usually #f by default.")
      (width ,ly:dimension? "The width of a grob measured in staff
 space.")
      (word-space ,ly:dimension? "Space to insert between words in
diff --git a/scm/define-grobs.scm b/scm/define-grobs.scm
index 79de22f001..7c459a0bca 100644
--- a/scm/define-grobs.scm
+++ b/scm/define-grobs.scm
@@ -1888,6 +1888,7 @@
 	(font-size . -2)
 	(stem-attachment . (0.0 . 1.35))
 	(stencil . ,ly:text-interface::print)
+	(whiteout . #t)
 	(X-offset . ,ly:self-alignment-interface::x-aligned-on-self)
 	(Y-offset . ,ly:staff-symbol-referencer::callback)
 	(meta . ((class . Item)
-- 
2.11.4.GIT