2 files changed, 39 insertions, 0 deletions
diff --git a/src/BlockArea.cpp b/src/BlockArea.cpp
index 2b950378a..543dbe04d 100644
--- a/src/BlockArea.cpp
+++ b/src/BlockArea.cpp
@@ -173,6 +173,21 @@ static inline void MergeCombinatorSpongePrint(BLOCKTYPE & a_DstType, BLOCKTYPE a
 
 
 
+/** Combinator used for cBlockArea::msMask merging */
+static inline void MergeCombinatorMask(BLOCKTYPE & a_DstType, BLOCKTYPE a_SrcType, NIBBLETYPE & a_DstMeta, NIBBLETYPE a_SrcMeta)
+{
+	// If the blocks are the same, keep the dest; otherwise replace with air
+	if ((a_SrcType != a_DstType) || (a_SrcMeta != a_DstMeta))
+	{
+		a_DstType = E_BLOCK_AIR;
+		a_DstMeta = 0;
+	}
+}
+
+
+
+
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 // cBlockArea:
 
@@ -710,6 +725,21 @@ void cBlockArea::Merge(const cBlockArea & a_Src, int a_RelX, int a_RelY, int a_R
 			break;
 		}  // case msSpongePrint
 		
+		case msMask:
+		{
+			InternalMergeBlocks(
+				m_BlockTypes, a_Src.GetBlockTypes(),
+				DstMetas, SrcMetas,
+				SizeX, SizeY, SizeZ,
+				SrcOffX, SrcOffY, SrcOffZ,
+				DstOffX, DstOffY, DstOffZ,
+				a_Src.GetSizeX(), a_Src.GetSizeY(), a_Src.GetSizeZ(),
+				m_Size.x, m_Size.y, m_Size.z,
+				MergeCombinatorMask
+			);
+			break;
+		}  // case msMask
+		
 		default:
 		{
 			LOGWARNING("Unknown block area merge strategy: %d", a_Strategy);
diff --git a/src/BlockArea.h b/src/BlockArea.h
index d37f0d182..34a0ef926 100644
--- a/src/BlockArea.h
+++ b/src/BlockArea.h
@@ -52,6 +52,7 @@ public:
 		msImprint,
 		msLake,
 		msSpongePrint,
+		msMask,
 	} ;
 	
 	cBlockArea(void);
@@ -152,6 +153,14 @@ public:
 	+----------+--------+--------+
 	| A        | sponge | A      |  Sponge is the NOP block
 	| *        | B      | B      |  Everything else overwrites anything
+	
+	msMask:
+	Combines two areas, the blocks that are the same are kept, differing ones are reset to air
+	|  area block  |        |
+	| this | Src   | result |
+	+------+-------+--------+
+	| A    | A     | A      |  Same blocks are kept
+	| A    | non-A | air    |  Everything else is replaced with air
 
 	*/
 	void Merge(const cBlockArea & a_Src, int a_RelX, int a_RelY, int a_RelZ, eMergeStrategy a_Strategy);