2 files changed, 54 insertions, 1 deletions

diff --git a/src/BlockArea.cpp b/src/BlockArea.cpp
index 7526e1c32..600940d96 100644
--- a/src/BlockArea.cpp
+++ b/src/BlockArea.cpp
@@ -245,6 +245,26 @@ void MergeCombinatorDifference(BLOCKTYPE & a_DstType, BLOCKTYPE a_SrcType, NIBBL
 
 
 
+/** Combinator used for cBlockArea::msSimpleCompare merging */
+template <bool MetaValid>
+void MergeCombinatorSimpleCompare(BLOCKTYPE & a_DstType, BLOCKTYPE a_SrcType, NIBBLETYPE & a_DstMeta, NIBBLETYPE a_SrcMeta)
+{
+	if ((a_DstType == a_SrcType) && (!MetaValid || (a_DstMeta == a_SrcMeta)))
+	{
+		// The blocktypes are the same, and the blockmetas are not present or are the same
+		a_DstType = E_BLOCK_AIR;
+	}
+	else
+	{
+		// The blocktypes or blockmetas differ
+		a_DstType = E_BLOCK_STONE;
+	}
+}
+
+
+
+
+
 /** Combinator used for cBlockArea::msMask merging */
 template <bool MetaValid>
 void MergeCombinatorMask(BLOCKTYPE & a_DstType, BLOCKTYPE a_SrcType, NIBBLETYPE & a_DstMeta, NIBBLETYPE a_SrcMeta)
@@ -2188,10 +2208,12 @@ void cBlockArea::RelSetData(
 
 
 
+
+
 template <bool MetasValid>
 void cBlockArea::MergeByStrategy(const cBlockArea & a_Src, int a_RelX, int a_RelY, int a_RelZ, eMergeStrategy a_Strategy, const NIBBLETYPE * SrcMetas, NIBBLETYPE * DstMetas)
 {
-	// Block types are compulsory, block metas are voluntary
+	// Block types are compulsory, block metas are optional
 	if (!HasBlockTypes() || !a_Src.HasBlockTypes())
 	{
 		LOGWARNING("%s: cannot merge because one of the areas doesn't have blocktypes.", __FUNCTION__);
@@ -2297,6 +2319,20 @@ void cBlockArea::MergeByStrategy(const cBlockArea & a_Src, int a_RelX, int a_Rel
 			return;
 		}  // case msDifference
 		
+		case cBlockArea::msSimpleCompare:
+		{
+			InternalMergeBlocks<MetasValid, MergeCombinatorSimpleCompare<MetasValid> >(
+				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
+			);
+			return;
+		}  // case msSimpleCompare
+		
 		case cBlockArea::msMask:
 		{
 			InternalMergeBlocks<MetasValid, MergeCombinatorMask<MetasValid> >(
diff --git a/src/BlockArea.h b/src/BlockArea.h
index 6b8b30443..ce417ceb4 100644
--- a/src/BlockArea.h
+++ b/src/BlockArea.h
@@ -54,6 +54,7 @@ public:
 		msLake,
 		msSpongePrint,
 		msDifference,
+		msSimpleCompare,
 		msMask,
 	} ;
 	
@@ -156,6 +157,22 @@ public:
 	| A        | sponge | A      |  Sponge is the NOP block
 	| *        | B      | B      |  Everything else overwrites anything
 	
+	msDifference:
+	Used to determine the differences between two areas. Only the differring blocks are preserved:
+	|  area block  |        |
+	| this | Src   | result |
+	+------+-------+--------+
+	| A    | A     | air    |  Same blocks are replaced with air
+	| A    | non-A | A      |  Differring blocks are kept from "this"
+
+	msSimpleCompare:
+	Used to determine the differences between two areas. Blocks that differ are replaced with stone, same blocks are replaced with air
+	|  area block  |        |
+	| this | Src   | result |
+	+------+-------+--------+
+	| A    | A     | air    |  Same blocks are replaced with air
+	| A    | non-A | stone  |  Differring blocks are replaced with stone
+
 	msMask:
 	Combines two areas, the blocks that are the same are kept, differing ones are reset to air
 	|  area block  |        |