3 files changed, 111 insertions, 20 deletions

diff --git a/src/BlockType.h b/src/BlockType.h
index 9f8c8fb55..50422b346 100644
--- a/src/BlockType.h
+++ b/src/BlockType.h
@@ -778,6 +778,13 @@ enum ENUM_BLOCK_META : NIBBLETYPE
 	E_META_RED_SANDSTONE_ORNAMENT = 1,
 	E_META_RED_SANDSTONE_SMOOTH   = 2,
 
+	// E_BLOCK_REDSTONE_REPEATER_ON / E_BLOCK_REDSTONE_REPEATER_OFF metas:
+	E_META_REDSTONE_REPEATER_FACING_ZM = 0,
+	E_META_REDSTONE_REPEATER_FACING_XP = 1,
+	E_META_REDSTONE_REPEATER_FACING_ZP = 2,
+	E_META_REDSTONE_REPEATER_FACING_XM = 3,
+	E_META_REDSTONE_REPEATER_FACING_MASK = 3,
+
 	// E_BLOCK_SAND metas:
 	E_META_SAND_NORMAL = 0,
 	E_META_SAND_RED    = 1,
diff --git a/src/Blocks/BlockRedstoneRepeater.h b/src/Blocks/BlockRedstoneRepeater.h
index 89cba2d35..25aa9b795 100644
--- a/src/Blocks/BlockRedstoneRepeater.h
+++ b/src/Blocks/BlockRedstoneRepeater.h
@@ -77,38 +77,42 @@ public:
 		return 11;
 	}
 
-
-	inline static Vector3i GetRearCoordinateOffset(NIBBLETYPE a_Meta)
+	inline static Vector3i GetLeftCoordinateOffset(NIBBLETYPE a_Meta)
 	{
-		switch (a_Meta & 0x3)  // We only want the direction (bottom) bits
+		switch (a_Meta & E_META_REDSTONE_REPEATER_FACING_MASK)  // We only want the direction (bottom) bits
 		{
-			case 0x0: return {0, 0, 1};
-			case 0x1: return {-1, 0, 0};
-			case 0x2: return {0, 0, -1};
-			case 0x3: return {1, 0, 0};
+			case E_META_REDSTONE_REPEATER_FACING_ZM: return { -1, 0, 0 };
+			case E_META_REDSTONE_REPEATER_FACING_XP: return { 0, 0, -1 };
+			case E_META_REDSTONE_REPEATER_FACING_ZP: return { 1, 0, 0 };
+			case E_META_REDSTONE_REPEATER_FACING_XM: return { 0, 0, 1 };
+
 			default:
 			{
 				LOGWARNING("%s: Unknown metadata: %d", __FUNCTION__, a_Meta);
 				ASSERT(!"Unknown metadata while determining orientation of repeater!");
-				return {0, 0, 0};
+				return { 0, 0, 0 };
 			}
 		}
 	}
 
-
 	inline static Vector3i GetFrontCoordinateOffset(NIBBLETYPE a_Meta)
 	{
-		switch (a_Meta & 0x3)  // We only want the direction (bottom) bits
+		return -GetRearCoordinateOffset(a_Meta);
+	}
+
+	inline static Vector3i GetRearCoordinateOffset(NIBBLETYPE a_Meta)
+	{
+		switch (a_Meta & E_META_REDSTONE_REPEATER_FACING_MASK)  // We only want the direction (bottom) bits
 		{
-			case 0x0: return {0, 0, -1};
-			case 0x1: return {1, 0, 0};
-			case 0x2: return {0, 0, 1};
-			case 0x3: return {-1, 0, 0};
+			case E_META_REDSTONE_REPEATER_FACING_ZM: return { 0, 0, 1 };
+			case E_META_REDSTONE_REPEATER_FACING_XP: return { -1, 0, 0 };
+			case E_META_REDSTONE_REPEATER_FACING_ZP: return { 0, 0, -1 };
+			case E_META_REDSTONE_REPEATER_FACING_XM: return { 1, 0, 0 };
 			default:
 			{
 				LOGWARNING("%s: Unknown metadata: %d", __FUNCTION__, a_Meta);
 				ASSERT(!"Unknown metadata while determining orientation of repeater!");
-				return {0, 0, 0};
+				return { 0, 0, 0 };
 			}
 		}
 	}
diff --git a/src/Simulator/IncrementalRedstoneSimulator/RedstoneRepeaterHandler.h b/src/Simulator/IncrementalRedstoneSimulator/RedstoneRepeaterHandler.h
index 9a0e26100..0cd65be53 100644
--- a/src/Simulator/IncrementalRedstoneSimulator/RedstoneRepeaterHandler.h
+++ b/src/Simulator/IncrementalRedstoneSimulator/RedstoneRepeaterHandler.h
@@ -15,11 +15,6 @@ class cRedstoneRepeaterHandler:
 
 public:
 
-	inline static bool IsOn(BLOCKTYPE a_Block)
-	{
-		return (a_Block == E_BLOCK_REDSTONE_REPEATER_ON);
-	}
-
 	virtual unsigned char GetPowerDeliveredToPosition(cWorld & a_World, Vector3i a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, Vector3i a_QueryPosition, BLOCKTYPE a_QueryBlockType) const override
 	{
 		return (
@@ -42,6 +37,17 @@ public:
 		auto Data = static_cast<cIncrementalRedstoneSimulator *>(a_World.GetRedstoneSimulator())->GetChunkData();
 		auto DelayInfo = Data->GetMechanismDelayInfo(a_Position);
 
+		// If the repeater is locked by another, ignore and forget all power changes:
+		if (IsLocked(a_World, a_Position, a_Meta))
+		{
+			if (DelayInfo != nullptr)
+			{
+				Data->m_MechanismDelays.erase(a_Position);
+			}
+
+			return {};
+		}
+
 		if (DelayInfo == nullptr)
 		{
 			bool ShouldBeOn = (a_PoweringData.PowerLevel != 0);
@@ -71,4 +77,78 @@ public:
 	{
 		return { cBlockRedstoneRepeaterHandler::GetRearCoordinateOffset(a_Meta) + a_Position };
 	}
+
+private:
+
+	inline static bool IsOn(BLOCKTYPE a_Block)
+	{
+		return (a_Block == E_BLOCK_REDSTONE_REPEATER_ON);
+	}
+
+	/** Returns a pair with first element indicating if the block at the given position is an activated repeater.
+	If it is activated, the second element is the repeater metadata. */
+	static std::pair<bool, NIBBLETYPE> IsOnRepeater(cWorld & a_World, const Vector3i a_Position)
+	{
+		BLOCKTYPE Type;
+		NIBBLETYPE Meta;
+
+		if (!a_World.GetBlockTypeMeta(a_Position, Type, Meta))
+		{
+			return std::make_pair(false, 0);
+		}
+
+		return std::make_pair(IsOn(Type), Meta);
+	}
+
+	/** Determine if a repeater is locked.
+	A locked repeater is one with another powered repeater facing them, to their immediate left or right sides.
+	"Left" is relative to the direction the repeater output faces, naturally. */
+	inline static bool IsLocked(cWorld & a_World, const Vector3i a_Position, const NIBBLETYPE a_Meta)
+	{
+		// The left hand side offset. Will be negated to get the rhs offset
+		const auto LhsOffset = cBlockRedstoneRepeaterHandler::GetLeftCoordinateOffset(a_Meta);
+
+		// Test the block to the left of us
+		const auto Lhs = IsOnRepeater(a_World, LhsOffset + a_Position);
+		if (Lhs.first && DoesLhsLockMe(Lhs.second, a_Meta))
+		{
+			return true;
+		}
+
+		// Test the right side, flipping the argument order to DoesLhsLockMe
+		const auto Rhs = IsOnRepeater(a_World, -LhsOffset + a_Position);
+		return Rhs.first && DoesLhsLockMe(a_Meta, Rhs.second);
+	}
+
+	/** Determine, from the metadata of a repeater on our left side, if they lock us.
+	To test a repeater on our right, simply invert the order of arguments provided.
+	"Left" is relative to the direction the repeater output faces, naturally. */
+	static bool DoesLhsLockMe(NIBBLETYPE a_MetaLhs, NIBBLETYPE a_MyMeta)
+	{
+		// Get the direction bits
+		a_MetaLhs &= E_META_REDSTONE_REPEATER_FACING_MASK;
+		a_MyMeta &= E_META_REDSTONE_REPEATER_FACING_MASK;
+
+		/*
+		Check for a valid locking configuration, where they are perpendicular and one snuggles into the other.
+
+		Order of comparisons:
+			XP >^ ZM
+			ZP |_ XP
+			XM <| ZP
+			ZP ^< xM
+
+		Key:
+			^ Facing up
+			_ Facing right
+			| Facing down
+			< Facing left
+		*/
+		return
+			((a_MetaLhs == E_META_REDSTONE_REPEATER_FACING_XP) && (a_MyMeta == E_META_REDSTONE_REPEATER_FACING_ZM)) ||
+			((a_MetaLhs == E_META_REDSTONE_REPEATER_FACING_ZP) && (a_MyMeta == E_META_REDSTONE_REPEATER_FACING_XP)) ||
+			((a_MetaLhs == E_META_REDSTONE_REPEATER_FACING_XM) && (a_MyMeta == E_META_REDSTONE_REPEATER_FACING_ZP)) ||
+			((a_MetaLhs == E_META_REDSTONE_REPEATER_FACING_ZM) && (a_MyMeta == E_META_REDSTONE_REPEATER_FACING_XM))
+		;
+	}
 };