1 files changed, 65 insertions, 0 deletions
diff --git a/src/Blocks/Mixins/SolidSurfaceUnderneath.h b/src/Blocks/Mixins/SolidSurfaceUnderneath.h
new file mode 100644
index 000000000..c54c064d6
--- /dev/null
+++ b/src/Blocks/Mixins/SolidSurfaceUnderneath.h
@@ -0,0 +1,65 @@
+
+#pragma once
+
+#include "../../Chunk.h"
+#include "../BlockSlab.h"
+#include "../BlockStairs.h"
+
+/** Mixin to ensure the block has a solid surface underneath. */
+template <class Base>
+class cSolidSurfaceUnderneath :
+	public Base
+{
+	using Super = Base;
+public:
+
+	using Super::Super;
+
+	constexpr cSolidSurfaceUnderneath(BLOCKTYPE a_BlockType):
+		Base(a_BlockType)
+	{
+	}
+
+protected:
+
+	~cSolidSurfaceUnderneath() = default;
+
+protected:
+
+	virtual bool CanBeAt(const cChunk & a_Chunk, const Vector3i a_Position, const NIBBLETYPE a_Meta) const override
+	{
+		if (!Super::CanBeAt(a_Chunk, a_Position, a_Meta))
+		{
+			return false;
+		}
+
+		const auto BelowPos = a_Position.addedY(-1);
+		if (!cChunkDef::IsValidHeight(BelowPos))
+		{
+			return false;
+		}
+
+		BLOCKTYPE BelowBlock;
+		NIBBLETYPE BelowBlockMeta;
+		a_Chunk.GetBlockTypeMeta(BelowPos, BelowBlock, BelowBlockMeta);
+
+		if (cBlockInfo::FullyOccupiesVoxel(BelowBlock))
+		{
+			return true;
+		}
+
+		// upside down slabs
+		if (cBlockSlabHandler::IsAnySlabType(BelowBlock))
+		{
+			return BelowBlockMeta & E_META_WOODEN_SLAB_UPSIDE_DOWN;
+		}
+
+		// upside down stairs
+		if (cBlockStairsHandler::IsAnyStairType(BelowBlock))
+		{
+			return BelowBlockMeta & E_BLOCK_STAIRS_UPSIDE_DOWN;
+		}
+
+		return false;
+	}
+};