3 files changed, 369 insertions, 0 deletions
diff --git a/src/Blocks/Mixins/DirtLikeUnderneath.h b/src/Blocks/Mixins/DirtLikeUnderneath.h
new file mode 100644
index 000000000..909f1601e
--- /dev/null
+++ b/src/Blocks/Mixins/DirtLikeUnderneath.h
@@ -0,0 +1,42 @@
+
+#pragma once
+
+#include "../../Chunk.h"
+
+/** Mixin to ensure the block has a dirt-like block underneath. */
+template <class Base>
+class cDirtLikeUnderneath :
+	public Base
+{
+	using Super = Base;
+public:
+
+	using Super::Super;
+
+	constexpr cDirtLikeUnderneath(BLOCKTYPE a_BlockType):
+		Base(a_BlockType)
+	{
+	}
+
+protected:
+
+	~cDirtLikeUnderneath() = 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;
+		}
+
+		return IsBlockTypeOfDirt(a_Chunk.GetBlock(BelowPos));
+	}
+};
diff --git a/src/Blocks/Mixins/Mixins.h b/src/Blocks/Mixins/Mixins.h
new file mode 100644
index 000000000..d9a233bad
--- /dev/null
+++ b/src/Blocks/Mixins/Mixins.h
@@ -0,0 +1,262 @@
+// Mixins.h
+
+// Provides various mixins for easier cBlockHandler descendant implementations
+
+/* The general use case is to derive a handler from these mixins, providing a suitable base to them:
+class cBlockAir: public cBlockWithNoDrops<cBlockHandler>;
+class cBlockLadder: public cMetaRotator<cClearMetaOnDrop, ...>
+*/
+
+#pragma once
+
+#include "../../Item.h"
+
+
+
+
+
+// MSVC generates warnings for the templated AssertIfNotMatched parameter conditions, so disable it:
+#ifdef _MSC_VER
+	#pragma warning(disable: 4127)  // Conditional expression is constant
+#endif
+
+
+
+
+
+/** Mixin to clear the block's meta value when converting to a pickup. */
+template <class Base>
+class cClearMetaOnDrop :
+	public Base
+{
+public:
+
+	constexpr cClearMetaOnDrop(BLOCKTYPE a_BlockType):
+		Base(a_BlockType)
+	{
+	}
+
+protected:
+
+	~cClearMetaOnDrop() = default;
+
+private:
+
+	virtual cItems ConvertToPickups(const NIBBLETYPE a_BlockMeta, const cItem * const a_Tool) const override
+	{
+		// Reset the meta to zero:
+		return cItem(this->m_BlockType);
+	}
+};
+
+
+
+
+
+/** Mixin for rotations and reflections following the standard pattern of "apply mask, then use a switch".
+Inherit from this class providing your base class as Base, the BitMask for the direction bits in bitmask and the masked value for the directions in North, East, South, West.
+There is also an aptional parameter AssertIfNotMatched, set this if it is invalid for a block to exist in any other state. */
+template <class Base, NIBBLETYPE BitMask, NIBBLETYPE North, NIBBLETYPE East, NIBBLETYPE South, NIBBLETYPE West, bool AssertIfNotMatched = false>
+class cMetaRotator :
+	public Base
+{
+public:
+
+	constexpr cMetaRotator(BLOCKTYPE a_BlockType):
+		Base(a_BlockType)
+	{
+	}
+
+protected:
+
+	~cMetaRotator() = default;
+
+	virtual NIBBLETYPE MetaRotateCCW(NIBBLETYPE a_Meta) const override
+	{
+		NIBBLETYPE OtherMeta = a_Meta & (~BitMask);
+		switch (a_Meta & BitMask)
+		{
+			case South: return East  | OtherMeta;
+			case East:  return North | OtherMeta;
+			case North: return West  | OtherMeta;
+			case West:  return South | OtherMeta;
+		}
+		if (AssertIfNotMatched)
+		{
+			ASSERT(!"Invalid Meta value");
+		}
+		return a_Meta;
+	}
+
+
+
+
+
+	virtual NIBBLETYPE MetaRotateCW(NIBBLETYPE a_Meta) const override
+	{
+		NIBBLETYPE OtherMeta = a_Meta & (~BitMask);
+		switch (a_Meta & BitMask)
+		{
+			case South: return West  | OtherMeta;
+			case West:  return North | OtherMeta;
+			case North: return East  | OtherMeta;
+			case East:  return South | OtherMeta;
+		}
+		if (AssertIfNotMatched)
+		{
+			ASSERT(!"Invalid Meta value");
+		}
+		return a_Meta;
+	}
+
+
+
+
+
+	virtual NIBBLETYPE MetaMirrorXY(NIBBLETYPE a_Meta) const override
+	{
+		NIBBLETYPE OtherMeta = a_Meta & (~BitMask);
+		switch (a_Meta & BitMask)
+		{
+			case South: return North | OtherMeta;
+			case North: return South | OtherMeta;
+		}
+		// Not Facing North or South; No change.
+		return a_Meta;
+	}
+
+
+
+
+
+	virtual NIBBLETYPE MetaMirrorYZ(NIBBLETYPE a_Meta) const override
+	{
+		NIBBLETYPE OtherMeta = a_Meta & (~BitMask);
+		switch (a_Meta & BitMask)
+		{
+			case West: return East | OtherMeta;
+			case East: return West | OtherMeta;
+		}
+		// Not Facing East or West; No change.
+		return a_Meta;
+	}
+};
+
+
+
+
+
+/** Mixin for blocks whose meta on placement depends on the yaw of the player placing the block. BitMask
+selects the direction bits from the block's meta values. */
+template <
+	class Base,
+	NIBBLETYPE BitMask = 0x07,
+	NIBBLETYPE North = 0x02,
+	NIBBLETYPE East = 0x05,
+	NIBBLETYPE South = 0x03,
+	NIBBLETYPE West = 0x04,
+	bool AssertIfNotMatched = false
+>
+class cYawRotator :
+	public cMetaRotator<Base, BitMask, North, East, South, West, AssertIfNotMatched>
+{
+	using Super = cMetaRotator<Base, BitMask, North, East, South, West, AssertIfNotMatched>;
+
+public:
+
+	using Super::Super;
+
+
+	/** Converts the rotation value as returned by cPlayer::GetYaw() to the appropriate metadata
+	value for a block placed by a player facing that way. */
+	static NIBBLETYPE YawToMetaData(double a_Rotation)
+	{
+		if ((a_Rotation >= -135) && (a_Rotation < -45))
+		{
+			return East;
+		}
+		else if ((a_Rotation >= -45) && (a_Rotation < 45))
+		{
+			return South;
+		}
+		else if ((a_Rotation >= 45) && (a_Rotation < 135))
+		{
+			return West;
+		}
+		else  // degrees jumping from 180 to -180
+		{
+			return North;
+		}
+	}
+
+protected:
+
+	~cYawRotator() = default;
+};
+
+
+
+
+
+/** Mixin for blocks whose meta on placement depends on the relative position of the player to the block in
+addition to the yaw of the player placing the block. BitMask selects the direction bits from the block's meta values. */
+template <
+	class Base,
+	NIBBLETYPE BitMask = 0x07,
+	NIBBLETYPE North = 0x02,
+	NIBBLETYPE East = 0x05,
+	NIBBLETYPE South = 0x03,
+	NIBBLETYPE West = 0x04,
+	NIBBLETYPE Up = 0x00,
+	NIBBLETYPE Down = 0x01
+>
+class cDisplacementYawRotator:
+	public cYawRotator<Base, BitMask, North, East, South, West>
+{
+	using Super = cYawRotator<Base, BitMask, North, East, South, West>;
+
+public:
+
+	using Super::Super;
+
+
+	/** Converts the placement position, eye position as returned by cPlayer::GetEyePosition(), and
+	rotation value as returned by cPlayer::GetYaw() to the appropriate metadata value for a block placed by a player facing that way. */
+	static NIBBLETYPE DisplacementYawToMetaData(const Vector3d a_PlacePosition, const Vector3d a_EyePosition, const double a_Rotation)
+	{
+		if (
+			const auto Displacement = a_EyePosition - a_PlacePosition.addedXZ(0.5, 0.5);
+			(std::abs(Displacement.x) < 2) && (std::abs(Displacement.z) < 2)
+		)
+		{
+			if (Displacement.y > 2)
+			{
+				return Up;
+			}
+
+			if (Displacement.y < 0)
+			{
+				return Down;
+			}
+		}
+
+		return Super::YawToMetaData(a_Rotation);
+	}
+
+protected:
+
+	~cDisplacementYawRotator() = default;
+
+
+	virtual NIBBLETYPE MetaMirrorXZ(NIBBLETYPE a_Meta) const override
+	{
+		NIBBLETYPE OtherMeta = a_Meta & (~BitMask);
+		switch (a_Meta & BitMask)
+		{
+			case Down: return Up | OtherMeta;  // Down -> Up
+			case Up: return Down | OtherMeta;  // Up -> Down
+		}
+		// Not Facing Up or Down; No change.
+		return a_Meta;
+	}
+};
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;
+	}
+};