Refactor minecart collision detection code. (#4712)

* Refactor minecart collision detection code.

 - Use new GetBoundingBox function.
 - Handle descending and ascending rails.
 - Snap to descending rails.

* Add message for UNREACHABLE

src/Entities/Minecart.cpp

@@ -158,6 +158,16 @@ void cMinecart::HandlePhysics(std::chrono::milliseconds a_Dt, cChunk & a_Chunk)
 			// Push cart upwards
 			AddPosY(1);
 		}
+		else
+		{
+			// When a minecart gets to a descending rail, it should go down.
+			chunk->GetBlockTypeMeta(relPos.addedY(-1), InsideType, InsideMeta);
+			if (IsBlockRail(InsideType))
+			{
+				// Push cart downwards
+				AddPosY(-1);
+			}
+		}
 	}
 
 	bool WasDetectorRail = false;
@@ -231,7 +241,8 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetSpeedX(0);  // Correct diagonal movement from curved rails
 
 			// Execute both the entity and block collision checks
-			bool BlckCol = TestBlockCollision(a_RailMeta), EntCol = TestEntityCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
 			if (EntCol || BlckCol)
 			{
 				return;
@@ -250,7 +261,8 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 					ApplyAcceleration({ 0.0, 0.0, -1.0 }, -0.1);
 				}
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_XM_XP:  // EASTWEST
 		{
@@ -259,7 +271,8 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetSpeedY(NO_SPEED);
 			SetSpeedZ(NO_SPEED);
 
-			bool BlckCol = TestBlockCollision(a_RailMeta), EntCol = TestEntityCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
 			if (EntCol || BlckCol)
 			{
 				return;
@@ -276,13 +289,21 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 					ApplyAcceleration({ -1.0, 0.0, 0.0 }, -0.1);
 				}
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_ASCEND_ZM:  // ASCEND NORTH
 		{
 			SetYaw(270);
 			SetSpeedX(0);
 
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
+
 			if (GetSpeedZ() >= 0)
 			{
 				// SpeedZ POSITIVE, going SOUTH
@@ -295,13 +316,21 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 				AddSpeedZ(1);  // Slow down
 				SetSpeedY(-GetSpeedZ());  // Upward movement is positive (0 minus negative number is positive number)
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_ASCEND_ZP:  // ASCEND SOUTH
 		{
 			SetYaw(270);
 			SetSpeedX(0);
 
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
+
 			if (GetSpeedZ() > 0)
 			{
 				// SpeedZ POSITIVE, going SOUTH
@@ -314,13 +343,21 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 				AddSpeedZ(-0.5);  // Speed up
 				SetSpeedY(GetSpeedZ());  // Downward movement negative
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_ASCEND_XM:  // ASCEND EAST
 		{
 			SetYaw(180);
 			SetSpeedZ(NO_SPEED);
 
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
+
 			if (GetSpeedX() >= NO_SPEED)
 			{
 				AddSpeedX(0.5);
@@ -331,13 +368,21 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 				AddSpeedX(1);
 				SetSpeedY(-GetSpeedX());
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_ASCEND_XP:  // ASCEND WEST
 		{
 			SetYaw(180);
 			SetSpeedZ(0);
 
+			auto BlckCol = TestBlockCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
+
 			if (GetSpeedX() > 0)
 			{
 				AddSpeedX(-1);
@@ -348,7 +393,8 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 				AddSpeedX(-0.5);
 				SetSpeedY(GetSpeedX());
 			}
-			break;
+
+			return;
 		}
 		case E_META_RAIL_CURVED_ZM_XM:  // Ends pointing NORTH and WEST
 		{
@@ -356,12 +402,16 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetPosY(floor(GetPosY()) + 0.55);  // Levitate dat cart
 			SetSpeedY(0);
 
-			TestBlockCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
-			TestEntityCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
 
 			// SnapToRail handles turning
 
-			break;
+			return;
 		}
 		case E_META_RAIL_CURVED_ZM_XP:  // Curved NORTH EAST
 		{
@@ -369,10 +419,14 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetPosY(floor(GetPosY()) + 0.55);
 			SetSpeedY(0);
 
-			TestBlockCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
-			TestEntityCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
 
-			break;
+			return;
 		}
 		case E_META_RAIL_CURVED_ZP_XM:  // Curved SOUTH WEST
 		{
@@ -380,10 +434,14 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetPosY(floor(GetPosY()) + 0.55);
 			SetSpeedY(0);
 
-			TestBlockCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
-			TestEntityCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
+			if (EntCol || BlckCol)
+			{
+				return;
+			}
 
-			break;
+			return;
 		}
 		case E_META_RAIL_CURVED_ZP_XP:  // Curved SOUTH EAST
 		{
@@ -391,17 +449,17 @@ void cMinecart::HandleRailPhysics(NIBBLETYPE a_RailMeta, std::chrono::millisecon
 			SetPosY(floor(GetPosY()) + 0.55);
 			SetSpeedY(0);
 
-			TestBlockCollision(a_RailMeta);
+			auto BlckCol = TestBlockCollision(a_RailMeta);
-			TestEntityCollision(a_RailMeta);
+			auto EntCol = TestEntityCollision(a_RailMeta);
-
+			if (EntCol || BlckCol)
-			break;
-		}
-		default:
 			{
-			ASSERT(!"Unhandled rail meta!");  // Dun dun DUN!
+				return;
-			break;
+			}
+
+			return;
 		}
 	}
+	UNREACHABLE("Unsupported rail meta type");
 }
 
 
@@ -724,14 +782,39 @@ void cMinecart::SnapToRail(NIBBLETYPE a_RailMeta)
 
 
 
+bool cMinecart::IsSolidBlockAtPosition(Vector3i a_Pos)
+{
+	BLOCKTYPE Block = m_World->GetBlock(a_Pos);
+	return !IsBlockRail(Block) && cBlockInfo::IsSolid(Block);
+}
+
+
+
+
+
 bool cMinecart::IsSolidBlockAtOffset(int a_XOffset, int a_YOffset, int a_ZOffset)
 {
-	BLOCKTYPE Block = m_World->GetBlock(POSX_TOINT + a_XOffset, POSY_TOINT + a_YOffset, POSZ_TOINT + a_ZOffset);
+	return IsSolidBlockAtPosition({POSX_TOINT + a_XOffset, POSY_TOINT + a_YOffset, POSZ_TOINT + a_ZOffset});
-	if (IsBlockRail(Block) || !cBlockInfo::IsSolid(Block))
+}
+
+
+
+
+
+bool cMinecart::IsBlockCollisionAtOffset(Vector3i a_Offset)
+{
+	auto BlockPosition = GetPosition().Floor() + a_Offset;
+	if (!IsSolidBlockAtPosition(BlockPosition))
 	{
 		return false;
 	}
-	return true;
+
+	auto bbBlock = cBoundingBox(
+		static_cast<Vector3d>(BlockPosition),
+		static_cast<Vector3d>(BlockPosition + Vector3i(1, 1, 1))
+	);
+
+	return GetBoundingBox().DoesIntersect(bbBlock);
 }
 
 
@@ -740,135 +823,218 @@ bool cMinecart::IsSolidBlockAtOffset(int a_XOffset, int a_YOffset, int a_ZOffset
 
 bool cMinecart::TestBlockCollision(NIBBLETYPE a_RailMeta)
 {
+	auto SpeedX = GetSpeedX();
+	auto SpeedZ = GetSpeedZ();
+
+	// Don't do anything if minecarts aren't moving.
+	#ifdef __clang__
+		#pragma clang diagnostic push
+		#pragma clang diagnostic ignored "-Wfloat-equal"
+	#endif
+
+	if ((SpeedX == 0) && (SpeedZ == 0))
+	{
+		return false;
+	}
+
+	#ifdef __clang__
+		#pragma clang diagnostic pop
+	#endif
+
+	auto StopTheCart = true;
+	auto StopOffset = Vector3d();
+
 	switch (a_RailMeta)
 	{
 		case E_META_RAIL_ZM_ZP:
 		{
-			if (GetSpeedZ() > 0)
+			if (SpeedZ > 0)
 			{
-				if (IsSolidBlockAtOffset(0, 0, 1))
+				StopOffset = Vector3d(0, 0, 0.4);
-				{
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, 1});
-					// We could try to detect a block in front based purely on coordinates, but xoft made a bounding box system - why not use? :P
-					cBoundingBox bbBlock(Vector3d(POSX_TOINT, POSY_TOINT, static_cast<int>(ceil(GetPosZ()))), 0.5, 1);
-					cBoundingBox bbMinecart(Vector3d(GetPosX(), floor(GetPosY()), GetPosZ()), GetWidth() / 2, GetHeight());
-
-					if (bbBlock.DoesIntersect(bbMinecart))
-					{
-						SetSpeed(0, 0, 0);
-						SetPosZ(floor(GetPosZ()) + 0.4);
-						return true;
 			}
-				}
+			else  // SpeedZ < 0
-			}
-			else if (GetSpeedZ() < 0)
 			{
-				if (IsSolidBlockAtOffset(0, 0, -1))
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, -1});
-				{
+				StopOffset = Vector3d(0, 0, 0.65);
-					cBoundingBox bbBlock(Vector3d(POSX_TOINT, POSY_TOINT, POSZ_TOINT - 1), 0.5, 1);
-					cBoundingBox bbMinecart(Vector3d(GetPosX(), floor(GetPosY()), GetPosZ() - 1), GetWidth() / 2, GetHeight());
-
-					if (bbBlock.DoesIntersect(bbMinecart))
-					{
-						SetSpeed(0, 0, 0);
-						SetPosZ(floor(GetPosZ()) + 0.65);
-						return true;
-					}
-				}
 			}
 			break;
 		}
 		case E_META_RAIL_XM_XP:
 		{
-			if (GetSpeedX() > 0)
+			if (SpeedX > 0)
 			{
-				if (IsSolidBlockAtOffset(1, 0, 0))
+				StopTheCart = IsBlockCollisionAtOffset({1, 0, 0});
-				{
+				StopOffset = Vector3d(0.4, 0, 0);
-					cBoundingBox bbBlock(Vector3d(static_cast<int>(ceil(GetPosX())), POSY_TOINT, POSZ_TOINT), 0.5, 1);
-					cBoundingBox bbMinecart(Vector3d(GetPosX(), floor(GetPosY()), GetPosZ()), GetWidth() / 2, GetHeight());
-
-					if (bbBlock.DoesIntersect(bbMinecart))
-					{
-						SetSpeed(0, 0, 0);
-						SetPosX(floor(GetPosX()) + 0.4);
-						return true;
 			}
-				}
+			else  // SpeedX < 0
-			}
-			else if (GetSpeedX() < 0)
 			{
-				if (IsSolidBlockAtOffset(-1, 0, 0))
+				StopTheCart = IsBlockCollisionAtOffset({-1, 0, 0});
-				{
+				StopOffset = Vector3d(0.65, 0, 0);
-					cBoundingBox bbBlock(Vector3d(POSX_TOINT - 1, POSY_TOINT, POSZ_TOINT), 0.5, 1);
-					cBoundingBox bbMinecart(Vector3d(GetPosX() - 1, floor(GetPosY()), GetPosZ()), GetWidth() / 2, GetHeight());
-
-					if (bbBlock.DoesIntersect(bbMinecart))
-					{
-						SetSpeed(0, 0, 0);
-						SetPosX(floor(GetPosX()) + 0.65);
-						return true;
-					}
-				}
 			}
 			break;
 		}
-		case E_META_RAIL_CURVED_ZM_XM:
-		{
-			bool IsBlockXM = IsSolidBlockAtOffset(-1, 0, 0);
-			bool IsBlockZM = IsSolidBlockAtOffset(0, 0, -1);
 
-			if (((GetSpeedZ() < 0) && IsBlockZM) || ((GetSpeedX() < 0) && IsBlockXM))
+		// Ascending rails check for one block on the way up, two on the way down.
+		case E_META_RAIL_ASCEND_XM:
 		{
-				SetSpeed(0, 0, 0);
+			StopOffset = Vector3d(0.5, 0, 0);
-				SetPosition(POSX_TOINT + 0.5, GetPosY(), POSZ_TOINT + 0.5);
+
-				return true;
+			if (SpeedX < 0)
-			}
+			{
-
+				StopTheCart = IsBlockCollisionAtOffset({-1, 1, 0});
-			break;
+			}
-		}
+			else  // SpeedX > 0
-		case E_META_RAIL_CURVED_ZM_XP:
+			{
-		{
+				StopTheCart = IsBlockCollisionAtOffset({1, 0, 0}) || IsBlockCollisionAtOffset({1, 1, 0});
-			bool IsBlockXP = IsSolidBlockAtOffset(1, 0, 0);
+			}
-			bool IsBlockZM = IsSolidBlockAtOffset(0, 0, -1);
+			break;
-
+		}
-			if (((GetSpeedZ() < 0) &&  IsBlockZM) || ((GetSpeedX() > 0) && IsBlockXP))
+		case E_META_RAIL_ASCEND_XP:
-			{
+		{
-				SetSpeed(0, 0, 0);
+			StopOffset = Vector3d(0.5, 0, 0);
-				SetPosition(POSX_TOINT + 0.5, GetPosY(), POSZ_TOINT + 0.5);
+
-				return true;
+			if (SpeedX > 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({1, 1, 0});
+			}
+			else  // SpeedX < 0
+			{
+				StopTheCart = IsBlockCollisionAtOffset({-1, 0, 0}) || IsBlockCollisionAtOffset({-1, 1, 0});
+			}
+			break;
+		}
+		case E_META_RAIL_ASCEND_ZM:
+		{
+			StopOffset = Vector3d(0, 0, 0.5);
+
+			if (SpeedZ < 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 1, -1});
+			}
+			else  // SpeedZ > 0
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, 1}) || IsBlockCollisionAtOffset({0, 1, 1});
+			}
+			break;
+		}
+		case E_META_RAIL_ASCEND_ZP:
+		{
+			StopOffset = Vector3d(0, 0, 0.5);
+
+			if (SpeedZ > 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 1, 1});
+			}
+			else  // SpeedZ < 0
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, -1}) || IsBlockCollisionAtOffset({0, 1, -1});
+			}
+			break;
+		}
+
+		// Curved rails allow movement across both the x and z axes. But when the cart is
+		// moving towards one of the rail endpoints, it will always have velocity towards
+		// the direction of that endpoint in the same axis.
+		case E_META_RAIL_CURVED_ZP_XP:
+		{
+			StopOffset = Vector3d(0.5, 0, 0.5);
+
+			if (SpeedZ > 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, 1});
+				break;
+			}
+			if (SpeedX > 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({1, 0, 0});
+				break;
 			}
 
 			break;
+			UNREACHABLE("Invalid minecart movement");
 		}
 		case E_META_RAIL_CURVED_ZP_XM:
 		{
-			bool IsBlockXM = IsSolidBlockAtOffset(-1, 0, 0);
+			StopOffset = Vector3d(0.5, 0, 0.5);
-			bool IsBlockZP = IsSolidBlockAtOffset(0, 0, +1);
 
-			if (((GetSpeedZ() > 0) && IsBlockZP) || ((GetSpeedX() < 0) && IsBlockXM))
+			if (SpeedZ > 0)
 			{
-				SetSpeed(0, 0, 0);
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, 1});
-				SetPosition(POSX_TOINT + 0.5, GetPosY(), POSZ_TOINT + 0.5);
+				break;
-				return true;
+			}
+			if (SpeedX < 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({-1, 0, 0});
+				break;
 			}
 
 			break;
+			UNREACHABLE("Invalid minecart movement");
 		}
-		case E_META_RAIL_CURVED_ZP_XP:
+		case E_META_RAIL_CURVED_ZM_XM:
 		{
-			bool IsBlockXP = IsSolidBlockAtOffset(1, 0, 0);
+			StopOffset = Vector3d(0.5, 0, 0.5);
-			bool IsBlockZP = IsSolidBlockAtOffset(0, 0, 1);
 
-			if (((GetSpeedZ() > 0) && IsBlockZP) || ((GetSpeedX() > 0) && IsBlockXP))
+			if (SpeedZ < 0)
 			{
-				SetSpeed(0, 0, 0);
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, -1});
-				SetPosition(POSX_TOINT + 0.5, GetPosY(), POSZ_TOINT + 0.5);
+				break;
-				return true;
+			}
+			if (SpeedX < 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({-1, 0, 0});
+				break;
 			}
 
 			break;
+			UNREACHABLE("Invalid minecart movement");
 		}
-		default: break;
+		case E_META_RAIL_CURVED_ZM_XP:
+		{
+			StopOffset = Vector3d(0.5, 0, 0.5);
+
+			if (SpeedZ < 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({0, 0, -1});
+				break;
 			}
+			if (SpeedX > 0)
+			{
+				StopTheCart = IsBlockCollisionAtOffset({1, 0, 0});
+				break;
+			}
+
+			break;
+			UNREACHABLE("Invalid minecart movement");
+		}
+	}
+
+	if (StopTheCart)
+	{
+		SetSpeed(0, 0, 0);
+
+		#ifdef __clang__
+			#pragma clang diagnostic push
+			#pragma clang diagnostic ignored "-Wfloat-equal"
+		#endif
+
+		if (StopOffset.x != 0)
+		{
+			SetPosX(POSX_TOINT + StopOffset.x);
+		}
+		if (StopOffset.z != 0)
+		{
+			SetPosZ(POSZ_TOINT + StopOffset.z);
+		}
+
+		#ifdef __clang__
+			#pragma clang diagnostic pop
+		#endif
+
+		return true;
+	}
+
 	return false;
 }
 

src/Entities/Minecart.h

@@ -83,8 +83,13 @@ protected:
 	void SnapToRail(NIBBLETYPE a_RailMeta);
 	/** Tests if a solid block is in front of a cart, and stops the cart (and returns true) if so; returns false if no obstruction */
 	bool TestBlockCollision(NIBBLETYPE a_RailMeta);
+	/** Tests if there is a block at the specified position which is impassable to minecarts */
+	bool IsSolidBlockAtPosition(Vector3i a_Offset);
 	/** Tests if a solid block is at a specific offset of the minecart position */
 	bool IsSolidBlockAtOffset(int a_XOffset, int a_YOffset, int a_ZOffset);
+
+	bool IsBlockCollisionAtOffset(Vector3i a_Offset);
+
 	/** Tests if this mincecart's bounding box is intersecting another entity's bounding box (collision) and pushes mincecart away if necessary */
 	bool TestEntityCollision(NIBBLETYPE a_RailMeta);