1 files changed, 295 insertions, 0 deletions

diff --git a/src/Physics/Explodinator.cpp b/src/Physics/Explodinator.cpp
new file mode 100644
index 000000000..3bfb78611
--- /dev/null
+++ b/src/Physics/Explodinator.cpp
@@ -0,0 +1,295 @@
+
+#include "Globals.h"
+#include "BlockInfo.h"
+#include "Blocks/BlockHandler.h"
+#include "Blocks/ChunkInterface.h"
+#include "Chunk.h"
+#include "ClientHandle.h"
+#include "Entities/FallingBlock.h"
+#include "LineBlockTracer.h"
+#include "Simulator/SandSimulator.h"
+
+
+
+
+
+namespace Explodinator
+{
+	const auto StepUnit = 0.3f;
+	const auto KnockbackFactor = 25U;
+	const auto StepAttenuation = 0.225f;
+	const auto TraceCubeSideLength = 16U;
+	const auto BoundingBoxStepUnit = 0.5f;
+
+	/** Converts an absolute floating-point Position into a Chunk-relative one. */
+	static Vector3f AbsoluteToRelative(const Vector3f a_Position, const cChunkCoords a_ChunkPosition)
+	{
+		return { a_Position.x - a_ChunkPosition.m_ChunkX * cChunkDef::Width, a_Position.y, a_Position.z - a_ChunkPosition.m_ChunkZ * cChunkDef::Width };
+	}
+
+	/** Make a From Chunk-relative Position into a To Chunk-relative position. */
+	static Vector3f RebaseRelativePosition(const cChunkCoords a_From, const cChunkCoords a_To, const Vector3f a_Position)
+	{
+		return
+		{
+			a_Position.x + (a_From.m_ChunkX - a_To.m_ChunkX) * cChunkDef::Width,
+			a_Position.y,
+			a_Position.z + (a_From.m_ChunkZ - a_To.m_ChunkZ) * cChunkDef::Width
+		};
+	}
+
+	/** Calculates the approximate percentage of an Entity's bounding box that is exposed to an explosion centred at Position. */
+	static float CalculateEntityExposure(cChunk & a_Chunk, const cEntity & a_Entity, const Vector3f a_Position, const float a_SquareRadius)
+	{
+		unsigned Unobstructed = 0, Total = 0;
+		const auto Box = a_Entity.GetBoundingBox();
+
+		for (float X = Box.GetMinX(); X < Box.GetMaxX(); X += BoundingBoxStepUnit)
+		{
+			for (float Y = Box.GetMinY(); Y < Box.GetMaxY(); Y += BoundingBoxStepUnit)
+			{
+				for (float Z = Box.GetMinZ(); Z < Box.GetMaxZ(); Z += BoundingBoxStepUnit)
+				{
+					const auto Destination = Vector3f(X, Y, Z);
+					if ((Destination - a_Position).SqrLength() > a_SquareRadius)
+					{
+						// Don't bother with points outside our designated area-of-effect
+						// This is, surprisingly, a massive amount of work saved (~3m to detonate a sphere of 37k TNT before, ~1m after):
+						continue;
+					}
+
+					if (cLineBlockTracer::LineOfSightTrace(*a_Chunk.GetWorld(), a_Position, Destination, cLineBlockTracer::eLineOfSight::losAir))
+					{
+						Unobstructed++;
+					}
+					Total++;
+				}
+			}
+		}
+
+		return static_cast<float>(Unobstructed) / Total;
+	}
+
+	/** Applies distance-based damage and knockback to all entities within the explosion's effect range. */
+	static void DamageEntities(cChunk & a_Chunk, const Vector3f a_Position, const unsigned a_Power)
+	{
+		const auto Radius = a_Power * 2.f;
+		const auto SquareRadius = Radius * Radius;
+
+		a_Chunk.GetWorld()->ForEachEntityInBox({ a_Position, Radius * 2 }, [&a_Chunk, a_Position, a_Power, Radius, SquareRadius](cEntity & Entity)
+		{
+			// Percentage of rays unobstructed.
+			const auto Exposure = CalculateEntityExposure(a_Chunk, Entity, a_Position, SquareRadius);
+			const auto Direction = Entity.GetPosition() - a_Position;
+			const auto Impact = (1 - (static_cast<float>(Direction.Length()) / Radius)) * Exposure;
+
+			// Don't apply damage to other TNT entities and falling blocks, they should be invincible:
+			if (!Entity.IsTNT() && !Entity.IsFallingBlock())
+			{
+				const auto Damage = (Impact * Impact + Impact) * 7 * a_Power + 1;
+				Entity.TakeDamage(dtExplosion, nullptr, FloorC(Damage), 0);
+			}
+
+			// Impact reduced by armour:
+			const auto ReducedImpact = Impact - Impact * Entity.GetEnchantmentBlastKnockbackReduction();  // TODO: call is very expensive, should only apply to Pawns
+			Entity.SetSpeed(Direction.NormalizeCopy() * KnockbackFactor * ReducedImpact);
+
+			// Continue iteration:
+			return false;
+		});
+	}
+
+	/** Sets the block at the given position, updating surroundings. */
+	static void DestroyBlock(cWorld & a_World, cChunk & a_Chunk, const Vector3i a_AbsolutePosition, const Vector3i a_RelativePosition, const BLOCKTYPE a_DestroyedBlock, const BLOCKTYPE a_NewBlock)
+	{
+		const auto DestroyedMeta = a_Chunk.GetMeta(a_RelativePosition);
+
+		// SetBlock wakes up all simulators for the area, so that water and lava flows and sand falls into the blasted holes
+		// It also is responsible for calling cBlockHandler::OnNeighborChanged to pop off blocks that fail CanBeAt
+		// An explicit call to cBlockHandler::OnBroken handles the destruction of multiblock structures
+		// References at (FS #391, GH #4418):
+		a_Chunk.SetBlock(a_RelativePosition, a_NewBlock, 0);
+
+		cChunkInterface Interface(a_World.GetChunkMap());
+		cBlockInfo::GetHandler(a_DestroyedBlock)->OnBroken(Interface, a_World, a_AbsolutePosition, a_DestroyedBlock, DestroyedMeta);
+	}
+
+	/** Sets the block at the given Position to air, updates surroundings, and spawns pickups, fire, shrapnel according to Minecraft rules.
+	OK, _mostly_ Minecraft rules. */
+	static void DestroyBlock(cChunk & a_Chunk, const Vector3i a_Position, const unsigned a_Power, const bool a_Fiery)
+	{
+		const auto DestroyedBlock = a_Chunk.GetBlock(a_Position);
+		if (DestroyedBlock == E_BLOCK_AIR)
+		{
+			// There's nothing left for us here, but a barren and empty land
+			// Let's go.
+			return;
+		}
+
+		auto & World = *a_Chunk.GetWorld();
+		auto & Random = GetRandomProvider();
+		const auto Absolute = cChunkDef::RelativeToAbsolute(a_Position, a_Chunk.GetPos());
+		if (DestroyedBlock == E_BLOCK_TNT)
+		{
+			// Random fuse between 10 to 30 game ticks.
+			const int FuseTime = Random.RandInt(10, 30);
+
+			// Activate the TNT, with initial velocity and no fuse sound:
+			World.SpawnPrimedTNT(Vector3d(0.5, 0, 0.5) + Absolute, FuseTime, 1, false);
+		}
+		else if (Random.RandBool(1.f / a_Power))
+		{
+			const auto DestroyedMeta = a_Chunk.GetMeta(a_Position);
+			a_Chunk.GetWorld()->SpawnItemPickups(
+				cBlockInfo::GetHandler(DestroyedBlock)->ConvertToPickups(DestroyedMeta, a_Chunk.GetBlockEntityRel(a_Position)),
+				Absolute
+			);
+		}
+		else if (a_Fiery && Random.RandBool(1.f / 3.f))  // 33% chance of starting fires if it can start fires
+		{
+			const auto Below = a_Position.addedY(-1);
+			if ((Below.y >= 0) && cBlockInfo::FullyOccupiesVoxel(a_Chunk.GetBlock(Below)))
+			{
+				// Start a fire:
+				DestroyBlock(World, a_Chunk, Absolute, a_Position, DestroyedBlock, E_BLOCK_FIRE);
+				return;
+			}
+		}
+		else if (const auto Shrapnel = World.GetTNTShrapnelLevel(); (Shrapnel > slNone) && Random.RandBool(0))  // 20% chance of flinging stuff around
+		{
+			// If the block is shrapnel-able, make a falling block entity out of it:
+			if (
+				((Shrapnel == slAll) && cBlockInfo::FullyOccupiesVoxel(DestroyedBlock)) ||
+				((Shrapnel == slGravityAffectedOnly) && cSandSimulator::IsAllowedBlock(DestroyedBlock))
+			)
+			{
+				const auto DestroyedMeta = a_Chunk.GetMeta(a_Position);
+				auto FallingBlock = std::make_unique<cFallingBlock>(Vector3d(0.5, 0, 0.5) + Absolute, DestroyedBlock, DestroyedMeta);
+				// TODO: correct velocity FallingBlock->SetSpeedY(40);
+				FallingBlock->Initialize(std::move(FallingBlock), World);
+			}
+		}
+
+		DestroyBlock(World, a_Chunk, Absolute, a_Position, DestroyedBlock, E_BLOCK_AIR);
+	}
+
+	/** Traces the path taken by one Explosion Lazor (tm) with given direction and intensity, that will destroy blocks until it is exhausted. */
+	static void DestructionTrace(cChunk * a_Chunk, Vector3f a_Origin, const Vector3f a_Destination, const unsigned a_Power, const bool a_Fiery, float a_Intensity)
+	{
+		// The current position the ray is at.
+		auto Checkpoint = a_Origin;
+
+		// The total displacement the ray must travel.
+		const auto TraceDisplacement = (a_Destination - a_Origin);
+
+		// The displacement that they ray in one iteration step should travel.
+		const auto Step = TraceDisplacement.NormalizeCopy() * StepUnit;
+
+		// Loop until we've reached the prescribed destination:
+		while (TraceDisplacement > (Checkpoint - a_Origin))
+		{
+			auto Position = Checkpoint.Floor();
+			if (!cChunkDef::IsValidHeight(Position.y))
+			{
+				break;
+			}
+
+			const auto Neighbour = a_Chunk->GetRelNeighborChunkAdjustCoords(Position);
+			if ((Neighbour == nullptr) || !Neighbour->IsValid())
+			{
+				break;
+			}
+
+			a_Intensity -= 0.3f * (0.3f + cBlockInfo::GetExplosionAbsorption(Neighbour->GetBlock(Position)));
+			if (a_Intensity <= 0)
+			{
+				// The ray is exhausted:
+				break;
+			}
+
+			DestroyBlock(*Neighbour, Position, a_Power, a_Fiery);
+
+			// Adjust coordinates to be relative to the neighbour chunk:
+			Checkpoint = RebaseRelativePosition(a_Chunk->GetPos(), Neighbour->GetPos(), Checkpoint);
+			a_Origin = RebaseRelativePosition(a_Chunk->GetPos(), Neighbour->GetPos(), a_Origin);
+			a_Chunk = Neighbour;
+
+			// Increment the simulation, weaken the ray:
+			Checkpoint += Step;
+			a_Intensity -= StepAttenuation;
+		}
+	}
+
+	/** Sends out Explosion Lazors (tm) originating from the given position that destroy blocks. */
+	static void DamageBlocks(cChunk & a_Chunk, const Vector3f a_Position, const unsigned a_Power, const bool a_Fiery)
+	{
+		const auto Intensity = a_Power * (0.7f + GetRandomProvider().RandReal(0.6f));
+		const auto ExplosionRadius = CeilC((Intensity / StepAttenuation) * StepUnit);
+
+		// Oh boy... Better hope you have a hot cache, 'cos this little manoeuvre's gonna cost us 1352 raytraces in one tick...
+		const int HalfSide = TraceCubeSideLength / 2;
+
+		// The following loops implement the tracing algorithm described in http://minecraft.gamepedia.com/Explosion
+
+		// Trace rays from the explosion centre to all points in a square of area TraceCubeSideLength * TraceCubeSideLength
+		// in the YM and YP directions:
+		for (int OffsetX = -HalfSide; OffsetX < HalfSide; OffsetX++)
+		{
+			for (int OffsetZ = -HalfSide; OffsetZ < HalfSide; OffsetZ++)
+			{
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(OffsetX, +ExplosionRadius, OffsetZ), a_Power, a_Fiery, Intensity);
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(OffsetX, -ExplosionRadius, OffsetZ), a_Power, a_Fiery, Intensity);
+			}
+		}
+
+		/*
+		Trace rays from the centre to the sides of the explosion cube, being careful to avoid duplicates:
+
+		Top view:
+		______
+		.       | (dot to make style checker happy)
+		|       |
+		|       |
+		|  ______
+
+		Side view:
+		+        +
+		|======  |
+		|     |  |
+		|======  |
+		+        +
+
+		*/
+		for (int Offset = -HalfSide; Offset < HalfSide - 1; Offset++)
+		{
+			for (int OffsetY = -HalfSide + 1; OffsetY < HalfSide - 1; OffsetY++)
+			{
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(ExplosionRadius, OffsetY, Offset + 1), a_Power, a_Fiery, Intensity);
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(-ExplosionRadius, OffsetY, Offset), a_Power, a_Fiery, Intensity);
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(Offset, OffsetY, ExplosionRadius), a_Power, a_Fiery, Intensity);
+				DestructionTrace(&a_Chunk, a_Position, a_Position + Vector3f(Offset + 1, OffsetY, -ExplosionRadius), a_Power, a_Fiery, Intensity);
+			}
+		}
+	}
+
+	/** Sends an explosion packet to all clients in the given chunk. */
+	static void LagTheClient(cChunk & a_Chunk, const Vector3f a_Position, const unsigned a_Power)
+	{
+		for (const auto Client : a_Chunk.GetAllClients())
+		{
+			Client->SendExplosion(a_Position, a_Power);
+		}
+	}
+
+	void Kaboom(cWorld & a_World, const Vector3f a_Position, const unsigned a_Power, const bool a_Fiery)
+	{
+		a_World.DoWithChunkAt(a_Position.Floor(), [a_Position, a_Power, a_Fiery](cChunk & a_Chunk)
+		{
+			LagTheClient(a_Chunk, a_Position, a_Power);
+			DamageEntities(a_Chunk, a_Position, a_Power);
+			DamageBlocks(a_Chunk, AbsoluteToRelative(a_Position, a_Chunk.GetPos()), a_Power, a_Fiery);
+
+			return false;
+		});
+	}
+}