JoltPhysics/Jolt/Physics/PhysicsSystem.h

// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

#pragma once

#include <Jolt/Physics/Body/BodyInterface.h>
#include <Jolt/Physics/Collision/NarrowPhaseQuery.h>
#include <Jolt/Physics/Collision/ContactListener.h>
#include <Jolt/Physics/Constraints/ContactConstraintManager.h>
#include <Jolt/Physics/Constraints/ConstraintManager.h>
#include <Jolt/Physics/IslandBuilder.h>
#include <Jolt/Physics/LargeIslandSplitter.h>
#include <Jolt/Physics/PhysicsUpdateContext.h>
#include <Jolt/Physics/PhysicsSettings.h>

JPH_NAMESPACE_BEGIN

class JobSystem;
class StateRecorder;
class TempAllocator;
class PhysicsStepListener;

/// The main class for the physics system. It contains all rigid bodies and simulates them.
///
/// The main simulation is performed by the Update() call on multiple threads (if the JobSystem is configured to use them). Please refer to the general architecture overview in the Docs folder for more information.
class PhysicsSystem : public NonCopyable
{
public:
	JPH_OVERRIDE_NEW_DELETE

	/// Constructor / Destructor
								PhysicsSystem()												: mContactManager(mPhysicsSettings) JPH_IF_ENABLE_ASSERTS(, mConstraintManager(&mBodyManager)) { }
								~PhysicsSystem();

	/// Initialize the system.
	/// @param inMaxBodies Maximum number of bodies to support.
	/// @param inNumBodyMutexes Number of body mutexes to use. Should be a power of 2 in the range [1, 64], use 0 to auto detect.
	/// @param inMaxBodyPairs Maximum amount of body pairs to process (anything else will fall through the world), this number should generally be much higher than the max amount of contact points as there will be lots of bodies close that are not actually touching.
	/// @param inMaxContactConstraints Maximum amount of contact constraints to process (anything else will fall through the world).
	/// @param inBroadPhaseLayerInterface Information on the mapping of object layers to broad phase layers. Since this is a virtual interface, the instance needs to stay alive during the lifetime of the PhysicsSystem.
	/// @param inObjectVsBroadPhaseLayerFilter Filter callback function that is used to determine if an object layer collides with a broad phase layer. Since this is a virtual interface, the instance needs to stay alive during the lifetime of the PhysicsSystem.
	/// @param inObjectLayerPairFilter Filter callback function that is used to determine if two object layers collide. Since this is a virtual interface, the instance needs to stay alive during the lifetime of the PhysicsSystem.
	void						Init(uint inMaxBodies, uint inNumBodyMutexes, uint inMaxBodyPairs, uint inMaxContactConstraints, const BroadPhaseLayerInterface &inBroadPhaseLayerInterface, const ObjectVsBroadPhaseLayerFilter &inObjectVsBroadPhaseLayerFilter, const ObjectLayerPairFilter &inObjectLayerPairFilter);
	
	/// Listener that is notified whenever a body is activated/deactivated
	void						SetBodyActivationListener(BodyActivationListener *inListener) { mBodyManager.SetBodyActivationListener(inListener); }
	BodyActivationListener *	GetBodyActivationListener() const							{ return mBodyManager.GetBodyActivationListener(); }

	/// Listener that is notified whenever a contact point between two bodies is added/updated/removed
	void						SetContactListener(ContactListener *inListener)				{ mContactManager.SetContactListener(inListener); }
	ContactListener *			GetContactListener() const									{ return mContactManager.GetContactListener(); }

	/// Set the function that combines the friction of two bodies and returns it
	/// Default method is the geometric mean: sqrt(friction1 * friction2).
	void						SetCombineFriction(ContactConstraintManager::CombineFunction inCombineFriction) { mContactManager.SetCombineFriction(inCombineFriction); }

	/// Set the function that combines the restitution of two bodies and returns it
	/// Default method is max(restitution1, restitution1)
	void						SetCombineRestitution(ContactConstraintManager::CombineFunction inCombineRestition) { mContactManager.SetCombineRestitution(inCombineRestition); }

	/// Control the main constants of the physics simulation
	void						SetPhysicsSettings(const PhysicsSettings &inSettings)		{ mPhysicsSettings = inSettings; }
	const PhysicsSettings &		GetPhysicsSettings() const									{ return mPhysicsSettings; }

	/// Access to the body interface. This interface allows to to create / remove bodies and to change their properties.
	const BodyInterface &		GetBodyInterface() const									{ return mBodyInterfaceLocking; }
	BodyInterface &				GetBodyInterface() 											{ return mBodyInterfaceLocking; }
	const BodyInterface &		GetBodyInterfaceNoLock() const								{ return mBodyInterfaceNoLock; } ///< Version that does not lock the bodies, use with great care!
	BodyInterface & 			GetBodyInterfaceNoLock()									{ return mBodyInterfaceNoLock; } ///< Version that does not lock the bodies, use with great care!

	/// Access to the broadphase interface that allows coarse collision queries
	const BroadPhaseQuery &		GetBroadPhaseQuery() const									{ return *mBroadPhase; }

	/// Interface that allows fine collision queries against first the broad phase and then the narrow phase.
	const NarrowPhaseQuery &	GetNarrowPhaseQuery() const									{ return mNarrowPhaseQueryLocking; }
	const NarrowPhaseQuery & 	GetNarrowPhaseQueryNoLock() const							{ return mNarrowPhaseQueryNoLock; } ///< Version that does not lock the bodies, use with great care!

	/// Add constraint to the world
	void						AddConstraint(Constraint *inConstraint)						{ mConstraintManager.Add(&inConstraint, 1); }
	
	/// Remove constraint from the world
	void						RemoveConstraint(Constraint *inConstraint)					{ mConstraintManager.Remove(&inConstraint, 1); }

	/// Batch add constraints. Note that the inConstraints array is allowed to have nullptrs, these will be ignored.
	void						AddConstraints(Constraint **inConstraints, int inNumber)	{ mConstraintManager.Add(inConstraints, inNumber); }

	/// Batch remove constraints. Note that the inConstraints array is allowed to have nullptrs, these will be ignored.
	void						RemoveConstraints(Constraint **inConstraints, int inNumber)	{ mConstraintManager.Remove(inConstraints, inNumber); }

	/// Get a list of all constraints
	Constraints					GetConstraints() const										{ return mConstraintManager.GetConstraints(); }

	/// Optimize the broadphase, needed only if you've added many bodies prior to calling Update() for the first time.
	void						OptimizeBroadPhase();

	/// Adds a new step listener
	void						AddStepListener(PhysicsStepListener *inListener);

	/// Removes a step listener
	void						RemoveStepListener(PhysicsStepListener *inListener);

	/// Simulate the system.
	/// The world steps for a total of inDeltaTime seconds. This is divided in inCollisionSteps iterations. Each iteration
	/// consists of collision detection followed by inIntegrationSubSteps integration steps.
	EPhysicsUpdateError			Update(float inDeltaTime, int inCollisionSteps, int inIntegrationSubSteps, TempAllocator *inTempAllocator, JobSystem *inJobSystem);

	/// Saving state for replay
	void						SaveState(StateRecorder &inStream) const;

	/// Restoring state for replay. Returns false if failed.
	bool						RestoreState(StateRecorder &inStream);

#ifdef JPH_DEBUG_RENDERER
	// Drawing properties
	static bool					sDrawMotionQualityLinearCast;								///< Draw debug info for objects that perform continuous collision detection through the linear cast motion quality

	/// Draw the state of the bodies (debugging purposes)
	void						DrawBodies(const BodyManager::DrawSettings &inSettings, DebugRenderer *inRenderer, const BodyDrawFilter *inBodyFilter = nullptr) { mBodyManager.Draw(inSettings, mPhysicsSettings, inRenderer, inBodyFilter); }

	/// Draw the constraints only (debugging purposes)
	void						DrawConstraints(DebugRenderer *inRenderer)					{ mConstraintManager.DrawConstraints(inRenderer); }

	/// Draw the constraint limits only (debugging purposes)
	void						DrawConstraintLimits(DebugRenderer *inRenderer)				{ mConstraintManager.DrawConstraintLimits(inRenderer); }

	/// Draw the constraint reference frames only (debugging purposes)
	void						DrawConstraintReferenceFrame(DebugRenderer *inRenderer)	{ mConstraintManager.DrawConstraintReferenceFrame(inRenderer); }
#endif // JPH_DEBUG_RENDERER

	/// Set gravity value
	void						SetGravity(Vec3Arg inGravity)								{ mGravity = inGravity; }
	Vec3		 				GetGravity() const											{ return mGravity; }

	/// Returns a locking interface that won't actually lock the body. Use with great care!
	inline const BodyLockInterfaceNoLock &	GetBodyLockInterfaceNoLock() const				{ return mBodyLockInterfaceNoLock; }

	/// Returns a locking interface that locks the body so other threads cannot modify it.
	inline const BodyLockInterfaceLocking &	GetBodyLockInterface() const					{ return mBodyLockInterfaceLocking; }

	/// Get an broadphase layer filter that uses the default pair filter and a specified object layer to determine if broadphase layers collide
	DefaultBroadPhaseLayerFilter GetDefaultBroadPhaseLayerFilter(ObjectLayer inLayer) const	{ return DefaultBroadPhaseLayerFilter(*mObjectVsBroadPhaseLayerFilter, inLayer); }

	/// Get an object layer filter that uses the default pair filter and a specified layer to determine if layers collide
	DefaultObjectLayerFilter	GetDefaultLayerFilter(ObjectLayer inLayer) const			{ return DefaultObjectLayerFilter(*mObjectLayerPairFilter, inLayer); }

	/// Gets the current amount of bodies that are in the body manager
	uint						GetNumBodies() const										{ return mBodyManager.GetNumBodies(); }

	/// Gets the current amount of active bodies that are in the body manager
	uint32						GetNumActiveBodies() const									{ return mBodyManager.GetNumActiveBodies(); }

	/// Get the maximum amount of bodies that this physics system supports
	uint						GetMaxBodies() const										{ return mBodyManager.GetMaxBodies(); }

	/// Helper struct that counts the number of bodies of each type
	using BodyStats = BodyManager::BodyStats;

	/// Get stats about the bodies in the body manager (slow, iterates through all bodies)
	BodyStats					GetBodyStats() const										{ return mBodyManager.GetBodyStats(); }

	/// Get copy of the list of all bodies under protection of a lock.
	/// @param outBodyIDs On return, this will contain the list of BodyIDs
	void						GetBodies(BodyIDVector &outBodyIDs) const					{ return mBodyManager.GetBodyIDs(outBodyIDs); }

	/// Get copy of the list of active bodies under protection of a lock.
	/// @param outBodyIDs On return, this will contain the list of BodyIDs
	void						GetActiveBodies(BodyIDVector &outBodyIDs) const				{ return mBodyManager.GetActiveBodies(outBodyIDs); }

	/// Check if 2 bodies were in contact during the last simulation step. Since contacts are only detected between active bodies, so at least one of the bodies must be active in order for this function to work.
	/// It queries the state at the time of the last PhysicsSystem::Update and will return true if the bodies were in contact, even if one of the bodies was moved / removed afterwards.
	/// This function can be called from any thread when the PhysicsSystem::Update is not running. During PhysicsSystem::Update this function is only valid during contact callbacks:
	/// - During the ContactListener::OnContactAdded callback this function can be used to determine if a different contact pair between the bodies was active in the previous simulation step (function returns true) or if this is the first step that the bodies are touching (function returns false).
	/// - During the ContactListener::OnContactRemoved callback this function can be used to determine if this is the last contact pair between the bodies (function returns false) or if there are other contacts still present (function returns true).
	bool						WereBodiesInContact(const BodyID &inBody1ID, const BodyID &inBody2ID) const { return mContactManager.WereBodiesInContact(inBody1ID, inBody2ID); }

#ifdef JPH_TRACK_BROADPHASE_STATS
	/// Trace the accumulated broadphase stats to the TTY
	void						ReportBroadphaseStats()										{ mBroadPhase->ReportStats(); }
#endif // JPH_TRACK_BROADPHASE_STATS

private:
	using CCDBody = PhysicsUpdateContext::SubStep::CCDBody;

	// Various job entry points
	void						JobStepListeners(PhysicsUpdateContext::Step *ioStep);
	void						JobDetermineActiveConstraints(PhysicsUpdateContext::Step *ioStep) const;
	void						JobApplyGravity(const PhysicsUpdateContext *ioContext, PhysicsUpdateContext::Step *ioStep);	
	void						JobSetupVelocityConstraints(float inDeltaTime, PhysicsUpdateContext::Step *ioStep) const;
	void						JobBuildIslandsFromConstraints(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::Step *ioStep);
	void						JobFindCollisions(PhysicsUpdateContext::Step *ioStep, int inJobIndex);
	void						JobFinalizeIslands(PhysicsUpdateContext *ioContext);
	void						JobBodySetIslandIndex();
	void						JobSolveVelocityConstraints(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);
	void						JobPreIntegrateVelocity(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);
	void						JobIntegrateVelocity(const PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);
	void						JobPostIntegrateVelocity(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep) const;
	void						JobFindCCDContacts(const PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);
	void						JobResolveCCDContacts(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);
	void						JobContactRemovedCallbacks(const PhysicsUpdateContext::Step *ioStep);
	void						JobSolvePositionConstraints(PhysicsUpdateContext *ioContext, PhysicsUpdateContext::SubStep *ioSubStep);

	/// Tries to spawn a new FindCollisions job if max concurrency hasn't been reached yet
	void						TrySpawnJobFindCollisions(PhysicsUpdateContext::Step *ioStep) const;

	using ContactAllocator = ContactConstraintManager::ContactAllocator;

	/// Process narrow phase for a single body pair
	void						ProcessBodyPair(ContactAllocator &ioContactAllocator, const BodyPair &inBodyPair);

	/// This helper batches up bodies that need to put to sleep to avoid contention on the activation mutex
	class BodiesToSleep;

	/// Called at the end of JobSolveVelocityConstraints to check if bodies need to go to sleep and to update their bounding box in the broadphase
	void						CheckSleepAndUpdateBounds(uint32 inIslandIndex, const PhysicsUpdateContext *ioContext, const PhysicsUpdateContext::SubStep *ioSubStep, BodiesToSleep &ioBodiesToSleep);

	/// Number of constraints to process at once in JobDetermineActiveConstraints
	static constexpr int		cDetermineActiveConstraintsBatchSize = 64;

	/// Number of bodies to process at once in JobApplyGravity
	static constexpr int		cApplyGravityBatchSize = 64;

	/// Number of active bodies to test for collisions per batch
	static constexpr int		cActiveBodiesBatchSize = 16;

	/// Number of active bodies to integrate velocities for
	static constexpr int		cIntegrateVelocityBatchSize = 64;

	/// Number of contacts that need to be queued before another narrow phase job is started
	static constexpr int		cNarrowPhaseBatchSize = 16;

	/// Number of continuous collision shape casts that need to be queued before another job is started
	static constexpr int		cNumCCDBodiesPerJob = 4;

	/// Broadphase layer filter that decides if two objects can collide
	const ObjectVsBroadPhaseLayerFilter *mObjectVsBroadPhaseLayerFilter = nullptr;

	/// Object layer filter that decides if two objects can collide
	const ObjectLayerPairFilter *mObjectLayerPairFilter = nullptr;

	/// The body manager keeps track which bodies are in the simulation
	BodyManager					mBodyManager;

	/// Body locking interfaces
	BodyLockInterfaceNoLock		mBodyLockInterfaceNoLock { mBodyManager };
	BodyLockInterfaceLocking	mBodyLockInterfaceLocking { mBodyManager };

	/// Body interfaces
	BodyInterface				mBodyInterfaceNoLock;
	BodyInterface				mBodyInterfaceLocking;

	/// Narrow phase query interface
	NarrowPhaseQuery			mNarrowPhaseQueryNoLock;
	NarrowPhaseQuery			mNarrowPhaseQueryLocking;

	/// The broadphase does quick collision detection between body pairs
	BroadPhase *				mBroadPhase = nullptr;
    
    /// Simulation settings
	PhysicsSettings				mPhysicsSettings;

	/// The contact manager resolves all contacts during a simulation step
	ContactConstraintManager	mContactManager;

	/// All non-contact constraints
	ConstraintManager			mConstraintManager;

	/// Keeps track of connected bodies and builds islands for multithreaded velocity/position update
	IslandBuilder				mIslandBuilder;

	/// Will split large islands into smaller groups of bodies that can be processed in parallel
	LargeIslandSplitter			mLargeIslandSplitter;

	/// Mutex protecting mStepListeners
	Mutex						mStepListenersMutex;

	/// List of physics step listeners
	using StepListeners = Array<PhysicsStepListener *>;
	StepListeners				mStepListeners;

	/// This is the global gravity vector
	Vec3						mGravity = Vec3(0, -9.81f, 0);

	/// Previous frame's delta time of one sub step to allow scaling previous frame's constraint impulses
	float						mPreviousSubStepDeltaTime = 0.0f;
};

JPH_NAMESPACE_END