JoltPhysics/Jolt/Physics/PhysicsUpdateContext.h

// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

#pragma once

#include <Physics/Body/BodyPair.h>
#include <Physics/Collision/ContactListener.h>
#include <Physics/Collision/BroadPhase/BroadPhase.h>
#include <Core/StaticArray.h>
#include <Core/JobSystem.h>

namespace JPH {

class PhysicsSystem;
class IslandBuilder;
class Constraint;
class TempAllocator;

/// Information used during the Update call
class PhysicsUpdateContext : public NonCopyable
{
public:
	/// Destructor
							~PhysicsUpdateContext();

	static constexpr int	cMaxConcurrency = 32;									///< Maximum supported amount of concurrent jobs
	static constexpr int	cMaxSteps = 4;											///< Maximum supported amount of collision steps
	static constexpr int	cMaxSubSteps = 4;										///< Maximum supported amount of integration sub steps

	using JobHandleArray = StaticArray<JobHandle, cMaxConcurrency>;

	struct Step;

	/// Structure that contains job handles for each integration sub step
	struct SubStep
	{
		Step *				mStep;													///< Step that this substeb belongs to

		bool				mIsFirst;												///< If this is the first substep in the step
		bool				mIsLast;												///< If this is the last substep in the step
		bool				mIsLastOfAll;											///< If this is the last substep in the last step

		atomic<uint32>		mSolveVelocityConstraintsNextIsland { 0 };				///< Next island that needs to be processed for the solve velocity constraints step (doesn't need own cache line since position jobs don't run at same time)
		atomic<uint32>		mSolvePositionConstraintsNextIsland { 0 };				///< Next island that needs to be processed for the solve position constraints step (doesn't need own cache line since velocity jobs don't run at same time)

		/// Contains the information needed to cast a body through the scene to do continuous collision detection
		struct CCDBody
		{
							CCDBody(BodyID inBodyID1, Vec3Arg inDeltaPosition, float inLinearCastThresholdSq, float inMaxPenetration) : mDeltaPosition(inDeltaPosition), mBodyID1(inBodyID1), mLinearCastThresholdSq(inLinearCastThresholdSq), mMaxPenetration(inMaxPenetration) { }

			Vec3			mDeltaPosition;											///< Desired rotation step
			Vec3			mContactNormal;											///< World space normal of closest hit (only valid if mFractionPlusSlop < 1)
			Vec3			mContactPointOn2;										///< World space contact point on body 2 of closest hit (only valid if mFractionPlusSlop < 1)
			BodyID			mBodyID1;												///< Body 1 (the body that is performing collision detection)
			BodyID			mBodyID2;												///< Body 2 (the body of the closest hit, only valid if mFractionPlusSlop < 1)
			float			mFraction = 1.0f;										///< Fraction at which the hit occurred
			float			mFractionPlusSlop = 1.0f;								///< Fraction at which the hit occurred + extra delta to allow body to penetrate by mMaxPenetration
			float			mLinearCastThresholdSq;									///< Maximum allowed squared movement before doing a linear cast (determined by inner radius of shape)
			float			mMaxPenetration;										///< Maximum allowed penetration (determined by inner radius of shape)
			ContactSettings	mContactSettings;										///< The contact settings for this contact
		};
		atomic<uint32>		mIntegrateVelocityReadIdx { 0 };						///< Next active body index to take when integrating velocities
		CCDBody *			mCCDBodies = nullptr;									///< List of bodies that need to do continuous collision detection
		uint32				mCCDBodiesCapacity = 0;									///< Capacity of the mCCDBodies list
		atomic<uint32>		mNumCCDBodies = 0;										///< Number of CCD bodies in mCCDBodies
		atomic<uint32>		mNextCCDBody { 0 };										///< Next unprocessed body index in mCCDBodies
		int *				mActiveBodyToCCDBody = nullptr;							///< A mapping between an index in BodyManager::mActiveBodies and the index in mCCDBodies
		uint32				mNumActiveBodyToCCDBody = 0;							///< Number of indices in mActiveBodyToCCDBody

		JobHandleArray		mSolveVelocityConstraints;								///< Solve the constraints in the velocity domain
		JobHandle			mPreIntegrateVelocity;									///< Setup integration of all body positions
		JobHandleArray		mIntegrateVelocity;										///< Integrate all body positions
		JobHandle			mPostIntegrateVelocity;									///< Finalize integration of all body positions
		JobHandle			mResolveCCDContacts;									///< Updates the positions and velocities for all bodies that need continuous collision detection
		JobHandleArray		mSolvePositionConstraints;								///< Solve all constraints in the position domain
		JobHandle			mStartNextSubStep;										///< Trampoline job that either kicks the next sub step or the next step
	};

	using SubSteps = StaticArray<SubStep, cMaxSubSteps>;

	struct BodyPairQueue
	{
		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32> mWriteIdx { 0 };				///< Next index to write in mBodyPair array (need to add thread index * mMaxBodyPairsPerQueue and modulo mMaxBodyPairsPerQueue) (moved to own cache line to avoid conflicts with consumer jobs)
		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32> mReadIdx { 0 };					///< Next index to read in mBodyPair array (need to add thread index * mMaxBodyPairsPerQueue and modulo mMaxBodyPairsPerQueue) (moved to own cache line to avoid conflicts with producer/consumer jobs)
	};

	using BodyPairQueues = StaticArray<BodyPairQueue, cMaxConcurrency>;

	using JobMask = uint32;															///< A mask that has as many bits as we can have concurrent jobs
	static_assert(sizeof(JobMask) * 8 >= cMaxConcurrency);

	/// Structure that contains data needed for each collision step.
	struct Step
	{
		PhysicsUpdateContext *mContext;												///< The physics update context

		BroadPhase::UpdateState	mBroadPhaseUpdateState;								///< Handle returned by Broadphase::UpdatePrepare

		uint32				mNumActiveBodiesAtStepStart;							///< Number of bodies that were active at the start of the physics update step. Only these bodies will receive gravity (they are the first N in the active body list).

		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32>	mConstraintReadIdx { 0 };		///< Next constraint for determine active constraints (moved to own cache line since its modified frequently by different jobs)

		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32>	mNumActiveConstraints { 0 };	///< Number of constraints in the mActiveConstraints array

		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32>	mStepListenerReadIdx { 0 };		///< Next step listener to call (moved to own cache line since its modified frequently by different jobs)

		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32>	mApplyGravityReadIdx { 0 };		///< Next body to apply gravity to (moved to own cache line since its modified frequently by different jobs)

		alignas(JPH_CACHE_LINE_SIZE) atomic<uint32>	mActiveBodyReadIdx { 0 };		///< Index of fist active body that has not yet been processed by the broadphase

		BodyPairQueues		mBodyPairQueues;										///< Queues in which to put body pairs that need to be tested by the narrowphase

		uint32				mMaxBodyPairsPerQueue;									///< Amount of body pairs that we can queue per queue

		atomic<JobMask>		mActiveFindCollisionJobs;								///< A bitmask that indicates which jobs are still active

		atomic<uint>		mNumBodyPairs { 0 };									///< The number of body pairs found in this step (used to size the contact cache in the next step)
		atomic<uint>		mNumManifolds { 0 };									///< The number of manifolds found in this step (used to size the contact cache in the next step)

		// Jobs in order of execution (some run in parallel)
		JobHandle			mBroadPhasePrepare;										///< Prepares the new tree in the background
		JobHandleArray		mStepListeners;											///< Listeners to notify of the beginning of a physics step
		JobHandleArray		mDetermineActiveConstraints;							///< Determine which constraints will be active during this step
		JobHandleArray		mApplyGravity;											///< Update velocities of bodies with gravity
		JobHandleArray		mFindCollisions;										///< Find all collisions between active bodies an the world
		JobHandle			mUpdateBroadphaseFinalize;								///< Swap the newly built tree with the current tree
		JobHandle			mSetupVelocityConstraints;								///< Calculate properties for all constraints in the constraint manager
		JobHandle			mBuildIslandsFromConstraints;							///< Go over all constraints and assign the bodies they're attached to to an island
		JobHandle			mFinalizeIslands;										///< Finalize calculation simulation islands
		JobHandle			mBodySetIslandIndex;									///< Set the current island index on each body (not used by the simulation, only for drawing purposes)
		SubSteps			mSubSteps;												///< Integration sub steps
		JobHandle			mContactRemovedCallbacks;								///< Calls the contact removed callbacks
		JobHandle			mStartNextStep;											///< Job that kicks the next step (empty for the last step)
	};

	using Steps = StaticArray<Step, cMaxSteps>;

	/// Maximum amount of concurrent jobs on this machine
	int						GetMaxConcurrency() const								{ const int max_concurrency = PhysicsUpdateContext::cMaxConcurrency; return min(max_concurrency, mJobSystem->GetMaxConcurrency()); } ///< Need to put max concurrency in temp var as min requires a reference

	PhysicsSystem *			mPhysicsSystem;											///< The physics system we belong to
	TempAllocator *			mTempAllocator;											///< Temporary allocator used during the update
	JobSystem *				mJobSystem;												///< Job system that processes jobs
	JobSystem::Barrier *	mBarrier;												///< Barrier used to wait for all physics jobs to complete

	float					mStepDeltaTime;											///< Delta time for a simulation step (collision step)
	float					mSubStepDeltaTime;										///< Delta time for a simulation sub step (integration step)
	float					mWarmStartImpulseRatio;									///< Ratio of this step delta time vs last step

	Constraint **			mActiveConstraints = nullptr;							///< Constraints that were active at the start of the physics update step (activating bodies can activate constraints and we need a consistent snapshot). Only these constraints will be resolved.

	BodyPair *				mBodyPairs = nullptr;									///< A list of body pairs found by the broadphase

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

	Steps					mSteps;
};

} // JPH