Add MLCP constraint solver for multibody

src/BulletDynamics/Featherstone/btMultiBodyMLCPConstraintSolver.h

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+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2018 Google Inc. http://bulletphysics.org
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it freely,
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef BT_MULTIBODY_MLCP_CONSTRAINT_SOLVER_H
+#define BT_MULTIBODY_MLCP_CONSTRAINT_SOLVER_H
+
+#include "LinearMath/btMatrixX.h"
+#include "LinearMath/btThreads.h"
+#include "BulletDynamics/Featherstone/btMultiBodyConstraintSolver.h"
+
+class btMLCPSolverInterface;
+class btMultiBody;
+
+class btMultiBodyMLCPConstraintSolver : public btMultiBodyConstraintSolver
+{
+protected:
+	/// \name MLCP Formulation for Rigid Bodies
+	/// \{
+
+	/// A matrix in the MLCP formulation
+	btMatrixXu m_A;
+
+	/// b vector in the MLCP formulation.
+	btVectorXu m_b;
+
+	/// Constraint impulse, which is an output of MLCP solving.
+	btVectorXu m_x;
+
+	/// Lower bound of constraint impulse, \c m_x.
+	btVectorXu m_lo;
+
+	/// Upper bound of constraint impulse, \c m_x.
+	btVectorXu m_hi;
+
+	/// \}
+
+	/// \name Cache Variables for Split Impulse for Rigid Bodies
+	/// When using 'split impulse' we solve two separate (M)LCPs
+	/// \{
+
+	/// Split impulse Cache vector corresponding to \c m_b.
+	btVectorXu m_bSplit;
+
+	/// Split impulse cache vector corresponding to \c m_x.
+	btVectorXu m_xSplit;
+
+	/// \}
+
+	/// \name MLCP Formulation for Multibodies
+	/// \{
+
+	/// A matrix in the MLCP formulation
+	btMatrixXu m_multiBodyA;
+
+	/// b vector in the MLCP formulation.
+	btVectorXu m_multiBodyB;
+
+	/// Constraint impulse, which is an output of MLCP solving.
+	btVectorXu m_multiBodyX;
+
+	/// Lower bound of constraint impulse, \c m_x.
+	btVectorXu m_multiBodyLo;
+
+	/// Upper bound of constraint impulse, \c m_x.
+	btVectorXu m_multiBodyHi;
+
+	/// \}
+
+	/// Indices of normal contact constraint associated with frictional contact constraint for rigid bodies.
+	///
+	/// This is used by the MLCP solver to update the upper bounds of frictional contact impulse given intermediate
+	/// normal contact impulse. For example, i-th element represents the index of a normal constraint that is
+	/// accosiated with i-th frictional contact constraint if i-th constraint is a frictional contact constraint.
+	/// Otherwise, -1.
+	btAlignedObjectArray<int> m_limitDependencies;
+
+	/// Indices of normal contact constraint associated with frictional contact constraint for multibodies.
+	///
+	/// This is used by the MLCP solver to update the upper bounds of frictional contact impulse given intermediate
+	/// normal contact impulse. For example, i-th element represents the index of a normal constraint that is
+	/// accosiated with i-th frictional contact constraint if i-th constraint is a frictional contact constraint.
+	/// Otherwise, -1.
+	btAlignedObjectArray<int> m_multiBodyLimitDependencies;
+
+	/// Array of all the rigid body constraints
+	btAlignedObjectArray<btSolverConstraint*> m_allConstraintPtrArray;
+
+	/// Array of all the multibody constraints
+	btAlignedObjectArray<btMultiBodySolverConstraint*> m_multiBodyAllConstraintPtrArray;
+
+	/// MLCP solver
+	btMLCPSolverInterface* m_solver;
+
+	/// Count of fallbacks of using btSequentialImpulseConstraintSolver, which happens when the MLCP solver fails.
+	int m_fallback;
+
+	/// \name MLCP Scratch Variables
+	/// The following scratch variables are not stateful -- contents are cleared prior to each use.
+	/// They are only cached here to avoid extra memory allocations and deallocations and to ensure
+	/// that multiple instances of the solver can be run in parallel.
+	///
+	/// \{
+
+	/// Cache variable for constraint Jacobian matrix.
+	btMatrixXu m_scratchJ3;
+
+	/// Cache variable for constraint Jacobian times inverse mass matrix.
+	btMatrixXu m_scratchJInvM3;
+
+	/// Cache variable for offsets.
+	btAlignedObjectArray<int> m_scratchOfs;
+
+	/// \}
+
+	/// Constructs MLCP terms, which are \c m_A, \c m_b, \c m_lo, and \c m_hi.
+	virtual void createMLCPFast(const btContactSolverInfo& infoGlobal);
+
+	/// Constructs MLCP terms for constraints of two rigid bodies
+	void createMLCPFastRigidBody(const btContactSolverInfo& infoGlobal);
+
+	/// Constructs MLCP terms for constraints of two multi-bodies or one rigid body and one multibody
+	void createMLCPFastMultiBody(const btContactSolverInfo& infoGlobal);
+
+	/// Solves MLCP and returns the success
+	virtual bool solveMLCP(const btContactSolverInfo& infoGlobal);
+
+	// Documentation inherited
+	btScalar solveGroupCacheFriendlySetup(
+		btCollisionObject** bodies,
+		int numBodies,
+		btPersistentManifold** manifoldPtr,
+		int numManifolds,
+		btTypedConstraint** constraints,
+		int numConstraints,
+		const btContactSolverInfo& infoGlobal,
+		btIDebugDraw* debugDrawer) BT_OVERRIDE;
+
+	// Documentation inherited
+	btScalar solveGroupCacheFriendlyIterations(
+		btCollisionObject** bodies,
+		int numBodies,
+		btPersistentManifold** manifoldPtr,
+		int numManifolds,
+		btTypedConstraint** constraints,
+		int numConstraints,
+		const btContactSolverInfo& infoGlobal,
+		btIDebugDraw* debugDrawer) BT_OVERRIDE;
+
+public:
+	BT_DECLARE_ALIGNED_ALLOCATOR()
+
+	/// Constructor
+	///
+	/// \param[in] solver MLCP solver. Assumed it's not null.
+	/// \param[in] maxLCPSize Maximum size of LCP to solve using MLCP solver. If the MLCP size exceeds this number, sequaltial impulse method will be used.
+	explicit btMultiBodyMLCPConstraintSolver(btMLCPSolverInterface* solver);
+
+	/// Destructor
+	virtual ~btMultiBodyMLCPConstraintSolver();
+
+	/// Sets MLCP solver. Assumed it's not null.
+	void setMLCPSolver(btMLCPSolverInterface* solver);
+
+	/// Returns the number of fallbacks of using btSequentialImpulseConstraintSolver, which happens when the MLCP
+	/// solver fails.
+	int getNumFallbacks() const;
+
+	/// Sets the number of fallbacks. This function may be used to reset the number to zero.
+	void setNumFallbacks(int num);
+
+	/// Returns the constraint solver type.
+	virtual btConstraintSolverType getSolverType() const;
+};
+
+#endif  // BT_MULTIBODY_MLCP_CONSTRAINT_SOLVER_H