improve rolling friction using anisotropic direction, to avoid resting in an instable position

(for implicit capsule, cylinder and cone shape)
See Bullet/Demos/RollingFrictionDemo for an example

Demos/CcdPhysicsDemo/CcdPhysicsDemo.cpp

@@ -281,8 +281,9 @@ void	CcdPhysicsDemo::initPhysics()
 			float mass = 1.f;
 
 			btRigidBody* body = localCreateRigidBody(mass,trans,shape);
+			body->setAnisotropicFriction(shape->getAnisotropicRollingFrictionDirection(),btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
 
-			body->setRollingFriction(0.1);	
+			body->setRollingFriction(.3);	
 			///when using m_ccdMode
 			if (m_ccdMode==USE_CCD)
 			{

Demos/RollingFrictionDemo/RollingFrictionDemo.cpp

@@ -171,9 +171,21 @@ void	RollingFrictionDemo::initPhysics()
 	{
 		//create a few dynamic rigidbodies
 		// Re-using the same collision is better for memory usage and performance
-
+#define NUM_SHAPES 10
-		btCollisionShape* colShape = new btSphereShape(btScalar(1.));
+		btCollisionShape* colShapes[NUM_SHAPES] = {
-		m_collisionShapes.push_back(colShape);
+			new btSphereShape(btScalar(1.)),
+			new btCapsuleShape(0.5,1),
+			new btCapsuleShapeX(0.5,1),
+			new btCapsuleShapeZ(0.5,1),
+			new btConeShape(0.5,1),
+			new btConeShapeX(0.5,1),
+			new btConeShapeZ(0.5,1),
+			new btCylinderShape(btVector3(0.5,1,0.1)),
+			new btCylinderShapeX(btVector3(1,0.5,0.1)),
+			new btCylinderShapeZ(btVector3(0.5,0.5,1)),
+		};
+		for (int i=0;i<NUM_SHAPES;i++)
+			m_collisionShapes.push_back(colShapes[i]);
 
 		/// Create Dynamic Objects
 		btTransform startTransform;
@@ -182,36 +194,44 @@ void	RollingFrictionDemo::initPhysics()
 		btScalar	mass(1.f);
 
 		//rigidbody is dynamic if and only if mass is non zero, otherwise static
-		bool isDynamic = (mass != 0.f);
+		
-
-		btVector3 localInertia(0,0,0);
-		if (isDynamic)
-			colShape->calculateLocalInertia(mass,localInertia);
-
 		float start_x = START_POS_X - ARRAY_SIZE_X/2;
 		float start_y = START_POS_Y;
 		float start_z = START_POS_Z - ARRAY_SIZE_Z/2;
 
-		for (int k=0;k<ARRAY_SIZE_Y;k++)
 		{
-			for (int i=0;i<ARRAY_SIZE_X;i++)
+			int shapeIndex = 0;
+			for (int k=0;k<ARRAY_SIZE_Y;k++)
 			{
-				for(int j = 0;j<ARRAY_SIZE_Z;j++)
+				for (int i=0;i<ARRAY_SIZE_X;i++)
 				{
-					startTransform.setOrigin(SCALING*btVector3(
+					for(int j = 0;j<ARRAY_SIZE_Z;j++)
-										btScalar(2.0*i + start_x),
+					{
-										btScalar(20+2.0*k + start_y),
+						startTransform.setOrigin(SCALING*btVector3(
-										btScalar(2.0*j + start_z)));
+											btScalar(2.0*i + start_x),
+											btScalar(20+2.0*k + start_y),
+											btScalar(2.0*j + start_z)));
 
-			
-					//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
-					btDefaultMotionState* myMotionState = new btDefaultMotionState(startTransform);
-					btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia);
-					btRigidBody* body = new btRigidBody(rbInfo);
-					body->setFriction(1.f);
-					body->setRollingFriction(.3);
 
-					m_dynamicsWorld->addRigidBody(body);
+						shapeIndex++;
+						btCollisionShape* colShape = colShapes[shapeIndex%NUM_SHAPES];
+						bool isDynamic = (mass != 0.f);
+						btVector3 localInertia(0,0,0);
+
+						if (isDynamic)
+							colShape->calculateLocalInertia(mass,localInertia);
+
+						//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
+						btDefaultMotionState* myMotionState = new btDefaultMotionState(startTransform);
+						btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia);
+						btRigidBody* body = new btRigidBody(rbInfo);
+						body->setFriction(1.f);
+						body->setRollingFriction(.3);
+						body->setAnisotropicFriction(colShape->getAnisotropicRollingFrictionDirection(),btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+
+
+						m_dynamicsWorld->addRigidBody(body);
+					}
 				}
 			}
 		}

src/BulletCollision/CollisionDispatch/btCollisionObject.h

@@ -138,6 +138,13 @@ public:
 		CO_USER_TYPE=32
 	};
 
+	enum AnisotropicFrictionFlags
+	{
+		CF_ANISOTROPIC_FRICTION_DISABLED=0,
+		CF_ANISOTROPIC_FRICTION = 1,
+		CF_ANISOTROPIC_ROLLING_FRICTION = 2
+	};
+
 	SIMD_FORCE_INLINE bool mergesSimulationIslands() const
 	{
 		///static objects, kinematic and object without contact response don't merge islands
@@ -148,14 +155,15 @@ public:
 	{
 		return m_anisotropicFriction;
 	}
-	void	setAnisotropicFriction(const btVector3& anisotropicFriction)
+	void	setAnisotropicFriction(const btVector3& anisotropicFriction, int frictionMode = CF_ANISOTROPIC_FRICTION)
 	{
 		m_anisotropicFriction = anisotropicFriction;
-		m_hasAnisotropicFriction = (anisotropicFriction[0]!=1.f) || (anisotropicFriction[1]!=1.f) || (anisotropicFriction[2]!=1.f);
+		bool isUnity = (anisotropicFriction[0]!=1.f) || (anisotropicFriction[1]!=1.f) || (anisotropicFriction[2]!=1.f);
+		m_hasAnisotropicFriction = isUnity?frictionMode : 0;
 	}
-	bool	hasAnisotropicFriction() const
+	bool	hasAnisotropicFriction(int frictionMode = CF_ANISOTROPIC_FRICTION) const
 	{
-		return m_hasAnisotropicFriction!=0;
+		return (m_hasAnisotropicFriction&frictionMode)!=0;
 	}
 
 	///the constraint solver can discard solving contacts, if the distance is above this threshold. 0 by default.

src/BulletCollision/CollisionShapes/btCapsuleShape.h

@@ -104,6 +104,14 @@ public:
 
 	}
 
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		btVector3 aniDir(0,0,0);
+		aniDir[getUpAxis()]=1;
+		return aniDir;
+	}
+
+
 	virtual	int	calculateSerializeBufferSize() const;
 
 	///fills the dataBuffer and returns the struct name (and 0 on failure)

src/BulletCollision/CollisionShapes/btCollisionShape.h

@@ -109,6 +109,13 @@ public:
 
 	
 	int		getShapeType() const { return m_shapeType; }
+
+	///the getAnisotropicRollingFrictionDirection can be used in combination with setAnisotropicFriction
+	///See Bullet/Demos/RollingFrictionDemo for an example
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		return btVector3(1,1,1);
+	}
 	virtual void	setMargin(btScalar margin) = 0;
 	virtual btScalar	getMargin() const = 0;
 

src/BulletCollision/CollisionShapes/btConeShape.h

@@ -84,6 +84,11 @@ public:
 			return m_coneIndices[1];
 		}
 
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		return btVector3 (0,1,0);
+	}
+
 	virtual void	setLocalScaling(const btVector3& scaling);
 
 };
@@ -93,6 +98,12 @@ class btConeShapeX : public btConeShape
 {
 	public:
 		btConeShapeX(btScalar radius,btScalar height);
+
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		return btVector3 (1,0,0);
+	}
+
 };
 
 ///btConeShapeZ implements a Cone shape, around the Z axis
@@ -100,6 +111,12 @@ class btConeShapeZ : public btConeShape
 {
 	public:
 		btConeShapeZ(btScalar radius,btScalar height);
+
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		return btVector3 (0,0,1);
+	}
+
 };
 #endif //BT_CONE_MINKOWSKI_H
 

src/BulletCollision/CollisionShapes/btCylinderShape.h

@@ -97,6 +97,13 @@ BT_DECLARE_ALIGNED_ALLOCATOR();
 		return m_upAxis;
 	}
 
+	virtual btVector3	getAnisotropicRollingFrictionDirection() const
+	{
+		btVector3 aniDir(0,0,0);
+		aniDir[getUpAxis()]=1;
+		return aniDir;
+	}
+
 	virtual btScalar getRadius() const
 	{
 		return getHalfExtentsWithMargin().getX();

src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.cpp

@@ -324,12 +324,12 @@ btScalar btSequentialImpulseConstraintSolver::restitutionCurve(btScalar rel_vel,
 
 
 
-static void	applyAnisotropicFriction(btCollisionObject* colObj,btVector3& frictionDirection);
+static void	applyAnisotropicFriction(btCollisionObject* colObj,btVector3& frictionDirection, int frictionMode);
-static void	applyAnisotropicFriction(btCollisionObject* colObj,btVector3& frictionDirection)
+static void	applyAnisotropicFriction(btCollisionObject* colObj,btVector3& frictionDirection, int frictionMode)
 {
 	
 
-	if (colObj && colObj->hasAnisotropicFriction())
+	if (colObj && colObj->hasAnisotropicFriction(frictionMode))
 	{
 		// transform to local coordinates
 		btVector3 loc_lateral = frictionDirection * colObj->getWorldTransform().getBasis();
@@ -807,15 +807,24 @@ void	btSequentialImpulseConstraintSolver::convertContact(btPersistentManifold* m
 				if (relAngVel.length()>infoGlobal.m_singleAxisRollingFrictionThreshold)
 				{
 					relAngVel.normalize();
-					addRollingFrictionConstraint(relAngVel,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
+					applyAnisotropicFriction(colObj0,relAngVel,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+					applyAnisotropicFriction(colObj1,relAngVel,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+					if (relAngVel.length()>0.001)
+						addRollingFrictionConstraint(relAngVel,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 
 				} else
 				{
 					addRollingFrictionConstraint(cp.m_normalWorldOnB,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 					btVector3 axis0,axis1;
 					btPlaneSpace1(cp.m_normalWorldOnB,axis0,axis1);
-					addRollingFrictionConstraint(axis0,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
+					applyAnisotropicFriction(colObj0,axis0,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
-					addRollingFrictionConstraint(axis1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
+					applyAnisotropicFriction(colObj1,axis0,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+					applyAnisotropicFriction(colObj0,axis1,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+					applyAnisotropicFriction(colObj1,axis1,btCollisionObject::CF_ANISOTROPIC_ROLLING_FRICTION);
+					if (axis0.length()>0.001)
+						addRollingFrictionConstraint(axis0,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
+					if (axis1.length()>0.001)
+						addRollingFrictionConstraint(axis1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 		
 				}
 			}
@@ -834,14 +843,14 @@ void	btSequentialImpulseConstraintSolver::convertContact(btPersistentManifold* m
 					{
 						cp.m_lateralFrictionDir2 = cp.m_lateralFrictionDir1.cross(cp.m_normalWorldOnB);
 						cp.m_lateralFrictionDir2.normalize();//??
-						applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir2);
+						applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir2,btCollisionObject::CF_ANISOTROPIC_FRICTION);
-						applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir2);
+						applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir2,btCollisionObject::CF_ANISOTROPIC_FRICTION);
 						addFrictionConstraint(cp.m_lateralFrictionDir2,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 
 					}
 
-					applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir1);
+					applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir1,btCollisionObject::CF_ANISOTROPIC_FRICTION);
-					applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir1);
+					applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir1,btCollisionObject::CF_ANISOTROPIC_FRICTION);
 					addFrictionConstraint(cp.m_lateralFrictionDir1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 
 			
@@ -853,13 +862,13 @@ void	btSequentialImpulseConstraintSolver::convertContact(btPersistentManifold* m
 
 					if ((infoGlobal.m_solverMode & SOLVER_USE_2_FRICTION_DIRECTIONS))
 					{
-						applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir2);
+						applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir2,btCollisionObject::CF_ANISOTROPIC_FRICTION);
-						applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir2);
+						applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir2,btCollisionObject::CF_ANISOTROPIC_FRICTION);
 						addFrictionConstraint(cp.m_lateralFrictionDir2,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);
 					}
 
-					applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir1);
+					applyAnisotropicFriction(colObj0,cp.m_lateralFrictionDir1,btCollisionObject::CF_ANISOTROPIC_FRICTION);
-					applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir1);
+					applyAnisotropicFriction(colObj1,cp.m_lateralFrictionDir1,btCollisionObject::CF_ANISOTROPIC_FRICTION);
 					addFrictionConstraint(cp.m_lateralFrictionDir1,solverBodyIdA,solverBodyIdB,frictionIndex,cp,rel_pos1,rel_pos2,colObj0,colObj1, relaxation);