add option to disable btMultiBody self-collision (for the entire hierarchy) or to disable parent-child collision for jointed links.

Demos/FeatherstoneMultiBodyDemo/FeatherstoneMultiBodyDemo.cpp

@@ -264,6 +264,7 @@ btMultiBody* FeatherstoneMultiBodyDemo::createFeatherstoneMultiBody(class btMult
 	
 	
 	btMultiBody * bod = new btMultiBody(n_links, mass, inertia, isFixedBase, canSleep);
+//		bod->setHasSelfCollision(false);
 
 	//btQuaternion orn(btVector3(0,0,1),-0.25*SIMD_HALF_PI);//0,0,0,1);
 	btQuaternion orn(0,0,0,1);
@@ -297,15 +298,17 @@ btMultiBody* FeatherstoneMultiBodyDemo::createFeatherstoneMultiBody(class btMult
 
 			const int child_link_num = link_num_counter++;
 
+			bool disableParentCollision = false;
+
 			if (usePrismatic)// && i==(n_links-1))
 			{
 					bod->setupPrismatic(child_link_num, mass, inertia, this_link_num,
-										parent_to_child, joint_axis_child_prismatic, quatRotate(parent_to_child , pos));
+										parent_to_child, joint_axis_child_prismatic, quatRotate(parent_to_child , pos),disableParentCollision);
 
 			} else
 			{
 				bod->setupRevolute(child_link_num, mass, inertia, this_link_num,parent_to_child, joint_axis_child_hinge,
-										joint_axis_position,quatRotate(parent_to_child , (pos - joint_axis_position)));
+										joint_axis_position,quatRotate(parent_to_child , (pos - joint_axis_position)),disableParentCollision);
 			}
 			bod->setJointPos(child_link_num, initial_joint_angle);
 			this_link_num = i;
@@ -381,7 +384,7 @@ btMultiBody* FeatherstoneMultiBodyDemo::createFeatherstoneMultiBody(class btMult
 				body->setWorldTransform(tr);
 				col->setWorldTransform(tr);
 				
-				world->addCollisionObject(col, 2,1);
+				world->addCollisionObject(col, 2,1+2);
 				col->setFriction(friction);
 				bod->setBaseCollider(col);
 				
@@ -415,7 +418,7 @@ btMultiBody* FeatherstoneMultiBodyDemo::createFeatherstoneMultiBody(class btMult
 			tr.setRotation(btQuaternion(quat[0],quat[1],quat[2],quat[3]));
 			col->setWorldTransform(tr);
 			col->setFriction(friction);
-			world->addCollisionObject(col,2,1);
+			world->addCollisionObject(col,2,1+2);
 			
 			bod->getLink(i).m_collider=col;
 			//app->drawBox(halfExtents, pos,quat);

src/BulletDynamics/Featherstone/btMultiBody.cpp

@@ -93,7 +93,8 @@ btMultiBody::btMultiBody(int n_links,
 		m_linearDamping(0.04f),
 		m_angularDamping(0.04f),
 		m_useGyroTerm(true),
-		m_maxAppliedImpulse(1000.f)
+		m_maxAppliedImpulse(1000.f),
+		m_hasSelfCollision(true)
 {
 	 links.resize(n_links);
 
@@ -115,7 +116,8 @@ void btMultiBody::setupPrismatic(int i,
                                int parent,
                                const btQuaternion &rot_parent_to_this,
                                const btVector3 &joint_axis,
-                               const btVector3 &r_vector_when_q_zero)
+                               const btVector3 &r_vector_when_q_zero,
+							   bool disableParentCollision)
 {
     links[i].mass = mass;
     links[i].inertia = inertia;
@@ -126,6 +128,9 @@ void btMultiBody::setupPrismatic(int i,
     links[i].e_vector = r_vector_when_q_zero;
     links[i].is_revolute = false;
     links[i].cached_rot_parent_to_this = rot_parent_to_this;
+	if (disableParentCollision)
+		links[i].m_flags |=BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION;
+
     links[i].updateCache();
 }
 
@@ -136,7 +141,8 @@ void btMultiBody::setupRevolute(int i,
                               const btQuaternion &zero_rot_parent_to_this,
                               const btVector3 &joint_axis,
                               const btVector3 &parent_axis_position,
-                              const btVector3 &my_axis_position)
+                              const btVector3 &my_axis_position,
+							  bool disableParentCollision)
 {
     links[i].mass = mass;
     links[i].inertia = inertia;
@@ -147,6 +153,8 @@ void btMultiBody::setupRevolute(int i,
     links[i].d_vector = my_axis_position;
     links[i].e_vector = parent_axis_position;
     links[i].is_revolute = true;
+	if (disableParentCollision)
+		links[i].m_flags |=BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION;
     links[i].updateCache();
 }
 

src/BulletDynamics/Featherstone/btMultiBody.h

@@ -59,7 +59,9 @@ public:
                         int parent,
                         const btQuaternion &rot_parent_to_this,  // rotate points in parent frame to my frame.
                         const btVector3 &joint_axis,             // in my frame
-                        const btVector3 &r_vector_when_q_zero);  // vector from parent COM to my COM, in my frame, when q = 0.
+                        const btVector3 &r_vector_when_q_zero,  // vector from parent COM to my COM, in my frame, when q = 0.
+						bool disableParentCollision=false
+						);
 
     void setupRevolute(int i,            // 0 to num_links-1
                        btScalar mass,
@@ -68,7 +70,8 @@ public:
                        const btQuaternion &zero_rot_parent_to_this,  // rotate points in parent frame to this frame, when q = 0
                        const btVector3 &joint_axis,    // in my frame
                        const btVector3 &parent_axis_position,    // vector from parent COM to joint axis, in PARENT frame
-                       const btVector3 &my_axis_position);       // vector from joint axis to my COM, in MY frame
+                       const btVector3 &my_axis_position,       // vector from joint axis to my COM, in MY frame
+					   bool disableParentCollision=false);
 	
 	const btMultibodyLink& getLink(int index) const
 	{
@@ -384,6 +387,15 @@ public:
 		m_maxAppliedImpulse = maxImp;
 	}
 
+	void	setHasSelfCollision(bool hasSelfCollision)
+	{
+		m_hasSelfCollision = hasSelfCollision;
+	}
+	bool hasSelfCollision() const
+	{
+		return m_hasSelfCollision;
+	}
+
 private:
     btMultiBody(const btMultiBody &);  // not implemented
     void operator=(const btMultiBody &);  // not implemented
@@ -448,6 +460,7 @@ private:
 	btScalar	m_angularDamping;
 	bool	m_useGyroTerm;
 	btScalar	m_maxAppliedImpulse;
+	bool		m_hasSelfCollision;
 };
 
 #endif

src/BulletDynamics/Featherstone/btMultiBodyLink.h

@@ -20,7 +20,10 @@ subject to the following restrictions:
 #include "LinearMath/btVector3.h"
 #include "BulletCollision/CollisionDispatch/btCollisionObject.h"
 
-
+enum	btMultiBodyLinkFlags
+{
+	BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION = 1
+};
 //
 // Link struct
 //
@@ -64,6 +67,7 @@ struct btMultibodyLink
     btScalar joint_torque;
 
 	class btMultiBodyLinkCollider* m_collider;
+	int m_flags;
 
     // ctor: set some sensible defaults
 	btMultibodyLink()
@@ -74,7 +78,8 @@ struct btMultibodyLink
 			is_revolute(false),
 			cached_rot_parent_to_this(1, 0, 0, 0),
 			joint_torque(0),
-			m_collider(0)
+			m_collider(0),
+			m_flags(0)
 	{
 		inertia.setValue(1, 1, 1);
 		axis_top.setValue(0, 0, 0);

src/BulletDynamics/Featherstone/btMultiBodyLinkCollider.h

@@ -33,6 +33,7 @@ public:
 		:m_multiBody(multiBody),
 		m_link(link)
 	{
+		m_checkCollideWith =  true;
 		//we need to remove the 'CF_STATIC_OBJECT' flag, otherwise links/base doesn't merge islands
 		//this means that some constraints might point to bodies that are not in the islands, causing crashes
 		//if (link>=0 || (multiBody && !multiBody->hasFixedBase()))
@@ -59,6 +60,32 @@ public:
 		return 0;
 	}
 
+	virtual bool checkCollideWithOverride(const  btCollisionObject* co) const
+	{
+		const btMultiBodyLinkCollider* other = btMultiBodyLinkCollider::upcast(co);
+		if (!other)
+			return true;
+		if (other->m_multiBody != this->m_multiBody)
+			return true;
+		if (!m_multiBody->hasSelfCollision())
+			return false;
+
+		//check if 'link' has collision disabled
+		if (m_link>=0)
+		{
+			const btMultibodyLink& link = m_multiBody->getLink(this->m_link);
+			if ((link.m_flags&BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION) && link.parent == other->m_link)
+				return false;
+		}
+		
+		if (other->m_link>=0)
+		{
+			const btMultibodyLink& otherLink = other->m_multiBody->getLink(other->m_link);
+			if ((otherLink.m_flags& BT_MULTIBODYLINKFLAGS_DISABLE_PARENT_COLLISION) && otherLink.parent == this->m_link)
+				return false;
+		}
+		return true;
+	}
 };
 
 #endif //BT_FEATHERSTONE_LINK_COLLIDER_H