Prevent objects from colliding with own child attachments (#7610)

Also, use a better distance calculation for 'collide with objects'.
Fixes the issue of a vehicle occasionally colliding with its own driver,
causing one of the velocity components to be set to zero.

src/clientobject.h

@@ -51,6 +51,7 @@ public:
 	virtual scene::ISceneNode *getSceneNode() { return NULL; }
 	virtual scene::IAnimatedMeshSceneNode *getAnimatedMeshSceneNode() { return NULL; }
 	virtual bool isLocalPlayer() const {return false;}
+	virtual ClientActiveObject *getParent() const { return nullptr; };
 	virtual void setAttachments() {}
 	virtual bool doShowSelectionBox(){return true;}
 

src/collision.cpp

@@ -360,11 +360,16 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 #ifndef SERVER
 		ClientEnvironment *c_env = dynamic_cast<ClientEnvironment*>(env);
 		if (c_env != 0) {
-			f32 distance = speed_f->getLength();
+			// Calculate distance by speed, add own extent and 1.5m of tolerance
+			f32 distance = speed_f->getLength() * dtime +
+				box_0.getExtent().getLength() + 1.5f * BS;
 			std::vector<DistanceSortedActiveObject> clientobjects;
-			c_env->getActiveObjects(*pos_f, distance * 1.5f, clientobjects);
+			c_env->getActiveObjects(*pos_f, distance, clientobjects);
+
 			for (auto &clientobject : clientobjects) {
-				if (!self || (self != clientobject.obj)) {
+				// Do collide with everything but itself and the parent CAO
+				if (!self || (self != clientobject.obj &&
+						self != clientobject.obj->getParent())) {
 					objects.push_back((ActiveObject*) clientobject.obj);
 				}
 			}
@@ -374,12 +379,17 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 		{
 			ServerEnvironment *s_env = dynamic_cast<ServerEnvironment*>(env);
 			if (s_env != NULL) {
-				f32 distance = speed_f->getLength();
+				// Calculate distance by speed, add own extent and 1.5m of tolerance
+				f32 distance = speed_f->getLength() * dtime +
+					box_0.getExtent().getLength() + 1.5f * BS;
 				std::vector<u16> s_objects;
-				s_env->getObjectsInsideRadius(s_objects, *pos_f, distance * 1.5f);
+				s_env->getObjectsInsideRadius(s_objects, *pos_f, distance);
+
 				for (u16 obj_id : s_objects) {
 					ServerActiveObject *current = s_env->getActiveObject(obj_id);
-					if (!self || (self != current)) {
+
+					if (!self || (self != current &&
+							self != current->getParent())) {
 						objects.push_back((ActiveObject*)current);
 					}
 				}

src/content_cao.h

@@ -139,8 +139,6 @@ public:
 
 	void processInitData(const std::string &data);
 
-	ClientActiveObject *getParent() const;
-
 	bool getCollisionBox(aabb3f *toset) const;
 
 	bool collideWithObjects() const;
@@ -181,6 +179,8 @@ public:
 
 	void setChildrenVisible(bool toset);
 
+	ClientActiveObject *getParent() const;
+
 	void setAttachments();
 
 	void removeFromScene(bool permanent);

src/content_sao.cpp

@@ -118,15 +118,14 @@ UnitSAO::UnitSAO(ServerEnvironment *env, v3f pos):
 	m_armor_groups["fleshy"] = 100;
 }
 
-bool UnitSAO::isAttached() const
+ServerActiveObject *UnitSAO::getParent() const
 {
 	if (!m_attachment_parent_id)
-		return false;
+		return nullptr;
 	// Check if the parent still exists
 	ServerActiveObject *obj = m_env->getActiveObject(m_attachment_parent_id);
-	if (obj)
+
-		return true;
+	return obj;
-	return false;
 }
 
 void UnitSAO::setArmorGroups(const ItemGroupList &armor_groups)

src/content_sao.h

@@ -42,7 +42,9 @@ public:
 	// Use a function, if isDead can be defined by other conditions
 	bool isDead() const { return m_hp == 0; }
 
-	bool isAttached() const;
+	inline bool isAttached() const
+	{ return getParent(); }
+
 	void setArmorGroups(const ItemGroupList &armor_groups);
 	const ItemGroupList &getArmorGroups();
 	void setAnimation(v2f frame_range, float frame_speed, float frame_blend, bool frame_loop);
@@ -57,6 +59,7 @@ public:
 	void addAttachmentChild(int child_id);
 	void removeAttachmentChild(int child_id);
 	const std::unordered_set<int> &getAttachmentChildIds();
+	ServerActiveObject *getParent() const;
 	ObjectProperties* accessObjectProperties();
 	void notifyObjectPropertiesModified();
 protected:

src/serverobject.h

@@ -173,6 +173,7 @@ public:
 	{}
 	virtual const std::unordered_set<int> &getAttachmentChildIds()
 	{ static const std::unordered_set<int> rv; return rv; }
+	virtual ServerActiveObject *getParent() const { return nullptr; }
 	virtual ObjectProperties* accessObjectProperties()
 	{ return NULL; }
 	virtual void notifyObjectPropertiesModified()