Implement first draft of parent child relation storage

Sources/FirebladeECS/Entity.swift

@@ -106,23 +106,24 @@ public struct Entity {
     /// - Parameter entity: The child entity.
     @discardableResult
     public func addChild(_ entity: Entity) -> Bool {
-        return false
+        return nexus.addChild(entity, to: self)
     }
 
     /// Remove entity as child.
     /// - Parameter entity: The child entity.
     @discardableResult
     public func removeChild(_ entity: Entity) -> Bool {
-        return false
+        return nexus.removeChild(entity, from: self)
     }
 
     /// Removes all children from this entity.
     public func removeAllChildren() {
+        return nexus.removeAllChildren(from: self)
     }
 
     /// Returns the number of children for this entity.
     public var numChildren: Int {
-        return 0
+        return nexus.numChildren(for: self)
     }
 }
 

Sources/FirebladeECS/Nexus+Entity.swift

@@ -56,6 +56,8 @@ extension Nexus {
             return false
         }
 
+        removeAllChildren(from: entity)
+
         if removeAll(componentes: entityId) {
             update(familyMembership: entityId)
         }

Sources/FirebladeECS/Nexus+SceneGraph.swift

@@ -0,0 +1,32 @@
+//
+//  Nexus+SceneGraph.swift
+//
+//
+//  Created by Christian Treffs on 30.09.19.
+//
+
+extension Nexus {
+    public final func addChild(_ child: Entity, to parent: Entity) -> Bool {
+        let inserted: Bool
+        if parentChildrenMap[parent.identifier] == nil {
+            parentChildrenMap[parent.identifier] = [child.identifier]
+            inserted = true
+        } else {
+            let (isNewMember, _) = parentChildrenMap[parent.identifier]!.insert(child.identifier)
+            inserted = isNewMember
+        }
+        return inserted
+    }
+
+    public final func removeChild(_ child: Entity, from parent: Entity) -> Bool {
+        return parentChildrenMap[parent.identifier]?.remove(child.identifier) != nil
+    }
+
+    public final func removeAllChildren(from parent: Entity) {
+        return parentChildrenMap[parent.identifier] = nil
+    }
+
+    public final func numChildren(for entity: Entity) -> Int {
+        return parentChildrenMap[entity.identifier]?.count ?? 0
+    }
+}

Sources/FirebladeECS/Nexus.swift

@@ -29,12 +29,15 @@ public final class Nexus {
     /// - Value: Tightly packed EntityIdentifiers that represent the association of an entity to the family.
     @usableFromInline final var familyMembersByTraits: [FamilyTraitSet: UnorderedSparseSet<EntityIdentifier>]
 
+    @usableFromInline final var parentChildrenMap: [EntityIdentifier: Set<EntityIdentifier>]
+
     public init() {
         entityStorage = UnorderedSparseSet<Entity>()
         componentsByType = [:]
         componentIdsByEntity = [:]
         freeEntities = ContiguousArray<EntityIdentifier>()
         familyMembersByTraits = [:]
+        parentChildrenMap = [:]
     }
 
     public final func clear() {
@@ -55,6 +58,7 @@ public final class Nexus {
         componentsByType.removeAll()
         componentIdsByEntity.removeAll()
         familyMembersByTraits.removeAll()
+        parentChildrenMap.removeAll()
     }
 
     deinit {