ecs: add callbackFiltered and emitFiltered

ecs/commonsystems/children.can

@@ -0,0 +1,40 @@
+--- Children system.
+-- Allows to build a hierarchy between entities.
+--
+-- An entity's parent entity is stored in its `parent` component.
+-- An entity's children are stored in its `children` component (list of children entities).
+--
+-- You can set theses values before adding the entity to the world; when you add the entity it will add itself
+-- to its parent children list and add all its children to the world.
+--
+-- If you remove an entity from the world, it will also remove all its children from the world.
+
+return {
+	name = "children",
+	filter = true,
+	onAdd = :(e)
+		if not e.children then e.children = {} end
+		if e.parent then -- add to parent
+			let parentchildren = e.parent.children
+			table.insert(parentchildren, e)
+		end
+		for _, o in ipairs(e.children) do -- add predefined children
+			o.parent = e
+			@world:add(o)
+		end
+	end,
+	onRemove = :(e)
+		for i=#e.children, 1, -1 do -- remove children
+			@world:remove(e.children[i])
+		end
+		if e.parent then -- remove from parent
+			let parentchildren = e.parent.children
+			for i=#parentchildren, 1, -1 do
+				if parentchildren[i] == e then
+					table.remove(parentchildren, i)
+					break
+				end
+			end
+		end
+	end
+}