Get a full gui node hierarchy from a specified root id in the Defold engine

build_hierarchy.lua

function build_hierarchy(root)
	local node_and_descendants = {}
	local node_info = {}
	local all_nodes = gui.get_tree(gui.get_node(root))

	-- Build an array of (node + its descendants) for each node
	for node_id,_ in pairs(all_nodes) do
		local nodes	
		if node_id == root then
			nodes = all_nodes -- avoid calling get_tree again for the root node
		else
			nodes = gui.get_tree(gui.get_node(node_id))
		end
		local node_ids = {}
		for k,v in pairs(nodes) do
			table.insert(node_ids, k)
		end
		node_and_descendants[node_id] = node_ids
	end

	-- Sort the array so that leaf nodes are first, and the root last
	local all_node_ids = node_and_descendants[root]
	table.sort(all_node_ids, function(a,b)
		return #node_and_descendants[a] < #node_and_descendants[b]
	end)

	local unparented_children = {}
	
	for _,node_id in ipairs(all_node_ids) do
		if #node_and_descendants[node_id] == 1 then
			-- leaf node, has no children
			node_info[node_id] = {id = node_id, node = all_nodes[node_id]}
		else
			children = {}
			for _,child_id in ipairs(node_and_descendants[node_id]) do
				if child_id ~= node_id and unparented_children[child_id] then
					children[child_id] = node_info[child_id]
					unparented_children[child_id] = nil
				end
			end
			node_info[node_id] = {id = node_id, node = all_nodes[node_id], children = children}
		end
		
		unparented_children[node_id] = node_info[node_id]
	end

	return node_info[root]
end