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Logic preferences

Ever wondered whether one should approach problem X with strategy Y or Z? This article covers a variety of topics related to these dilemmas.

Adding nodes and changing properties: which first?

When initializing nodes from a script at runtime, you may need to change properties such as the node's name or position. A common dilemma is, when should you change those values?

It is the best practice to change values on a node before adding it to the scene tree. Some property's setters have code to update other corresponding values, and that code can be slow! For most cases, this code has no impact on your game's performance, but in heavy use cases such as procedural generation, it can bring your game to a crawl.

For these reasons, it is always a best practice to set the initial values of a node before adding it to the scene tree.

Loading vs. preloading

In GDScript, there exists the global preload method. It loads resources as early as possible to front-load the "loading" operations and avoid loading resources while in the middle of performance-sensitive code.

Its counterpart, the load method, loads a resource only when it reaches the load statement. That is, it will load a resource in-place which can cause slowdowns when it occurs in the middle of sensitive processes. The load() function is also an alias for ResourceLoader.load(path) which is accessible to all scripting languages.

So, when exactly does preloading occur versus loading, and when should one use either? Let's see an example:

# my_buildings.gd
extends Node

# Note how constant scripts/scenes have a different naming scheme than
# their property variants.

# This value is a constant, so it spawns when the Script object loads.
# The script is preloading the value. The advantage here is that the editor
# can offer autocompletion since it must be a static path.
const BuildingScn = preload("res://building.tscn")

# 1. The script preloads the value, so it will load as a dependency
#    of the 'my_buildings.gd' script file. But, because this is a
#    property rather than a constant, the object won't copy the preloaded
#    PackedScene resource into the property until the script instantiates
#    with .new().
# 2. The preloaded value is inaccessible from the Script object alone. As
#    such, preloading the value here actually does not benefit anyone.
# 3. Because the user exports the value, if this script stored on
#    a node in a scene file, the scene instantiation code will overwrite the
#    preloaded initial value anyway (wasting it). It's usually better to
#    provide null, empty, or otherwise invalid default values for exports.
# 4. It is when one instantiates this script on its own with .new() that
#    one will load "office.tscn" rather than the exported value.
export(PackedScene) var a_building = preload("office.tscn")

# Uh oh! This results in an error!
# One must assign constant values to constants. Because `load` performs a
# runtime lookup by its very nature, one cannot use it to initialize a
# constant.
const OfficeScn = load("res://office.tscn")

# Successfully loads and only when one instantiates the script! Yay!
var office_scn = load("res://office.tscn")