Preferências de lógica

Já se perguntou se devemos abordar o problema X com a estratégia Y ou Z? Este artigo cobre uma variedade de tópicos relacionados a esses dilemas.

Adicionar nós e alterar propriedades: qual fazer primeiro?

Ao inicializar nós a partir de um script em tempo de execução, pode ser necessário alterar propriedades como o nome ou a posição do nó. Uma dúvida comum é: quando você deve alterar esses valores?

It is the best practice to change values on a node before adding it to the scene tree. Some properties' 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 usually best practice to set the initial values of a node before adding it to the scene tree. There are some exceptions where values can't be set before being added to the scene tree, like setting global position.

Carregamento vs. pré-carregamento

No GDScript, existe o método global preload. Ele carrega recursos o mais cedo possível para antecipar as operações de "carregamento" e evitar o carregamento de recursos no meio de um código sensível ao desempenho.

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.

Então, quando exatamente ocorre o pré-carregamento versus carregamento, e quando se deve usar qualquer algum deles? Vejamos um exemplo:

# 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 provide any benefit.
#
# 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. Instantiating the script on its own with .new() triggers
#    `load("office.tscn")`, ignoring any value set through the export.
@export var a_building : PackedScene = 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")

using Godot;

// C# and other languages have no concept of "preloading".
public partial class MyBuildings : Node
{
    //This is a read-only field, it can only be assigned when it's declared or during a constructor.
    public readonly PackedScene Building = ResourceLoader.Load<PackedScene>("res://building.tscn");

    public PackedScene ABuilding;

    public override void _Ready()
    {
        // Can assign the value during initialization.
        ABuilding = GD.Load<PackedScene>("res://Office.tscn");
    }
}

using namespace godot;

class MyBuildings : public Node {
    GDCLASS(MyBuildings, Node)

public:
    const Ref<PackedScene> building = ResourceLoader::get_singleton()->load("res://building.tscn");
    Ref<PackedScene> a_building;

    virtual void _ready() override {
        // Can assign the value during initialization.
        a_building = ResourceLoader::get_singleton()->load("res://office.tscn");
    }
};

Preloading allows the script to handle all the loading the moment one loads the script. Preloading is useful, but there are also times when one doesn't wish to use it. Here are a few considerations when determining which to use:

If one cannot determine when the script might load, then preloading a resource (especially a scene or script) could result in additional loads one does not expect. This could lead to unintentional, variable-length load times on top of the original script's load operations.
Se algo mais pudesse substituir o valor (como a inicialização exportada de uma cena), então pre-carregar o valor não teria sentido. Este ponto não é um fator significativo se a intenção é sempre criar o script por conta própria.
Se alguém deseja apenas 'importar' outro recurso de classe (script ou cena), usar uma constante pré-carregada é geralmente o melhor curso de ação. No entanto, em casos excepcionais, não se deseja fazer isso:
1. If the 'imported' class is liable to change, then it should be a property instead, initialized either using an @export or a load() (and perhaps not even initialized until later).
2. If the script requires a great many dependencies, and one does not wish to consume so much memory, then one may wish to load and unload various dependencies at runtime as circumstances change. If one preloads resources into constants, then the only way to unload these resources would be to unload the entire script. If they are instead loaded as properties, then one can set these properties to null and remove all references to the resource (which, as a RefCounted-extending type, will cause the resources to delete themselves from memory).

Fases grandes: estática vs. dinâmica

If one is creating a large level, which circumstances are most appropriate? Is it better to create the level as one static space? Or is it better to load the level in pieces and shift the world's content as needed?

Well, the simple answer is, "when the performance requires it." The dilemma associated with the two options is one of the age-old programming choices: does one optimize memory over speed, or vice versa?

A resposta ingênua é usar uma fase estática que carrega tudo ao mesmo tempo. Mas, dependendo do projeto, isto pode consumir uma grande quantidade de memória. Desperdiçar a RAM dos usuários leva a programas executarem devagar ou travamento total de tudo o que o computador tenta fazer ao mesmo tempo.

Não importa o que aconteça. deve-se quebrar cenas maiores em cenas menores (para ajudar na reutilização de assets). Desenvolvedores podem então projetar um nó que gerencia criação/carregamento e exclusão/descarregamento de recursos e nós em tempo real. Jogos com ambientes variáveis e grandes ou elementos gerados proceduralmente geralmente implementam estas estratégias para evitar o desperdício de memória.

On the flip side, coding a dynamic system is more complex; it uses more programmed logic which results in opportunities for errors and bugs. If one isn't careful, they can develop a system that bloats the technical debt of the application.

Sendo assim, as melhores opções seriam...

Use static levels for smaller games.
If one has the time/resources on a medium/large game, create a library or plugin that can manage nodes and resources with code. If refined over time so as to improve usability and stability, then it could evolve into a reliable tool across projects.
Use dynamic logic for a medium/large game because one has the coding skills, but not the time or resources to refine the code (game's gotta get done). Could potentially refactor later to outsource the code into a plugin.

Para um exemplo das várias formas de trocar cenas durante a execução, por favor veja a documentação "Mudar cenas manualmente".