Applying object-oriented principles in Godot

The engine offers two main ways to create reusable objects: scripts and scenes. Neither of these technically define classes under the hood.

Still, many best practices using Godot involve applying object-oriented programming principles to the scripts and scenes that compose your game. That is why it's useful to understand how we can think of them as classes.

This guide briefly explains how scripts and scenes work in the engine's core to help you understand how they work under the hood.

How scripts work in the engine

The engine provides built-in classes like Node. You can extend those to create derived types using a script.

These scripts are not technically classes. Instead, they are resources that tell the engine a sequence of initializations to perform on one of the engine's built-in classes.

Godot的内部类具有使用一个 ClassDB 注册一个类数据的方法。该数据库提供对类信息的运行时访问。ClassDB 包含有关类的信息,例如:

  • Properties.
  • Methods.
  • Constants.
  • Signals.

This ClassDB is what objects check against when performing an operation like accessing a property or calling a method. It checks the database's records and the object's base types' records to see if the object supports the operation.

Attaching a Script to your object extends the methods, properties, and signals available from the ClassDB.

注解

Even scripts that don't use the extends keyword implicitly inherit from the engine's base Reference class. As a result, you can instantiate scripts without the extends keyword from code. Since they extend Reference though, you cannot attach them to a Node.

场景

The behavior of scenes has many similarities to classes, so it can make sense to think of a scene as a class. Scenes are reusable, instantiable, and inheritable groups of nodes. Creating a scene is similar to having a script that creates nodes and adds them as children using add_child().

We often pair a scene with a scripted root node that makes use of the scene's nodes. As such, the scene is often an extension of the script's declarative code.

场景的内容有助于定义:

  • 脚本可使用哪些节点
  • 它们是如何组织的
  • How they are initialized
  • 它们彼此之间有什么信号连接

Why is any of this important to scene organization? Because instances of scenes are objects. As a result, many object-oriented principles that apply to written code also apply to scenes: single responsibility, encapsulation, and others.

The scene is always an extension of the script attached to its root node, so you can interpret it as part of a class.

Most of the techniques explained in this best practices series build on this point.