Fix: GDExtension Classes Running In Editor Issue

by Alex Johnson 49 views

GDExtensions are a powerful way to extend the Godot Engine, but sometimes unexpected behavior can occur when these extensions run in the editor. This article delves into a specific issue where runtime (non-tool) GDExtension classes are being executed within the Godot editor, which can lead to unforeseen consequences. We'll explore the problem, its causes, and how to address it effectively.

Understanding the Issue: Runtime GDExtension Classes in the Editor

The core of the problem lies in the lifecycle methods of GDExtension classes, such as _ready, _process, and others, being triggered while in the Godot editor. This behavior is unexpected for classes intended for runtime use, as they should ideally remain as placeholders within the editor environment. This means that instances of these classes might execute code meant for the game environment, leading to potential conflicts or errors within the editor.

To illustrate this, consider a scenario where you have a custom class named ExampleClass derived from Node. This class is designed to print a message and then immediately free itself when the game starts. If this class is inadvertently instantiated in the editor, it will execute its _ready function, printing the message and removing itself, which is not the desired outcome during editing.

This issue was initially discovered and reported in the context of the Godot-Rust GDExtension, highlighting that the problem is not isolated to a specific language binding but rather a more general behavior within Godot's GDExtension system. The critical point is that classes designed for runtime behavior should not be active within the editor environment, and understanding how to prevent this is crucial for maintaining a stable and predictable development workflow.

Root Cause Analysis: Why Are Runtime Classes Executing in the Editor?

To effectively address the issue of runtime GDExtension classes running in the editor, it’s essential to understand the underlying causes. The primary reason for this behavior stems from how Godot handles class instantiation and the distinction between tool and non-tool classes.

Class Instantiation Methods

In Godot, there are two primary ways to instantiate a class: directly using the .new() method and indirectly through the ClassDB.instantiate() method. The key difference lies in how these methods treat classes designated as non-tool (runtime) classes.

  • .new() Method: When you use .new() to create an instance of a non-tool class, Godot instantiates the class as a real instance, meaning its lifecycle methods (_ready, _process, etc.) are executed immediately. This is the intended behavior during runtime but not within the editor.
  • ClassDB.instantiate() Method: This method, on the other hand, is designed to create a placeholder instance of a class. A placeholder instance is a non-functional object that exists solely for editing purposes. Its lifecycle methods are not executed, making it suitable for use in the editor.

The problem arises when developers inadvertently use .new() to instantiate runtime classes in editor scripts, leading to the unintended execution of their methods. This is particularly problematic because it violates the expectation that editor scripts should only manipulate the scene without triggering runtime behavior.

Lack of Consistent Behavior Across GDExtensions

Another contributing factor is the inconsistent behavior across different GDExtension implementations. For instance, in Godot-cpp, there are mechanisms in place to mitigate this issue: memnew(T) returns nullptr when used against a non-tool class, and ClassDB::instantiate() creates a placeholder. However, this behavior is not uniformly enforced across all GDExtensions, leading to discrepancies and potential confusion.

The lack of a consistent approach means that developers need to be acutely aware of the specific instantiation behaviors of the GDExtension they are using. This adds complexity and increases the risk of errors, as the same code might behave differently depending on the extension in use.

Impact on Development Workflow

The consequences of runtime classes executing in the editor can be significant. It can lead to unexpected side effects, such as modifying scene data, triggering network requests, or causing crashes. These issues can be challenging to debug, as the code execution path differs from what is expected in the editor environment.

Furthermore, this behavior undermines the principle of separation between editor and runtime logic. Editor scripts should focus on scene manipulation and tool functionality, while runtime classes should handle game-specific behavior. When these boundaries are blurred, it can make the codebase harder to maintain and reason about.

Reproducing the Issue: A Step-by-Step Guide

To better understand the problem of GDExtension classes running in the editor, it's helpful to reproduce the issue in a controlled environment. This section provides a detailed, step-by-step guide to recreate the scenario and observe the unexpected behavior firsthand.

Prerequisites

  1. Godot Engine: Ensure you have Godot Engine version 4.2 or later installed. This issue has been observed and confirmed in versions from 4.2 onward, including the current master branch.
  2. Godot-cpp Template: It's recommended to use the Godot-cpp template for this reproduction, as it provides a pre-configured environment for creating GDExtensions in C++. You can find the template on GitHub.

Step-by-Step Instructions

  1. Set up a New Project:

    • Create a new Godot project using the Godot-cpp template or a similar GDExtension setup.
    • Ensure your project is configured to build and load GDExtensions.

  2. Declare a Runtime Class:

    • Create a new C++ class that inherits from a Godot class (e.g., Node). This class will represent the runtime (non-tool) class that exhibits the issue.
    • Define the class in a header file (e.g., example_class.h) with the necessary Godot macros (GDCLASS).
    • Implement the class in a source file (e.g., example_class.cpp).
    // example_class.h
#ifndef EXAMPLE_CLASS_H
#define EXAMPLE_CLASS_H

#include <godot_cpp/classes/node.hpp>
#include <godot_cpp/core/class_db.hpp>
#include <godot_cpp/variant/string.hpp>

class ExampleClass : public godot::Node {
	GDCLASS(ExampleClass, godot::Node)

protected:
	static void _bind_methods();

public:
	void _ready() override;
	ExampleClass() = default;
	~ExampleClass() override = default;
};

#endif

    // example_class.cpp
#include "example_class.h"
#include <godot_cpp/core/print_macros.hpp>

using namespace godot;

void ExampleClass::_bind_methods() {}

void ExampleClass::_ready() {
	print_line(String("Hello from editor!"));
	queue_free();
}

  3. Register the Class:

    • In your GDExtension initialization function, register the class using GDREGISTER_RUNTIME_CLASS.
    // gdextension.cpp
#include <gdextension_interface.h>
#include <godot_cpp/core/defs.hpp>
#include <godot_cpp/core/class_db.hpp>
#include <godot_cpp/godot.hpp>

#include "example_class.h"

using namespace godot;

void initialize_gdextension_types(ModuleInitializationLevel p_level) {
	if (p_level != MODULE_INITIALIZATION_LEVEL_SCENE) {
		return;
	}
	GDREGISTER_RUNTIME_CLASS(ExampleClass);
}

void uninitialize_gdextension_types(ModuleInitializationLevel p_level) {
	if (p_level != MODULE_INITIALIZATION_LEVEL_SCENE) {
		return;
	}
}

extern "C" {
// Initialization.
GDExtensionBool GDE_EXPORT gdextension_entry(const GDExtensionInterface *p_interface, GDExtensionClassLibraryPtr p_library, GDExtensionInitialization *r_initialization) {
	GDExtensionBinding::InitObject init_obj(p_interface, p_library, r_initialization);

	init_obj.register_initializer(initialize_gdextension_types);
	init_obj.register_terminator(uninitialize_gdextension_types);
	init_obj.set_minimum_library_initialization_level(MODULE_INITIALIZATION_LEVEL_SCENE);

	return init_obj.init();
}

  4. Create a Test Scene:

    • Create a new scene in the Godot editor.
    • Add a root node (e.g., Node) to the scene.
    • Attach a GDScript script to the root node.

  5. Write the Test Script:

    • In the GDScript script, instantiate the runtime class using both .new() and ClassDB.instantiate().
    • Add the instances to the scene as children of the root node.
    • Set the owner of the instances to the edited scene root.
    @tool
extends Node

func _ready() -> void:
	print("Hello from script!")
	var example := ExampleClass.new()
	self.add_child(example)
	example.owner = get_tree().edited_scene_root

	var other_example = ClassDB.instantiate("ExampleClass")
	print(other_example)
	self.add_child(other_example)
	other_example.name = "Not a tool class"
	other_example.owner = get_tree().edited_scene_root

  6. Observe the Output:

    • Run the scene in the Godot editor.
    • Check the output console. You should see the message "Hello from editor!" printed once, indicating that the _ready function of the ExampleClass instance created with .new() was executed.
    • In the scene tree, you will notice that the instance created with ClassDB.instantiate() remains as a child node, while the one created with .new() is likely gone (due to queue_free()).

Expected vs. Actual Behavior

  • Expected Behavior: Neither instance should execute its _ready function in the editor. Both should remain as placeholders.
  • Actual Behavior: The instance created with .new() executes its _ready function, while the instance created with ClassDB.instantiate() remains a placeholder.

By following these steps, you can clearly observe the issue of runtime GDExtension classes running in the editor when instantiated using .new(). This reproduction helps to solidify the understanding of the problem and motivates the need for effective solutions.

Solutions and Best Practices: Preventing Runtime Execution in the Editor

Now that we've identified the problem and reproduced it, let's explore solutions and best practices to prevent runtime GDExtension classes from running in the editor. The key is to ensure that editor-time instantiation does not trigger runtime behavior.

1. Always Use ClassDB.instantiate() for Editor-Time Instantiation

The most straightforward solution is to consistently use ClassDB.instantiate() when creating instances of GDExtension classes within editor scripts. As mentioned earlier, this method is designed to produce placeholder instances that do not execute lifecycle methods.

By adhering to this practice, you can ensure that your editor scripts manipulate scene elements without inadvertently triggering runtime logic. This approach provides a clear separation between editor and runtime behavior, making your codebase more predictable and maintainable.

2. Implement Tool-Specific Logic

Another effective strategy is to implement tool-specific logic within your GDExtension classes. Godot provides the @tool annotation in GDScript and the is_tool() method in C++ to help you differentiate between editor and runtime environments.

By wrapping runtime-specific code blocks within conditional checks, you can prevent them from executing in the editor. This approach allows you to create classes that behave differently depending on the environment, providing flexibility and control over their behavior.

Example in C++

void ExampleClass::_ready() {
	if (!is_tool()) { // Check if running in the editor
		print_line(String("Hello from runtime!"));
		queue_free();
	}
}

Example in GDScript

@tool
extends Node

func _ready() -> void:
	if not Engine.is_editor_hint(): # Check if running in the editor
		print("Hello from runtime!")
		queue_free()

3. Standardize GDExtension Behavior

For a more robust solution, it's essential to standardize the behavior of class instantiation across all GDExtensions. This means ensuring that all extensions consistently create placeholder instances in the editor and real instances at runtime.

This can be achieved by:

  • Deprecating the use of .new() for non-tool classes in editor scripts.
  • Providing clear guidelines and documentation on how to instantiate classes correctly in different contexts.
  • Implementing mechanisms within GDExtension bindings to enforce this behavior.

4. Utilize Design Patterns

Employing design patterns such as the Factory Pattern can also help manage object creation and ensure proper instantiation based on the environment. A factory class can encapsulate the logic for creating instances, allowing you to abstract away the details of whether to use .new() or ClassDB.instantiate().

This approach promotes code reusability and reduces the risk of errors by centralizing the instantiation logic in a single location.

5. Testing and Validation

Finally, rigorous testing and validation are crucial to ensure that your GDExtension classes behave as expected in both the editor and runtime environments. Create test cases that specifically check the instantiation behavior of your classes and verify that runtime logic is not being executed in the editor.

By implementing these solutions and best practices, you can effectively prevent runtime GDExtension classes from running in the editor, leading to a more stable and predictable development workflow. This will not only save you time and effort in debugging but also improve the overall quality and maintainability of your Godot projects.

The Godot-cpp Approach: A Model for Consistent Behavior

As we've discussed, one of the challenges in preventing runtime GDExtension classes from running in the editor is the inconsistency in how different GDExtension bindings handle class instantiation. In this context, the approach taken by Godot-cpp provides a valuable model for achieving consistent behavior.

How Godot-cpp Handles Instantiation

Godot-cpp, the official C++ binding for Godot Engine, has implemented specific mechanisms to address the issue of editor-time instantiation. These mechanisms ensure that runtime classes are not inadvertently executed within the editor environment.

The key strategies employed by Godot-cpp include:

  1. memnew(T) Behavior: In Godot-cpp, the memnew(T) macro, which is commonly used to allocate memory for new objects, returns nullptr when used against a non-tool (runtime) class in the editor. This effectively prevents the creation of real instances of these classes, as any attempt to use the resulting null pointer will lead to a crash or error.
  2. ClassDB::instantiate() for Placeholders: Godot-cpp ensures that ClassDB::instantiate() always returns a placeholder instance for non-tool classes in the editor. This aligns with the intended behavior of this method, providing a safe and predictable way to create editor-time representations of runtime classes.

Benefits of the Godot-cpp Approach

The Godot-cpp approach offers several significant benefits:

  • Consistency: By consistently returning nullptr for memnew(T) and creating placeholders with ClassDB::instantiate(), Godot-cpp ensures a uniform instantiation behavior across the editor and runtime environments.
  • Safety: Preventing the creation of real instances of runtime classes in the editor reduces the risk of unexpected side effects and errors. This improves the stability and reliability of the editor environment.
  • Clarity: The clear distinction between instantiation methods makes it easier for developers to understand the intended behavior and write code that adheres to best practices.

Adopting the Godot-cpp Model

Given the effectiveness of the Godot-cpp approach, it's recommended that other GDExtension bindings consider adopting similar mechanisms. This would help to standardize class instantiation behavior across the Godot ecosystem, making it easier for developers to work with different extensions and avoid common pitfalls.

Specifically, other GDExtension bindings could:

  • Implement a similar check in their memory allocation functions to return a null pointer for non-tool classes in the editor.
  • Ensure that their equivalent of ClassDB::instantiate() creates placeholder instances for runtime classes.
  • Provide clear documentation and examples on how to instantiate classes correctly in different contexts.

By adopting the Godot-cpp model, the Godot community can move towards a more consistent and predictable GDExtension environment, empowering developers to create high-quality tools and games with greater ease and confidence.

Conclusion: Ensuring a Smooth Godot Development Experience

The issue of runtime GDExtension classes running in the editor highlights the importance of understanding the nuances of the Godot Engine and its extension system. By recognizing the problem, its causes, and potential solutions, developers can ensure a smoother and more efficient development experience.

The key takeaways from this article are:

  • Runtime classes should not execute their lifecycle methods in the editor.
  • ClassDB.instantiate() should be used for editor-time instantiation to create placeholders.
  • Tool-specific logic can be implemented using is_tool() or Engine.is_editor_hint() to differentiate between editor and runtime environments.
  • Standardizing GDExtension behavior across different bindings is crucial for consistency.
  • The Godot-cpp approach provides a valuable model for handling class instantiation.

By implementing these best practices, you can avoid the pitfalls of runtime classes running in the editor and create more robust and maintainable Godot projects. This will not only save you time and effort in debugging but also improve the overall quality of your games and tools.

For further information and resources on Godot Engine and GDExtensions, consider visiting the official Godot Engine website and documentation: Godot Engine Official Website