josephcatrambone / godot-go

Go language bindings for the Godot Engine's GDNative API.

Godot-Go

Go language bindings for the Godot Engine's GDNative API.

NOTE: These bindings are currently a work in progress. Any help is welcome!

Usage

The Godot Engine can interface with code written in Go using the GDNative module. It works by using Go's ability to compile code as a shared library (.so, .dylib, .dll), which the Godot Engine can load to call Go methods.

The godot-go library provides you with a method called godot.Register, which will allow you to expose a Go struct that follows the godot.Class interface to the Godot Engine when it loads your shared library. It also provides bindings to all of the available Godot Engine classes and their methods, so you can call Godot functions from your Go code.

Setup

go get github.com/ShadowApex/godot-go/godot

Build

When you're ready to build your code as a dynamic library that can be imported into Godot, use the instructions below depending on your platform.

Linux

go build -v -buildmode=c-shared -o libgodot.so <your_go_library>.go

Mac OS X

go build -v -buildmode=c-shared -o libgodot.dylib <your_go_library>.go

Tutorial

To write a Go shared library that can be used in Godot, you'll first need to create a .go file that will act as the entrypoint to your library. This file must have package main as the package name along with main() and init() functions defined. The main() function will be empty, but is required to compile it as a shared library:

package main

func init() {
}

func main() {
}

After setting this up, we can define a new struct that we want to be available in Godot. In our struct, we can embed one of any available Godot class so it implements the godot.Class interface. Note that embedding multiple Godot structs is not supported.

// SimpleClass is a simple go struct that can be attached to a Godot Node2D object.
type SimpleClass struct {
	godot.Node2D
}

Once we have our struct defined, we can now attach method receivers to our struct. All methods attached to this struct will be callable from Godot, provided that they take and/or return built-in or godot types. Let's go ahead and define a method receiver for the X_ready method, which Godot will call when our node enters the scene.

// X_ready is called as soon as the node enters the scene.
func (h *SimpleClass) X_ready() {
	godot.Log.Warning("Hello World!")
}

Now that we have a struct and a method defined, we need to create a constructor function that will return a new instance of our SimpleClass struct. This method will be called by Godot whenever it needs to create a new instance of your object.

// NewSimpleClass is a constructor that we can pass to godot.
func NewSimpleClass() godot.Class {
	return &SimpleClass{}
}

Now that we have a constructor function, we can register the function with Godot, so it knows how to create a new instance of your struct and call its methods. We can register the class by calling the godot.Register method in our init() function, which is a special Go function that will be executed when our shared library is loaded, and passing our constructor function.

func init() {
	// Register will register the given class constructor with Godot.
	godot.Register(NewSimpleClass)
}

The godot.Register function works by calling your constructor and inspecting your Godot struct with reflection for all public receiver methods and struct fields. It will then register the constructor and your struct's methods and fields with Godot through Godot's GDNative C API.

Now we can compile our project into a shared library:

Linux
go build -v -buildmode=c-shared -o libgodot.so <your_go_library>.go

Mac OS X
go build -v -buildmode=c-shared -o libgodot.dylib <your_go_library>.go

This will create a shared library object that you can use in Godot! To learn how to set up your library in Godot, refer to the section below.

How do I use native scripts from the editor?

First, copy your .so, .dylib, and/or .dll library that you compiled into your project folder.

Create a new GDNativeLibrary resource by clicking the new icon in the inspector. A GDNativeLibrary resource is a platform-agnostic abstraction of our native library. With it, it allows us to specify different shared library object files for different platforms, such as .so for Linux platforms, .dylib for Mac, and .dll for Windows.

Select GDNativeLibrary from the list of resource types.

Select the folder icon next to the platform that you want to support in the inspector. For Linux platforms, you'll want to select a .so file, .dylib for Mac, and .dll for Windows. You can add each shared library file for each platform you want to support.

Select your shared library file from your project directory.

Click the save icon and then click "Save As.."

Save your GDNativeLibrary resource to your project directory. This file simply contains the paths to the shared library objects for each platform you want to support.

Now create a new node that you want to attach your Go library to.

Click the add script icon to attach your Go library to the node.

Select "NativeScript" as the script language, and enter the name of the struct that you registered in your Go library that you would like to be attached to this node. You should also select "Built-in Script", so this setting is built in to the scene.

With your node selected, you can now attach our GDNativeLibrary resource that we created earlier to this node.