Creating Android plugins (Godot 3.2.2+)

Introduction

Android plugins are powerful tools to extend the capabilities of the Godot engine by tapping into the functionality provided by the Android platform and ecosystem.

Mobile gaming monetization is one such example since it requires features and capabilities that don’t belong to the core feature set of a game engine:

  • Analytics
  • In-app purchases
  • Receipt validation
  • Install tracking
  • Ads
  • Video ads
  • Cross-promotion
  • In-game soft & hard currencies
  • Promo codes
  • A/B testing
  • Login
  • Cloud saves
  • Leaderboards and scores
  • User support & feedback
  • Posting to Facebook, Twitter, etc.
  • Push notifications

Making modifications to the Android export template is another use-case since using a plugin for that task allows the project to remain compatible with newer Godot versions.

Android plugin

While introduced in Godot 3.2.0, the Android plugin system got a significant architecture update starting with Godot 3.2.2. In Godot 4.0, the new architecture became the default, rendering plugins for Godot 3.2.0 incompatible with Godot 4.0.

As a prerequisite, make sure you understand how to set up a custom build environment for Android.

At its core, a Godot Android plugin is a Android archive library (aar archive file) with the following caveats:

  • The library must have a dependency on the Godot engine library (godot-lib.x.y.aar). A stable version is made available for each Godot release.
  • The library must include a specifically configured <meta-data> tag in its manifest file.

Building a Android plugin

Prerequisite: Android Studio is strongly recommended as the IDE to use to create Android plugins. The instructions below assumes that you’re using Android Studio.

  1. Follow these instructions to create an Android library module for your plugin.

  2. Add the Godot engine library as a dependency to your plugin module:

    • Download the Godot engine library (godot-lib.x.y.aar)
    • Follow these instructions to add the Godot engine library as a dependency for your plugin.
    • In the plugin module’s build.gradle file, replace implementation with compileOnly for the dependency line for the Godot engine library.

  3. Create a new class in the plugin module and make sure it extends org.godotengine.godot.plugin.GodotPlugin. At runtime, it will be used to instantiate a singleton object that will be used by the Godot engine to load, initialize and run the plugin.

  4. Update the plugin AndroidManifest.xml file:

    • Open the plugin AndroidManifest.xml file.

    • Add the <application></application> tag if it’s missing.

    • In the <application> tag, add a <meta-data> tag setup as follow:

      <meta-data
    android:name="org.godotengine.plugin.v1.[PluginName]"
    android:value="[plugin.init.ClassFullName]" />

      Where PluginName is the name of the plugin, and plugin.init.ClassFullName is the full name (package + class name) of the plugin loading class.

  5. Add the remaining logic for your plugin and run the gradlew build command to generate the plugin’s aar file. The build will likely generate both a debug and release aar files. Depending on your need, pick only one version (usually the release one) which to provide your users with.

Note: The plugin’s aar filename must match the following pattern: [PluginName]*.aar where PluginName is the name of the plugin in camel case (e.g: GodotPayment.release.aar).

Loading and using a Android plugin

Once you have access to the plugin aar file, move it to the Godot project res://android/plugins directory.

From your script:

if Engine.has_singleton("MyPlugin"):
    var singleton = Engine.get_singleton("MyPlugin")
    print(singleton.myPluginFunction("World"))

When exporting the project, you need to add the plugin’s name to the Custom Template -> Plugins section. If trying to add multiple plugins, separate their names by a comma (,).

Bundling GDNative resources

A Android plugin can define and provide C/C++ GDNative resources, either to provide and/or access functionality from the game logic. The GDNative resources can be bundled within the plugin aar file which simplifies the distribution and deployment process:

  • The shared libraries (.so) for the defined GDNative libraries will be automatically bundled by the aar build system.
  • Godot *.gdnlib and *.gdns resource files must be manually defined in the plugin assets directory. The recommended path for these resources relative to the assets directory should be: godot/plugin/v1/[PluginName]/.

For GDNative libraries, the plugin singleton object must override the org.godotengine.godot.plugin.GodotPlugin::getPluginGDNativeLibrariesPaths() method, and return the paths to the bundled GDNative libraries config files (*.gdnlib). The paths must be relative to the assets directory. At runtime, the plugin will provide these paths to Godot core which will use them to load and initialize the bundled GDNative libraries.

Troubleshooting

Godot crashes upon load

Check adb logcat for possible problems, then:

  • Check that the methods used in the Java singleton only use simple Java datatypes. More complex datatypes are not supported.