Modify GameActivity bridge code

GameActivity interacts with Unity via a bridge that you can modify to make changes and implement additional features. The code that makes up the bridge is written in C++ and during the build process, GameActivity builds it into a shared library called libgame.so.

You can’t modify bridge code within Unity itself; you must first export your project. After you export your project, you can find the files that comprise the bridge code in <exported_project_directory>/unityLibrary/src/main/cpp/GameActivity/. Most of the code files in this directory contain utility code. The following table shows you the purpose of the most important bridge code files.

During the project export process, Unity’s incremental build pipeline might overwrite any changes you make in the exported project. If you want your changes to persist:

1. Export your project.
2. Create a new directory that’s outside your Unity project. This new directory is your modified bridge code directory.
3. Copy the code files that you want to modify from the <exported_project_directory>/unityLibrary/src/main/cpp/GameActivity/ directory into your modified bridge code directory.
4. In Unity, create a new C# script that uses Android.IPostGenerateGradleAndroidProject to copy the code files from your modified bridge code directory back into the <exported_project_directory>/unityLibrary/src/main/cpp/GameActivity/ directory. When Unity builds your application, this code will overwrite the default bridge code files with your modified versions.
5. Make any bridge code modifications in the files in your modified bridge code directory.

Expand GameActivity bridge code

You can add extra source files to the existing GameActivity bridge files which are then compiled together.

For example:

1. Create a C# script in Unity and name it SendMessageReceiver.cs.

   using UnityEngine;
   
   public class SendMessageReceiver : MonoBehaviour
   {
       public void SendMessageFromCpp(string message)
       {
           Debug.LogFormat(LogType.Log, LogOption.NoStacktrace, null, message);
       }
   }
   

2. Create a new GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
   See in Glossary and name it SendMessageReceiver.

3. Attach the SendMessageReceiver script to the SendMessageReceiver GameObject.

4. Create MyFile.cpp in \<unityproject\>/ExtraSourceFiles directory.

   Note: Don’t place .cpp files in the Assets directory, because they will link into IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
   See in Glossary’s libil2cpp.so shared library and won’t compile.

   The following code calls a C# method SendMessageFromCpp on a GameObject called SendMessageReceiver and passes HelloFromBridge as an extra parameter whenever you touch the phone screen.

   #include "UGAApplication.h"
   #include "game-activity/native_app_glue/android_native_app_glue.h"
   
   void UnityGameActivityPluginLoad(Unity::UnityApplication& application)
   {
       application.GetEvents().Register<Unity::UnityEventProcessInput>([](const Unity::UnityEventProcessInput& e)
       {
           auto inputBuffer = e.GetInputBuffer();
   
           if (inputBuffer->motionEventsCount != 0) {
               for (uint64_t i = 0; i < inputBuffer->motionEventsCount; ++i) {
                   GameActivityMotionEvent* motionEvent = &inputBuffer->motionEvents[i];
                   if (motionEvent->action == AKEY_EVENT_ACTION_DOWN)
                       e.GetApplication().SendMessage("SendMessageReceiver", "SendMessageFromCpp", "HelloFromBridge");
               }
           }
       });
   }
   

5. Place the following editor script PostProcessor.cs in Assets/Editor:

   (It ensures that ExtraSourceFiles/MyFile.cpp is copied to unityLibrary/src/main/cpp/GameActivity/CustomFolder/MyFile.cpp in an incremental build friendly way.)

   using System;
   using UnityEditor.Android;
   using UnityEditor;
   using UnityEngine;
   
   public class PostProcessor : AndroidProjectFilesModifier
   {
       const string CustomSourceFileSrc = "ExtraSourceFiles/MyFile.cpp";
       const string CustomSourceFileDst = "unityLibrary/src/main/cpp/GameActivity/CustomFolder/MyFile.cpp";
   
       public override AndroidProjectFilesModifierContext Setup()
       {
           var ctx = new AndroidProjectFilesModifierContext();
           ctx.Dependencies.DependencyFiles = new[]
           {
               CustomSourceFileSrc
           };
           ctx.AddFileToCopy(CustomSourceFileSrc, CustomSourceFileDst);
   
           return ctx;
       }
   
       public override void OnModifyAndroidProjectFiles(AndroidProjectFiles projectFiles)
       {
       }
   }
   

6. Select GameActivity Application Entry Point in Android Player settings (menu: Edit > Project Settings > Player > Other Settings > Configuration).

7. Click Build & Run.

8. Touch the phone screen and check the Logcat.

You should now see HelloFromBridge log, sent from MyFile.cpp and printed by SendMessageReceiver.cs script.

Notes:

• UnityGameActivityPluginLoad in MyFile.cpp is weakly linked and is called when GameActivity bridge initializes. There’s also ShutdownUserCode if you need it.
• MyFile.cpp contains UnityEventProcessInput event. You can find more events in UGAEvents.h file.

Additional resources

• Update the GameActivity library