Use APL (Android Programming Language) to make an Android plugin for Unreal Engine 4

Question

I am trying to develop an Unreal Engine 4 plugin for Android Camera API 2.

As I could read on the unreal engine forums, there are two ways to make a plugin for Android.

The first is to change the base UE Android project (GameActivity).

The second is a standalone plugin that allows you to transfer plugins to any project.

According to this post, you can create a standalone Api1 plugin that uses the APL.xml file to add java code.

But I think that it is very limited by game activity, like the code below.

<?xml version="1.0" encoding="utf-8"?> <!--ARToolKit plugin additions--> <root xmlns:android="http://schemas.android.com/apk/res/android"> <!-- init section is always evaluated once per architecture --> <init> <log text="AndroidCamera init"/> </init> <androidManifestUpdates> <addPermission android:name="android.permission.CAMERA"/> <addFeature android:name="android.hardware.camera"/> <addFeature android:name="android.hardware.camera.autofocus"/> </androidManifestUpdates> <!-- optional additions to the GameActivity imports in GameActivity.java --> <gameActivityImportAdditions> <insert> import android.widget.Toast; import android.hardware.Camera; import android.hardware.Camera.CameraInfo; import android.hardware.Camera.Parameters; import android.hardware.Camera.PreviewCallback; import android.graphics.SurfaceTexture; import android.graphics.ImageFormat; import android.graphics.PixelFormat; import java.util.List; import java.io.IOException; import android.util.Log; </insert> </gameActivityImportAdditions> <gameActivityClassAdditions> <insert> static String msg = "yes i am a rock!"; SurfaceTexture surfaceTexture; Camera camera; public native boolean nativeGetFrameData(int frameWidth, int frameHeight, byte[] data); public void AndroidThunkJava_Toast() { try { _activity.runOnUiThread(new Runnable() { public void run() { Toast.makeText(_activity.getApplicationContext(), "cam o yeah!", Toast.LENGTH_SHORT).show(); } }); } catch (Exception e) { Log.debug("Toast failed with exception " + e.getMessage()); } } public void AndroidThunkJava_startCamera() { surfaceTexture = new SurfaceTexture(10); surfaceTexture.setDefaultBufferSize(320,240); camera = Camera.open(); try { camera.setPreviewTexture(surfaceTexture); } catch (IOException t) { android.util.Log.e("ARToolKitLog", "Cannot set preview texture target!", t); } Parameters cameraParam = camera.getParameters(); cameraParam.setPreviewFormat(ImageFormat.NV21); cameraParam.setPreviewSize(320, 240); camera.setParameters(cameraParam); camera.setPreviewCallback(new PreviewCallback() { @Override public void onPreviewFrame(byte[] data, Camera camera) { int Height = camera.getParameters().getPreviewSize().height; int Width = camera.getParameters().getPreviewSize().width; nativeGetFrameData(Width, Height, data); } }); camera.startPreview(); } public void AndroidThunkJava_stopCamera() { if (camera != null) { camera.stopPreview(); camera.release(); camera = null; } } </insert> </gameActivityClassAdditions> <!-- optional additions to GameActivity onCreate in GameActivity.java --> <gameActivityOnCreateAdditions> <insert> //Toast.makeText(this,msg,Toast.LENGTH_LONG).show(); //AndroidThunkJava_Toast(); </insert> </gameActivityOnCreateAdditions> </root> 

So my questions are:

Is this the only way to make a standalone plugin for Unreal Engine 4?

Is there an XML tag to add custom classes to these APL files?

Answer 1

I found another way to use custom Java classes:

If I am not mistaken, the unreal engine _APL.xml file is associated with the ANT build system.

So, as in _APL.xml files, in addition to defining Java code in gameActivityClassAdditions, there is a tag that copies our .java files to the Unreal Engine build directory.

I took the idea from this Unreal Engine plugin: https://github.com/jeevcat/GoogleMapsUE4Plugin

So, I made the plugin in 4 stages:

• Copy the custom Java classes to the plugin source directory with the folder order of the package, so the resulting folder structure should look something like this.

2.- Add a tag of pre-created copies to apply the Java class in the assembly directory:

 <prebuildCopies> <copyDir src="$S(PluginDir)/Java" dst="$S(BuildDir)" /> </prebuildCopies> 

3.- Add import to gameActivityImportAdditions:

 import org.samples.camera2.CameraHandler; 

4.- use custom class

  public void AndroidThunkJava_startCamera() { m_camHandler = new CameraHandler(); m_camHandler.setCallback(new CameraCallback() { @Override public void onGetFrame(byte[] data, int width, int height) { Log.d(LOG_TAG,"MY CUSTOM CALLBACK"+width); nativeGetFrameData(width, height, data); } }); m_camHandler.init(_activity, 0, 320, 240); m_camHandler.start(); } 

Finally, I will show the resulting _APL.xml file:

 <?xml version="1.0" encoding="utf-8"?> <!--ARToolKit plugin additions--> <root xmlns:android="http://schemas.android.com/apk/res/android"> <!-- init section is always evaluated once per architecture --> <init> <log text="AndroidCamera init"/> </init> <androidManifestUpdates> <addPermission android:name="android.permission.CAMERA" /> <addFeature android:name="android.hardware.camera" /> <addFeature android:name="android.hardware.camera.autofocus" /> <addFeature android:name="android.hardware.camera2" /> </androidManifestUpdates> <prebuildCopies> <copyDir src="$S(PluginDir)/Java" dst="$S(BuildDir)" /> </prebuildCopies> <!-- optional additions to the GameActivity imports in GameActivity.java --> <gameActivityImportAdditions> <insert> import android.widget.Toast; import android.hardware.Camera; import android.hardware.Camera.CameraInfo; import android.hardware.Camera.Parameters; import android.hardware.Camera.PreviewCallback; import android.graphics.SurfaceTexture; import android.graphics.ImageFormat; import android.graphics.PixelFormat; import java.util.List; import java.io.IOException; import android.util.Log; import org.samples.camera2.CameraHandler; </insert> </gameActivityImportAdditions> <gameActivityClassAdditions> <insert> static String msg = "yes i am a rock!"; SurfaceTexture surfaceTexture; Camera camera; CameraHandler m_camHandler; public native boolean nativeGetFrameData(int frameWidth, int frameHeight, byte[] data); public void AndroidThunkJava_Toast() { try { _activity.runOnUiThread(new Runnable() { public void run() { Toast.makeText(_activity.getApplicationContext(), "cam o yeah!", Toast.LENGTH_SHORT).show(); } }); } catch (Exception e) { Log.debug("Toast failed with exception " + e.getMessage()); } } public void AndroidThunkJava_startCamera() { m_camHandler = new CameraHandler(); m_camHandler.setCallback(new CameraCallback() { @Override public void onGetFrame(byte[] data, int width, int height) { Log.d(LOG_TAG,"MY CUSTOM CALLBACK"+width); nativeGetFrameData(width, height, data); } }); m_camHandler.init(_activity, 0, 320, 240); m_camHandler.start(); } public void AndroidThunkJava_stopCamera() { } </insert> </gameActivityClassAdditions> <!-- optional additions to GameActivity onCreate in GameActivity.java --> <gameActivityOnCreateAdditions> <insert> </insert> </gameActivityOnCreateAdditions> </root>