This is my first attempt to include FXGL, a game engine, in a mobile app. For now it... fails. But only partially.

This example is based on Hello Gluon which in turn is based on "Hello Gluon" from Gluon Mobile samples. It consists of the Main class which sets up a JavaFX app in the same way as in Hello Gluon, and then uses the main window to display an FXGL view. In theory it should enable us to code a game in FXGL while still being able to draw JavaFX widgets on top of it, just as this example draws the "search" button.

Please refer to How to compile and run an example for details on how to, well, compile and run this example.

The app works when it's run as a standard Java app with mvn gluonfx:run and as a desktop native app, compiled with GraalVM Native Image (mvn gluonfx:build gluonfx:nativerun). In the second case we see some warnings, but they don't seem to be serious:

WARN  SystemBundleService  - Failed to load: java.io.FileNotFoundException: /home/makingthematrix/workspace/scalaonandroid/HelloFXGL/system/fxgl.bundle (No such file or directory)
WARN  FXGLAssetLoaderServi - Asset "/assets/languages/english.lang" was not found!
FXGLAssetLoaderServi - Failed to load PROPERTY_MAP
WARN  LocalizationService  - menu.pressAnyKey is not localized for language ENGLISH

Unfortunately when we compile the example for Android (mvn -Pandroid gluonfx:build gluonfx:package), install it on a mobile device and open it, it crashes with the following error:

E AndroidRuntime: FATAL EXCEPTION: main
E AndroidRuntime: Process: io.makingthematrix.scalaonandroid.hellofxgl, PID: 2777
E AndroidRuntime: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "JNI_OnLoad_awt" referenced by "/data/app/io.makingthematrix.scalaonandroid.hellofxgl-yn4tm0Ly6KLJ5U46m2A6KQ==/lib/arm64/libsubstrate.so"...
E AndroidRuntime: 	at java.lang.Runtime.loadLibrary0(Runtime.java:1071)
E AndroidRuntime: 	at java.lang.Runtime.loadLibrary0(Runtime.java:1007)
E AndroidRuntime: 	at java.lang.System.loadLibrary(System.java:1667)
E AndroidRuntime: 	at com.gluonhq.helloandroid.MainActivity.surfaceCreated(MainActivity.java:104)

This is addressed in an issue on the gluonfx-maven-plugin GitHub repo and the answer for now is that "there is no support yet for AWT on Android" :( Does it mean FXGL can't be used on Android at all? I will try to learn more about it.

In the meantime, this is still a perfectly good way to write native desktop games with FXGL (*). Also, please note that embedding FXGL makes sense for mobile apps, but on the desktop you can decide to run FXGL from the very start by specifying the main FXGL class that extends com.almasb.fxgl.app.GameApplication as the main class of the app. Unfortunately, Maven has some problems with understanding how Scala implements its static methods in companion objects instead of directly in the classes. There are tricks to go around it: this example uses one of them but as far as I know it doesn't work for FXGL. Instead, I'd suggest to write the Main class in Java, make it extend com.almasb.fxgl.app.GameApplication instead of com.gluonhq.charm.glisten.application.MobileApplication, and call Scala code from there.

*) If you look into pom.xml you will see a long list of FXGL services I had to put in the reflectionList for gluonfx-maven-plugin. It would look better if I put them in a seperate file but Ialso wonder if really all of them need to be on the reflection list even if I don't use them.

Update It looks like this is GraalVM Native Image issue which started to appear from GraalVM 21.1. The Android app should work if you downgrade to GraalVM 20.0.x and use the old Gluon's maven-client-plugin instead ofgluonfx-maven-plugin. Or you can wait for a fix.