DragonRuby on Android

This is a little less-polished-than-usual post about how to build/install Android applications with DragonRuby Pro. on a Linux system. The higher tiers of features in DragonRuby tend to be less well-documented, so here is a bit of a braindump on getting games running on a real Android device.

(Mostly to remind myself how I did all this.)

Building the Package

To be clear, you will need the "Pro" version of DragonRuby to follow this guide.

Running

dragonruby-publish --package

will generate binaries and packages for all supported platforms and dump them in builds/.

Signing

Creating a Keystore

Following the DragonRuby documentation, create a keystore file like this:

keytool -genkey -v -keystore YOUR_APP.keystore -alias your_app_name -keyalg RSA -keysize 2048 -validity 10000

This will generate a file called YOUR_APP.keystore.

keytool is probably already on your system, but if not you'll need to install a Java JDK package using your system tools.

Getting apksigner

To install the package on your Android device, you'll need to sign the .apk build using apksigner. I'm only going to cover one specific way of getting this program on Linux. Your experience may vary.

The easiest way to get apksigner is probably to install Android Studio and go from there. However, I prefer doing things the hard way (and not installing a whole IDE to get one binary...)

First, go to https://developer.android.com/studio/ and scroll allll the way to the bottom to "Command line tools only". Grab the .zip file from there.

Unzip it and find the sdkmanager binary, likely in latest/bin.

Run ./sdkmanager --list | grep build-tools to find the latest version of build-tools.

Then run something like ./sdkmanager --install "build-tools;34.0.0" to install.

The files will probably end up somewhere like ../../../build-tools. In there you'll find apksigner!

Signing the Package

apksigner sign -ks YOUR_APP.keystore builds/YOUR-GAME-android.apk

You'll need to figure out paths for apksigner, YOUR_APP.keystore, etc.

See the official docs for more, especially if publishing to the Google Play store.

Installing on Device

Enable Debug Mode

On your Android device setup developer options, enable USB debug mode, and plug your device into your computer.

Getting adb

The adb tool can be downloaded as part of the SDK Platform tools here: https://developer.android.com/tools/releases/platform-tools#downloads.html

Install the APK

adb install builds/your-game-android.apk

Viewing Logs

To view logs from the device:

adb logcat -e your-game

where your-game is the gameid or packageid configured in mygame/metadata/game_metadata.txt.

Remote Hotload

Building, signing, and installing packages becomes a bit painful if you are doing all that during development.

How about hot-loading code on your Android device just like you can on your development machine?

Setup

When running dragonruby, it opens up a webserver on port 9001. Besides what's obviously visible on the webpage, it's also how your device can connect and load code dynamically.

For that all to work, your development machine and Android device need to be on the same network, and your firewall needs to allow TCP connections on port 9001.

To verify it's working, try opening up your development machines IP on port 9001 from your Android device (e.g., visit https://YOUR.DEV.IP:9001 in a browser).

Building

Run

dragonruby-publish --package-with-remote-hotload

To create a hotloading version of the game, then sign+install like above.

Running

Make sure your are running dragonruby locally on your development machine.

Then open your game on your mobile device - it should flash "Remote hotload enabled" at the bottom if it has been built properly. This does not ensure it actually connected to the development server, though!

To test, try making a visible change to a file on your local machine and see if the change is reflected on the Android device.

Somehow, magically, the hot-loaded changes will persist even through restarts. However, only changes made while the development server is running will be picked up.

Bonus: Detecting the "Back" "Button"

I am old, so I still use the virtual "back" button on Android.

In DragonRuby, this can be detected with

args.inputs.keyboard.key_down.ac_back

For example:

if inputs.keyboard.key_down.ac_back
  gtk.request_quit
end