The legacy Android project was converted to use the gradle build system via Android Studio. While we suggest you build through Android Studio, it is not required. Since it has already been converted you should be able to open it up via the "Open Exsiting Android Studio Project" option.
This project makes use of common C++ code which is built via the NDK. Please see the Android Developer docs on getting started with the NDK for the most up to date information on setting up the NDK on your machine.
To allow us to more easily use the C++ code found in the Common folder, the Android-NDK folder which contains the relevant NDK make and wrapper files has been placed as a top level folder in this repo.
Gradle is used to build all components for the project. Before building any application files, the gradle script will copy over shared assets from the Common/Data folder and the C++ code should be automatically compiled (via the Android-NDK/Android.mk file). If there is an issue generating the C++ component of the project, you may need to manually select `Build -> Refresh Linked C++ Projects" and then run your gradle assemble again.