android-luajit-launcher

Android NativeActivity based launcher for LuaJIT, implementing the main loop within Lua land via FFI.

NativeActivity is available starting with platform android-9.

Have a look at the Android NDK's "native-plasma" sample activity to get an idea what it does - or rather, is theoretically able to do. While the sample from NDK implements everything in C, in our case, we create a LuaJIT instance and hand off control to it instead. LuaJIT then handles the main loop. In this programming model, we have a thread which presents us with a "main" entry point and allow us to follow our own program flow as long as we poll for and react to events.

A good number of Android native API headers are readily presented via FFI already. I'll probably add more along the way.

For now - and probably ever, since Mike Pall recommends strongly to do so - the compilation of LuaJIT is not integrated into the Android build framework and has to be run separately.

A wrapper script for building LuaJIT is provided.

Have a look at KOReader's llapp_main.lua file. You can use it as a starting point for your own app.

The real starting point, called from JNI/C, is the run() function in android.lua. It sets up a few things, namely FFI definitions for the Android native API (since it uses that itself for a few things) and some wrapper functions for logging. Also, it registers the "android" module in package.loaded, so you can access it in your own code via require("android"). It also registers a new package loader which can load Lua code from the activity's asset store, so you can use require() for Lua code stored there.

STARTING:

• init/update the submodules (LuaJIT for now):

git submodule init
git submodule sync
git submodule update

• update the project for your Android SDK/NDK (needs "android" tool in your PATH):

android update project --path .

• compile LuaJIT for your target architecture(s):

./mk-luajit.sh armeabi-v7a
./mk-luajit.sh clean
./mk-luajit.sh armeabi

• compile NDK/native code:

ndk-build

• compile and package APK (debug variant):

ant debug

TODO:

• a concept to deal with native Lua modules.
• a loader for native modules that have been put into the activity's library directory?
• a loader for obb storage, maybe? We could put native Lua modules there, for example.
• example code for framebuffer access and more