The development of this Android app has to be done on Linux, it's currently not possible to
build the native parts on Windows.

* Compile LibreOffice master for Android.

  Do this in the folder where you cloned the LibreOffice core (e.g master-android).

  Create an autogen.input file:

      --build=x86_64-unknown-linux-gnu
      --with-android-ndk=/home/$USER/Android/Sdk/ndk-bundle
      --with-android-sdk=/home/$USER/Android/Sdk
      --with-distro=LibreOfficeAndroid
      --enable-sal-log

  Run ./autogen.sh && make

* Build zstd for Android

git clone https://android.googlesource.com/platform/external/zstd/ android-zstd
cd android-zstd
mkdir -p install/armeabi-v7a
cd install/armeabi-v7a

NDK_PATH=~/Android/Sdk/ndk-bundle
cmake \
  -DCMAKE_TOOLCHAIN_FILE=${NDK_PATH}/build/cmake/android.toolchain.cmake \
  -DANDROID_ABI=armeabi-v7a \
  -DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a \
  -DANDROID_NDK=${NDK_PATH} \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_SYSTEM_NAME=Android \
  -DCMAKE_SYSTEM_VERSION=21 \
  ../../build/cmake
make

* Build zstd for several platforms:

  scripts/build-zstd.sh ~/Android/Sdk/ndk-bundle /opt/libreoffice

This will create a set of folders in install/ that you can configure with.

* Build the POCO for Android

  # clone the poco repository in the same folder where LibreOffice core and online folders are placed.
  git clone https://github.com/pocoproject/poco poco-android
  cd poco-android

  # use the 1.10.1 branch
  git checkout -b poco-1.10.1 origin/poco-1.10.1

  # configure
  ./configure --config=Android --no-samples --no-tests --omit=Crypto,NetSSL_OpenSSL,Zip,Data,Data/SQLite,Data/ODBC,Data/MySQL,MongoDB,PDF,CppParser,PageCompiler,JWT

  # make it
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=armeabi-v7a CC=armv7a-linux-androideabi21-clang CXX=armv7a-linux-androideabi21-clang++ SYSLIBS=-static-libstdc++

  # install it to /opt/poco-android
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=armeabi-v7a CC=armv7a-linux-androideabi21-clang CXX=armv7a-linux-androideabi21-clang++ SYSLIBS=-static-libstdc++ install INSTALLDIR=/opt/poco-android

* 64bit POCO for Android

  # checkout the 1.10.1 in a different location and apply the following patch:
  --- a/build/config/Android
  +++ b/build/config/Android
  @@ -21,6 +21,11 @@ TOOL      = arm-linux-androideabi
   ARCHFLAGS = -march=armv7-a -mfloat-abi=softfp
   LINKFLAGS = -Wl,--fix-cortex-a8
   else
  +ifeq ($(ANDROID_ABI),arm64-v8a)
  +TOOL      = aarch64-linux-android
  +#ARCHFLAGS = -march=armv7-a -mfloat-abi=softfp
  +#LINKFLAGS = -Wl,--fix-cortex-a8
  +else
   ifeq ($(ANDROID_ABI),x86)
   TOOL      = i686-linux-android
   ARCHFLAGS = -march=i686 -msse3 -mstackrealign -mfpmath=sse
  @@ -29,6 +34,7 @@ $(error Invalid ABI specified in ANDROID_ABI)
   endif
   endif
   endif
  +endif

   #
   # Define Tools

  # configure as above:
  ./configure --config=Android --no-samples --no-tests --omit=Crypto,NetSSL_OpenSSL,Zip,Data,Data/SQLite,Data/ODBC,Data/MySQL,MongoDB,PDF,CppParser,PageCompiler,JWT

  # and make it:
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=arm64-v8a CC=aarch64-linux-android21-clang CXX=aarch64-linux-android21-clang++ SYSLIBS=-static-libstdc++

  # install
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=arm64-v8a CC=aarch64-linux-android21-clang CXX=aarch64-linux-android21-clang++ SYSLIBS=-static-libstdc++ install INSTALLDIR=/opt/poco-android-64bit

* Poco for x86 (if you want to add the support for that into the APK too):

  # checkout the 1.10.1 in yet another location
  git clone https://github.com/pocoproject/poco poco-android-x86
  cd poco-android-x86
  git checkout -b poco-1.10.1 origin/poco-1.10.1

  # configure
  ./configure --config=Android --no-samples --no-tests --omit=Crypto,NetSSL_OpenSSL,Zip,Data,Data/SQLite,Data/ODBC,Data/MySQL,MongoDB,PDF,CppParser,PageCompiler,JWT

  # build
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=x86 CC=i686-linux-android21-clang CXX=i686-linux-android21-clang++ SYSLIBS=-static-libstdc++

  # install
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=x86 CC=i686-linux-android21-clang CXX=i686-linux-android21-clang++ SYSLIBS=-static-libstdc++ install INSTALLDIR=/opt/poco-android-x86

* Poco for x86_64 (if you want to add the support for that into the APK too):

  # checkout the 1.10.1 in yet another location
  git clone https://github.com/pocoproject/poco poco-android-x86-64
  cd poco-android-x86-64
  git checkout -b poco-1.10.1 origin/poco-1.10.1

  # and apply the following patch:
  diff --git a/build/config/Android b/build/config/Android
  index 9227a3352..1abf6df7c 100644
  --- a/build/config/Android
  +++ b/build/config/Android
  @@ -25,10 +25,14 @@ ifeq ($(ANDROID_ABI),x86)
   TOOL      = i686-linux-android
   ARCHFLAGS = -march=i686 -msse3 -mstackrealign -mfpmath=sse
   else
  +ifeq ($(ANDROID_ABI),x86_64)
  +TOOL      = x86_64-linux-android
  +else
   $(error Invalid ABI specified in ANDROID_ABI)
   endif
   endif
   endif
  +endif
   
   #
   # Define Tools

  # configure
  ./configure --config=Android --no-samples --no-tests --omit=Crypto,NetSSL_OpenSSL,Zip,Data,Data/SQLite,Data/ODBC,Data/MySQL,MongoDB,PDF,CppParser,PageCompiler,JWT

  # build
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=x86_64 CC=x86_64-linux-android21-clang CXX=x86_64-linux-android21-clang++ SYSLIBS=-static-libstdc++

  # install
  PATH="$PATH":~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin make -j8 ANDROID_ABI=x86_64 CC=x86_64-linux-android21-clang CXX=x86_64-linux-android21-clang++ SYSLIBS=-static-libstdc++ install INSTALLDIR=/opt/poco-android-x86-64

* Configure the online.git (eg. in online-android folder)

  Don't forget to change --with-lo-builddir in the following:

  ./autogen.sh && ./configure CC=~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi21-clang CXX=~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi21-clang++ --host=arm-linux-androideabi --enable-androidapp --with-lo-builddir=/local/libreoffice/master-android --with-poco-includes=/opt/poco-android/include --with-poco-libs=/opt/poco-android/lib --with-zstd-includes=/opt/libreoffice/android-zstd/lib --with-zstd-libs=/opt/libreoffice/android-zstd/install/armeabi-v7a/lib --disable-setcap --enable-silent-rules --enable-debug

* Build the JavaScript, HTML and CSS files also in the online-android folder

  # just run 'make'
  make

* Build the actual app

  + Start Android Studio
  + Open this 'android' subdir as a project
  + Build from Android Studio (Build -> Make Project)

Or

  + command line:  ./gradlew build

== Building 32bit + 64bit combined .apk ==

  + you need to build both a 32bit (armeabi-v7a) and 64bit (arm64-v8a) core
  + you need to build both a 32bit and 64bit POCO
  + and then provide paths to both to the ./configure, separated by a colon ':',
    like:

    --with-lo-builddir=/local/libreoffice/master-android-release:/local/libreoffice/master-android-release-64bit \
    --with-poco-includes=/opt/poco-android/include:/opt/poco-android-64bit/include \
    --with-poco-libs=/opt/poco-android/lib:/opt/poco-android-64bit/lib \

== Debugging ==

To debug the native code in Android Studio, you need the debugging symbols and
to setup lldb to actually read & use them.

* Add debugging symbols for the modules you are interested in

  To autogen.input, add something like:

    --enable-symbols="vcl/ desktop/ sal/ svx/ framework/ sfx2/ tools/ cppu/ cppuhelper/ filter/ comphelper/ Library_sw Library_swd Library_swui"

  clean the appropriate modules, like

    make vcl.clean desktop.clean sal.clean svx.clean framework.clean sfx2.clean tools.clean cppu.clean cppuhelper.clean filter.clean comphelper.clean sw.clean

  and rebuild using 'make'.

* Add android/obj/local/armeabi-v7a from core.git as a Symbol Directory

  In Android Studio, choose Run -> Debug... -> Edit Configurations...

  There go to the Android App -> app, choose the Debugger tab, and:

  Debug type: Auto (or Dual)

  Symbol Directories: here add the full path, like

    /local/libreoffice/master-android/android/obj/local/armeabi-v7a

  This path contains the non-stripped version of the liblo-native-code.so, and
  the debugger will read the symbols from that one (even if the APK contains
  the stripped version). *NB* ensure that this is before any internal source
  directories - since the internal source contains stripped native code.

  [Alternatively you can add the following to your ~/.lldbinit instead:

    settings set target.inline-breakpoint-strategy always
    settings append target.exec-search-paths /local/libreoffice/master-android/android/obj/local/armeabi-v7a
  ]

* To use pretty printers for types like OUString, add the following to your
  ~/.lldbinit:

  command script import '/local/libreoffice/master-android/solenv/lldb/libreoffice/LO.py'

From now on, you will be able to debug directly in the Android Studio
debugger.  Happy debugging!

Note: to re-build your app with a newly compiled libnative-lo code - it is

== Tip: How to speed up your core.git build ==

If you use icecream for parallel building, you can use it for
cross-compilation too.

  # first generate a tarball with the toolchain (once)
  icecc-create-env ~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi21-clang ~/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi21-clang++

And add it and the paths to the compiler as the first things to the
autogen.input:

  CC=icecc [here copy what the output of ./autogen.sh without icecream said for C compiler]
  CXX=icecc [here copy what the output of ./autogen.sh without icecream said for C++ compiler]
  ICECC_VERSION=/path/to/the/tarball/generated/above/955ceb546ceb7a5715bf0223ddd788fe.tar.gz
  --with-parallelism=[amount of cpu threads in your icecream farm]
  --enable-icecream
  [...the original autogen.input...]

So the result will look something like this:

  CC=icecc /home/$USER/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang -mthumb -march=armv7-a -mfloat-abi=softfp -mfpu=neon -Wl,--fix-cortex-a8 -gcc-toolchain /home/$USER/Android/Sdk/ndk-bundle/to>
  CXX=icecc /home/$USER/Android/Sdk/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ -mthumb -march=armv7-a -mfloat-abi=softfp -mfpu=neon -Wl,--fix-cortex-a8 -gcc-toolchain /home/$USER/Android/Sdk/ndk-bundle>
  ICECC_VERSION=/local/libreoffice/android/955ceb546ceb7a5715bf0223ddd788fe.tar.gz
  --with-parallelism=25
  --enable-icecream
  --build=x86_64-unknown-linux-gnu
  --with-android-ndk=/home/$USER/Android/Sdk/ndk-bundle
  --with-android-sdk=/home/$USER/Android/Sdk
  --with-distro=LibreOfficeAndroid
  --enable-sal-log