Platform-specific guides » Android

Building and running console applications

Android allows to run arbitrary console utilities and tests via ADB. Assuming you have Magnum installed in the NDK path as described in Crosscompiling for Android, build your project simply as this (adapt version numbers and ABIs as needed):

mkdir build-android-arm64 && cd build-android-arm64
cmake .. \
    -DCMAKE_SYSTEM_NAME=Android \
    -DCMAKE_SYSTEM_VERSION=22 \
    -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
    -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \
    -DCMAKE_ANDROID_STL_TYPE=c++_static \
    -DCMAKE_BUILD_TYPE=Release
cmake --build .

After that you can use ADB to upload your executable to the device and run it there. The global temporary directory is /data/local/tmp and while the parent directories often don't have permissions, it's possible to cd into it and create arbitrary files there. Assuming you built an executable in build-android-arm64/src/my-application, the workflow would be like this:

adb push build-android-arm64/src/my-application /data/local/tmp
adb shell /data/local/tmp/my-application

You can also use adb shell to enter the device shell directly and continue from there. Besides plain command-line apps it's also possible to create an EGL context without any extra setup using Platform::WindowlessEglApplication. See also GL::OpenGLTester for information about OpenGL testing.

Building and installing graphics apps

Building of graphics applications is managed fully using Gradle, which also builds your CMake project internally. It's possible to use other means such as ndk-build, but CMake is the officially preferred way. The following guide assumes you have Gradle installed in a system-wide location available in $PATH. See the Gradle installation docs for more information, see below if you want to use the gradlew wrappers instead.

In case you don't have an OpenGL ES build set up yet, you need to copy FindEGL.cmake and FindOpenGLES2.cmake (or FindOpenGLES3.cmake) from the modules/ directory in Magnum source to the modules/ dir in your project so it is able to find EGL and OpenGL ES libraries.

Magnum provides Android application wrapper in Platform::AndroidApplication. See its documentation for more information about general usage. You can also use the Android Native Activity directly or any other way.

The first thing you need compared to building an app for other platforms is creating a shared library instead of an executable:

if(NOT CORRADE_TARGET_ANDROID)
    add_executable(my-application MyApplication.cpp)
else()
    add_library(my-application SHARED MyApplication.cpp)
endif()

Then you need to create a build.gradle file that references your root CMakeLists.txt. Assuming it's saved right next to your root CMakeLists.txt, the most minimal version might look like this:

buildscript {
    repositories {
        jcenter()
        google()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
    }
}

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25

    defaultConfig {
        minSdkVersion 22

        externalNativeBuild {
            cmake {
                arguments '-DANDROID_STL=c++_static'
            }
        }
        ndk {
            abiFilters 'arm64-v8a'
        }
    }

    externalNativeBuild {
        cmake {
            path 'CMakeLists.txt'
        }
    }
}

Important things are compileSdkVersion and minSdkVersion, which set SDK version that will be used to compile the project and minimal SDK version that the app can run on. You can add further CMake parameters in the arguments line (here it's just requesting to use static libc++) and the abiFilters allow you to restrict which ABIs will the project be built for — Gradle by default builds for both 32 and 64-bit ARM, MIPS and x86, which might be quite annoying to wait for (during development at least). The path then references your CMakeLists.txt file. Gradle by default bundles all shared library targets defined in the CMake project, so there's no need to specify a particular library name.

The official documentation contains a more complete overview of all possibilities.

Another important file is src/main/AndroidManifest.xml, which says some properties about the Android package. The location is also important, it has to be placed inside src/main subdirectory, not straight besides the build.gradle file. A minimal stripped-down version is:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="{{ package }}" android:versionCode="1" android:versionName="1.0">
  <uses-feature android:glEsVersion="0x00020000" />
  <application android:label="{{ app_name }}" android:hasCode="false">
    <activity android:name="android.app.NativeActivity" android:label="{{ app_name }}">
      <meta-data android:name="android.app.lib_name" android:value="{{ lib_name }}" />
      <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
      </intent-filter>
    </activity>
  </application>
</manifest>

Replace {{ package }} with Java-like package name for your app (in this case it could be e.g. "cz.mosra.magnum.my_application", for example), {{ app_name }} with human-readable app name that's displayed in the system (so e.g. "My Application") and finally the {{ lib_name }} is name of the library that you compiled with CMake, which in this case would be "my-application".

The <uses-feature android:glEsVersion="0x00020000" /> says that the minimal OpenGL ES version is 2.0, change it in case you require a different version. Consult the Android developer documentation for further information about the manifest file.

With everything set up, you are now ready to build the project by simply executing the following from the directory with your build.gradle. During the first run, Gradle will download a huge amount of random stuff when building even the simplest thing. Close your eyes and ignore that it happened.

gradle build

Installing on a connected device or emulator is then a matter of

gradle installDebug

after which you can launch the app from your home screen. See the Troubleshooting section below if you ran into problems.

Building for multiple ABIs and system versions

The above guide simplifies things a bit and builds for just a single ARM64 ABI. In order to support multiple platforms, you need to separately build and install the dependencies for all ABIs of choice — create separate build directories and run CMake with different CMAKE_ANDROID_ARCH_ABI and corresponding CMAKE_INSTALL_PREFIX. Similarly with SDK versions, adapt CMAKE_SYSTEM_VERSION and CMAKE_INSTALL_PREFIX to a desired version. The headers are shared and should be always installed into <ndk>/sysroot/usr regardless of ABI or SDK version. The supported ABI values are:

After that, you can add the additional ABIs to the abiFilters list in your build.gradle.

For example, building Magnum for 32-bit and 64-bit ARM with SDK version 24 could look like this:

mkdir build-android-arm && cd build-android-arm
cmake .. \
    -DCMAKE_SYSTEM_NAME=Android \
    -DCMAKE_SYSTEM_VERSION=24 \
    -DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a \
    -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \
    -DCMAKE_ANDROID_STL_TYPE=c++_static \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=<ndk>/platforms/android-24/arch-arm/usr \
    -DMAGNUM_INCLUDE_INSTALL_PREFIX=<ndk>/sysroot/usr
cmake --build . --target install

cd ..

mkdir build-android-arm64 && cd build-android-arm64
cmake .. \
    -DCMAKE_SYSTEM_NAME=Android \
    -DCMAKE_SYSTEM_VERSION=24 \
    -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
    -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \
    -DCMAKE_ANDROID_STL_TYPE=c++_static \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=<ndk>/platforms/android-24/arch-arm64/usr \
    -DMAGNUM_INCLUDE_INSTALL_PREFIX=<ndk>/sysroot/usr
cmake --build . --target install

And the build.gradle for your app then looks like this:

buildscript {
    repositories {
        jcenter()
        google()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
    }
}

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25

    defaultConfig {
        minSdkVersion 24

        externalNativeBuild {
            cmake {
                arguments '-DANDROID_STL=c++_static'
            }
        }
        ndk {
            abiFilters 'armeabi-v7a', 'arm64-v8a'
        }
    }

    externalNativeBuild {
        cmake {
            path 'CMakeLists.txt'
        }
    }
}

See the official documentation about ABIs for more information.

Redirecting output to Android log buffer

While printing to standard output and standard error output "just works" with command-line apps, you might want to redirect your Debug, Warning and Error output to Android log buffer. so it can be accessed through the adb logcat utility. See Corrade::Utility::AndroidLogStreamBuffer for more information.

The Platform::AndroidApplication sets this up implicitly with a magnum tag, you can then filter it out like this, for example:

$ adb logcat *:S magnum
...
03-16 17:35:26.703 17726 17745 I magnum  : Renderer: Mali-G71 by ARM
03-16 17:35:26.703 17726 17745 I magnum  : OpenGL version: OpenGL ES 3.2 v1.r2p0
03-16 17:35:26.703 17726 17745 I magnum  : Using optional features:
03-16 17:35:26.703 17726 17745 I magnum  :     GL_EXT_robustness

Using system-wide CMake installation

According to the official documentation, it's possible to use system CMake installation without needing to install Android SDK version of CMake 3.6. Simply update the externalNativeBuild in your build.gradle file to specify CMake version that you have installed in your system, for example:

android {
    ...
    externalNativeBuild {
        cmake {
            path 'CMakeLists.txt'
            ...
            version '3.10.2'
        }
    }
}

However, be aware that this is an experimental feature and may be broken. At the time of writing (March 2018), it didn't work for me with NDK r16b, Android buid plugin 3.0.1 and CMake 3.10.

Using gradlew wrappers instead of a system installation

It's possible to bundle Gradle in the project itself as opposed to requiring a pre-existing system installation. It has the downside of having a bit more boilerplate files in your project, though.

First, add the following to your build.gradle file:

task wrapper(type: Wrapper) {
    gradleVersion = '4.0'
}

Then run this on a system that has Gradle installed:

gradle wrapper

This will generate the following files that you can then add to version control:

• gradlew shell script for Unix-like systems
• gradle.bat batch script for Windows
• gradle/ directory with wrapper binaries

With this in place, you can just use gradlew instead of gradle.

Setting up Android build on Travis CI

For simple compilation tests, add the following to your .travis.yml matrix builds. According to the Travis Android documentation, build-tools-22.0.1 and android-22 are always present, so your builds shouldn't get any extra delay when requesting them. The $TARGET environment variable is used here only to disambiguate later, you might or might not need it.

matrix:
  include:
  # ...
  - language: android
    os: linux
    dist: trusty
    env:
    - TARGET=android
    android:
      components:
      - build-tools-22.0.1
      - android-22

At the time of writing (March 2018), while the generic Ubuntu 14.04 images already have CMake 3.9.2, for some reason the Android Ubuntu 14.04 images have just CMake 3.2. Android support is builtin since version 3.7, but an important fix for the LLVM toolchain was merged as late as in 3.9.2, so you may want to grab that version. Example .travis.yml setup that downloads the binary and extracts it to $HOME/cmake, with $PATH setup and caching:

cache:
  directories:
  - $HOME/cmake

install:
- >
  if [ "$TARGET" == "android" ] && [ ! -e "$HOME/cmake/bin" ]; then
    cd $HOME ;
    wget https://cmake.org/files/v3.9/cmake-3.9.2-Linux-x86_64.tar.gz &&
    mkdir -p cmake &&
    cd cmake &&
    tar --strip-components=1 -xzf ../cmake-3.9.2-Linux-x86_64.tar.gz &&
    cd $TRAVIS_BUILD_DIR ;
  fi
- >
  if [ "$TARGET" == "android" ]; then
    export PATH=$HOME/cmake/bin:$PATH &&
    cmake --version ;
  fi

The NDK can be fetched as a simple *.zip file. However, version r16b has over 800 MB, so you might want to explore creation of a Standalone Toolchain with only the things you need to speed up the build. Again, downlading it into $HOME/android-ndk-r16b is a matter of adding this into your install: section:

- >
  if [ "$TARGET" == "android" ]; then
    cd $HOME ;
    wget https://dl.google.com/android/repository/android-ndk-r16b-linux-x86_64.zip &&
    unzip -q android-*.zip &&
    cd $TRAVIS_BUILD_DIR ;
  fi

Travis CI discourages caching the NDK, as downloading the cache will take roughly the same amount of time as downloading it from upstream.

Building your actual code is just a matter of setting up a correct NDK path. You can install the dependencies to any location as long as you specify the same location in CMAKE_PREFIX_PATH and CMAKE_FIND_ROOT_PATH in depending projects. Using armeabi-v7a instead of arm64-v8a ensures that you can run the code in a preinstalled emulator later, see below.

mkdir build-android-arm && cd build-android-arm
cmake .. \
    -DCMAKE_ANDROID_NDK=$HOME/android-ndk-r16b \
    -DCMAKE_SYSTEM_NAME=Android \
    -DCMAKE_SYSTEM_VERSION=22 \
    -DCMAKE_ANDROID_ARCH_ABI=armeabi-v7a \
    -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \
    -DCMAKE_ANDROID_STL_TYPE=c++_static \
    -DCMAKE_PREFIX_PATH=$HOME/deps \
    -DCMAKE_FIND_ROOT_PATH=$HOME/deps \
    ...

matrix:
  include:
  - language: android
    # ...
    android:
      components:
      # ...
      - sys-img-armeabi-v7a-android-22

echo no | android create avd --force -n test -t android-22 --abi armeabi-v7a
emulator -avd test -no-audio -no-window &
android-wait-for-emulator
CORRADE_TEST_COLOR=ON ctest -V

buildscript {
    // ...
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.3'
    }
}

// ...

android {
    compileSdkVersion 22
    buildToolsVersion '26.0.2'

    defaultConfig {
        minSdkVersion 22
        // ...

before_install:
- if [ "$TARGET" == "android" ]; then yes | sdkmanager "cmake;3.6.4111459"; fi

cmake .. \
    -DCMAKE_INSTALL_PREFIX=$HOME/android-ndk-r16b/platforms/android-22/arch-arm64/usr \
    -DCORRADE_INCLUDE_INSTALL_PREFIX=$HOME/android-ndk-r16b/sysroot/usr \
    ...

export ANDROID_NDK_HOME=$HOME/android-ndk-r16b
export CMAKE_PREFIX_PATH=$HOME/deps-native/

gradle build

Troubleshooting

export CMAKE_PREFIX_PATH=<path-where-your-dependencies-are-installed>
gradle build

$ gradle build

FAILURE: Build failed with an exception.

  What went wrong:
Could not open terminal for stdout: could not get termcap entry

TERM=xterm gradle build

sdkmanager --licenses # and then manually accept all of them

> Failed to install the following SDK components:
  [Android SDK Build-Tools 26.0.2, Android SDK Platform 25]
  The SDK directory (/opt/android-sdk) is not writeable,
  please update the directory permissions.