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Table of Contents

Building SDL2 for Android

Existing documentation

A lot of information can be found in SDL/docs/README-android.md.

This page is more walkthrough-oriented.

Pre-requisites

  • Install minimal Java environment. For instance, in Debian/Ubuntu:
<syntaxhighlight lang="bash"> sudo apt install openjdk-8-jdk ant android-sdk-platform-tools-common </syntaxhighlight>
  • Install NDK (tested with r10e)
  • Install the latest SDK, run tools/bin/sdkmanager (or tools/android pre-2017) and install one API (>=12; >= 19 for SDL >= 2.0.8; >=26 if for SDL >= 2.0.9)
  • Configure your environment variables, e.g.:
<syntaxhighlight lang="bash"> PATH="/usr/src/android-ndk-rXXx:$PATH" # for 'ndk-build' PATH="/usr/src/android-sdk-linux/tools:$PATH" # for 'android' PATH="/usr/src/android-sdk-linux/platform-tools:$PATH" # for 'adb' export ANDROID_HOME="/usr/src/android-sdk-linux" # for gradle export ANDROID_NDK_HOME="/usr/src/android-ndk-rXXx" # for gradle </syntaxhighlight>

Simple builds

SDL wrapper for simple programs

  • Compile a sample app (calls ndk-build):
<syntaxhighlight lang="bash"> cd /usr/src/SDL2/build-scripts/ ./androidbuild.sh org.libsdl.testgles ../test/testgles.c </syntaxhighlight>
  • Follow the instructions to install on your device:
<syntaxhighlight lang="bash"> cd /usr/src/SDL2/build/org.libsdl.testgles/ ant debug install # SDL <= 2.0.7 ./gradlew installDebug # SDL >= 2.0.8 </syntaxhighlight>

Notes:

  • multiple targets armeabi-v7a/arm64-v8a/x86/x86_64 compilation
  • application doesn't quit

Troubleshooting

  • use OpenJDK 8: execute sudo update-alternatives --config java and select jdk-8 as default; or use JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64 ./gradlew
  • fixed in 2.0.9: in /android-project/build.gradle change (in BOTH places in the file code appears) from
<syntaxhighlight lang="c"> repositories { jcenter() } </syntaxhighlight> to <syntaxhighlight lang="c"> repositories { jcenter() google() } </syntaxhighlight>
  • javax/xml/bind/annotation/XmlSchema, Could not initialize class com.android.sdklib.repository.AndroidSdkHandler: check the Android Gradle Plugin version in /android-project/build.gradle, e.g.
classpath 'com.android.tools.build:gradle:3.1.0'
  • You can customize the Gradle version in /android-project/gradle/wrapper/gradle-wrapper.properties:
distributionUrl=https\://services.gradle.org/distributions/gradle-4.9-all.zip
  • You can customize your SDK/NDK versions in android-project/app/build.gradle:
<syntaxhighlight lang="c"> android { buildToolsVersion "28.0.1" compileSdkVersion 28 </syntaxhighlight>
  • You can customize your targets depending on the NDK version:
<syntaxhighlight lang="c"> externalNativeBuild { ndkBuild { arguments "APP_PLATFORM=android-14" abiFilters 'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64' </syntaxhighlight>
  • ABIs [x86_64, arm64-v8a] are not supported for platform. Supported ABIs are [armeabi, armeabi-v7a, x86, mips]: upgrade to NDK >= 10
  • Using ant (SDL <= 2.0.7): edit build-scripts/androidbuild.sh, find the $ANDROID update project line, and add --target android-XX to it (replace XX with your installed API number)
  • TODO: check how we can use the distro's gradle instead of executing stuff from the Internet - apt install gradle libgradle-android-plugin-java

SDL wrapper + SDL_image NDK module

Let's modify SDL2_image/showimage.c to show a simple embedded image (e.g. XPM).

<syntaxhighlight lang="c">
  1. include "SDL.h"
  2. include "SDL_image.h"
/* XPM */ static char * icon_xpm[] = { "32 23 3 1", " c #FFFFFF", ". c #000000", "+ c #FFFF00", " ", " ........ ", " ..++++++++.. ", " .++++++++++++. ", " .++++++++++++++. ", " .++++++++++++++++. ", " .++++++++++++++++++. ", " .+++....++++....+++. ", " .++++.. .++++.. .++++. ", " .++++....++++....++++. ", " .++++++++++++++++++++. ", " .++++++++++++++++++++. ", " .+++++++++..+++++++++. ", " .+++++++++..+++++++++. ", " .++++++++++++++++++++. ", " .++++++++++++++++++. ", " .++...++++++++...++. ", " .++............++. ", " .++..........++. ", " .+++......+++. ", " ..++++++++.. ", " ........ ", " "}; int main(int argc, char *argv[]) { SDL_Window *window; SDL_Renderer *renderer; SDL_Surface *surface; SDL_Texture *texture; int done; SDL_Event event; if (SDL_CreateWindowAndRenderer(0, 0, 0, &window, &renderer) < 0) { SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "SDL_CreateWindowAndRenderer() failed: %s", SDL_GetError()); return(2); } surface = IMG_ReadXPMFromArray(icon_xpm); texture = SDL_CreateTextureFromSurface(renderer, surface); if (!texture) { SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't load texture: %s", SDL_GetError()); return(2); } SDL_SetWindowSize(window, 800, 480); done = 0; while (!done) { while (SDL_PollEvent(&event)) { if (event.type == SDL_QUIT) done = 1; } SDL_RenderCopy(renderer, texture, NULL, NULL); SDL_RenderPresent(renderer); SDL_Delay(100); } SDL_DestroyTexture(texture); SDL_Quit(); return(0); } </syntaxhighlight>

Then let's make an Android app out of it. To compile: 

cd /usr/src/SDL2/build-scripts/
./androidbuild.sh org.libsdl.showimage /usr/src/SDL2_image/showimage.c
cd /usr/src/SDL2/build/org.libsdl.showimage/
ln -s /usr/src/SDL2_image jni/
ln -s /usr/src/SDL2_image/external/libwebp-0.3.0 jni/webp
sed -i -e 's/^LOCAL_SHARED_LIBRARIES.*/& SDL2_image/' jni/src/Android.mk
ndk-build -j$(nproc)
ant debug install

Notes:

  • application doesn't restart properly

Build an autotools-friendly environment

You use autotools in your project and can't be bothering understanding ndk-build's cryptic errors? This guide is for you!

Note: this environment can be used for CMake too.

Compile a shared binaries bundle for SDL and SDL_*

  • Get the latests SDL2_* releases:
<syntaxhighlight lang="bash"> cd /usr/src/ wget https://libsdl.org/release/SDL2-2.0.5.tar.gz wget https://www.libsdl.org/projects/SDL_image/release/SDL2_image-2.0.1.tar.gz wget https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-2.0.1.tar.gz wget https://www.libsdl.org/projects/SDL_net/release/SDL2_net-2.0.1.tar.gz wget https://www.libsdl.org/projects/SDL_ttf/release/SDL2_ttf-2.0.14.tar.gz tar xf SDL2-2.0.5.tar.gz tar xf SDL2_image-2.0.1.tar.gz tar xf SDL2_mixer-2.0.1.tar.gz tar xf SDL2_net-2.0.1.tar.gz tar xf SDL2_ttf-2.0.14.tar.gz ln -s SDL2-2.0.5 SDL2 ln -s SDL2_image-2.0.1 SDL2_image ln -s SDL2_mixer-2.0.1 SDL2_mixer ln -s SDL2_net-2.0.1 SDL2_net ln -s SDL2_ttf-2.0.14 SDL2_ttf </syntaxhighlight>

  • Start with a minimal build:
<syntaxhighlight lang="bash"> cd /usr/src/SDL2/ cd build-scripts/
  1. hg revert --all # remove traces of previous builds
  2. edit androidbuild.sh and modify $ANDROID update project --target android-XX
./androidbuild.sh org.libsdl /dev/null
  1. doesn't matter if the actual build fails, it's just for setup
cd ../build/org.libsdl/ </syntaxhighlight>
  • Remove reference to our dummy file:
<syntaxhighlight lang="bash"> rm -rf jni/src/ </syntaxhighlight>
  • Reference SDL_image, SDL_mixer, SDL_ttf, and their dependencies, as NDK modules:
<syntaxhighlight lang="bash"> ln -s /usr/src/SDL2_image jni/ ln -s /usr/src/SDL2_image/external/libwebp-0.3.0 jni/webp ln -s /usr/src/SDL2_mixer jni/ ln -s /usr/src/SDL2_mixer/external/libmikmod-3.1.12 jni/libmikmod ln -s /usr/src/SDL2_mixer/external/smpeg2-2.0.0 jni/smpeg2 ln -s /usr/src/SDL2_net jni/ ln -s /usr/src/SDL2_ttf jni/ </syntaxhighlight>
  • Optionnaly edit jni/Android.mk to disable some formats, e.g.:
<syntaxhighlight lang="make"> SUPPORT_MP3_SMPEG := false include $(call all-subdir-makefiles) </syntaxhighlight>
  • Launch the build!
<syntaxhighlight lang="bash"> ndk-build -j$(nproc) </syntaxhighlight>

Note: no need to add System.loadLibrary calls in SDLActivity.java, your application will be linked to them and Android's ld-linux loads them automatically.

Install SDL in a GCC toolchain

Now:

  • Copy the NDK into a traditional GCC toolchain (leave android-14 as-is):
<syntaxhighlight lang="bash"> /usr/src/android-ndk-r8c/build/tools/make-standalone-toolchain.sh \ --platform=android-14 --install-dir=/usr/src/ndk-standalone-14-arm --arch=arm </syntaxhighlight>
  • Set your PATH (important, do it before any build):
<syntaxhighlight lang="bash"> NDK_STANDALONE=/usr/src/ndk-standalone-14-arm PATH=$NDK_STANDALONE/bin:$PATH </syntaxhighlight>
  • Install the SDL2 binaries in the toolchain:
<syntaxhighlight lang="bash"> cd /usr/src/SDL2/build/org.libsdl/ for i in libs/armeabi/*; do ln -nfs $(pwd)/$i $NDK_STANDALONE/sysroot/usr/lib/; done mkdir $NDK_STANDALONE/sysroot/usr/include/SDL2/ \cp jni/SDL/include/* $NDK_STANDALONE/sysroot/usr/include/SDL2/ \cp jni/*/SDL*.h $NDK_STANDALONE/sysroot/usr/include/SDL2/ </syntaxhighlight>
  • Install pkg-config and install a host-triplet-prefixed symlink in the PATH (auto-detected by autoconf):
<syntaxhighlight lang="bash"> VERSION=0.9.12 cd /usr/src/ wget http://rabbit.dereferenced.org/~nenolod/distfiles/pkgconf-$VERSION.tar.gz tar xf pkgconf-$VERSION.tar.gz cd pkgconf-$VERSION/ mkdir native-android/ && cd native-android/ ../configure --prefix=$NDK_STANDALONE/sysroot/usr make -j$(nproc) make install ln -s ../sysroot/usr/bin/pkgconf $NDK_STANDALONE/bin/arm-linux-androideabi-pkg-config mkdir $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/ </syntaxhighlight>

  • Install pkg-config .pc files for SDL:
<syntaxhighlight lang="bash"> cat <<'EOF' > $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/sdl2.pc prefix=/usr/src/ndk-standalone-14-arm/sysroot/usr exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: sdl2 Description: Simple DirectMedia Layer is a cross-platform multimedia library designed to provide low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D video framebuffer. Version: 2.0.5 Requires: Conflicts: Libs: -lSDL2 Cflags: -I${includedir}/SDL2 -D_REENTRANT EOF cat <<'EOF' > $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/SDL2_image.pc prefix=/usr/src/ndk-standalone-14-arm/sysroot/usr exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: SDL2_image Description: image loading library for Simple DirectMedia Layer Version: 2.0.1 Requires: sdl2 >= 2.0.0 Libs: -L${libdir} -lSDL2_image Cflags: -I${includedir}/SDL2 EOF cat <<'EOF' > $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/SDL2_mixer.pc prefix=/usr/src/ndk-standalone-14-arm/sysroot/usr exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: SDL2_mixer Description: mixer library for Simple DirectMedia Layer Version: 2.0.1 Requires: sdl2 >= 2.0.0 Libs: -L${libdir} -lSDL2_mixer Cflags: -I${includedir}/SDL2 EOF cat <<'EOF' > $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/SDL2_net.pc prefix=/usr/src/ndk-standalone-14-arm/sysroot/usr exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: SDL2_net Description: net library for Simple DirectMedia Layer Version: 2.0.1 Requires: sdl2 >= 2.0.0 Libs: -L${libdir} -lSDL2_net Cflags: -I${includedir}/SDL2 EOF cat <<'EOF' > $NDK_STANDALONE/sysroot/usr/lib/pkgconfig/SDL2_ttf.pc prefix=/usr/src/ndk-standalone-14-arm/sysroot/usr exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: SDL2_ttf Description: ttf library for Simple DirectMedia Layer with FreeType 2 support Version: 2.0.14 Requires: sdl2 >= 2.0.0 Libs: -L${libdir} -lSDL2_ttf Cflags: -I${includedir}/SDL2 EOF </syntaxhighlight>

Building other dependencies

You can add any other libraries (e.g.: SDL2_gfx, freetype, gettext, gmp...) using commands like: <syntaxhighlight lang="bash"> mkdir cross-android/ && cd cross-android/ ../configure --host=arm-linux-androideabi --prefix=$NDK_STANDALONE/sysroot/usr \ --with-some-option --enable-another-option \ --disable-shared make -j$(nproc) make install </syntaxhighlight>

Static builds (--disable-shared) are recommended for simplicity (no additional .so to declare).

<syntaxhighlight lang="bash"> Example with SDL2_gfx: VERSION=1.0.3 wget http://www.ferzkopp.net/Software/SDL2_gfx/SDL2_gfx-$VERSION.tar.gz tar xf SDL2_gfx-$VERSION.tar.gz mv SDL2_gfx-$VERSION/ SDL2_gfx/ cd SDL2_gfx/ mkdir cross-android/ && cd cross-android/ ../configure --host=arm-linux-androideabi --prefix=$NDK_STANDALONE/sysroot/usr \ --disable-shared --disable-mmx make -j$(nproc) make install </syntaxhighlight>

You can compile YOUR application using this technique, with some more steps to tell Android how to run it using JNI.

Build your autotools app

First, prepare an Android project:

  • Copy and adapt the /usr/src/SDL2/android-project skeleton as explained in README-android.md. You can leave it as-is in a first step.
  • Make links to the SDL binaries as well:
<syntaxhighlight lang="bash"> mkdir -p libs/armeabi/ for i in /usr/src/SDL2/build/org.libsdl/libs/armeabi/*; do ln -nfs $i libs/armeabi/; done </syntaxhighlight>

Make your project Android-aware:

  • Add /usr/src/SDL2/src/main/android/SDL_android_main.c in your project (comment out the line referencing "SDL_internal.h"). Compile it as C (not C++).
  • In your configure.ac, detect Android:
<syntaxhighlight lang="c"> AM_CONDITIONAL(ANDROID, test "$host" = "arm-unknown-linux-androideabi") </syntaxhighlight>

  • In your Makefile.am, tell Automake you'll build executables as libraries, using something like:
<syntaxhighlight lang="C"> if ANDROID AM_CFLAGS = -fPIC AM_LDFLAGS += -shared COMMON_OBJS += SDL_android_main.c endif </syntaxhighlight>

  • Cross-compile your project using the GCC toolchain environment we created:
<syntaxhighlight lang="bash"> PATH=$NDK_STANDALONE/bin:$PATH mkdir cross-android/ && cd cross-android/ ../configure --host=arm-linux-androideabi \ --prefix=/android-aint-posix \ --with-your-option --enable-your-other-option ... make </syntaxhighlight>
  • Do this again for any additional arch you want to support (TODO: see how to support armeabi-v7a and document what devices support it); something like:
<syntaxhighlight lang="bash"> mkdir cross-android-v7a/ && cd cross-android-v7a/
  1. .o: -march=armv5te -mtune=xscale -msoft-float -mthumb => -march=armv7-a -mfpu=vfpv3-d16 -mfloat-abi=softfp -mthumb
  2. .so: -march=armv7-a -Wl,--fix-cortex-a8
CFLAGS="-g -O2 -march=armv7-a -mfpu=vfpv3-d16 -mfloat-abi=softfp -mthumb" LFDLAGS="-march=armv7-a -Wl,--fix-cortex-a8" \ ../configure --host=arm-linux-androideabi \ ... </syntaxhighlight>

Now you can install your pre-built binaries and build the Android project:

  • Copy your program in android-project/libs/armeabi/libmain.so.
  • Build your Android .apk:
<syntaxhighlight lang="bash"> android update project --name your_app --path . --target android-XX ant debug ant installd </syntaxhighlight>
  • You can run the application remotely:
<syntaxhighlight lang="bash"> adb shell am start -a android.intenon.MAIN -n org.libsdl.app/org.libsdl.app.SDLActivity # replace with your app package </syntaxhighlight>
  • Your SDL2 Android app is running!

Build your CMake app

(Work In Progress)

You can use our Android GCC toolchain using a simple toolchain file: <syntaxhighlight lang="cmake">

  1. CMake toolchain file
SET(CMAKE_SYSTEM_NAME Linux) # Tell CMake we're cross-compiling include(CMakeForceCompiler)
  1. Prefix detection only works with compiler id "GNU"
CMAKE_FORCE_C_COMPILER(arm-linux-androideabi-gcc GNU) SET(ANDROID TRUE) </syntaxhighlight>

You then call CMake like this: <syntaxhighlight lang="bash"> PATH=$NDK_STANDALONE/bin:$PATH cmake \ -D CMAKE_TOOLCHAIN_FILE=../android_toolchain.cmake \ ... </syntaxhighlight>

Troubleshootings

If ant installd categorically refuses to install with Failure [INSTALL_FAILED_INSUFFICIENT_STORAGE], even if you have free local storage, that may mean anything. Check logcat first: <syntaxhighlight lang="bash"> adb logcat </syntaxhighlight> If the error logs are not helpful (likely ;')) try locating all past traces of the application: <syntaxhighlight lang="bash"> find / -name "org...." </syntaxhighlight> and remove them all.

If the problem persists, you may try installing on the SD card: <syntaxhighlight lang="bash"> adb install -s bin/app-debug.apk </syntaxhighlight>

If you get in your logcat:

SDL: Couldn't locate Java callbacks, check that they're named and typed correctly

this probably means your SDLActivity.java is out-of-sync with your libSDL2.so.