sdl

README-android.md (20326B)

---

 Android
 ================================================================================
 
 Matt Styles wrote a tutorial on building SDL for Android with Visual Studio:
 http://trederia.blogspot.de/2017/03/building-sdl2-for-android-with-visual.html
 
 The rest of this README covers the Android gradle style build process.
 
 If you are using the older ant build process, it is no longer officially
 supported, but you can use the "android-project-ant" directory as a template.
 
 
 ================================================================================
  Requirements
 ================================================================================
 
 Android SDK (version 26 or later)
 https://developer.android.com/sdk/index.html
 
 Android NDK r15c or later
 https://developer.android.com/tools/sdk/ndk/index.html
 
 Minimum API level supported by SDL: 16 (Android 4.1)
 
 
 ================================================================================
  How the port works
 ================================================================================
 
 - Android applications are Java-based, optionally with parts written in C
 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
   the SDL library
 - This means that your application C code must be placed inside an Android 
   Java project, along with some C support code that communicates with Java
 - This eventually produces a standard Android .apk package
 
 The Android Java code implements an "Activity" and can be found in:
 android-project/app/src/main/java/org/libsdl/app/SDLActivity.java
 
 The Java code loads your game code, the SDL shared library, and
 dispatches to native functions implemented in the SDL library:
 src/core/android/SDL_android.c
 
 
 ================================================================================
  Building an app
 ================================================================================
 
 For simple projects you can use the script located at build-scripts/androidbuild.sh
 
 There's two ways of using it:
 
     androidbuild.sh com.yourcompany.yourapp < sources.list
     androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
 
 sources.list should be a text file with a source file name in each line
 Filenames should be specified relative to the current directory, for example if
 you are in the build-scripts directory and want to create the testgles.c test, you'll
 run:
 
     ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
 
 One limitation of this script is that all sources provided will be aggregated into
 a single directory, thus all your source files should have a unique name.
 
 Once the project is complete the script will tell you where the debug APK is located.
 If you want to create a signed release APK, you can use the project created by this
 utility to generate it.
 
 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
 done in the build directory for the app!
 
 
 For more complex projects, follow these instructions:
     
 1. Copy the android-project directory wherever you want to keep your projects
    and rename it to the name of your project.
 2. Move or symlink this SDL directory into the "<project>/app/jni" directory
 3. Edit "<project>/app/jni/src/Android.mk" to include your source files
 
 4a. If you want to use Android Studio, simply open your <project> directory and start building.
 
 4b. If you want to build manually, run './gradlew installDebug' in the project directory. This compiles the .java, creates an .apk with the native code embedded, and installs it on any connected Android device
 
 
 If you already have a project that uses CMake, the instructions change somewhat:
 
 1. Do points 1 and 2 from the instruction above.
 2. Edit "<project>/app/build.gradle" to comment out or remove sections containing ndk-build
    and uncomment the cmake sections. Add arguments to the CMake invocation as needed.
 3. Edit "<project>/app/jni/CMakeLists.txt" to include your project (it defaults to
    adding the "src" subdirectory). Note that you'll have SDL2, SDL2main and SDL2-static
    as targets in your project, so you should have "target_link_libraries(yourgame SDL2 SDL2main)"
    in your CMakeLists.txt file. Also be aware that you should use add_library() instead of
    add_executable() for the target containing your "main" function.
 
 If you wish to use Android Studio, you can skip the last step.
 
 4. Run './gradlew installDebug' or './gradlew installRelease' in the project directory. It will build and install your .apk on any
    connected Android device
 
 Here's an explanation of the files in the Android project, so you can customize them:
 
     android-project/app
         build.gradle            - build info including the application version and SDK
         src/main/AndroidManifest.xml	- package manifest. Among others, it contains the class name of the main Activity and the package name of the application.
         jni/			- directory holding native code
         jni/Application.mk	- Application JNI settings, including target platform and STL library
         jni/Android.mk		- Android makefile that can call recursively the Android.mk files in all subdirectories
         jni/CMakeLists.txt	- Top-level CMake project that adds SDL as a subproject
         jni/SDL/		- (symlink to) directory holding the SDL library files
         jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
         jni/src/		- directory holding your C/C++ source
         jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
         jni/src/CMakeLists.txt	- CMake file that you may customize to include your source code and any library references
         src/main/assets/	- directory holding asset files for your application
         src/main/res/		- directory holding resources for your application
         src/main/res/mipmap-*	- directories holding icons for different phone hardware
         src/main/res/values/strings.xml	- strings used in your application, including the application name
         src/main/java/org/libsdl/app/SDLActivity.java - the Java class handling the initialization and binding to SDL. Be very careful changing this, as the SDL library relies on this implementation. You should instead subclass this for your application.
 
 
 ================================================================================
  Customizing your application name
 ================================================================================
 
 To customize your application name, edit AndroidManifest.xml and replace
 "org.libsdl.app" with an identifier for your product package.
 
 Then create a Java class extending SDLActivity and place it in a directory
 under src matching your package, e.g.
 
     src/com/gamemaker/game/MyGame.java
 
 Here's an example of a minimal class file:
 
     --- MyGame.java --------------------------
     package com.gamemaker.game;
     
     import org.libsdl.app.SDLActivity; 
     
     /**
      * A sample wrapper class that just calls SDLActivity 
      */ 
     
     public class MyGame extends SDLActivity { }
     
     ------------------------------------------
 
 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
 class, .e.g. "MyGame"
 
 
 ================================================================================
  Customizing your application icon
 ================================================================================
 
 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
 the drawable directories under the res directory. There are several directories
 for different screen sizes.
 
 
 ================================================================================
  Loading assets
 ================================================================================
 
 Any files you put in the "app/src/main/assets" directory of your project
 directory will get bundled into the application package and you can load
 them using the standard functions in SDL_rwops.h.
 
 There are also a few Android specific functions that allow you to get other
 useful paths for saving and loading data:
 * SDL_AndroidGetInternalStoragePath()
 * SDL_AndroidGetExternalStorageState()
 * SDL_AndroidGetExternalStoragePath()
 
 See SDL_system.h for more details on these functions.
 
 The asset packaging system will, by default, compress certain file extensions.
 SDL includes two asset file access mechanisms, the preferred one is the so
 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
 GC, but given this method does not work on compressed assets, there is also the
 "Input Stream" method, which is automatically used as a fall back by SDL. You
 may want to keep this fact in mind when building your APK, specially when large
 files are involved.
 For more information on which extensions get compressed by default and how to
 disable this behaviour, see for example:
     
 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
 
 
 ================================================================================
  Pause / Resume behaviour
 ================================================================================
 
 If SDL_HINT_ANDROID_BLOCK_ON_PAUSE hint is set (the default),
 the event loop will block itself when the app is paused (ie, when the user
 returns to the main Android dashboard). Blocking is better in terms of battery
 use, and it allows your app to spring back to life instantaneously after resume
 (versus polling for a resume message).
 
 Upon resume, SDL will attempt to restore the GL context automatically.
 In modern devices (Android 3.0 and up) this will most likely succeed and your
 app can continue to operate as it was.
 
 However, there's a chance (on older hardware, or on systems under heavy load),
 where the GL context can not be restored. In that case you have to listen for
 a specific message, (which is not yet implemented!) and restore your textures
 manually or quit the app (which is actually the kind of behaviour you'll see
 under iOS, if the OS can not restore your GL context it will just kill your app)
 
 
 ================================================================================
  Threads and the Java VM
 ================================================================================
 
 For a quick tour on how Linux native threads interoperate with the Java VM, take
 a look here: https://developer.android.com/guide/practices/jni.html
 
 If you want to use threads in your SDL app, it's strongly recommended that you
 do so by creating them using SDL functions. This way, the required attach/detach
 handling is managed by SDL automagically. If you have threads created by other
 means and they make calls to SDL functions, make sure that you call
 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
 your thread automatically anyway (when you make an SDL call), but it'll never
 detach it.
 
 
 ================================================================================
  Using STL
 ================================================================================
 
 You can use STL in your project by creating an Application.mk file in the jni
 folder and adding the following line:
 
     APP_STL := c++_shared
 
 For more information go here:
 	https://developer.android.com/ndk/guides/cpp-support
 
 
 ================================================================================
  Using the emulator
 ================================================================================
 
 There are some good tips and tricks for getting the most out of the
 emulator here: https://developer.android.com/tools/devices/emulator.html
 
 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
 
 Notice that this software emulator is incredibly slow and needs a lot of disk space.
 Using a real device works better.
 
 
 ================================================================================
  Troubleshooting
 ================================================================================
 
 You can see if adb can see any devices with the following command:
 
     adb devices
 
 You can see the output of log messages on the default device with:
 
     adb logcat
 
 You can push files to the device with:
 
     adb push local_file remote_path_and_file
 
 You can push files to the SD Card at /sdcard, for example:
 
     adb push moose.dat /sdcard/moose.dat
 
 You can see the files on the SD card with a shell command:
 
     adb shell ls /sdcard/
 
 You can start a command shell on the default device with:
 
     adb shell
 
 You can remove the library files of your project (and not the SDL lib files) with:
 
     ndk-build clean
 
 You can do a build with the following command:
 
     ndk-build
 
 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
 
     ndk-build V=1
 
 If your application crashes in native code, you can use ndk-stack to get a symbolic stack trace:
 	https://developer.android.com/ndk/guides/ndk-stack
 
 If you want to go through the process manually, you can use addr2line to convert the
 addresses in the stack trace to lines in your code.
 
 For example, if your crash looks like this:
 
     I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
     I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
     I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
     I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
     I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
     I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
     I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
     I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
     I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
 
 You can see that there's a crash in the C library being called from the main code.
 I run addr2line with the debug version of my code:
 
     arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
 
 and then paste in the number after "pc" in the call stack, from the line that I care about:
 000014bc
 
 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
 
 You can add logging to your code to help show what's happening:
 
     #include <android/log.h>
     
     __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
 
 If you need to build without optimization turned on, you can create a file called
 "Application.mk" in the jni directory, with the following line in it:
 
     APP_OPTIM := debug
 
 
 ================================================================================
  Memory debugging
 ================================================================================
 
 The best (and slowest) way to debug memory issues on Android is valgrind.
 Valgrind has support for Android out of the box, just grab code using:
 
     svn co svn://svn.valgrind.org/valgrind/trunk valgrind
 
 ... and follow the instructions in the file README.android to build it.
 
 One thing I needed to do on Mac OS X was change the path to the toolchain,
 and add ranlib to the environment variables:
 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
 
 Once valgrind is built, you can create a wrapper script to launch your
 application with it, changing org.libsdl.app to your package identifier:
 
     --- start_valgrind_app -------------------
     #!/system/bin/sh
     export TMPDIR=/data/data/org.libsdl.app
     exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
     ------------------------------------------
 
 Then push it to the device:
 
     adb push start_valgrind_app /data/local
 
 and make it executable:
 
     adb shell chmod 755 /data/local/start_valgrind_app
 
 and tell Android to use the script to launch your application:
 
     adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
 
 If the setprop command says "could not set property", it's likely that
 your package name is too long and you should make it shorter by changing
 AndroidManifest.xml and the path to your class file in android-project/src
 
 You can then launch your application normally and waaaaaaaiiittt for it.
 You can monitor the startup process with the logcat command above, and
 when it's done (or even while it's running) you can grab the valgrind
 output file:
 
     adb pull /sdcard/valgrind.log
 
 When you're done instrumenting with valgrind, you can disable the wrapper:
 
     adb shell setprop wrap.org.libsdl.app ""
 
 
 ================================================================================
  Graphics debugging
 ================================================================================
 
 If you are developing on a compatible Tegra-based tablet, NVidia provides
 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
 and GLES libraries, you must follow their instructions for installing the
 interposer library on a rooted device. The non-rooted instructions are not
 compatible with applications that use SDL2 for video.
 
 The Tegra Graphics Debugger is available from NVidia here:
 https://developer.nvidia.com/tegra-graphics-debugger
 
 
 ================================================================================
  Why is API level 16 the minimum required?
 ================================================================================
 
 The latest NDK toolchain doesn't support targeting earlier than API level 16.
 As of this writing, according to https://developer.android.com/about/dashboards/index.html
 about 99% of the Android devices accessing Google Play support API level 16 or
 higher (January 2018).
 
 
 ================================================================================
  A note regarding the use of the "dirty rectangles" rendering technique
 ================================================================================
 
 If your app uses a variation of the "dirty rectangles" rendering technique,
 where you only update a portion of the screen on each frame, you may notice a
 variety of visual glitches on Android, that are not present on other platforms.
 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
 contexts, in particular the use of the eglSwapBuffers function. As stated in the
 documentation for the function "The contents of ancillary buffers are always 
 undefined after calling eglSwapBuffers".
 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
 is not possible for SDL as it requires EGL 1.4, available only on the API level
 17+, so the only workaround available on this platform is to redraw the entire
 screen each frame.
 
 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
 
 
 ================================================================================
  Ending your application
 ================================================================================
 
 Two legitimate ways:
 
 - return from your main() function. Java side will automatically terminate the
 Activity by calling Activity.finish().
 
 - Android OS can decide to terminate your application by calling onDestroy()
 (see Activity life cycle). Your application will receive a SDL_QUIT event you 
 can handle to save things and quit.
 
 Don't call exit() as it stops the activity badly.
 
 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
 SDLK_AC_BACK, for any purpose.
 
 ================================================================================
  Known issues
 ================================================================================
 
 - The number of buttons reported for each joystick is hardcoded to be 36, which
 is the current maximum number of buttons Android can report.