docs/README-android.md
author Ozkan Sezer
Thu, 21 Nov 2019 10:33:56 +0300
changeset 13265 5ae5e0b567a5
parent 13006 4a410f099040
permissions -rw-r--r--
CMakeLists.txt: add several missing function checks for unix case.
     1 Android
     2 ================================================================================
     3 
     4 Matt Styles wrote a tutorial on building SDL for Android with Visual Studio:
     5 http://trederia.blogspot.de/2017/03/building-sdl2-for-android-with-visual.html
     6 
     7 The rest of this README covers the Android gradle style build process.
     8 
     9 If you are using the older ant build process, it is no longer officially
    10 supported, but you can use the "android-project-ant" directory as a template.
    11 
    12 
    13 ================================================================================
    14  Requirements
    15 ================================================================================
    16 
    17 Android SDK (version 26 or later)
    18 https://developer.android.com/sdk/index.html
    19 
    20 Android NDK r15c or later
    21 https://developer.android.com/tools/sdk/ndk/index.html
    22 
    23 Minimum API level supported by SDL: 16 (Android 4.1)
    24 
    25 
    26 ================================================================================
    27  How the port works
    28 ================================================================================
    29 
    30 - Android applications are Java-based, optionally with parts written in C
    31 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    32   the SDL library
    33 - This means that your application C code must be placed inside an Android 
    34   Java project, along with some C support code that communicates with Java
    35 - This eventually produces a standard Android .apk package
    36 
    37 The Android Java code implements an "Activity" and can be found in:
    38 android-project/app/src/main/java/org/libsdl/app/SDLActivity.java
    39 
    40 The Java code loads your game code, the SDL shared library, and
    41 dispatches to native functions implemented in the SDL library:
    42 src/core/android/SDL_android.c
    43 
    44 
    45 ================================================================================
    46  Building an app
    47 ================================================================================
    48 
    49 For simple projects you can use the script located at build-scripts/androidbuild.sh
    50 
    51 There's two ways of using it:
    52 
    53     androidbuild.sh com.yourcompany.yourapp < sources.list
    54     androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
    55 
    56 sources.list should be a text file with a source file name in each line
    57 Filenames should be specified relative to the current directory, for example if
    58 you are in the build-scripts directory and want to create the testgles.c test, you'll
    59 run:
    60 
    61     ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
    62 
    63 One limitation of this script is that all sources provided will be aggregated into
    64 a single directory, thus all your source files should have a unique name.
    65 
    66 Once the project is complete the script will tell you where the debug APK is located.
    67 If you want to create a signed release APK, you can use the project created by this
    68 utility to generate it.
    69 
    70 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
    71 done in the build directory for the app!
    72 
    73 
    74 For more complex projects, follow these instructions:
    75     
    76 1. Copy the android-project directory wherever you want to keep your projects
    77    and rename it to the name of your project.
    78 2. Move or symlink this SDL directory into the "<project>/app/jni" directory
    79 3. Edit "<project>/app/jni/src/Android.mk" to include your source files
    80 
    81 4a. If you want to use Android Studio, simply open your <project> directory and start building.
    82 
    83 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
    84 
    85 
    86 If you already have a project that uses CMake, the instructions change somewhat:
    87 
    88 1. Do points 1 and 2 from the instruction above.
    89 2. Edit "<project>/app/build.gradle" to comment out or remove sections containing ndk-build
    90    and uncomment the cmake sections. Add arguments to the CMake invocation as needed.
    91 3. Edit "<project>/app/jni/CMakeLists.txt" to include your project (it defaults to
    92    adding the "src" subdirectory). Note that you'll have SDL2, SDL2main and SDL2-static
    93    as targets in your project, so you should have "target_link_libraries(yourgame SDL2 SDL2main)"
    94    in your CMakeLists.txt file. Also be aware that you should use add_library() instead of
    95    add_executable() for the target containing your "main" function.
    96 
    97 If you wish to use Android Studio, you can skip the last step.
    98 
    99 4. Run './gradlew installDebug' or './gradlew installRelease' in the project directory. It will build and install your .apk on any
   100    connected Android device
   101 
   102 Here's an explanation of the files in the Android project, so you can customize them:
   103 
   104     android-project/app
   105         build.gradle            - build info including the application version and SDK
   106         src/main/AndroidManifest.xml	- package manifest. Among others, it contains the class name of the main Activity and the package name of the application.
   107         jni/			- directory holding native code
   108         jni/Application.mk	- Application JNI settings, including target platform and STL library
   109         jni/Android.mk		- Android makefile that can call recursively the Android.mk files in all subdirectories
   110         jni/CMakeLists.txt	- Top-level CMake project that adds SDL as a subproject
   111         jni/SDL/		- (symlink to) directory holding the SDL library files
   112         jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
   113         jni/src/		- directory holding your C/C++ source
   114         jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
   115         jni/src/CMakeLists.txt	- CMake file that you may customize to include your source code and any library references
   116         src/main/assets/	- directory holding asset files for your application
   117         src/main/res/		- directory holding resources for your application
   118         src/main/res/mipmap-*	- directories holding icons for different phone hardware
   119         src/main/res/values/strings.xml	- strings used in your application, including the application name
   120         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.
   121 
   122 
   123 ================================================================================
   124  Customizing your application name
   125 ================================================================================
   126 
   127 To customize your application name, edit AndroidManifest.xml and replace
   128 "org.libsdl.app" with an identifier for your product package.
   129 
   130 Then create a Java class extending SDLActivity and place it in a directory
   131 under src matching your package, e.g.
   132 
   133     src/com/gamemaker/game/MyGame.java
   134 
   135 Here's an example of a minimal class file:
   136 
   137     --- MyGame.java --------------------------
   138     package com.gamemaker.game;
   139     
   140     import org.libsdl.app.SDLActivity; 
   141     
   142     /**
   143      * A sample wrapper class that just calls SDLActivity 
   144      */ 
   145     
   146     public class MyGame extends SDLActivity { }
   147     
   148     ------------------------------------------
   149 
   150 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   151 class, .e.g. "MyGame"
   152 
   153 
   154 ================================================================================
   155  Customizing your application icon
   156 ================================================================================
   157 
   158 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   159 the drawable directories under the res directory. There are several directories
   160 for different screen sizes.
   161 
   162 
   163 ================================================================================
   164  Loading assets
   165 ================================================================================
   166 
   167 Any files you put in the "app/src/main/assets" directory of your project
   168 directory will get bundled into the application package and you can load
   169 them using the standard functions in SDL_rwops.h.
   170 
   171 There are also a few Android specific functions that allow you to get other
   172 useful paths for saving and loading data:
   173 * SDL_AndroidGetInternalStoragePath()
   174 * SDL_AndroidGetExternalStorageState()
   175 * SDL_AndroidGetExternalStoragePath()
   176 
   177 See SDL_system.h for more details on these functions.
   178 
   179 The asset packaging system will, by default, compress certain file extensions.
   180 SDL includes two asset file access mechanisms, the preferred one is the so
   181 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   182 GC, but given this method does not work on compressed assets, there is also the
   183 "Input Stream" method, which is automatically used as a fall back by SDL. You
   184 may want to keep this fact in mind when building your APK, specially when large
   185 files are involved.
   186 For more information on which extensions get compressed by default and how to
   187 disable this behaviour, see for example:
   188     
   189 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
   190 
   191 
   192 ================================================================================
   193  Pause / Resume behaviour
   194 ================================================================================
   195 
   196 If SDL_HINT_ANDROID_BLOCK_ON_PAUSE hint is set (the default),
   197 the event loop will block itself when the app is paused (ie, when the user
   198 returns to the main Android dashboard). Blocking is better in terms of battery
   199 use, and it allows your app to spring back to life instantaneously after resume
   200 (versus polling for a resume message).
   201 
   202 Upon resume, SDL will attempt to restore the GL context automatically.
   203 In modern devices (Android 3.0 and up) this will most likely succeed and your
   204 app can continue to operate as it was.
   205 
   206 However, there's a chance (on older hardware, or on systems under heavy load),
   207 where the GL context can not be restored. In that case you have to listen for
   208 a specific message, (which is not yet implemented!) and restore your textures
   209 manually or quit the app (which is actually the kind of behaviour you'll see
   210 under iOS, if the OS can not restore your GL context it will just kill your app)
   211 
   212 
   213 ================================================================================
   214  Threads and the Java VM
   215 ================================================================================
   216 
   217 For a quick tour on how Linux native threads interoperate with the Java VM, take
   218 a look here: https://developer.android.com/guide/practices/jni.html
   219 
   220 If you want to use threads in your SDL app, it's strongly recommended that you
   221 do so by creating them using SDL functions. This way, the required attach/detach
   222 handling is managed by SDL automagically. If you have threads created by other
   223 means and they make calls to SDL functions, make sure that you call
   224 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
   225 your thread automatically anyway (when you make an SDL call), but it'll never
   226 detach it.
   227 
   228 
   229 ================================================================================
   230  Using STL
   231 ================================================================================
   232 
   233 You can use STL in your project by creating an Application.mk file in the jni
   234 folder and adding the following line:
   235 
   236     APP_STL := c++_shared
   237 
   238 For more information go here:
   239 	https://developer.android.com/ndk/guides/cpp-support
   240 
   241 
   242 ================================================================================
   243  Using the emulator
   244 ================================================================================
   245 
   246 There are some good tips and tricks for getting the most out of the
   247 emulator here: https://developer.android.com/tools/devices/emulator.html
   248 
   249 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   250 
   251 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   252 Using a real device works better.
   253 
   254 
   255 ================================================================================
   256  Troubleshooting
   257 ================================================================================
   258 
   259 You can see if adb can see any devices with the following command:
   260 
   261     adb devices
   262 
   263 You can see the output of log messages on the default device with:
   264 
   265     adb logcat
   266 
   267 You can push files to the device with:
   268 
   269     adb push local_file remote_path_and_file
   270 
   271 You can push files to the SD Card at /sdcard, for example:
   272 
   273     adb push moose.dat /sdcard/moose.dat
   274 
   275 You can see the files on the SD card with a shell command:
   276 
   277     adb shell ls /sdcard/
   278 
   279 You can start a command shell on the default device with:
   280 
   281     adb shell
   282 
   283 You can remove the library files of your project (and not the SDL lib files) with:
   284 
   285     ndk-build clean
   286 
   287 You can do a build with the following command:
   288 
   289     ndk-build
   290 
   291 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   292 
   293     ndk-build V=1
   294 
   295 If your application crashes in native code, you can use ndk-stack to get a symbolic stack trace:
   296 	https://developer.android.com/ndk/guides/ndk-stack
   297 
   298 If you want to go through the process manually, you can use addr2line to convert the
   299 addresses in the stack trace to lines in your code.
   300 
   301 For example, if your crash looks like this:
   302 
   303     I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   304     I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   305     I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   306     I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   307     I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   308     I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   309     I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   310     I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   311     I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   312 
   313 You can see that there's a crash in the C library being called from the main code.
   314 I run addr2line with the debug version of my code:
   315 
   316     arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   317 
   318 and then paste in the number after "pc" in the call stack, from the line that I care about:
   319 000014bc
   320 
   321 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   322 
   323 You can add logging to your code to help show what's happening:
   324 
   325     #include <android/log.h>
   326     
   327     __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   328 
   329 If you need to build without optimization turned on, you can create a file called
   330 "Application.mk" in the jni directory, with the following line in it:
   331 
   332     APP_OPTIM := debug
   333 
   334 
   335 ================================================================================
   336  Memory debugging
   337 ================================================================================
   338 
   339 The best (and slowest) way to debug memory issues on Android is valgrind.
   340 Valgrind has support for Android out of the box, just grab code using:
   341 
   342     svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   343 
   344 ... and follow the instructions in the file README.android to build it.
   345 
   346 One thing I needed to do on Mac OS X was change the path to the toolchain,
   347 and add ranlib to the environment variables:
   348 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   349 
   350 Once valgrind is built, you can create a wrapper script to launch your
   351 application with it, changing org.libsdl.app to your package identifier:
   352 
   353     --- start_valgrind_app -------------------
   354     #!/system/bin/sh
   355     export TMPDIR=/data/data/org.libsdl.app
   356     exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   357     ------------------------------------------
   358 
   359 Then push it to the device:
   360 
   361     adb push start_valgrind_app /data/local
   362 
   363 and make it executable:
   364 
   365     adb shell chmod 755 /data/local/start_valgrind_app
   366 
   367 and tell Android to use the script to launch your application:
   368 
   369     adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   370 
   371 If the setprop command says "could not set property", it's likely that
   372 your package name is too long and you should make it shorter by changing
   373 AndroidManifest.xml and the path to your class file in android-project/src
   374 
   375 You can then launch your application normally and waaaaaaaiiittt for it.
   376 You can monitor the startup process with the logcat command above, and
   377 when it's done (or even while it's running) you can grab the valgrind
   378 output file:
   379 
   380     adb pull /sdcard/valgrind.log
   381 
   382 When you're done instrumenting with valgrind, you can disable the wrapper:
   383 
   384     adb shell setprop wrap.org.libsdl.app ""
   385 
   386 
   387 ================================================================================
   388  Graphics debugging
   389 ================================================================================
   390 
   391 If you are developing on a compatible Tegra-based tablet, NVidia provides
   392 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
   393 and GLES libraries, you must follow their instructions for installing the
   394 interposer library on a rooted device. The non-rooted instructions are not
   395 compatible with applications that use SDL2 for video.
   396 
   397 The Tegra Graphics Debugger is available from NVidia here:
   398 https://developer.nvidia.com/tegra-graphics-debugger
   399 
   400 
   401 ================================================================================
   402  Why is API level 16 the minimum required?
   403 ================================================================================
   404 
   405 The latest NDK toolchain doesn't support targeting earlier than API level 16.
   406 As of this writing, according to https://developer.android.com/about/dashboards/index.html
   407 about 99% of the Android devices accessing Google Play support API level 16 or
   408 higher (January 2018).
   409 
   410 
   411 ================================================================================
   412  A note regarding the use of the "dirty rectangles" rendering technique
   413 ================================================================================
   414 
   415 If your app uses a variation of the "dirty rectangles" rendering technique,
   416 where you only update a portion of the screen on each frame, you may notice a
   417 variety of visual glitches on Android, that are not present on other platforms.
   418 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   419 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   420 documentation for the function "The contents of ancillary buffers are always 
   421 undefined after calling eglSwapBuffers".
   422 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   423 is not possible for SDL as it requires EGL 1.4, available only on the API level
   424 17+, so the only workaround available on this platform is to redraw the entire
   425 screen each frame.
   426 
   427 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
   428 
   429 
   430 ================================================================================
   431  Ending your application
   432 ================================================================================
   433 
   434 Two legitimate ways:
   435 
   436 - return from your main() function. Java side will automatically terminate the
   437 Activity by calling Activity.finish().
   438 
   439 - Android OS can decide to terminate your application by calling onDestroy()
   440 (see Activity life cycle). Your application will receive a SDL_QUIT event you 
   441 can handle to save things and quit.
   442 
   443 Don't call exit() as it stops the activity badly.
   444 
   445 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
   446 SDLK_AC_BACK, for any purpose.
   447 
   448 ================================================================================
   449  Known issues
   450 ================================================================================
   451 
   452 - The number of buttons reported for each joystick is hardcoded to be 36, which
   453 is the current maximum number of buttons Android can report.
   454