docs/README-android.md
author Sam Lantinga <slouken@libsdl.org>
Mon, 23 Oct 2017 23:23:47 -0700
changeset 11649 fe6769530709
parent 11647 5816b27073a4
child 11659 b2fd0f264cd3
permissions -rw-r--r--
Updated Android build tools version, which bumped minimum deployment target to API 14
Also added native code to the Android gradle project, which allows using gradle or Android Studio to build the entire SDL application without a separate ndk-build step.
     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 traditional style build process.
     8 
     9 
    10 ================================================================================
    11  Requirements
    12 ================================================================================
    13 
    14 Android SDK (version 16 or later)
    15 https://developer.android.com/sdk/index.html
    16 
    17 Android NDK r10e or later
    18 https://developer.android.com/tools/sdk/ndk/index.html
    19 
    20 Minimum API level supported by SDL: 14 (Android 4.0.1)
    21 
    22 
    23 ================================================================================
    24  How the port works
    25 ================================================================================
    26 
    27 - Android applications are Java-based, optionally with parts written in C
    28 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    29   the SDL library
    30 - This means that your application C code must be placed inside an Android 
    31   Java project, along with some C support code that communicates with Java
    32 - This eventually produces a standard Android .apk package
    33 
    34 The Android Java code implements an "Activity" and can be found in:
    35 android-project/app/src/main/java/org/libsdl/app/SDLActivity.java
    36 
    37 The Java code loads your game code, the SDL shared library, and
    38 dispatches to native functions implemented in the SDL library:
    39 src/core/android/SDL_android.c
    40 
    41 
    42 ================================================================================
    43  Building an app
    44 ================================================================================
    45 
    46 For simple projects you can use the script located at build-scripts/androidbuild.sh
    47 
    48 There's two ways of using it:
    49 
    50     androidbuild.sh com.yourcompany.yourapp < sources.list
    51     androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
    52 
    53 sources.list should be a text file with a source file name in each line
    54 Filenames should be specified relative to the current directory, for example if
    55 you are in the build-scripts directory and want to create the testgles.c test, you'll
    56 run:
    57 
    58     ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
    59 
    60 One limitation of this script is that all sources provided will be aggregated into
    61 a single directory, thus all your source files should have a unique name.
    62 
    63 Once the project is complete the script will tell you where the debug APK is located.
    64 If you want to create a signed release APK, you can use the project created by this
    65 utility to generate it.
    66 
    67 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
    68 done in the build directory for the app!
    69 
    70 
    71 For more complex projects, follow these instructions:
    72     
    73 1. Copy the android-project directory wherever you want to keep your projects
    74    and rename it to the name of your project.
    75 2. Move or symlink this SDL directory into the "<project>/app/jni" directory
    76 3. Edit "<project>/app/jni/src/Android.mk" to include your source files
    77 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    78 
    79 If you want to use Android Studio (recommended), skip to the Android Studio section below.
    80 
    81 5. 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
    82 
    83 Here's an explanation of the files in the Android project, so you can customize them:
    84 
    85     android-project/app
    86         build.gradle            - build info including the application version and SDK
    87         src/main/AndroidManifest.xml	- package manifest. Among others, it contains the class name
    88         			  of the main Activity and the package name of the application.
    89         jni/			- directory holding native code
    90         jni/Application.mk	- Application JNI settings, including target platform and STL library
    91         jni/Android.mk		- Android makefile that can call recursively the Android.mk files in all subdirectories
    92         jni/SDL/		- (symlink to) directory holding the SDL library files
    93         jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
    94         jni/src/		- directory holding your C/C++ source
    95         jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
    96         src/main/assets/	- directory holding asset files for your application
    97         src/main/res/		- directory holding resources for your application
    98         src/main/res/mipmap-*	- directories holding icons for different phone hardware
    99         src/main/res/values/strings.xml	- strings used in your application, including the application name
   100         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.
   101 
   102 
   103 ================================================================================
   104  Customizing your application name
   105 ================================================================================
   106 
   107 To customize your application name, edit AndroidManifest.xml and replace
   108 "org.libsdl.app" with an identifier for your product package.
   109 
   110 Then create a Java class extending SDLActivity and place it in a directory
   111 under src matching your package, e.g.
   112 
   113     src/com/gamemaker/game/MyGame.java
   114 
   115 Here's an example of a minimal class file:
   116 
   117     --- MyGame.java --------------------------
   118     package com.gamemaker.game;
   119     
   120     import org.libsdl.app.SDLActivity; 
   121     
   122     /**
   123      * A sample wrapper class that just calls SDLActivity 
   124      */ 
   125     
   126     public class MyGame extends SDLActivity { }
   127     
   128     ------------------------------------------
   129 
   130 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   131 class, .e.g. "MyGame"
   132 
   133 
   134 ================================================================================
   135  Customizing your application icon
   136 ================================================================================
   137 
   138 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   139 the drawable directories under the res directory. There are several directories
   140 for different screen sizes.
   141 
   142 
   143 ================================================================================
   144  Loading assets
   145 ================================================================================
   146 
   147 Any files you put in the "app/src/main/assets" directory of your project
   148 directory will get bundled into the application package and you can load
   149 them using the standard functions in SDL_rwops.h.
   150 
   151 There are also a few Android specific functions that allow you to get other
   152 useful paths for saving and loading data:
   153 * SDL_AndroidGetInternalStoragePath()
   154 * SDL_AndroidGetExternalStorageState()
   155 * SDL_AndroidGetExternalStoragePath()
   156 
   157 See SDL_system.h for more details on these functions.
   158 
   159 The asset packaging system will, by default, compress certain file extensions.
   160 SDL includes two asset file access mechanisms, the preferred one is the so
   161 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   162 GC, but given this method does not work on compressed assets, there is also the
   163 "Input Stream" method, which is automatically used as a fall back by SDL. You
   164 may want to keep this fact in mind when building your APK, specially when large
   165 files are involved.
   166 For more information on which extensions get compressed by default and how to
   167 disable this behaviour, see for example:
   168     
   169 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
   170 
   171 
   172 ================================================================================
   173  Pause / Resume behaviour
   174 ================================================================================
   175 
   176 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   177 the event loop will block itself when the app is paused (ie, when the user
   178 returns to the main Android dashboard). Blocking is better in terms of battery
   179 use, and it allows your app to spring back to life instantaneously after resume
   180 (versus polling for a resume message).
   181 
   182 Upon resume, SDL will attempt to restore the GL context automatically.
   183 In modern devices (Android 3.0 and up) this will most likely succeed and your
   184 app can continue to operate as it was.
   185 
   186 However, there's a chance (on older hardware, or on systems under heavy load),
   187 where the GL context can not be restored. In that case you have to listen for
   188 a specific message, (which is not yet implemented!) and restore your textures
   189 manually or quit the app (which is actually the kind of behaviour you'll see
   190 under iOS, if the OS can not restore your GL context it will just kill your app)
   191 
   192 
   193 ================================================================================
   194  Threads and the Java VM
   195 ================================================================================
   196 
   197 For a quick tour on how Linux native threads interoperate with the Java VM, take
   198 a look here: https://developer.android.com/guide/practices/jni.html
   199 
   200 If you want to use threads in your SDL app, it's strongly recommended that you
   201 do so by creating them using SDL functions. This way, the required attach/detach
   202 handling is managed by SDL automagically. If you have threads created by other
   203 means and they make calls to SDL functions, make sure that you call
   204 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
   205 your thread automatically anyway (when you make an SDL call), but it'll never
   206 detach it.
   207 
   208 
   209 ================================================================================
   210  Using STL
   211 ================================================================================
   212 
   213 You can use STL in your project by creating an Application.mk file in the jni
   214 folder and adding the following line:
   215 
   216     APP_STL := stlport_static
   217 
   218 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   219 
   220 
   221 ================================================================================
   222  Additional documentation
   223 ================================================================================
   224 
   225 The documentation in the NDK docs directory is very helpful in understanding the
   226 build process and how to work with native code on the Android platform.
   227 
   228 The best place to start is with docs/OVERVIEW.TXT
   229 
   230 
   231 ================================================================================
   232  Using Android Studio
   233 ================================================================================
   234 
   235 You can open your project directory with Android Studio and run it normally.
   236 
   237 
   238 ================================================================================
   239  Using the emulator
   240 ================================================================================
   241 
   242 There are some good tips and tricks for getting the most out of the
   243 emulator here: https://developer.android.com/tools/devices/emulator.html
   244 
   245 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   246 
   247 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   248 Using a real device works better.
   249 
   250 
   251 ================================================================================
   252  Troubleshooting
   253 ================================================================================
   254 
   255 You can see if adb can see any devices with the following command:
   256 
   257     adb devices
   258 
   259 You can see the output of log messages on the default device with:
   260 
   261     adb logcat
   262 
   263 You can push files to the device with:
   264 
   265     adb push local_file remote_path_and_file
   266 
   267 You can push files to the SD Card at /sdcard, for example:
   268 
   269     adb push moose.dat /sdcard/moose.dat
   270 
   271 You can see the files on the SD card with a shell command:
   272 
   273     adb shell ls /sdcard/
   274 
   275 You can start a command shell on the default device with:
   276 
   277     adb shell
   278 
   279 You can remove the library files of your project (and not the SDL lib files) with:
   280 
   281     ndk-build clean
   282 
   283 You can do a build with the following command:
   284 
   285     ndk-build
   286 
   287 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   288 
   289     ndk-build V=1
   290 
   291 If your application crashes in native code, you can use addr2line to convert the
   292 addresses in the stack trace to lines in your code.
   293 
   294 For example, if your crash looks like this:
   295 
   296     I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   297     I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   298     I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   299     I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   300     I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   301     I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   302     I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   303     I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   304     I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   305 
   306 You can see that there's a crash in the C library being called from the main code.
   307 I run addr2line with the debug version of my code:
   308 
   309     arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   310 
   311 and then paste in the number after "pc" in the call stack, from the line that I care about:
   312 000014bc
   313 
   314 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   315 
   316 You can add logging to your code to help show what's happening:
   317 
   318     #include <android/log.h>
   319     
   320     __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   321 
   322 If you need to build without optimization turned on, you can create a file called
   323 "Application.mk" in the jni directory, with the following line in it:
   324 
   325     APP_OPTIM := debug
   326 
   327 
   328 ================================================================================
   329  Memory debugging
   330 ================================================================================
   331 
   332 The best (and slowest) way to debug memory issues on Android is valgrind.
   333 Valgrind has support for Android out of the box, just grab code using:
   334 
   335     svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   336 
   337 ... and follow the instructions in the file README.android to build it.
   338 
   339 One thing I needed to do on Mac OS X was change the path to the toolchain,
   340 and add ranlib to the environment variables:
   341 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   342 
   343 Once valgrind is built, you can create a wrapper script to launch your
   344 application with it, changing org.libsdl.app to your package identifier:
   345 
   346     --- start_valgrind_app -------------------
   347     #!/system/bin/sh
   348     export TMPDIR=/data/data/org.libsdl.app
   349     exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   350     ------------------------------------------
   351 
   352 Then push it to the device:
   353 
   354     adb push start_valgrind_app /data/local
   355 
   356 and make it executable:
   357 
   358     adb shell chmod 755 /data/local/start_valgrind_app
   359 
   360 and tell Android to use the script to launch your application:
   361 
   362     adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   363 
   364 If the setprop command says "could not set property", it's likely that
   365 your package name is too long and you should make it shorter by changing
   366 AndroidManifest.xml and the path to your class file in android-project/src
   367 
   368 You can then launch your application normally and waaaaaaaiiittt for it.
   369 You can monitor the startup process with the logcat command above, and
   370 when it's done (or even while it's running) you can grab the valgrind
   371 output file:
   372 
   373     adb pull /sdcard/valgrind.log
   374 
   375 When you're done instrumenting with valgrind, you can disable the wrapper:
   376 
   377     adb shell setprop wrap.org.libsdl.app ""
   378 
   379 
   380 ================================================================================
   381  Graphics debugging
   382 ================================================================================
   383 
   384 If you are developing on a compatible Tegra-based tablet, NVidia provides
   385 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
   386 and GLES libraries, you must follow their instructions for installing the
   387 interposer library on a rooted device. The non-rooted instructions are not
   388 compatible with applications that use SDL2 for video.
   389 
   390 The Tegra Graphics Debugger is available from NVidia here:
   391 https://developer.nvidia.com/tegra-graphics-debugger
   392 
   393 
   394 ================================================================================
   395  Why is API level 14 the minimum required?
   396 ================================================================================
   397 
   398 The latest NDK toolchain doesn't support targeting earlier than API level 14.
   399 As of this writing, according to https://developer.android.com/about/dashboards/index.html
   400 about 99% of the Android devices accessing Google Play support API level 14 or
   401 higher (October 2017).
   402 
   403 
   404 ================================================================================
   405  A note regarding the use of the "dirty rectangles" rendering technique
   406 ================================================================================
   407 
   408 If your app uses a variation of the "dirty rectangles" rendering technique,
   409 where you only update a portion of the screen on each frame, you may notice a
   410 variety of visual glitches on Android, that are not present on other platforms.
   411 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   412 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   413 documentation for the function "The contents of ancillary buffers are always 
   414 undefined after calling eglSwapBuffers".
   415 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   416 is not possible for SDL as it requires EGL 1.4, available only on the API level
   417 17+, so the only workaround available on this platform is to redraw the entire
   418 screen each frame.
   419 
   420 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
   421 
   422 
   423 ================================================================================
   424  Known issues
   425 ================================================================================
   426 
   427 - The number of buttons reported for each joystick is hardcoded to be 36, which
   428 is the current maximum number of buttons Android can report.
   429