README-android.txt
author Sam Lantinga <slouken@libsdl.org>
Thu, 10 Oct 2013 21:51:39 -0700
changeset 7804 1f85fb33694b
parent 7793 6463a850229d
child 7907 24b4e98c6010
permissions -rw-r--r--
Fixed bug 2146 - Enable static linking of libSDL on Android

Denis Bernard

This patch to Android.mk adds support for static linking of libSDL for Android applications. A patched readme with static build instructions is also provided.

It does not break existing build environments setup according to the README-android.txt since the static library version will not be built in not required.

The static build uses the Android NDK module system (see docs/IMPORT-MODULE.html in the NDK folder and step 5 in the instructions below).

Instructions:
1. Copy the android-project directory wherever you want to keep your projects
and rename it to the name of your project.
2. Create a symlink to SDL/src/main/android/SDL_android_main.c as
<project>/jni/src/SDL_android_main.c
3. Rename <project>/jni/src/Android_static.mk to <project>/jni/src/Android.mk
(overwrite the existing one)
4. Edit <project>/jni/src/Android.mk to include your source files
5. create and export an environment variable named NDK_MODULE_PATH that points
to the parent directory of this SDL directory. e.g.:

export NDK_MODULE_PATH="$PWD"/..

6. Edit <project>/src/org/libsdl/app/SDLActivity.java and remove the call to
System.loadLibrary("SDL2") line 42.
7. Run 'ndk-build' (a script provided by the NDK). This compiles the C source

Although this requires an environment variable to be setup, it can be added once and for all to the main Android.mk of the project.
     1 ================================================================================
     2 Simple DirectMedia Layer for Android
     3 ================================================================================
     4 
     5 Requirements:
     6 
     7 Android SDK (version 10 or later)
     8 http://developer.android.com/sdk/index.html
     9 
    10 Android NDK r7 or later
    11 http://developer.android.com/sdk/ndk/index.html
    12 
    13 Minimum API level supported by SDL: 10 (Android 2.3.3)
    14 
    15 ================================================================================
    16  How the port works
    17 ================================================================================
    18 
    19 - Android applications are Java-based, optionally with parts written in C
    20 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    21 the SDL library
    22 - This means that your application C code must be placed inside an Android 
    23 Java project, along with some C support code that communicates with Java
    24 - This eventually produces a standard Android .apk package
    25 
    26 The Android Java code implements an "Activity" and can be found in:
    27 android-project/src/org/libsdl/app/SDLActivity.java
    28 
    29 The Java code loads your game code, the SDL shared library, and
    30 dispatches to native functions implemented in the SDL library:
    31 src/SDL_android.c
    32 
    33 Your project must include some glue code that starts your main() routine:
    34 src/main/android/SDL_android_main.c
    35 
    36 
    37 ================================================================================
    38  Building an app
    39 ================================================================================
    40 
    41 For simple projects you can use the script located at build-scripts/androidbuild.sh
    42 
    43 There's two ways of using it:
    44 
    45 androidbuild.sh com.yourcompany.yourapp < sources.list
    46 androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
    47 
    48 sources.list should be a text file with a source file name in each line
    49 Filenames should be specified relative to the current directory, for example if
    50 you are in the build-scripts directory and want to create the testgles.c test, you'll
    51 run:
    52     
    53 ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
    54 
    55 One limitation of this script is that all sources provided will be aggregated into
    56 a single directory, thus all your source files should have a unique name.
    57 
    58 Once the project is complete the script will tell you where the debug APK is located.
    59 If you want to create a signed release APK, you can use the project created by this
    60 utility to generate it.
    61 
    62 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
    63 done in the build directory for the app!
    64 
    65 
    66 For more complex projects, follow these instructions:
    67     
    68 1. Copy the android-project directory wherever you want to keep your projects
    69    and rename it to the name of your project.
    70 2. Move or symlink this SDL directory into the <project>/jni directory
    71 3. Edit <project>/jni/src/Android.mk to include your source files
    72 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    73 
    74 If you want to use the Eclipse IDE, skip to the Eclipse section below.
    75 
    76 5. Create <project>/local.properties and use that to point to the Android SDK directory, by writing a line with the following form:
    77 sdk.dir=PATH_TO_ANDROID_SDK
    78 6. Run 'ant debug' in android/project. This compiles the .java and eventually 
    79    creates a .apk with the native code embedded
    80 7. 'ant debug install' will push the apk to the device or emulator (if connected)
    81 
    82 Here's an explanation of the files in the Android project, so you can customize them:
    83 
    84 android-project/
    85 	AndroidManifest.xml	- package manifest. Among others, it contains the class name
    86 				  of the main Activity and the package name of the application.
    87 	build.properties	- empty
    88 	build.xml		- build description file, used by ant. The actual application name
    89 				  is specified here.
    90 	default.properties	- holds the target ABI for the application, android-10 and up
    91 	project.properties	- holds the target ABI for the application, android-10 and up
    92 	local.properties	- holds the SDK path, you should change this to the path to your SDK
    93 	jni/			- directory holding native code
    94 	jni/Android.mk		- Android makefile that can call recursively the Android.mk files
    95 				  in all subdirectories
    96 	jni/SDL/		- (symlink to) directory holding the SDL library files
    97 	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
    98 	jni/src/		- directory holding your C/C++ source
    99 	jni/src/Android.mk	- Android makefile that you should customize to include your 
   100                                   source code and any library references
   101 	res/			- directory holding resources for your application
   102 	res/drawable-*		- directories holding icons for different phone hardware. Could be
   103 				  one dir called "drawable".
   104 	res/layout/main.xml	- Usually contains a file main.xml, which declares the screen layout.
   105 				  We don't need it because we use the SDL video output.
   106 	res/values/strings.xml	- strings used in your application, including the application name
   107 				  shown on the phone.
   108 	src/org/libsdl/app/SDLActivity.java - the Java class handling the initialization and binding
   109 				  to SDL.  Be very careful changing this, as the SDL library relies
   110 				  on this implementation.
   111 
   112 
   113 ================================================================================
   114  Build an app with static linking of libSDL
   115 ================================================================================
   116 
   117 This build uses the Android NDK module system.
   118 
   119 Instructions:
   120 1. Copy the android-project directory wherever you want to keep your projects
   121    and rename it to the name of your project.
   122 2. Rename <project>/jni/src/Android_static.mk to <project>/jni/src/Android.mk
   123    (overwrite the existing one)
   124 3. Edit <project>/jni/src/Android.mk to include your source files
   125 4. create and export an environment variable named NDK_MODULE_PATH that points
   126    to the parent directory of this SDL directory. e.g.:
   127 
   128    export NDK_MODULE_PATH="$PWD"/..
   129 
   130 5. Edit <project>/src/org/libsdl/app/SDLActivity.java and remove the call to
   131    System.loadLibrary("SDL2") line 42.
   132 6. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
   133 
   134 
   135 ================================================================================
   136  Customizing your application name
   137 ================================================================================
   138 
   139 To customize your application name, edit AndroidManifest.xml and replace
   140 "org.libsdl.app" with an identifier for your product package.
   141 
   142 Then create a Java class extending SDLActivity and place it in a directory
   143 under src matching your package, e.g.
   144 	src/com/gamemaker/game/MyGame.java
   145 
   146 Here's an example of a minimal class file:
   147 --- MyGame.java --------------------------
   148 package com.gamemaker.game;
   149 
   150 import org.libsdl.app.SDLActivity; 
   151 
   152 /* 
   153  * A sample wrapper class that just calls SDLActivity 
   154  */ 
   155 
   156 public class MyGame extends SDLActivity { }
   157 
   158 ------------------------------------------
   159 
   160 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   161 class, .e.g. "MyGame"
   162 
   163 ================================================================================
   164  Customizing your application icon
   165 ================================================================================
   166 
   167 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   168 the drawable directories under the res directory. There are four directories for
   169 different screen sizes. These can be replaced with one dir called "drawable",
   170 containing an icon file "ic_launcher.png" with dimensions 48x48 or 72x72.
   171 
   172 You may need to change the name of your icon in AndroidManifest.xml to match
   173 this icon filename.
   174 
   175 ================================================================================
   176  Loading assets
   177 ================================================================================
   178 
   179 Any files you put in the "assets" directory of your android-project directory
   180 will get bundled into the application package and you can load them using the
   181 standard functions in SDL_rwops.h.
   182 
   183 There are also a few Android specific functions that allow you to get other
   184 useful paths for saving and loading data:
   185 SDL_AndroidGetInternalStoragePath()
   186 SDL_AndroidGetExternalStorageState()
   187 SDL_AndroidGetExternalStoragePath()
   188 
   189 See SDL_system.h for more details on these functions.
   190 
   191 The asset packaging system will, by default, compress certain file extensions.
   192 SDL includes two asset file access mechanisms, the preferred one is the so
   193 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   194 GC, but given this method does not work on compressed assets, there is also the
   195 "Input Stream" method, which is automatically used as a fall back by SDL. You
   196 may want to keep this fact in mind when building your APK, specially when large
   197 files are involved.
   198 For more information on which extensions get compressed by default and how to
   199 disable this behaviour, see for example:
   200     
   201 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
   202 
   203 ================================================================================
   204  Pause / Resume behaviour
   205 ================================================================================
   206 
   207 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   208 the event loop will block itself when the app is paused (ie, when the user
   209 returns to the main Android dashboard). Blocking is better in terms of battery
   210 use, and it allows your app to spring back to life instantaneously after resume
   211 (versus polling for a resume message).
   212 
   213 Upon resume, SDL will attempt to restore the GL context automatically.
   214 In modern devices (Android 3.0 and up) this will most likely succeed and your
   215 app can continue to operate as it was.
   216 
   217 However, there's a chance (on older hardware, or on systems under heavy load),
   218 where the GL context can not be restored. In that case you have to listen for
   219 a specific message, (which is not yet implemented!) and restore your textures
   220 manually or quit the app (which is actually the kind of behaviour you'll see
   221 under iOS, if the OS can not restore your GL context it will just kill your app)
   222 
   223 ================================================================================
   224  Threads and the Java VM
   225 ================================================================================
   226 
   227 For a quick tour on how Linux native threads interoperate with the Java VM, take
   228 a look here: http://developer.android.com/guide/practices/jni.html
   229 If you want to use threads in your SDL app, it's strongly recommended that you
   230 do so by creating them using SDL functions. This way, the required attach/detach
   231 handling is managed by SDL automagically. If you have threads created by other
   232 means and they make calls to SDL functions, make sure that you call
   233 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   234 your thread automatically anyway (when you make an SDL call), but it'll never
   235 detach it.
   236 
   237 ================================================================================
   238  Using STL
   239 ================================================================================
   240 
   241 You can use STL in your project by creating an Application.mk file in the jni
   242 folder and adding the following line:
   243 APP_STL := stlport_static
   244 
   245 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   246 
   247 ================================================================================
   248  Additional documentation
   249 ================================================================================
   250 
   251 The documentation in the NDK docs directory is very helpful in understanding the
   252 build process and how to work with native code on the Android platform.
   253 
   254 The best place to start is with docs/OVERVIEW.TXT
   255 
   256 
   257 ================================================================================
   258  Using Eclipse
   259 ================================================================================
   260 
   261 First make sure that you've installed Eclipse and the Android extensions as described here:
   262 	http://developer.android.com/sdk/eclipse-adt.html
   263 
   264 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   265  * File -> New -> Other
   266  * Select the Android -> Android Project wizard and click Next
   267  * Enter the name you'd like your project to have
   268  * Select "Create project from existing source" and browse for your project directory
   269  * Make sure the Build Target is set to Android 2.0
   270  * Click Finish
   271 
   272 
   273 ================================================================================
   274  Using the emulator
   275 ================================================================================
   276 
   277 There are some good tips and tricks for getting the most out of the
   278 emulator here: http://developer.android.com/tools/devices/emulator.html
   279 
   280 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   281 
   282 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   283 Using a real device works better.
   284 
   285 ================================================================================
   286  Troubleshooting
   287 ================================================================================
   288 
   289 You can create and run an emulator from the Eclipse IDE:
   290  * Window -> Android SDK and AVD Manager
   291 
   292 You can see if adb can see any devices with the following command:
   293 	adb devices
   294 
   295 You can see the output of log messages on the default device with:
   296 	adb logcat
   297 
   298 You can push files to the device with:
   299 	adb push local_file remote_path_and_file
   300 
   301 You can push files to the SD Card at /sdcard, for example:
   302 	adb push moose.dat /sdcard/moose.dat
   303 
   304 You can see the files on the SD card with a shell command:
   305 	adb shell ls /sdcard/
   306 
   307 You can start a command shell on the default device with:
   308 	adb shell
   309 
   310 You can remove the library files of your project (and not the SDL lib files) with:
   311 	ndk-build clean
   312 
   313 You can do a build with the following command:
   314 	ndk-build
   315 
   316 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   317 	ndk-build V=1
   318 
   319 If your application crashes in native code, you can use addr2line to convert the
   320 addresses in the stack trace to lines in your code.
   321 
   322 For example, if your crash looks like this:
   323 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   324 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   325 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   326 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   327 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   328 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   329 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   330 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   331 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   332 
   333 You can see that there's a crash in the C library being called from the main code.
   334 I run addr2line with the debug version of my code:
   335 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   336 and then paste in the number after "pc" in the call stack, from the line that I care about:
   337 000014bc
   338 
   339 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   340 
   341 You can add logging to your code to help show what's happening:
   342 
   343 #include <android/log.h>
   344 
   345 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   346 
   347 If you need to build without optimization turned on, you can create a file called
   348 "Application.mk" in the jni directory, with the following line in it:
   349 APP_OPTIM := debug
   350 
   351 
   352 ================================================================================
   353  Memory debugging
   354 ================================================================================
   355 
   356 The best (and slowest) way to debug memory issues on Android is valgrind.
   357 Valgrind has support for Android out of the box, just grab code using:
   358 	svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   359 ... and follow the instructions in the file README.android to build it.
   360 
   361 One thing I needed to do on Mac OS X was change the path to the toolchain,
   362 and add ranlib to the environment variables:
   363 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   364 
   365 Once valgrind is built, you can create a wrapper script to launch your
   366 application with it, changing org.libsdl.app to your package identifier:
   367 --- start_valgrind_app -------------------
   368 #!/system/bin/sh
   369 export TMPDIR=/data/data/org.libsdl.app
   370 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   371 ------------------------------------------
   372 
   373 Then push it to the device:
   374 	adb push start_valgrind_app /data/local
   375 
   376 and make it executable:
   377 	adb shell chmod 755 /data/local/start_valgrind_app
   378 
   379 and tell Android to use the script to launch your application:
   380 	adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   381 
   382 If the setprop command says "could not set property", it's likely that
   383 your package name is too long and you should make it shorter by changing
   384 AndroidManifest.xml and the path to your class file in android-project/src
   385 
   386 You can then launch your application normally and waaaaaaaiiittt for it.
   387 You can monitor the startup process with the logcat command above, and
   388 when it's done (or even while it's running) you can grab the valgrind
   389 output file:
   390 	adb pull /sdcard/valgrind.log
   391 
   392 When you're done instrumenting with valgrind, you can disable the wrapper:
   393 	adb shell setprop wrap.org.libsdl.app ""
   394 
   395 ================================================================================
   396  Why is API level 10 the minimum required?
   397 ================================================================================
   398 
   399 API level 10 is required because SDL requires some functionality for running not
   400 available on older devices and some for building which is not in older NDK/SDKs.
   401 
   402 Support for native OpenGL ES and ES2 applications was introduced in the NDK for
   403 API level 4 and 8. EGL was made a stable API in the NDK for API level 9, which
   404 has since then been obsoleted, with the recommendation to developers to bump the
   405 required API level to 10.
   406 As of this writing, according to http://developer.android.com/about/dashboards/index.html
   407 about 90% of the Android devices accessing Google Play support API level 10 or
   408 higher (March 2013).
   409 
   410 ================================================================================
   411  A note regarding the use of the "dirty rectangles" rendering technique
   412 ================================================================================
   413 
   414 If your app uses a variation of the "dirty rectangles" rendering technique,
   415 where you only update a portion of the screen on each frame, you may notice a
   416 variety of visual glitches on Android, that are not present on other platforms.
   417 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   418 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   419 documentation for the function "The contents of ancillary buffers are always 
   420 undefined after calling eglSwapBuffers".
   421 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   422 is not possible for SDL as it requires EGL 1.4, available only on the API level
   423 17+, so the only workaround available on this platform is to redraw the entire
   424 screen each frame.
   425 
   426 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
   427 
   428 ================================================================================
   429  Known issues
   430 ================================================================================
   431 
   432 - TODO. I'm sure there's a bunch more stuff I haven't thought of