README-android.txt
author Gabriel Jacobo <gabomdq@gmail.com>
Wed, 09 Oct 2013 10:29:01 -0300
changeset 7793 6463a850229d
parent 7501 b27825bb5879
child 7804 1f85fb33694b
permissions -rw-r--r--
Adds test framework to Android.mk and a simple utility to build Android projects
     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  Customizing your application name
   115 ================================================================================
   116 
   117 To customize your application name, edit AndroidManifest.xml and replace
   118 "org.libsdl.app" with an identifier for your product package.
   119 
   120 Then create a Java class extending SDLActivity and place it in a directory
   121 under src matching your package, e.g.
   122 	src/com/gamemaker/game/MyGame.java
   123 
   124 Here's an example of a minimal class file:
   125 --- MyGame.java --------------------------
   126 package com.gamemaker.game;
   127 
   128 import org.libsdl.app.SDLActivity; 
   129 
   130 /* 
   131  * A sample wrapper class that just calls SDLActivity 
   132  */ 
   133 
   134 public class MyGame extends SDLActivity { }
   135 
   136 ------------------------------------------
   137 
   138 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   139 class, .e.g. "MyGame"
   140 
   141 ================================================================================
   142  Customizing your application icon
   143 ================================================================================
   144 
   145 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   146 the drawable directories under the res directory. There are four directories for
   147 different screen sizes. These can be replaced with one dir called "drawable",
   148 containing an icon file "ic_launcher.png" with dimensions 48x48 or 72x72.
   149 
   150 You may need to change the name of your icon in AndroidManifest.xml to match
   151 this icon filename.
   152 
   153 ================================================================================
   154  Loading assets
   155 ================================================================================
   156 
   157 Any files you put in the "assets" directory of your android-project directory
   158 will get bundled into the application package and you can load them using the
   159 standard functions in SDL_rwops.h.
   160 
   161 There are also a few Android specific functions that allow you to get other
   162 useful paths for saving and loading data:
   163 SDL_AndroidGetInternalStoragePath()
   164 SDL_AndroidGetExternalStorageState()
   165 SDL_AndroidGetExternalStoragePath()
   166 
   167 See SDL_system.h for more details on these functions.
   168 
   169 The asset packaging system will, by default, compress certain file extensions.
   170 SDL includes two asset file access mechanisms, the preferred one is the so
   171 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   172 GC, but given this method does not work on compressed assets, there is also the
   173 "Input Stream" method, which is automatically used as a fall back by SDL. You
   174 may want to keep this fact in mind when building your APK, specially when large
   175 files are involved.
   176 For more information on which extensions get compressed by default and how to
   177 disable this behaviour, see for example:
   178     
   179 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
   180 
   181 ================================================================================
   182  Pause / Resume behaviour
   183 ================================================================================
   184 
   185 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   186 the event loop will block itself when the app is paused (ie, when the user
   187 returns to the main Android dashboard). Blocking is better in terms of battery
   188 use, and it allows your app to spring back to life instantaneously after resume
   189 (versus polling for a resume message).
   190 
   191 Upon resume, SDL will attempt to restore the GL context automatically.
   192 In modern devices (Android 3.0 and up) this will most likely succeed and your
   193 app can continue to operate as it was.
   194 
   195 However, there's a chance (on older hardware, or on systems under heavy load),
   196 where the GL context can not be restored. In that case you have to listen for
   197 a specific message, (which is not yet implemented!) and restore your textures
   198 manually or quit the app (which is actually the kind of behaviour you'll see
   199 under iOS, if the OS can not restore your GL context it will just kill your app)
   200 
   201 ================================================================================
   202  Threads and the Java VM
   203 ================================================================================
   204 
   205 For a quick tour on how Linux native threads interoperate with the Java VM, take
   206 a look here: http://developer.android.com/guide/practices/jni.html
   207 If you want to use threads in your SDL app, it's strongly recommended that you
   208 do so by creating them using SDL functions. This way, the required attach/detach
   209 handling is managed by SDL automagically. If you have threads created by other
   210 means and they make calls to SDL functions, make sure that you call
   211 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   212 your thread automatically anyway (when you make an SDL call), but it'll never
   213 detach it.
   214 
   215 ================================================================================
   216  Using STL
   217 ================================================================================
   218 
   219 You can use STL in your project by creating an Application.mk file in the jni
   220 folder and adding the following line:
   221 APP_STL := stlport_static
   222 
   223 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   224 
   225 ================================================================================
   226  Additional documentation
   227 ================================================================================
   228 
   229 The documentation in the NDK docs directory is very helpful in understanding the
   230 build process and how to work with native code on the Android platform.
   231 
   232 The best place to start is with docs/OVERVIEW.TXT
   233 
   234 
   235 ================================================================================
   236  Using Eclipse
   237 ================================================================================
   238 
   239 First make sure that you've installed Eclipse and the Android extensions as described here:
   240 	http://developer.android.com/sdk/eclipse-adt.html
   241 
   242 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   243  * File -> New -> Other
   244  * Select the Android -> Android Project wizard and click Next
   245  * Enter the name you'd like your project to have
   246  * Select "Create project from existing source" and browse for your project directory
   247  * Make sure the Build Target is set to Android 2.0
   248  * Click Finish
   249 
   250 
   251 ================================================================================
   252  Using the emulator
   253 ================================================================================
   254 
   255 There are some good tips and tricks for getting the most out of the
   256 emulator here: http://developer.android.com/tools/devices/emulator.html
   257 
   258 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   259 
   260 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   261 Using a real device works better.
   262 
   263 ================================================================================
   264  Troubleshooting
   265 ================================================================================
   266 
   267 You can create and run an emulator from the Eclipse IDE:
   268  * Window -> Android SDK and AVD Manager
   269 
   270 You can see if adb can see any devices with the following command:
   271 	adb devices
   272 
   273 You can see the output of log messages on the default device with:
   274 	adb logcat
   275 
   276 You can push files to the device with:
   277 	adb push local_file remote_path_and_file
   278 
   279 You can push files to the SD Card at /sdcard, for example:
   280 	adb push moose.dat /sdcard/moose.dat
   281 
   282 You can see the files on the SD card with a shell command:
   283 	adb shell ls /sdcard/
   284 
   285 You can start a command shell on the default device with:
   286 	adb shell
   287 
   288 You can remove the library files of your project (and not the SDL lib files) with:
   289 	ndk-build clean
   290 
   291 You can do a build with the following command:
   292 	ndk-build
   293 
   294 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   295 	ndk-build V=1
   296 
   297 If your application crashes in native code, you can use addr2line to convert the
   298 addresses in the stack trace to lines in your code.
   299 
   300 For example, if your crash looks like this:
   301 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   302 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   303 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   304 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   305 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   306 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   307 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   308 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   309 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   310 
   311 You can see that there's a crash in the C library being called from the main code.
   312 I run addr2line with the debug version of my code:
   313 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   314 and then paste in the number after "pc" in the call stack, from the line that I care about:
   315 000014bc
   316 
   317 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   318 
   319 You can add logging to your code to help show what's happening:
   320 
   321 #include <android/log.h>
   322 
   323 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   324 
   325 If you need to build without optimization turned on, you can create a file called
   326 "Application.mk" in the jni directory, with the following line in it:
   327 APP_OPTIM := debug
   328 
   329 
   330 ================================================================================
   331  Memory debugging
   332 ================================================================================
   333 
   334 The best (and slowest) way to debug memory issues on Android is valgrind.
   335 Valgrind has support for Android out of the box, just grab code using:
   336 	svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   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 --- start_valgrind_app -------------------
   346 #!/system/bin/sh
   347 export TMPDIR=/data/data/org.libsdl.app
   348 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   349 ------------------------------------------
   350 
   351 Then push it to the device:
   352 	adb push start_valgrind_app /data/local
   353 
   354 and make it executable:
   355 	adb shell chmod 755 /data/local/start_valgrind_app
   356 
   357 and tell Android to use the script to launch your application:
   358 	adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   359 
   360 If the setprop command says "could not set property", it's likely that
   361 your package name is too long and you should make it shorter by changing
   362 AndroidManifest.xml and the path to your class file in android-project/src
   363 
   364 You can then launch your application normally and waaaaaaaiiittt for it.
   365 You can monitor the startup process with the logcat command above, and
   366 when it's done (or even while it's running) you can grab the valgrind
   367 output file:
   368 	adb pull /sdcard/valgrind.log
   369 
   370 When you're done instrumenting with valgrind, you can disable the wrapper:
   371 	adb shell setprop wrap.org.libsdl.app ""
   372 
   373 ================================================================================
   374  Why is API level 10 the minimum required?
   375 ================================================================================
   376 
   377 API level 10 is required because SDL requires some functionality for running not
   378 available on older devices and some for building which is not in older NDK/SDKs.
   379 
   380 Support for native OpenGL ES and ES2 applications was introduced in the NDK for
   381 API level 4 and 8. EGL was made a stable API in the NDK for API level 9, which
   382 has since then been obsoleted, with the recommendation to developers to bump the
   383 required API level to 10.
   384 As of this writing, according to http://developer.android.com/about/dashboards/index.html
   385 about 90% of the Android devices accessing Google Play support API level 10 or
   386 higher (March 2013).
   387 
   388 ================================================================================
   389  A note regarding the use of the "dirty rectangles" rendering technique
   390 ================================================================================
   391 
   392 If your app uses a variation of the "dirty rectangles" rendering technique,
   393 where you only update a portion of the screen on each frame, you may notice a
   394 variety of visual glitches on Android, that are not present on other platforms.
   395 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   396 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   397 documentation for the function "The contents of ancillary buffers are always 
   398 undefined after calling eglSwapBuffers".
   399 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   400 is not possible for SDL as it requires EGL 1.4, available only on the API level
   401 17+, so the only workaround available on this platform is to redraw the entire
   402 screen each frame.
   403 
   404 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
   405 
   406 ================================================================================
   407  Known issues
   408 ================================================================================
   409 
   410 - TODO. I'm sure there's a bunch more stuff I haven't thought of