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