README.android
author Sam Lantinga <slouken@libsdl.org>
Wed, 07 Nov 2012 20:17:27 -0800
changeset 6664 2deb17aefbaf
parent 6657 35de500cc918
child 6678 afb9be20f8d2
permissions -rw-r--r--
Improved default behavior for pause/resume on Android
     1 ================================================================================
     2 Simple DirectMedia Layer for Android
     3 ================================================================================
     4 
     5 Requirements:
     6 
     7 Android SDK
     8 http://developer.android.com/sdk/index.html
     9 
    10 Android NDK r4 or later
    11 http://developer.android.com/sdk/ndk/index.html
    12 
    13 
    14 ================================================================================
    15  How the port works
    16 ================================================================================
    17 
    18 - Android applications are Java-based, optionally with parts written in C
    19 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    20 the SDL library
    21 - This means that your application C code must be placed inside an android 
    22 Java project, along with some C support code that communicates with Java
    23 - This eventually produces a standard Android .apk package
    24 
    25 The Android Java code implements an "activity" and can be found in:
    26 android-project/src/org/libsdl/app/SDLActivity.java
    27 
    28 The Java code loads your game code, the SDL shared library, and
    29 dispatches to native functions implemented in the SDL library:
    30 src/SDL_android.cpp
    31 
    32 Your project must include some glue code that starts your main() routine:
    33 src/main/android/SDL_android_main.cpp
    34 
    35 
    36 ================================================================================
    37  Building an app
    38 ================================================================================
    39 
    40 Instructions:
    41 1. Copy the android-project directory wherever you want to keep your projects and rename it to the name of your project.
    42 2. Move or symlink this SDL directory into the <project>/jni directory
    43 3. Edit <project>/jni/src/Android.mk to include your source files
    44 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    45 
    46 If you want to use the Eclipse IDE, skip to the Eclipse section below.
    47 
    48 5. Edit <project>/local.properties to point to the Android SDK directory
    49 6. Run 'ant debug' in android/project. This compiles the .java and eventually 
    50 creates a .apk with the native code embedded
    51 7. 'ant debug install' will push the apk to the device or emulator (if connected)
    52 
    53 Here's an explanation of the files in the Android project, so you can customize them:
    54 
    55 android-project/
    56 	AndroidManifest.xml	- package manifest, customize this for your app
    57 	build.properties	- empty
    58 	build.xml		- build description file, used by ant
    59 	default.properties	- holds the ABI for the application, currently android-5 which corresponds to the Android 2.0 system image
    60 	local.properties	- holds the SDK path, you should change this to the path to your SDK
    61 	jni/			- directory holding native code
    62 	jni/Android.mk		- Android makefile that includes all subdirectories
    63 	jni/SDL/		- directory holding the SDL library files
    64 	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
    65 	jni/src/		- directory holding your C/C++ source
    66 	jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
    67 	res/			- directory holding resources for your application
    68 	res/drawable-*		- directories holding icons for different phone hardware
    69 	res/layout/main.xml	- place holder for the main screen layout, overridden by the SDL video output
    70 	res/values/strings.xml	- strings used in your application, including the application name shown on the phone.
    71 	src/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.
    72 
    73 
    74 ================================================================================
    75  Customizing your application name
    76 ================================================================================
    77 
    78 To customize your application name, edit AndroidManifest.xml and replace
    79 "org.libsdl.app" with an identifier for your product package.
    80 
    81 Then create a Java class extending SDLActivity and place it in a directory
    82 under src matching your package, e.g.
    83 	src/com/gamemaker/game/MyGame.java
    84 
    85 Here's an example of a minimal class file:
    86 --- MyGame.java --------------------------
    87 package com.gamemaker.game;
    88 
    89 import org.libsdl.app.SDLActivity; 
    90 import android.os.*; 
    91 
    92 /* 
    93  * A sample wrapper class that just calls SDLActivity 
    94  */ 
    95 
    96 public class MyGame extends SDLActivity { 
    97     protected void onCreate(Bundle savedInstanceState) { 
    98 	super.onCreate(savedInstanceState); 
    99     } 
   100    
   101     protected void onDestroy() { 
   102 	super.onDestroy(); 
   103     } 
   104 }
   105 ------------------------------------------
   106 
   107 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   108 class, .e.g. "MyGame"
   109 
   110 ================================================================================
   111  Customizing your application icon
   112 ================================================================================
   113 
   114 Conceptually changing your icon is just replacing the icon.png files in the
   115 drawable directories under the res directory.
   116 
   117 The easiest way to create a set of icons for your project is to remove all
   118 the existing icon.png files, and then use the Eclipse IDE to create a dummy
   119 project.  During the process of doing this Eclipse will prompt you to create
   120 an icon. Then just copy the drawable directories it creates over to your
   121 res directory.
   122 
   123 You may need to change the name of your icon in AndroidManifest.xml to match
   124 the filename used by Eclipse.
   125 
   126 ================================================================================
   127  Loading assets
   128 ================================================================================
   129 
   130 Any files you put in the "assets" directory of your android-project directory
   131 will get bundled into the application package and you can load them using the
   132 standard functions in SDL_rwops.h.
   133 
   134 There are also a few Android specific functions that allow you to get other
   135 useful paths for saving and loading data:
   136 SDL_AndroidGetInternalStoragePath()
   137 SDL_AndroidGetExternalStorageState()
   138 SDL_AndroidGetExternalStoragePath()
   139 
   140 See SDL_system.h for more details on these functions.
   141 
   142 ================================================================================
   143  Pause / Resume behaviour
   144 ================================================================================
   145 
   146 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   147 the event loop will block itself when the app is paused (ie, when the user
   148 returns to the main Android dashboard). Blocking is better in terms of battery
   149 use, and it allows your app to spring back to life instantaneously after resume
   150 (versus polling for a resume message).
   151 
   152 Upon resume, SDL will attempt to restore the GL context automatically.
   153 In modern devices (Android 3.0 and up) this will most likely succeed and your
   154 app can continue to operate as it was.
   155 
   156 However, there's a chance (on older hardware, or on systems under heavy load),
   157 where the GL context can not be restored. In that case you have to listen for
   158 a specific message, (which is not yet implemented!) and restore your textures
   159 manually or quit the app (which is actually the kind of behaviour you'll see
   160 under iOS, if the OS can not restore your GL context it will just kill your app)
   161 
   162 ================================================================================
   163  Threads and the JAVA VM
   164 ================================================================================
   165 
   166 For a quick tour on how Linux native threads interoperate with the JAVA VM, take
   167 a look here: http://developer.android.com/guide/practices/jni.html
   168 If you want to use threads in your SDL app, it's strongly recommended that you
   169 do so by creating them using SDL functions. This way, the required attach/detach
   170 handling is managed by SDL automagically. If you have threads created by other
   171 means and they make calls to SDL functions, make sure that you call
   172 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   173 your thread automatically anyway (when you make an SDL call), but it'll never
   174 detach it.
   175 
   176 ================================================================================
   177  Using STL
   178 ================================================================================
   179 
   180 You can use STL in your project by creating an Application.mk file in the jni
   181 folder and adding the following line:
   182 APP_STL := stlport_static
   183 
   184 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   185 
   186 ================================================================================
   187  Additional documentation
   188 ================================================================================
   189 
   190 The documentation in the NDK docs directory is very helpful in understanding the build process and how to work with native code on the Android platform.
   191 
   192 The best place to start is with docs/OVERVIEW.TXT
   193 
   194 
   195 ================================================================================
   196  Using Eclipse
   197 ================================================================================
   198 
   199 First make sure that you've installed Eclipse and the Android extensions as described here:
   200 	http://developer.android.com/sdk/eclipse-adt.html
   201 
   202 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   203  * File -> New -> Other
   204  * Select the Android -> Android Project wizard and click Next
   205  * Enter the name you'd like your project to have
   206  * Select "Create project from existing source" and browse for your project directory
   207  * Make sure the Build Target is set to Android 2.0
   208  * Click Finish
   209 
   210 
   211 ================================================================================
   212  Using the emulator
   213 ================================================================================
   214 
   215 There are some good tips and tricks for getting the most out of the
   216 emulator here: http://developer.android.com/tools/devices/emulator.html
   217 
   218 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   219 
   220 
   221 ================================================================================
   222  Troubleshooting
   223 ================================================================================
   224 
   225 You can create and run an emulator from the Eclipse IDE:
   226  * Window -> Android SDK and AVD Manager
   227 
   228 You can see if adb can see any devices with the following command:
   229 	adb devices
   230 
   231 You can see the output of log messages on the default device with:
   232 	adb logcat
   233 
   234 You can push files to the device with:
   235 	adb push local_file remote_path_and_file
   236 
   237 You can push files to the SD Card at /sdcard, for example:
   238 	adb push moose.dat /sdcard/moose.dat
   239 
   240 You can see the files on the SD card with a shell command:
   241 	adb shell ls /sdcard/
   242 
   243 You can start a command shell on the default device with:
   244 	adb shell
   245 
   246 You can do a clean build with the following commands:
   247 	ndk-build clean
   248 	ndk-build
   249 
   250 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   251 	ndk-build V=1
   252 
   253 If your application crashes in native code, you can use addr2line to convert the addresses in the stack trace to lines in your code.
   254 
   255 For example, if your crash looks like this:
   256 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   257 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   258 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   259 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   260 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   261 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   262 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   263 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   264 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   265 
   266 You can see that there's a crash in the C library being called from the main code.  I run addr2line with the debug version of my code:
   267 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   268 and then paste in the number after "pc" in the call stack, from the line that I care about:
   269 000014bc
   270 
   271 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   272 
   273 You can add logging to your code to help show what's happening:
   274 
   275 #include <android/log.h>
   276 
   277 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   278 
   279 If you need to build without optimization turned on, you can create a file called "Application.mk" in the jni directory, with the following line in it:
   280 APP_OPTIM := debug
   281 
   282 
   283 ================================================================================
   284  Memory debugging
   285 ================================================================================
   286 
   287 The best (and slowest) way to debug memory issues on Android is valgrind.
   288 Valgrind has support for Android out of the box, just grab code using:
   289 	svn co svn://svn.valgrind.org/valgrind/trunk valgrind
   290 ... and follow the instructions in the file README.android to build it.
   291 
   292 One thing I needed to do on Mac OS X was change the path to the toolchain,
   293 and add ranlib to the environment variables:
   294 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   295 
   296 Once valgrind is built, you can create a wrapper script to launch your
   297 application with it, changing org.libsdl.app to your package identifier:
   298 --- start_valgrind_app -------------------
   299 #!/system/bin/sh
   300 export TMPDIR=/data/data/org.libsdl.app
   301 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   302 ------------------------------------------
   303 
   304 Then push it to the device:
   305 	adb push start_valgrind_app /data/local
   306 
   307 and make it executable:
   308 	adb shell chmod 755 /data/local/start_valgrind_app
   309 
   310 and tell Android to use the script to launch your application:
   311 	adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
   312 
   313 If the setprop command says "could not set property", it's likely that
   314 your package name is too long and you should make it shorter by changing
   315 AndroidManifest.xml and the path to your class file in android-project/src
   316 
   317 You can then launch your application normally and waaaaaaaiiittt for it.
   318 You can monitor the startup process with the logcat command above, and
   319 when it's done (or even while it's running) you can grab the valgrind
   320 output file:
   321 	adb pull /sdcard/valgrind.log
   322 
   323 When you're done instrumenting with valgrind, you can disable the wrapper:
   324 	adb shell setprop wrap.org.libsdl.app ""
   325 
   326 
   327 ================================================================================
   328  Known issues
   329 ================================================================================
   330 
   331 - SDL audio (although it's mostly written, just not working properly yet)
   332 - TODO. I'm sure there's a bunch more stuff I haven't thought of