README.android
author Gabriel Jacobo <gabomdq@gmail.com>
Mon, 09 Jul 2012 18:08:06 -0300
changeset 6354 17840f487124
parent 6330 0fa55ca2efdd
child 6387 58f0fb54bf88
permissions -rw-r--r--
Fixes #1422, removes global JNI Env, uses per thread copies, adds thread auto detaching.
     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 this SDL directory into the <project>/jni directory and then copy
    43 SDL_config_android.h to SDL_config.h inside the include folder
    44 3. Place your application source files in the <project>/jni/src directory
    45 4. Edit <project>/jni/src/Android.mk to include your source files
    46 5. 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 6. Edit <project>/local.properties to point to the Android SDK directory
    51 7. Run 'ant debug' in android/project. This compiles the .java and eventually 
    52 creates a .apk with the native code embedded
    53 8. 'ant install' will push the apk to the device or emulator (if connected)
    54 
    55 Here's an explanation of the files in the Android project, so you can customize them:
    56 
    57 android-project/
    58 	AndroidManifest.xml	- package manifest, do not modify
    59 	build.properties	- empty
    60 	build.xml		- build description file, used by ant
    61 	default.properties	- holds the ABI for the application, currently android-4 which corresponds to the Android 1.6 system image
    62 	local.properties	- holds the SDK path, you should change this to the path to your SDK
    63 	jni/			- directory holding native code
    64 	jni/Android.mk		- Android makefile that includes all subdirectories
    65 	jni/SDL/		- directory holding the SDL library files
    66 	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
    67 	jni/src/		- directory holding your C/C++ source
    68 	jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
    69 	res/			- directory holding resources for your application
    70 	res/drawable-*		- directories holding icons for different phone hardware
    71 	res/layout/main.xml	- place holder for the main screen layout, overridden by the SDL video output
    72 	res/values/strings.xml	- strings used in your application, including the application name shown on the phone.
    73 	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.
    74 
    75 
    76 ================================================================================
    77  Pause / Resume behaviour
    78 ================================================================================
    79 
    80 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined, the event loop will
    81 block itself when the app is paused (ie, when the user returns to the main
    82 Android dashboard). Blocking is better in terms of battery use, and it allows your
    83 app to spring back to life instantaneously after resume (versus polling for
    84 a resume message).
    85 Upon resume, SDL will attempt to restore the GL context automatically.
    86 In modern devices (Android 3.0 and up) this will most likely succeed and your
    87 app can continue to operate as it was.
    88 However, there's a chance (on older hardware, or on systems under heavy load),
    89 where the GL context can not be restored. In that case you have to listen for
    90 a specific message, (which is not yet implemented!) and restore your textures
    91 manually or quit the app (which is actually the kind of behaviour you'll see
    92 under iOS, if the OS can not restore your GL context it will just kill your app)
    93 
    94 ================================================================================
    95  Threads and the JAVA VM
    96 ================================================================================
    97 
    98 For a quick tour on how Linux native threads interoperate with the JAVA VM, take
    99 a look here: http://developer.android.com/guide/practices/jni.html
   100 If you want to use threads in your SDL app, it's strongly recommended that you
   101 do so by creating them using SDL functions. This way, the required attach/detach
   102 handling is managed by SDL automagically. If you have threads created by other
   103 means and they make calls to SDL functions, make sure that you call
   104 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   105 your thread automatically anyway (when you make an SDL call), but it'll never
   106 detach it.
   107 
   108 ================================================================================
   109  Additional documentation
   110 ================================================================================
   111 
   112 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.
   113 
   114 The best place to start is with docs/OVERVIEW.TXT
   115 
   116 
   117 ================================================================================
   118  Using Eclipse
   119 ================================================================================
   120 
   121 First make sure that you've installed Eclipse and the Android extensions as described here:
   122 	http://developer.android.com/sdk/eclipse-adt.html
   123 
   124 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   125  * File -> New -> Other
   126  * Select the Android -> Android Project wizard and click Next
   127  * Enter the name you'd like your project to have
   128  * Select "Create project from existing source" and browse for your project directory
   129  * Make sure the Build Target is set to Android 1.6
   130  * Click Finish
   131 
   132 
   133 ================================================================================
   134  Loading files and resources
   135 ================================================================================
   136 
   137 NEED CONTENT
   138 
   139 
   140 ================================================================================
   141  Troubleshooting
   142 ================================================================================
   143 
   144 You can create and run an emulator from the Eclipse IDE:
   145  * Window -> Android SDK and AVD Manager
   146 
   147 You can see if adb can see any devices with the following command:
   148 	adb devices
   149 
   150 You can see the output of log messages on the default device with:
   151 	adb logcat
   152 
   153 You can push files to the device with:
   154 	adb push local_file remote_path_and_file
   155 
   156 You can push files to the SD Card at /sdcard, for example:
   157 	adb push moose.dat /sdcard/moose.dat
   158 
   159 You can see the files on the SD card with a shell command:
   160 	adb shell ls /sdcard/
   161 
   162 You can start a command shell on the default device with:
   163 	adb shell
   164 
   165 You can do a clean build with the following commands:
   166 	ndk-build clean
   167 	ndk-build
   168 
   169 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   170 	ndk-build V=1
   171 
   172 If your application crashes in native code, you can use addr2line to convert the addresses in the stack trace to lines in your code.
   173 
   174 For example, if your crash looks like this:
   175 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   176 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   177 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   178 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   179 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   180 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   181 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   182 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   183 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   184 
   185 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:
   186 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   187 and then paste in the number after "pc" in the call stack, from the line that I care about:
   188 000014bc
   189 
   190 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   191 
   192 You can add logging to your code to help show what's happening:
   193 
   194 #include <android/log.h>
   195 
   196 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   197 
   198 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:
   199 APP_OPTIM := debug
   200 
   201 
   202 ================================================================================
   203  Known issues
   204 ================================================================================
   205 
   206 - SDL audio (although it's mostly written, just not working properly yet)
   207 - TODO. I'm sure there's a bunch more stuff I haven't thought of