README.android
author Sam Lantinga <slouken@libsdl.org>
Sun, 04 Nov 2012 09:45:18 -0800
changeset 6646 dd32cce44d3c
parent 6631 47ab7ba21530
child 6650 d36232135316
permissions -rw-r--r--
Added documentation on loading assets 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 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, do not modify
    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 event loop will
   147 block itself when the app is paused (ie, when the user returns to the main
   148 Android dashboard). Blocking is better in terms of battery use, and it allows your
   149 app to spring back to life instantaneously after resume (versus polling for
   150 a resume message).
   151 Upon resume, SDL will attempt to restore the GL context automatically.
   152 In modern devices (Android 3.0 and up) this will most likely succeed and your
   153 app can continue to operate as it was.
   154 However, there's a chance (on older hardware, or on systems under heavy load),
   155 where the GL context can not be restored. In that case you have to listen for
   156 a specific message, (which is not yet implemented!) and restore your textures
   157 manually or quit the app (which is actually the kind of behaviour you'll see
   158 under iOS, if the OS can not restore your GL context it will just kill your app)
   159 
   160 ================================================================================
   161  Threads and the JAVA VM
   162 ================================================================================
   163 
   164 For a quick tour on how Linux native threads interoperate with the JAVA VM, take
   165 a look here: http://developer.android.com/guide/practices/jni.html
   166 If you want to use threads in your SDL app, it's strongly recommended that you
   167 do so by creating them using SDL functions. This way, the required attach/detach
   168 handling is managed by SDL automagically. If you have threads created by other
   169 means and they make calls to SDL functions, make sure that you call
   170 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   171 your thread automatically anyway (when you make an SDL call), but it'll never
   172 detach it.
   173 
   174 ================================================================================
   175  Using STL
   176 ================================================================================
   177 
   178 You can use STL in your project by creating an Application.mk file in the jni
   179 folder and adding the following line:
   180 APP_STL := stlport_static
   181 
   182 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   183 
   184 ================================================================================
   185  Additional documentation
   186 ================================================================================
   187 
   188 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.
   189 
   190 The best place to start is with docs/OVERVIEW.TXT
   191 
   192 
   193 ================================================================================
   194  Using Eclipse
   195 ================================================================================
   196 
   197 First make sure that you've installed Eclipse and the Android extensions as described here:
   198 	http://developer.android.com/sdk/eclipse-adt.html
   199 
   200 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   201  * File -> New -> Other
   202  * Select the Android -> Android Project wizard and click Next
   203  * Enter the name you'd like your project to have
   204  * Select "Create project from existing source" and browse for your project directory
   205  * Make sure the Build Target is set to Android 2.0
   206  * Click Finish
   207 
   208 
   209 ================================================================================
   210  Loading files and resources
   211 ================================================================================
   212 
   213 NEED CONTENT
   214 
   215 
   216 ================================================================================
   217  Troubleshooting
   218 ================================================================================
   219 
   220 You can create and run an emulator from the Eclipse IDE:
   221  * Window -> Android SDK and AVD Manager
   222 
   223 You can see if adb can see any devices with the following command:
   224 	adb devices
   225 
   226 You can see the output of log messages on the default device with:
   227 	adb logcat
   228 
   229 You can push files to the device with:
   230 	adb push local_file remote_path_and_file
   231 
   232 You can push files to the SD Card at /sdcard, for example:
   233 	adb push moose.dat /sdcard/moose.dat
   234 
   235 You can see the files on the SD card with a shell command:
   236 	adb shell ls /sdcard/
   237 
   238 You can start a command shell on the default device with:
   239 	adb shell
   240 
   241 You can do a clean build with the following commands:
   242 	ndk-build clean
   243 	ndk-build
   244 
   245 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   246 	ndk-build V=1
   247 
   248 If your application crashes in native code, you can use addr2line to convert the addresses in the stack trace to lines in your code.
   249 
   250 For example, if your crash looks like this:
   251 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   252 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   253 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   254 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   255 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   256 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
   257 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
   258 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
   259 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
   260 
   261 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:
   262 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
   263 and then paste in the number after "pc" in the call stack, from the line that I care about:
   264 000014bc
   265 
   266 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   267 
   268 You can add logging to your code to help show what's happening:
   269 
   270 #include <android/log.h>
   271 
   272 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   273 
   274 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:
   275 APP_OPTIM := debug
   276 
   277 
   278 ================================================================================
   279  Known issues
   280 ================================================================================
   281 
   282 - SDL audio (although it's mostly written, just not working properly yet)
   283 - TODO. I'm sure there's a bunch more stuff I haven't thought of