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 Simple DirectMedia Layer for Android

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 Requirements:

 Android SDK

 http://developer.android.com/sdk/index.html

 Android NDK r4 or later

 http://developer.android.com/sdk/ndk/index.html

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  How the port works

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 - Android applications are Java-based, optionally with parts written in C

 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 

 the SDL library

 - This means that your application C code must be placed inside an android 

 Java project, along with some C support code that communicates with Java

 - This eventually produces a standard Android .apk package

 The Android Java code implements an "activity" and can be found in:

 android-project/src/org/libsdl/app/SDLActivity.java

 The Java code loads your game code, the SDL shared library, and

 dispatches to native functions implemented in the SDL library:

 src/SDL_android.cpp

 Your project must include some glue code that starts your main() routine:

 src/main/android/SDL_android_main.cpp

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  Building an app

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 Instructions:

 1. Copy the android-project directory wherever you want to keep your projects

    and rename it to the name of your project.

 2. Move or symlink this SDL directory into the <project>/jni directory

 3. Edit <project>/jni/src/Android.mk to include your source files

 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source

 If you want to use the Eclipse IDE, skip to the Eclipse section below.

 5. Edit <project>/local.properties to point to the Android SDK directory

 6. Run 'ant debug' in android/project. This compiles the .java and eventually 

    creates a .apk with the native code embedded

 7. 'ant debug install' will push the apk to the device or emulator (if connected)

 Here's an explanation of the files in the Android project, so you can customize them:

 android-project/

 	AndroidManifest.xml	- package manifest. Among others, it contains the class name

 				  of the main activity.

 	build.properties	- empty

 	build.xml		- build description file, used by ant. The actual application name

 				  is specified here.

 	default.properties	- holds the target ABI for the application, can range between

 				  android-5 and android-16

 	local.properties	- holds the SDK path, you should change this to the path to your SDK

 	jni/			- directory holding native code

 	jni/Android.mk		- Android makefile that can call recursively the Android.mk files

 				  in all subdirectories

 	jni/SDL/		- (symlink to) directory holding the SDL library files

 	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library

 	jni/src/		- directory holding your C/C++ source

 	jni/src/Android.mk	- Android makefile that you should customize to include your 

                                   source code and any library references

 	res/			- directory holding resources for your application

 	res/drawable-*		- directories holding icons for different phone hardware. Could be

 				  one dir called "drawable".

 	res/layout/main.xml	- Usually contains a file main.xml, which declares the screen layout.

 				  We don't need it because we use the SDL video output.

 	res/values/strings.xml	- strings used in your application, including the application name

 				  shown on the phone.

 	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.

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  Customizing your application name

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 To customize your application name, edit AndroidManifest.xml and replace

 "org.libsdl.app" with an identifier for your product package.

 Then create a Java class extending SDLActivity and place it in a directory

 under src matching your package, e.g.

 	src/com/gamemaker/game/MyGame.java

 Here's an example of a minimal class file:

 --- MyGame.java --------------------------

 package com.gamemaker.game;

 import org.libsdl.app.SDLActivity; 

 /* 

  * A sample wrapper class that just calls SDLActivity 

  */ 

 public class MyGame extends SDLActivity { }

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 Then replace "SDLActivity" in AndroidManifest.xml with the name of your

 class, .e.g. "MyGame"

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  Customizing your application icon

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 Conceptually changing your icon is just replacing the icon.png files in the

 drawable directories under the res directory. There are 3 directories for

 different screen sizes. These can be replaced with 1 dir called 'drawable',

 containing an icon file 'icon.png' with dimensions 48x48 or 72x72.

 You may need to change the name of your icon in AndroidManifest.xml to match

 this icon filename.

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  Loading assets

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 Any files you put in the "assets" directory of your android-project directory

 will get bundled into the application package and you can load them using the

 standard functions in SDL_rwops.h.

 There are also a few Android specific functions that allow you to get other

 useful paths for saving and loading data:

 SDL_AndroidGetInternalStoragePath()

 SDL_AndroidGetExternalStorageState()

 SDL_AndroidGetExternalStoragePath()

 See SDL_system.h for more details on these functions.

 The asset packaging system will, by default, compress certain file extensions.

 SDL includes two asset file access mechanisms, the preferred one is the so

 called "File Descriptor" method, which is faster and doesn't involve the Dalvik

 GC, but given this method does not work on compressed assets, there is also the

 "Input Stream" method, which is automatically used as a fall back by SDL. You

 may want to keep this fact in mind when building your APK, specially when large

 files are involved.

 For more information on which extensions get compressed by default and how to

 disable this behaviour, see for example:

 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/

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  Pause / Resume behaviour

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 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),

 the event loop will block itself when the app is paused (ie, when the user

 returns to the main Android dashboard). Blocking is better in terms of battery

 use, and it allows your app to spring back to life instantaneously after resume

 (versus polling for a resume message).

 Upon resume, SDL will attempt to restore the GL context automatically.

 In modern devices (Android 3.0 and up) this will most likely succeed and your

 app can continue to operate as it was.

 However, there's a chance (on older hardware, or on systems under heavy load),

 where the GL context can not be restored. In that case you have to listen for

 a specific message, (which is not yet implemented!) and restore your textures

 manually or quit the app (which is actually the kind of behaviour you'll see

 under iOS, if the OS can not restore your GL context it will just kill your app)

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  Threads and the JAVA VM

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 For a quick tour on how Linux native threads interoperate with the JAVA VM, take

 a look here: http://developer.android.com/guide/practices/jni.html

 If you want to use threads in your SDL app, it's strongly recommended that you

 do so by creating them using SDL functions. This way, the required attach/detach

 handling is managed by SDL automagically. If you have threads created by other

 means and they make calls to SDL functions, make sure that you call

 Android_JNI_SetupThread before doing anything else otherwise SDL will attach

 your thread automatically anyway (when you make an SDL call), but it'll never

 detach it.

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  Using STL

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 You can use STL in your project by creating an Application.mk file in the jni

 folder and adding the following line:

 APP_STL := stlport_static

 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.

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  Additional documentation

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 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.

 The best place to start is with docs/OVERVIEW.TXT

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  Using Eclipse

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 First make sure that you've installed Eclipse and the Android extensions as described here:

 	http://developer.android.com/sdk/eclipse-adt.html

 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:

  * File -> New -> Other

  * Select the Android -> Android Project wizard and click Next

  * Enter the name you'd like your project to have

  * Select "Create project from existing source" and browse for your project directory

  * Make sure the Build Target is set to Android 2.0

  * Click Finish

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  Using the emulator

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 There are some good tips and tricks for getting the most out of the

 emulator here: http://developer.android.com/tools/devices/emulator.html

 Especially useful is the info on setting up OpenGL ES 2.0 emulation.

 Notice that this software emulator is incredibly slow and needs a lot of disk space.

 Using a real device works better.

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  Troubleshooting

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 You can create and run an emulator from the Eclipse IDE:

  * Window -> Android SDK and AVD Manager

 You can see if adb can see any devices with the following command:

 	adb devices

 You can see the output of log messages on the default device with:

 	adb logcat

 You can push files to the device with:

 	adb push local_file remote_path_and_file

 You can push files to the SD Card at /sdcard, for example:

 	adb push moose.dat /sdcard/moose.dat

 You can see the files on the SD card with a shell command:

 	adb shell ls /sdcard/

 You can start a command shell on the default device with:

 	adb shell

 You can remove the library files of your project (and not the SDL lib files) with:

 	ndk-build clean

 You can do a build with the following command:

 	ndk-build

 You can see the complete command line that ndk-build is using by passing V=1 on the command line:

 	ndk-build V=1

 If your application crashes in native code, you can use addr2line to convert the

 addresses in the stack trace to lines in your code.

 For example, if your crash looks like this:

 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0

 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4

 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c

 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c

 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030

 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so

 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so

 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so

 I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so

 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:

 	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so

 and then paste in the number after "pc" in the call stack, from the line that I care about:

 000014bc

 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.

 You can add logging to your code to help show what's happening:

 #include <android/log.h>

 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);

 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:

 APP_OPTIM := debug

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  Memory debugging

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 The best (and slowest) way to debug memory issues on Android is valgrind.

 Valgrind has support for Android out of the box, just grab code using:

 	svn co svn://svn.valgrind.org/valgrind/trunk valgrind

 ... and follow the instructions in the file README.android to build it.

 One thing I needed to do on Mac OS X was change the path to the toolchain,

 and add ranlib to the environment variables:

 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib

 Once valgrind is built, you can create a wrapper script to launch your

 application with it, changing org.libsdl.app to your package identifier:

 --- start_valgrind_app -------------------

 #!/system/bin/sh

 export TMPDIR=/data/data/org.libsdl.app

 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*

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 Then push it to the device:

 	adb push start_valgrind_app /data/local

 and make it executable:

 	adb shell chmod 755 /data/local/start_valgrind_app

 and tell Android to use the script to launch your application:

 	adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"

 If the setprop command says "could not set property", it's likely that

 your package name is too long and you should make it shorter by changing

 AndroidManifest.xml and the path to your class file in android-project/src

 You can then launch your application normally and waaaaaaaiiittt for it.

 You can monitor the startup process with the logcat command above, and

 when it's done (or even while it's running) you can grab the valgrind

 output file:

 	adb pull /sdcard/valgrind.log

 When you're done instrumenting with valgrind, you can disable the wrapper:

 	adb shell setprop wrap.org.libsdl.app ""

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  Known issues

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 - TODO. I'm sure there's a bunch more stuff I haven't thought of