README.android
author Sam Lantinga <slouken@libsdl.org>
Wed, 12 Jan 2011 12:34:23 -0800
changeset 4974 1cd0a891b69a
parent 4973 067b6ec8b751
child 4975 6fbc7044f343
permissions -rw-r--r--
Added info for building your code without optimizations on
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Simple DirectMedia Layer for Android
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================================================================================
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Requirements:
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Android SDK
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http://developer.android.com/sdk/index.html
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Android NDK r4 or later
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http://developer.android.com/sdk/ndk/index.html
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================================================================================
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 How the port works
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- Android applications are Java-based, optionally with parts written in C
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- As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
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the SDL library
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- This means that your application C code must be placed inside an android 
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Java project, along with some C support code that communicates with Java
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- This eventually produces a standard Android .apk package
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The Android Java code implements an "activity" and can be found in:
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android-project/src/org/libsdl/app/SDLActivity.java
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The Java code loads your game code, the SDL shared library, and
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dispatches to native functions implemented in the SDL library:
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src/SDL_android.cpp
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Your project must include some glue code that starts your main() routine:
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src/main/android/SDL_android_main.cpp
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================================================================================
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 Building an app
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Instructions:
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1. Copy the android-project directory wherever you want to keep your projects and rename it to the name of your project.
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2. Move this SDL directory into the <project>/jni directory
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3. Place your application source files in the <project>/jni/src directory
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4. Edit <project>/jni/src/Android.mk to include your source files
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5. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
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If you want to use the Eclipse IDE, skip to the Eclipse section below.
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6. Edit <project>/local.properties to point to the Android SDK directory
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7. Run 'ant debug' in android/project. This compiles the .java and eventually 
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creates a .apk with the native code embedded
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8. 'ant install' will push the apk to the device or emulator (if connected)
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Here's an explanation of the files in the Android project, so you can customize them:
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android-project/
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	AndroidManifest.xml	- package manifest, do not modify
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	build.properties	- empty
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	build.xml		- build description file, used by ant
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	default.properties	- holds the ABI for the application, currently android-4 which corresponds to the Android 1.6 system image
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	local.properties	- holds the SDK path, you should change this to the path to your SDK
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	jni/			- directory holding native code
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	jni/Android.mk		- Android makefile that includes all subdirectories
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	jni/SDL/		- directory holding the SDL library files
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	jni/SDL/Android.mk	- Android makefile for creating the SDL shared library
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	jni/src/		- directory holding your C/C++ source
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	jni/src/Android.mk	- Android makefile that you should customize to include your source code and any library references
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	res/			- directory holding resources for your application
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	res/drawable-*		- directories holding icons for different phone hardware
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	res/layout/main.xml	- place holder for the main screen layout, overridden by the SDL video output
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	res/values/strings.xml	- strings used in your application, including the application name shown on the phone.
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	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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================================================================================
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 Additional documentation
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================================================================================
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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.
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The best place to start is with docs/OVERVIEW.TXT
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================================================================================
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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:
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	http://developer.android.com/sdk/eclipse-adt.html
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Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
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 * File -> New -> Other
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 * Select the Android -> Android Project wizard and click Next
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 * Enter the name you'd like your project to have
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 * Select "Create project from existing source" and browse for your project directory
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 * Make sure the Build Target is set to Android 1.6
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 * Click Finish
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================================================================================
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 Loading files and resources
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NEED CONTENT
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================================================================================
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 Troubleshooting
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You can create and run an emulator from the Eclipse IDE:
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 * Window -> Android SDK and AVD Manager
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You can see if adb can see any devices with the following command:
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	adb devices
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You can see the output of log messages on the default device with:
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	adb logcat
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You can push files to the device with:
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	adb push local_file remote_path_and_file
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You can push files to the SD Card at /sdcard, for example:
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	adb push moose.dat /sdcard/moose.dat
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You can see the complete command line that ndk-build is using by passing V=1 on the command line:
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	ndk-build V=1
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If your application crashes in native code, you can use addr2line to convert the addresses in the stack trace to lines in your code.
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For example, if your crash looks like this:
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I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
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I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
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I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
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I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
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I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
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I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/libc.so
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I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/libc.so
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I/DEBUG   (   31):          #02  pc 000014bc  /data/data/org.libsdl.app/lib/libmain.so
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I/DEBUG   (   31):          #03  pc 00001506  /data/data/org.libsdl.app/lib/libmain.so
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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:
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	arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
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and then paste in the number after "pc" in the call stack, from the line that I care about:
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000014bc
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I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
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You can add logging to your code to help show what's happening:
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#include <android/log.h>
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	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
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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:
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APP_OPTIM := debug
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================================================================================
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 Known issues
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- SDL audio (although it's mostly written, just not working properly yet)
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- TODO. I'm sure there's a bunch more stuff I haven't thought of