author Eric Wing <ewing . public |-at-| gmail . com>
Mon, 22 Jul 2013 02:51:45 -0700
changeset 7501 b27825bb5879
parent 7241 28602f5ca96d
child 7793 6463a850229d
permissions -rw-r--r--
Android: Removed all unnecessary dependencies on C++.

C++ is a bit of a minefield on Android. Much functionality still doesn't work, and Android can't decide on which C++ standard library to use, so it provides 3 different ones, all of which are incompatible with each other. (It looks like clang is coming too which will add a new compiler and a 4th standard library.)

As middleware, SDL might be distributed as a binary and intermixed with other projects already using C++. If C++ is intermixed in a bad way, bad things will happen. Removing dependencies on C++ will avoid this problem and downstream users won't have to worry/care.
     1 ================================================================================
     2 Simple DirectMedia Layer for Android
     3 ================================================================================
     5 Requirements:
     7 Android SDK (version 10 or later)
    10 Android NDK r7 or later
    13 Minimum API level supported by SDL: 10 (Android 2.3.3)
    15 ================================================================================
    16  How the port works
    17 ================================================================================
    19 - Android applications are Java-based, optionally with parts written in C
    20 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    21 the SDL library
    22 - This means that your application C code must be placed inside an Android 
    23 Java project, along with some C support code that communicates with Java
    24 - This eventually produces a standard Android .apk package
    26 The Android Java code implements an "Activity" and can be found in:
    27 android-project/src/org/libsdl/app/
    29 The Java code loads your game code, the SDL shared library, and
    30 dispatches to native functions implemented in the SDL library:
    31 src/SDL_android.c
    33 Your project must include some glue code that starts your main() routine:
    34 src/main/android/SDL_android_main.c
    37 ================================================================================
    38  Building an app
    39 ================================================================================
    41 Instructions:
    42 1. Copy the android-project directory wherever you want to keep your projects
    43    and rename it to the name of your project.
    44 2. Move or symlink this SDL directory into the <project>/jni directory
    45 3. Edit <project>/jni/src/ to include your source files
    46 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    48 If you want to use the Eclipse IDE, skip to the Eclipse section below.
    50 5. Create <project>/ and use that to point to the Android SDK directory, by writing a line with the following form:
    51 sdk.dir=PATH_TO_ANDROID_SDK
    52 6. Run 'ant debug' in android/project. This compiles the .java and eventually 
    53    creates a .apk with the native code embedded
    54 7. 'ant debug install' will push the apk to the device or emulator (if connected)
    56 Here's an explanation of the files in the Android project, so you can customize them:
    58 android-project/
    59 	AndroidManifest.xml	- package manifest. Among others, it contains the class name
    60 				  of the main Activity and the package name of the application.
    61	- empty
    62 	build.xml		- build description file, used by ant. The actual application name
    63 				  is specified here.
    64	- holds the target ABI for the application, android-10 and up
    65	- holds the target ABI for the application, android-10 and up
    66	- holds the SDK path, you should change this to the path to your SDK
    67 	jni/			- directory holding native code
    68 	jni/		- Android makefile that can call recursively the files
    69 				  in all subdirectories
    70 	jni/SDL/		- (symlink to) directory holding the SDL library files
    71 	jni/SDL/	- Android makefile for creating the SDL shared library
    72 	jni/src/		- directory holding your C/C++ source
    73 	jni/src/	- Android makefile that you should customize to include your 
    74                                   source code and any library references
    75 	res/			- directory holding resources for your application
    76 	res/drawable-*		- directories holding icons for different phone hardware. Could be
    77 				  one dir called "drawable".
    78 	res/layout/main.xml	- Usually contains a file main.xml, which declares the screen layout.
    79 				  We don't need it because we use the SDL video output.
    80 	res/values/strings.xml	- strings used in your application, including the application name
    81 				  shown on the phone.
    82 	src/org/libsdl/app/ - the Java class handling the initialization and binding
    83 				  to SDL.  Be very careful changing this, as the SDL library relies
    84 				  on this implementation.
    87 ================================================================================
    88  Customizing your application name
    89 ================================================================================
    91 To customize your application name, edit AndroidManifest.xml and replace
    92 "" with an identifier for your product package.
    94 Then create a Java class extending SDLActivity and place it in a directory
    95 under src matching your package, e.g.
    96 	src/com/gamemaker/game/
    98 Here's an example of a minimal class file:
    99 --- --------------------------
   100 package;
   102 import; 
   104 /* 
   105  * A sample wrapper class that just calls SDLActivity 
   106  */ 
   108 public class MyGame extends SDLActivity { }
   110 ------------------------------------------
   112 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   113 class, .e.g. "MyGame"
   115 ================================================================================
   116  Customizing your application icon
   117 ================================================================================
   119 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   120 the drawable directories under the res directory. There are four directories for
   121 different screen sizes. These can be replaced with one dir called "drawable",
   122 containing an icon file "ic_launcher.png" with dimensions 48x48 or 72x72.
   124 You may need to change the name of your icon in AndroidManifest.xml to match
   125 this icon filename.
   127 ================================================================================
   128  Loading assets
   129 ================================================================================
   131 Any files you put in the "assets" directory of your android-project directory
   132 will get bundled into the application package and you can load them using the
   133 standard functions in SDL_rwops.h.
   135 There are also a few Android specific functions that allow you to get other
   136 useful paths for saving and loading data:
   137 SDL_AndroidGetInternalStoragePath()
   138 SDL_AndroidGetExternalStorageState()
   139 SDL_AndroidGetExternalStoragePath()
   141 See SDL_system.h for more details on these functions.
   143 The asset packaging system will, by default, compress certain file extensions.
   144 SDL includes two asset file access mechanisms, the preferred one is the so
   145 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   146 GC, but given this method does not work on compressed assets, there is also the
   147 "Input Stream" method, which is automatically used as a fall back by SDL. You
   148 may want to keep this fact in mind when building your APK, specially when large
   149 files are involved.
   150 For more information on which extensions get compressed by default and how to
   151 disable this behaviour, see for example:
   155 ================================================================================
   156  Pause / Resume behaviour
   157 ================================================================================
   159 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   160 the event loop will block itself when the app is paused (ie, when the user
   161 returns to the main Android dashboard). Blocking is better in terms of battery
   162 use, and it allows your app to spring back to life instantaneously after resume
   163 (versus polling for a resume message).
   165 Upon resume, SDL will attempt to restore the GL context automatically.
   166 In modern devices (Android 3.0 and up) this will most likely succeed and your
   167 app can continue to operate as it was.
   169 However, there's a chance (on older hardware, or on systems under heavy load),
   170 where the GL context can not be restored. In that case you have to listen for
   171 a specific message, (which is not yet implemented!) and restore your textures
   172 manually or quit the app (which is actually the kind of behaviour you'll see
   173 under iOS, if the OS can not restore your GL context it will just kill your app)
   175 ================================================================================
   176  Threads and the Java VM
   177 ================================================================================
   179 For a quick tour on how Linux native threads interoperate with the Java VM, take
   180 a look here:
   181 If you want to use threads in your SDL app, it's strongly recommended that you
   182 do so by creating them using SDL functions. This way, the required attach/detach
   183 handling is managed by SDL automagically. If you have threads created by other
   184 means and they make calls to SDL functions, make sure that you call
   185 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   186 your thread automatically anyway (when you make an SDL call), but it'll never
   187 detach it.
   189 ================================================================================
   190  Using STL
   191 ================================================================================
   193 You can use STL in your project by creating an file in the jni
   194 folder and adding the following line:
   195 APP_STL := stlport_static
   197 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   199 ================================================================================
   200  Additional documentation
   201 ================================================================================
   203 The documentation in the NDK docs directory is very helpful in understanding the
   204 build process and how to work with native code on the Android platform.
   206 The best place to start is with docs/OVERVIEW.TXT
   209 ================================================================================
   210  Using Eclipse
   211 ================================================================================
   213 First make sure that you've installed Eclipse and the Android extensions as described here:
   216 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   217  * File -> New -> Other
   218  * Select the Android -> Android Project wizard and click Next
   219  * Enter the name you'd like your project to have
   220  * Select "Create project from existing source" and browse for your project directory
   221  * Make sure the Build Target is set to Android 2.0
   222  * Click Finish
   225 ================================================================================
   226  Using the emulator
   227 ================================================================================
   229 There are some good tips and tricks for getting the most out of the
   230 emulator here:
   232 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   234 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   235 Using a real device works better.
   237 ================================================================================
   238  Troubleshooting
   239 ================================================================================
   241 You can create and run an emulator from the Eclipse IDE:
   242  * Window -> Android SDK and AVD Manager
   244 You can see if adb can see any devices with the following command:
   245 	adb devices
   247 You can see the output of log messages on the default device with:
   248 	adb logcat
   250 You can push files to the device with:
   251 	adb push local_file remote_path_and_file
   253 You can push files to the SD Card at /sdcard, for example:
   254 	adb push moose.dat /sdcard/moose.dat
   256 You can see the files on the SD card with a shell command:
   257 	adb shell ls /sdcard/
   259 You can start a command shell on the default device with:
   260 	adb shell
   262 You can remove the library files of your project (and not the SDL lib files) with:
   263 	ndk-build clean
   265 You can do a build with the following command:
   266 	ndk-build
   268 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   269 	ndk-build V=1
   271 If your application crashes in native code, you can use addr2line to convert the
   272 addresses in the stack trace to lines in your code.
   274 For example, if your crash looks like this:
   275 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   276 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   277 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   278 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   279 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   280 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/
   281 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/
   282 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/
   283 I/DEBUG   (   31):          #03  pc 00001506  /data/data/
   285 You can see that there's a crash in the C library being called from the main code.
   286 I run addr2line with the debug version of my code:
   287 	arm-eabi-addr2line -C -f -e obj/local/armeabi/
   288 and then paste in the number after "pc" in the call stack, from the line that I care about:
   289 000014bc
   291 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   293 You can add logging to your code to help show what's happening:
   295 #include <android/log.h>
   297 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   299 If you need to build without optimization turned on, you can create a file called
   300 "" in the jni directory, with the following line in it:
   301 APP_OPTIM := debug
   304 ================================================================================
   305  Memory debugging
   306 ================================================================================
   308 The best (and slowest) way to debug memory issues on Android is valgrind.
   309 Valgrind has support for Android out of the box, just grab code using:
   310 	svn co svn:// valgrind
   311 ... and follow the instructions in the file to build it.
   313 One thing I needed to do on Mac OS X was change the path to the toolchain,
   314 and add ranlib to the environment variables:
   315 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   317 Once valgrind is built, you can create a wrapper script to launch your
   318 application with it, changing to your package identifier:
   319 --- start_valgrind_app -------------------
   320 #!/system/bin/sh
   321 export TMPDIR=/data/data/
   322 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   323 ------------------------------------------
   325 Then push it to the device:
   326 	adb push start_valgrind_app /data/local
   328 and make it executable:
   329 	adb shell chmod 755 /data/local/start_valgrind_app
   331 and tell Android to use the script to launch your application:
   332 	adb shell setprop "logwrapper /data/local/start_valgrind_app"
   334 If the setprop command says "could not set property", it's likely that
   335 your package name is too long and you should make it shorter by changing
   336 AndroidManifest.xml and the path to your class file in android-project/src
   338 You can then launch your application normally and waaaaaaaiiittt for it.
   339 You can monitor the startup process with the logcat command above, and
   340 when it's done (or even while it's running) you can grab the valgrind
   341 output file:
   342 	adb pull /sdcard/valgrind.log
   344 When you're done instrumenting with valgrind, you can disable the wrapper:
   345 	adb shell setprop ""
   347 ================================================================================
   348  Why is API level 10 the minimum required?
   349 ================================================================================
   351 API level 10 is required because SDL requires some functionality for running not
   352 available on older devices and some for building which is not in older NDK/SDKs.
   354 Support for native OpenGL ES and ES2 applications was introduced in the NDK for
   355 API level 4 and 8. EGL was made a stable API in the NDK for API level 9, which
   356 has since then been obsoleted, with the recommendation to developers to bump the
   357 required API level to 10.
   358 As of this writing, according to
   359 about 90% of the Android devices accessing Google Play support API level 10 or
   360 higher (March 2013).
   362 ================================================================================
   363  A note regarding the use of the "dirty rectangles" rendering technique
   364 ================================================================================
   366 If your app uses a variation of the "dirty rectangles" rendering technique,
   367 where you only update a portion of the screen on each frame, you may notice a
   368 variety of visual glitches on Android, that are not present on other platforms.
   369 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   370 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   371 documentation for the function "The contents of ancillary buffers are always 
   372 undefined after calling eglSwapBuffers".
   373 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   374 is not possible for SDL as it requires EGL 1.4, available only on the API level
   375 17+, so the only workaround available on this platform is to redraw the entire
   376 screen each frame.
   378 Reference:
   380 ================================================================================
   381  Known issues
   382 ================================================================================
   384 - TODO. I'm sure there's a bunch more stuff I haven't thought of