author Sam Lantinga <>
Sat, 21 Jun 2014 11:52:53 -0700
changeset 8888 75c7095a5e8e
parent 8079 f8ef325265ed
permissions -rw-r--r--
Fixed bug 2596 - SDL_SetError fails on on NULL on systems with vsnprintf


On systems with vsnprintf call SDL_SetError fails when passed a NULL as an argument. SDL's implementation checks for NULL (as seen in the commit:, but system implementation may crash.
     1 ================================================================================
     2 Simple DirectMedia Layer for Android
     3 ================================================================================
     5 Requirements:
     7 Android SDK (version 12 or later)
    10 Android NDK r7 or later
    13 Minimum API level supported by SDL: 10 (Android 2.3.3)
    14 Joystick support is available for API level >=12 devices.
    16 ================================================================================
    17  How the port works
    18 ================================================================================
    20 - Android applications are Java-based, optionally with parts written in C
    21 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to 
    22 the SDL library
    23 - This means that your application C code must be placed inside an Android 
    24 Java project, along with some C support code that communicates with Java
    25 - This eventually produces a standard Android .apk package
    27 The Android Java code implements an "Activity" and can be found in:
    28 android-project/src/org/libsdl/app/
    30 The Java code loads your game code, the SDL shared library, and
    31 dispatches to native functions implemented in the SDL library:
    32 src/core/android/SDL_android.c
    34 Your project must include some glue code that starts your main() routine:
    35 src/main/android/SDL_android_main.c
    38 ================================================================================
    39  Building an app
    40 ================================================================================
    42 For simple projects you can use the script located at build-scripts/
    44 There's two ways of using it:
    46 com.yourcompany.yourapp < sources.list
    47 com.yourcompany.yourapp source1.c source2.c ...sourceN.c
    49 sources.list should be a text file with a source file name in each line
    50 Filenames should be specified relative to the current directory, for example if
    51 you are in the build-scripts directory and want to create the testgles.c test, you'll
    52 run:
    54 ./ org.libsdl.testgles ../test/testgles.c
    56 One limitation of this script is that all sources provided will be aggregated into
    57 a single directory, thus all your source files should have a unique name.
    59 Once the project is complete the script will tell you where the debug APK is located.
    60 If you want to create a signed release APK, you can use the project created by this
    61 utility to generate it.
    63 Finally, a word of caution: re running wipes any changes you may have
    64 done in the build directory for the app!
    67 For more complex projects, follow these instructions:
    69 1. Copy the android-project directory wherever you want to keep your projects
    70    and rename it to the name of your project.
    71 2. Move or symlink this SDL directory into the <project>/jni directory
    72 3. Edit <project>/jni/src/ to include your source files
    73 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
    75 If you want to use the Eclipse IDE, skip to the Eclipse section below.
    77 5. Create <project>/ and use that to point to the Android SDK directory, by writing a line with the following form:
    78 sdk.dir=PATH_TO_ANDROID_SDK
    79 6. Run 'ant debug' in android/project. This compiles the .java and eventually 
    80    creates a .apk with the native code embedded
    81 7. 'ant debug install' will push the apk to the device or emulator (if connected)
    83 Here's an explanation of the files in the Android project, so you can customize them:
    85 android-project/
    86 	AndroidManifest.xml	- package manifest. Among others, it contains the class name
    87 				  of the main Activity and the package name of the application.
    88	- empty
    89 	build.xml		- build description file, used by ant. The actual application name
    90 				  is specified here.
    91	- holds the target ABI for the application, android-10 and up
    92	- holds the target ABI for the application, android-10 and up
    93	- holds the SDK path, you should change this to the path to your SDK
    94 	jni/			- directory holding native code
    95 	jni/		- Android makefile that can call recursively the files
    96 				  in all subdirectories
    97 	jni/SDL/		- (symlink to) directory holding the SDL library files
    98 	jni/SDL/	- Android makefile for creating the SDL shared library
    99 	jni/src/		- directory holding your C/C++ source
   100 	jni/src/	- Android makefile that you should customize to include your 
   101                                   source code and any library references
   102 	res/			- directory holding resources for your application
   103 	res/drawable-*		- directories holding icons for different phone hardware. Could be
   104 				  one dir called "drawable".
   105 	res/layout/main.xml	- Usually contains a file main.xml, which declares the screen layout.
   106 				  We don't need it because we use the SDL video output.
   107 	res/values/strings.xml	- strings used in your application, including the application name
   108 				  shown on the phone.
   109 	src/org/libsdl/app/ - the Java class handling the initialization and binding
   110 				  to SDL.  Be very careful changing this, as the SDL library relies
   111 				  on this implementation.
   114 ================================================================================
   115  Build an app with static linking of libSDL
   116 ================================================================================
   118 This build uses the Android NDK module system.
   120 Instructions:
   121 1. Copy the android-project directory wherever you want to keep your projects
   122    and rename it to the name of your project.
   123 2. Rename <project>/jni/src/ to <project>/jni/src/
   124    (overwrite the existing one)
   125 3. Edit <project>/jni/src/ to include your source files
   126 4. create and export an environment variable named NDK_MODULE_PATH that points
   127    to the parent directory of this SDL directory. e.g.:
   129    export NDK_MODULE_PATH="$PWD"/..
   131 5. Edit <project>/src/org/libsdl/app/ and remove the call to
   132    System.loadLibrary("SDL2") line 42.
   133 6. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
   136 ================================================================================
   137  Customizing your application name
   138 ================================================================================
   140 To customize your application name, edit AndroidManifest.xml and replace
   141 "" with an identifier for your product package.
   143 Then create a Java class extending SDLActivity and place it in a directory
   144 under src matching your package, e.g.
   145 	src/com/gamemaker/game/
   147 Here's an example of a minimal class file:
   148 --- --------------------------
   149 package;
   151 import; 
   153 /* 
   154  * A sample wrapper class that just calls SDLActivity 
   155  */ 
   157 public class MyGame extends SDLActivity { }
   159 ------------------------------------------
   161 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
   162 class, .e.g. "MyGame"
   164 ================================================================================
   165  Customizing your application icon
   166 ================================================================================
   168 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
   169 the drawable directories under the res directory. There are four directories for
   170 different screen sizes. These can be replaced with one dir called "drawable",
   171 containing an icon file "ic_launcher.png" with dimensions 48x48 or 72x72.
   173 You may need to change the name of your icon in AndroidManifest.xml to match
   174 this icon filename.
   176 ================================================================================
   177  Loading assets
   178 ================================================================================
   180 Any files you put in the "assets" directory of your android-project directory
   181 will get bundled into the application package and you can load them using the
   182 standard functions in SDL_rwops.h.
   184 There are also a few Android specific functions that allow you to get other
   185 useful paths for saving and loading data:
   186 SDL_AndroidGetInternalStoragePath()
   187 SDL_AndroidGetExternalStorageState()
   188 SDL_AndroidGetExternalStoragePath()
   190 See SDL_system.h for more details on these functions.
   192 The asset packaging system will, by default, compress certain file extensions.
   193 SDL includes two asset file access mechanisms, the preferred one is the so
   194 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
   195 GC, but given this method does not work on compressed assets, there is also the
   196 "Input Stream" method, which is automatically used as a fall back by SDL. You
   197 may want to keep this fact in mind when building your APK, specially when large
   198 files are involved.
   199 For more information on which extensions get compressed by default and how to
   200 disable this behaviour, see for example:
   204 ================================================================================
   205  Pause / Resume behaviour
   206 ================================================================================
   208 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
   209 the event loop will block itself when the app is paused (ie, when the user
   210 returns to the main Android dashboard). Blocking is better in terms of battery
   211 use, and it allows your app to spring back to life instantaneously after resume
   212 (versus polling for a resume message).
   214 Upon resume, SDL will attempt to restore the GL context automatically.
   215 In modern devices (Android 3.0 and up) this will most likely succeed and your
   216 app can continue to operate as it was.
   218 However, there's a chance (on older hardware, or on systems under heavy load),
   219 where the GL context can not be restored. In that case you have to listen for
   220 a specific message, (which is not yet implemented!) and restore your textures
   221 manually or quit the app (which is actually the kind of behaviour you'll see
   222 under iOS, if the OS can not restore your GL context it will just kill your app)
   224 ================================================================================
   225  Threads and the Java VM
   226 ================================================================================
   228 For a quick tour on how Linux native threads interoperate with the Java VM, take
   229 a look here:
   230 If you want to use threads in your SDL app, it's strongly recommended that you
   231 do so by creating them using SDL functions. This way, the required attach/detach
   232 handling is managed by SDL automagically. If you have threads created by other
   233 means and they make calls to SDL functions, make sure that you call
   234 Android_JNI_SetupThread before doing anything else otherwise SDL will attach
   235 your thread automatically anyway (when you make an SDL call), but it'll never
   236 detach it.
   238 ================================================================================
   239  Using STL
   240 ================================================================================
   242 You can use STL in your project by creating an file in the jni
   243 folder and adding the following line:
   244 APP_STL := stlport_static
   246 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
   248 ================================================================================
   249  Additional documentation
   250 ================================================================================
   252 The documentation in the NDK docs directory is very helpful in understanding the
   253 build process and how to work with native code on the Android platform.
   255 The best place to start is with docs/OVERVIEW.TXT
   258 ================================================================================
   259  Using Eclipse
   260 ================================================================================
   262 First make sure that you've installed Eclipse and the Android extensions as described here:
   265 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
   266  * File -> New -> Other
   267  * Select the Android -> Android Project wizard and click Next
   268  * Enter the name you'd like your project to have
   269  * Select "Create project from existing source" and browse for your project directory
   270  * Make sure the Build Target is set to Android 2.0
   271  * Click Finish
   274 ================================================================================
   275  Using the emulator
   276 ================================================================================
   278 There are some good tips and tricks for getting the most out of the
   279 emulator here:
   281 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
   283 Notice that this software emulator is incredibly slow and needs a lot of disk space.
   284 Using a real device works better.
   286 ================================================================================
   287  Troubleshooting
   288 ================================================================================
   290 You can create and run an emulator from the Eclipse IDE:
   291  * Window -> Android SDK and AVD Manager
   293 You can see if adb can see any devices with the following command:
   294 	adb devices
   296 You can see the output of log messages on the default device with:
   297 	adb logcat
   299 You can push files to the device with:
   300 	adb push local_file remote_path_and_file
   302 You can push files to the SD Card at /sdcard, for example:
   303 	adb push moose.dat /sdcard/moose.dat
   305 You can see the files on the SD card with a shell command:
   306 	adb shell ls /sdcard/
   308 You can start a command shell on the default device with:
   309 	adb shell
   311 You can remove the library files of your project (and not the SDL lib files) with:
   312 	ndk-build clean
   314 You can do a build with the following command:
   315 	ndk-build
   317 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
   318 	ndk-build V=1
   320 If your application crashes in native code, you can use addr2line to convert the
   321 addresses in the stack trace to lines in your code.
   323 For example, if your crash looks like this:
   324 I/DEBUG   (   31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
   325 I/DEBUG   (   31):  r0 00000000  r1 00001000  r2 00000003  r3 400085d4
   326 I/DEBUG   (   31):  r4 400085d0  r5 40008000  r6 afd41504  r7 436c6a7c
   327 I/DEBUG   (   31):  r8 436c6b30  r9 435c6fb0  10 435c6f9c  fp 4168d82c
   328 I/DEBUG   (   31):  ip 8346aff0  sp 436c6a60  lr afd1c8ff  pc afd1c902  cpsr 60000030
   329 I/DEBUG   (   31):          #00  pc 0001c902  /system/lib/
   330 I/DEBUG   (   31):          #01  pc 0001ccf6  /system/lib/
   331 I/DEBUG   (   31):          #02  pc 000014bc  /data/data/
   332 I/DEBUG   (   31):          #03  pc 00001506  /data/data/
   334 You can see that there's a crash in the C library being called from the main code.
   335 I run addr2line with the debug version of my code:
   336 	arm-eabi-addr2line -C -f -e obj/local/armeabi/
   337 and then paste in the number after "pc" in the call stack, from the line that I care about:
   338 000014bc
   340 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
   342 You can add logging to your code to help show what's happening:
   344 #include <android/log.h>
   346 	__android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
   348 If you need to build without optimization turned on, you can create a file called
   349 "" in the jni directory, with the following line in it:
   350 APP_OPTIM := debug
   353 ================================================================================
   354  Memory debugging
   355 ================================================================================
   357 The best (and slowest) way to debug memory issues on Android is valgrind.
   358 Valgrind has support for Android out of the box, just grab code using:
   359 	svn co svn:// valgrind
   360 ... and follow the instructions in the file to build it.
   362 One thing I needed to do on Mac OS X was change the path to the toolchain,
   363 and add ranlib to the environment variables:
   364 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
   366 Once valgrind is built, you can create a wrapper script to launch your
   367 application with it, changing to your package identifier:
   368 --- start_valgrind_app -------------------
   369 #!/system/bin/sh
   370 export TMPDIR=/data/data/
   371 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
   372 ------------------------------------------
   374 Then push it to the device:
   375 	adb push start_valgrind_app /data/local
   377 and make it executable:
   378 	adb shell chmod 755 /data/local/start_valgrind_app
   380 and tell Android to use the script to launch your application:
   381 	adb shell setprop "logwrapper /data/local/start_valgrind_app"
   383 If the setprop command says "could not set property", it's likely that
   384 your package name is too long and you should make it shorter by changing
   385 AndroidManifest.xml and the path to your class file in android-project/src
   387 You can then launch your application normally and waaaaaaaiiittt for it.
   388 You can monitor the startup process with the logcat command above, and
   389 when it's done (or even while it's running) you can grab the valgrind
   390 output file:
   391 	adb pull /sdcard/valgrind.log
   393 When you're done instrumenting with valgrind, you can disable the wrapper:
   394 	adb shell setprop ""
   396 ================================================================================
   397  Why is API level 10 the minimum required?
   398 ================================================================================
   400 API level 10 is the minimum required level at runtime (that is, on the device) 
   401 because SDL requires some functionality for running not
   402 available on older devices. Since the incorporation of joystick support into SDL,
   403 the minimum SDK required to *build* SDL is version 12. Devices running API levels
   404 10-11 are still supported, only with the joystick functionality disabled.
   406 Support for native OpenGL ES and ES2 applications was introduced in the NDK for
   407 API level 4 and 8. EGL was made a stable API in the NDK for API level 9, which
   408 has since then been obsoleted, with the recommendation to developers to bump the
   409 required API level to 10.
   410 As of this writing, according to
   411 about 90% of the Android devices accessing Google Play support API level 10 or
   412 higher (March 2013).
   414 ================================================================================
   415  A note regarding the use of the "dirty rectangles" rendering technique
   416 ================================================================================
   418 If your app uses a variation of the "dirty rectangles" rendering technique,
   419 where you only update a portion of the screen on each frame, you may notice a
   420 variety of visual glitches on Android, that are not present on other platforms.
   421 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
   422 contexts, in particular the use of the eglSwapBuffers function. As stated in the
   423 documentation for the function "The contents of ancillary buffers are always 
   424 undefined after calling eglSwapBuffers".
   425 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
   426 is not possible for SDL as it requires EGL 1.4, available only on the API level
   427 17+, so the only workaround available on this platform is to redraw the entire
   428 screen each frame.
   430 Reference:
   432 ================================================================================
   433  Known issues
   434 ================================================================================
   436 - The number of buttons reported for each joystick is hardcoded to be 36, which
   437 is the current maximum number of buttons Android can report.