2 ================================================================================
4 Matt Styles wrote a tutorial on building SDL for Android with Visual Studio:
5 http://trederia.blogspot.de/2017/03/building-sdl2-for-android-with-visual.html
7 The rest of this README covers the Android gradle style build process.
9 If you are using the older ant build process, it is no longer officially
10 supported, but you can use the "android-project-ant" directory as a template.
13 ================================================================================
15 ================================================================================
17 Android SDK (version 26 or later)
18 https://developer.android.com/sdk/index.html
20 Android NDK r15c or later
21 https://developer.android.com/tools/sdk/ndk/index.html
23 Minimum API level supported by SDL: 16 (Android 4.1)
26 ================================================================================
28 ================================================================================
30 - Android applications are Java-based, optionally with parts written in C
31 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to
33 - This means that your application C code must be placed inside an Android
34 Java project, along with some C support code that communicates with Java
35 - This eventually produces a standard Android .apk package
37 The Android Java code implements an "Activity" and can be found in:
38 android-project/app/src/main/java/org/libsdl/app/SDLActivity.java
40 The Java code loads your game code, the SDL shared library, and
41 dispatches to native functions implemented in the SDL library:
42 src/core/android/SDL_android.c
45 ================================================================================
47 ================================================================================
49 For simple projects you can use the script located at build-scripts/androidbuild.sh
51 There's two ways of using it:
53 androidbuild.sh com.yourcompany.yourapp < sources.list
54 androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
56 sources.list should be a text file with a source file name in each line
57 Filenames should be specified relative to the current directory, for example if
58 you are in the build-scripts directory and want to create the testgles.c test, you'll
61 ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
63 One limitation of this script is that all sources provided will be aggregated into
64 a single directory, thus all your source files should have a unique name.
66 Once the project is complete the script will tell you where the debug APK is located.
67 If you want to create a signed release APK, you can use the project created by this
68 utility to generate it.
70 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
71 done in the build directory for the app!
74 For more complex projects, follow these instructions:
76 1. Copy the android-project directory wherever you want to keep your projects
77 and rename it to the name of your project.
78 2. Move or symlink this SDL directory into the "<project>/app/jni" directory
79 3. Edit "<project>/app/jni/src/Android.mk" to include your source files
81 4a. If you want to use Android Studio, simply open your <project> directory and start building.
83 4b. If you want to build manually, run './gradlew installDebug' in the project directory. This compiles the .java, creates an .apk with the native code embedded, and installs it on any connected Android device
86 If you already have a project that uses CMake, the instructions change somewhat:
88 1. Do points 1 and 2 from the instruction above.
89 2. Edit "<project>/app/build.gradle" to comment out or remove sections containing ndk-build
90 and uncomment the cmake sections. Add arguments to the CMake invocation as needed.
91 3. Edit "<project>/app/jni/CMakeLists.txt" to include your project (it defaults to
92 adding the "src" subdirectory). Note that you'll have SDL2, SDL2main and SDL2-static
93 as targets in your project, so you should have "target_link_libraries(yourgame SDL2 SDL2main)"
94 in your CMakeLists.txt file. Also be aware that you should use add_library() instead of
95 add_executable() for the target containing your "main" function.
97 If you wish to use Android Studio, you can skip the last step.
99 4. Run './gradlew installDebug' or './gradlew installRelease' in the project directory. It will build and install your .apk on any
100 connected Android device
102 Here's an explanation of the files in the Android project, so you can customize them:
105 build.gradle - build info including the application version and SDK
106 src/main/AndroidManifest.xml - package manifest. Among others, it contains the class name of the main Activity and the package name of the application.
107 jni/ - directory holding native code
108 jni/Application.mk - Application JNI settings, including target platform and STL library
109 jni/Android.mk - Android makefile that can call recursively the Android.mk files in all subdirectories
110 jni/CMakeLists.txt - Top-level CMake project that adds SDL as a subproject
111 jni/SDL/ - (symlink to) directory holding the SDL library files
112 jni/SDL/Android.mk - Android makefile for creating the SDL shared library
113 jni/src/ - directory holding your C/C++ source
114 jni/src/Android.mk - Android makefile that you should customize to include your source code and any library references
115 jni/src/CMakeLists.txt - CMake file that you may customize to include your source code and any library references
116 src/main/assets/ - directory holding asset files for your application
117 src/main/res/ - directory holding resources for your application
118 src/main/res/mipmap-* - directories holding icons for different phone hardware
119 src/main/res/values/strings.xml - strings used in your application, including the application name
120 src/main/java/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. You should instead subclass this for your application.
123 ================================================================================
124 Customizing your application name
125 ================================================================================
127 To customize your application name, edit AndroidManifest.xml and replace
128 "org.libsdl.app" with an identifier for your product package.
130 Then create a Java class extending SDLActivity and place it in a directory
131 under src matching your package, e.g.
133 src/com/gamemaker/game/MyGame.java
135 Here's an example of a minimal class file:
137 --- MyGame.java --------------------------
138 package com.gamemaker.game;
140 import org.libsdl.app.SDLActivity;
143 * A sample wrapper class that just calls SDLActivity
146 public class MyGame extends SDLActivity { }
148 ------------------------------------------
150 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
151 class, .e.g. "MyGame"
154 ================================================================================
155 Customizing your application icon
156 ================================================================================
158 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
159 the drawable directories under the res directory. There are several directories
160 for different screen sizes.
163 ================================================================================
165 ================================================================================
167 Any files you put in the "app/src/main/assets" directory of your project
168 directory will get bundled into the application package and you can load
169 them using the standard functions in SDL_rwops.h.
171 There are also a few Android specific functions that allow you to get other
172 useful paths for saving and loading data:
173 * SDL_AndroidGetInternalStoragePath()
174 * SDL_AndroidGetExternalStorageState()
175 * SDL_AndroidGetExternalStoragePath()
177 See SDL_system.h for more details on these functions.
179 The asset packaging system will, by default, compress certain file extensions.
180 SDL includes two asset file access mechanisms, the preferred one is the so
181 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
182 GC, but given this method does not work on compressed assets, there is also the
183 "Input Stream" method, which is automatically used as a fall back by SDL. You
184 may want to keep this fact in mind when building your APK, specially when large
186 For more information on which extensions get compressed by default and how to
187 disable this behaviour, see for example:
189 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
192 ================================================================================
193 Pause / Resume behaviour
194 ================================================================================
196 If SDL_HINT_ANDROID_BLOCK_ON_PAUSE hint is set (the default),
197 the event loop will block itself when the app is paused (ie, when the user
198 returns to the main Android dashboard). Blocking is better in terms of battery
199 use, and it allows your app to spring back to life instantaneously after resume
200 (versus polling for a resume message).
202 Upon resume, SDL will attempt to restore the GL context automatically.
203 In modern devices (Android 3.0 and up) this will most likely succeed and your
204 app can continue to operate as it was.
206 However, there's a chance (on older hardware, or on systems under heavy load),
207 where the GL context can not be restored. In that case you have to listen for
208 a specific message, (which is not yet implemented!) and restore your textures
209 manually or quit the app (which is actually the kind of behaviour you'll see
210 under iOS, if the OS can not restore your GL context it will just kill your app)
213 ================================================================================
214 Threads and the Java VM
215 ================================================================================
217 For a quick tour on how Linux native threads interoperate with the Java VM, take
218 a look here: https://developer.android.com/guide/practices/jni.html
220 If you want to use threads in your SDL app, it's strongly recommended that you
221 do so by creating them using SDL functions. This way, the required attach/detach
222 handling is managed by SDL automagically. If you have threads created by other
223 means and they make calls to SDL functions, make sure that you call
224 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
225 your thread automatically anyway (when you make an SDL call), but it'll never
229 ================================================================================
231 ================================================================================
233 You can use STL in your project by creating an Application.mk file in the jni
234 folder and adding the following line:
236 APP_STL := c++_shared
238 For more information go here:
239 https://developer.android.com/ndk/guides/cpp-support
242 ================================================================================
244 ================================================================================
246 There are some good tips and tricks for getting the most out of the
247 emulator here: https://developer.android.com/tools/devices/emulator.html
249 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
251 Notice that this software emulator is incredibly slow and needs a lot of disk space.
252 Using a real device works better.
255 ================================================================================
257 ================================================================================
259 You can see if adb can see any devices with the following command:
263 You can see the output of log messages on the default device with:
267 You can push files to the device with:
269 adb push local_file remote_path_and_file
271 You can push files to the SD Card at /sdcard, for example:
273 adb push moose.dat /sdcard/moose.dat
275 You can see the files on the SD card with a shell command:
277 adb shell ls /sdcard/
279 You can start a command shell on the default device with:
283 You can remove the library files of your project (and not the SDL lib files) with:
287 You can do a build with the following command:
291 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
295 If your application crashes in native code, you can use ndk-stack to get a symbolic stack trace:
296 https://developer.android.com/ndk/guides/ndk-stack
298 If you want to go through the process manually, you can use addr2line to convert the
299 addresses in the stack trace to lines in your code.
301 For example, if your crash looks like this:
303 I/DEBUG ( 31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
304 I/DEBUG ( 31): r0 00000000 r1 00001000 r2 00000003 r3 400085d4
305 I/DEBUG ( 31): r4 400085d0 r5 40008000 r6 afd41504 r7 436c6a7c
306 I/DEBUG ( 31): r8 436c6b30 r9 435c6fb0 10 435c6f9c fp 4168d82c
307 I/DEBUG ( 31): ip 8346aff0 sp 436c6a60 lr afd1c8ff pc afd1c902 cpsr 60000030
308 I/DEBUG ( 31): #00 pc 0001c902 /system/lib/libc.so
309 I/DEBUG ( 31): #01 pc 0001ccf6 /system/lib/libc.so
310 I/DEBUG ( 31): #02 pc 000014bc /data/data/org.libsdl.app/lib/libmain.so
311 I/DEBUG ( 31): #03 pc 00001506 /data/data/org.libsdl.app/lib/libmain.so
313 You can see that there's a crash in the C library being called from the main code.
314 I run addr2line with the debug version of my code:
316 arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
318 and then paste in the number after "pc" in the call stack, from the line that I care about:
321 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
323 You can add logging to your code to help show what's happening:
325 #include <android/log.h>
327 __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
329 If you need to build without optimization turned on, you can create a file called
330 "Application.mk" in the jni directory, with the following line in it:
335 ================================================================================
337 ================================================================================
339 The best (and slowest) way to debug memory issues on Android is valgrind.
340 Valgrind has support for Android out of the box, just grab code using:
342 svn co svn://svn.valgrind.org/valgrind/trunk valgrind
344 ... and follow the instructions in the file README.android to build it.
346 One thing I needed to do on Mac OS X was change the path to the toolchain,
347 and add ranlib to the environment variables:
348 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
350 Once valgrind is built, you can create a wrapper script to launch your
351 application with it, changing org.libsdl.app to your package identifier:
353 --- start_valgrind_app -------------------
355 export TMPDIR=/data/data/org.libsdl.app
356 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
357 ------------------------------------------
359 Then push it to the device:
361 adb push start_valgrind_app /data/local
363 and make it executable:
365 adb shell chmod 755 /data/local/start_valgrind_app
367 and tell Android to use the script to launch your application:
369 adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
371 If the setprop command says "could not set property", it's likely that
372 your package name is too long and you should make it shorter by changing
373 AndroidManifest.xml and the path to your class file in android-project/src
375 You can then launch your application normally and waaaaaaaiiittt for it.
376 You can monitor the startup process with the logcat command above, and
377 when it's done (or even while it's running) you can grab the valgrind
380 adb pull /sdcard/valgrind.log
382 When you're done instrumenting with valgrind, you can disable the wrapper:
384 adb shell setprop wrap.org.libsdl.app ""
387 ================================================================================
389 ================================================================================
391 If you are developing on a compatible Tegra-based tablet, NVidia provides
392 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
393 and GLES libraries, you must follow their instructions for installing the
394 interposer library on a rooted device. The non-rooted instructions are not
395 compatible with applications that use SDL2 for video.
397 The Tegra Graphics Debugger is available from NVidia here:
398 https://developer.nvidia.com/tegra-graphics-debugger
401 ================================================================================
402 Why is API level 16 the minimum required?
403 ================================================================================
405 The latest NDK toolchain doesn't support targeting earlier than API level 16.
406 As of this writing, according to https://developer.android.com/about/dashboards/index.html
407 about 99% of the Android devices accessing Google Play support API level 16 or
408 higher (January 2018).
411 ================================================================================
412 A note regarding the use of the "dirty rectangles" rendering technique
413 ================================================================================
415 If your app uses a variation of the "dirty rectangles" rendering technique,
416 where you only update a portion of the screen on each frame, you may notice a
417 variety of visual glitches on Android, that are not present on other platforms.
418 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
419 contexts, in particular the use of the eglSwapBuffers function. As stated in the
420 documentation for the function "The contents of ancillary buffers are always
421 undefined after calling eglSwapBuffers".
422 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
423 is not possible for SDL as it requires EGL 1.4, available only on the API level
424 17+, so the only workaround available on this platform is to redraw the entire
427 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
430 ================================================================================
431 Ending your application
432 ================================================================================
436 - return from your main() function. Java side will automatically terminate the
437 Activity by calling Activity.finish().
439 - Android OS can decide to terminate your application by calling onDestroy()
440 (see Activity life cycle). Your application will receive a SDL_QUIT event you
441 can handle to save things and quit.
443 Don't call exit() as it stops the activity badly.
445 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
446 SDLK_AC_BACK, for any purpose.
448 ================================================================================
450 ================================================================================
452 - The number of buttons reported for each joystick is hardcoded to be 36, which
453 is the current maximum number of buttons Android can report.