SDL  2.0
README-android.md
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1 Android
2 ================================================================================
3 
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
6 
7 The rest of this README covers the Android gradle style build process.
8 
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.
11 
12 
13 Requirements
14 ================================================================================
15 
16 Android SDK (version 26 or later)
17 https://developer.android.com/sdk/index.html
18 
19 Android NDK r15c or later
20 https://developer.android.com/tools/sdk/ndk/index.html
21 
22 Minimum API level supported by SDL: 16 (Android 4.1)
23 
24 
25 How the port works
26 ================================================================================
27 
28 - Android applications are Java-based, optionally with parts written in C
29 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to
30  the SDL library
31 - This means that your application C code must be placed inside an Android
32  Java project, along with some C support code that communicates with Java
33 - This eventually produces a standard Android .apk package
34 
35 The Android Java code implements an "Activity" and can be found in:
36 android-project/app/src/main/java/org/libsdl/app/SDLActivity.java
37 
38 The Java code loads your game code, the SDL shared library, and
39 dispatches to native functions implemented in the SDL library:
40 src/core/android/SDL_android.c
41 
42 
43 Building an app
44 ================================================================================
45 
46 For simple projects you can use the script located at build-scripts/androidbuild.sh
47 
48 There's two ways of using it:
49 
50  androidbuild.sh com.yourcompany.yourapp < sources.list
51  androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
52 
53 sources.list should be a text file with a source file name in each line
54 Filenames should be specified relative to the current directory, for example if
55 you are in the build-scripts directory and want to create the testgles.c test, you'll
56 run:
57 
58  ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
59 
60 One limitation of this script is that all sources provided will be aggregated into
61 a single directory, thus all your source files should have a unique name.
62 
63 Once the project is complete the script will tell you where the debug APK is located.
64 If you want to create a signed release APK, you can use the project created by this
65 utility to generate it.
66 
67 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
68 done in the build directory for the app!
69 
70 
71 For more complex projects, follow these instructions:
72 
73 1. Copy the android-project directory wherever you want to keep your projects
74  and rename it to the name of your project.
75 2. Move or symlink this SDL directory into the "<project>/app/jni" directory
76 3. Edit "<project>/app/jni/src/Android.mk" to include your source files
77 
78 4a. If you want to use Android Studio, simply open your <project> directory and start building.
79 
80 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
81 
82 
83 If you already have a project that uses CMake, the instructions change somewhat:
84 
85 1. Do points 1 and 2 from the instruction above.
86 2. Edit "<project>/app/build.gradle" to comment out or remove sections containing ndk-build
87  and uncomment the cmake sections. Add arguments to the CMake invocation as needed.
88 3. Edit "<project>/app/jni/CMakeLists.txt" to include your project (it defaults to
89  adding the "src" subdirectory). Note that you'll have SDL2, SDL2main and SDL2-static
90  as targets in your project, so you should have "target_link_libraries(yourgame SDL2 SDL2main)"
91  in your CMakeLists.txt file. Also be aware that you should use add_library() instead of
92  add_executable() for the target containing your "main" function.
93 
94 If you wish to use Android Studio, you can skip the last step.
95 
96 4. Run './gradlew installDebug' or './gradlew installRelease' in the project directory. It will build and install your .apk on any
97  connected Android device
98 
99 Here's an explanation of the files in the Android project, so you can customize them:
100 
101  android-project/app
102  build.gradle - build info including the application version and SDK
103  src/main/AndroidManifest.xml - package manifest. Among others, it contains the class name of the main Activity and the package name of the application.
104  jni/ - directory holding native code
105  jni/Application.mk - Application JNI settings, including target platform and STL library
106  jni/Android.mk - Android makefile that can call recursively the Android.mk files in all subdirectories
107  jni/CMakeLists.txt - Top-level CMake project that adds SDL as a subproject
108  jni/SDL/ - (symlink to) directory holding the SDL library files
109  jni/SDL/Android.mk - Android makefile for creating the SDL shared library
110  jni/src/ - directory holding your C/C++ source
111  jni/src/Android.mk - Android makefile that you should customize to include your source code and any library references
112  jni/src/CMakeLists.txt - CMake file that you may customize to include your source code and any library references
113  src/main/assets/ - directory holding asset files for your application
114  src/main/res/ - directory holding resources for your application
115  src/main/res/mipmap-* - directories holding icons for different phone hardware
116  src/main/res/values/strings.xml - strings used in your application, including the application name
117  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.
118 
119 
120 Customizing your application name
121 ================================================================================
122 
123 To customize your application name, edit AndroidManifest.xml and replace
124 "org.libsdl.app" with an identifier for your product package.
125 
126 Then create a Java class extending SDLActivity and place it in a directory
127 under src matching your package, e.g.
128 
129  src/com/gamemaker/game/MyGame.java
130 
131 Here's an example of a minimal class file:
132 
133  --- MyGame.java --------------------------
134  package com.gamemaker.game;
135 
136  import org.libsdl.app.SDLActivity;
137 
138  /**
139  * A sample wrapper class that just calls SDLActivity
140  */
141 
142  public class MyGame extends SDLActivity { }
143 
144  ------------------------------------------
145 
146 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
147 class, .e.g. "MyGame"
148 
149 
150 Customizing your application icon
151 ================================================================================
152 
153 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
154 the drawable directories under the res directory. There are several directories
155 for different screen sizes.
156 
157 
158 Loading assets
159 ================================================================================
160 
161 Any files you put in the "app/src/main/assets" directory of your project
162 directory will get bundled into the application package and you can load
163 them using the standard functions in SDL_rwops.h.
164 
165 There are also a few Android specific functions that allow you to get other
166 useful paths for saving and loading data:
167 * SDL_AndroidGetInternalStoragePath()
168 * SDL_AndroidGetExternalStorageState()
169 * SDL_AndroidGetExternalStoragePath()
170 
171 See SDL_system.h for more details on these functions.
172 
173 The asset packaging system will, by default, compress certain file extensions.
174 SDL includes two asset file access mechanisms, the preferred one is the so
175 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
176 GC, but given this method does not work on compressed assets, there is also the
177 "Input Stream" method, which is automatically used as a fall back by SDL. You
178 may want to keep this fact in mind when building your APK, specially when large
179 files are involved.
180 For more information on which extensions get compressed by default and how to
181 disable this behaviour, see for example:
182 
183 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
184 
185 
186 Pause / Resume behaviour
187 ================================================================================
188 
189 If SDL_HINT_ANDROID_BLOCK_ON_PAUSE hint is set (the default),
190 the event loop will block itself when the app is paused (ie, when the user
191 returns to the main Android dashboard). Blocking is better in terms of battery
192 use, and it allows your app to spring back to life instantaneously after resume
193 (versus polling for a resume message).
194 
195 Upon resume, SDL will attempt to restore the GL context automatically.
196 In modern devices (Android 3.0 and up) this will most likely succeed and your
197 app can continue to operate as it was.
198 
199 However, there's a chance (on older hardware, or on systems under heavy load),
200 where the GL context can not be restored. In that case you have to listen for
201 a specific message (SDL_RENDER_DEVICE_RESET) and restore your textures
202 manually or quit the app.
203 
204 You should not use the SDL renderer API while the app going in background:
205 - SDL_APP_WILLENTERBACKGROUND:
206  after you read this message, GL context gets backed-up and you should not
207  use the SDL renderer API.
208 
209 - SDL_APP_DIDENTERFOREGROUND:
210  GL context is restored, and the SDL renderer API is available (unless you
211  receive SDL_RENDER_DEVICE_RESET).
212 
213 Mouse / Touch events
214 ================================================================================
215 
216 In some case, SDL generates synthetic mouse (resp. touch) events for touch
217 (resp. mouse) devices.
218 To enable/disable this behavior, see SDL_hints.h:
219 - SDL_HINT_TOUCH_MOUSE_EVENTS
220 - SDL_HINT_MOUSE_TOUCH_EVENTS
221 
222 Misc
223 ================================================================================
224 
225 For some device, it appears to works better setting explicitly GL attributes
226 before creating a window:
227  SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
228  SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 6);
229  SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
230 
231 Threads and the Java VM
232 ================================================================================
233 
234 For a quick tour on how Linux native threads interoperate with the Java VM, take
235 a look here: https://developer.android.com/guide/practices/jni.html
236 
237 If you want to use threads in your SDL app, it's strongly recommended that you
238 do so by creating them using SDL functions. This way, the required attach/detach
239 handling is managed by SDL automagically. If you have threads created by other
240 means and they make calls to SDL functions, make sure that you call
241 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
242 your thread automatically anyway (when you make an SDL call), but it'll never
243 detach it.
244 
245 
246 If you ever want to use JNI in a native thread (created by "SDL_CreateThread()"),
247 it won't be able to find your java class and method because of the java class loader
248 which is different for native threads, than for java threads (eg your "main()").
249 
250 the work-around is to find class/method, in you "main()" thread, and to use them
251 in your native thread.
252 
253 see:
254 https://developer.android.com/training/articles/perf-jni#faq:-why-didnt-findclass-find-my-class
255 
256 Using STL
257 ================================================================================
258 
259 You can use STL in your project by creating an Application.mk file in the jni
260 folder and adding the following line:
261 
262  APP_STL := c++_shared
263 
264 For more information go here:
265  https://developer.android.com/ndk/guides/cpp-support
266 
267 
268 Using the emulator
269 ================================================================================
270 
271 There are some good tips and tricks for getting the most out of the
272 emulator here: https://developer.android.com/tools/devices/emulator.html
273 
274 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
275 
276 Notice that this software emulator is incredibly slow and needs a lot of disk space.
277 Using a real device works better.
278 
279 
280 Troubleshooting
281 ================================================================================
282 
283 You can see if adb can see any devices with the following command:
284 
285  adb devices
286 
287 You can see the output of log messages on the default device with:
288 
289  adb logcat
290 
291 You can push files to the device with:
292 
293  adb push local_file remote_path_and_file
294 
295 You can push files to the SD Card at /sdcard, for example:
296 
297  adb push moose.dat /sdcard/moose.dat
298 
299 You can see the files on the SD card with a shell command:
300 
301  adb shell ls /sdcard/
302 
303 You can start a command shell on the default device with:
304 
305  adb shell
306 
307 You can remove the library files of your project (and not the SDL lib files) with:
308 
309  ndk-build clean
310 
311 You can do a build with the following command:
312 
313  ndk-build
314 
315 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
316 
317  ndk-build V=1
318 
319 If your application crashes in native code, you can use ndk-stack to get a symbolic stack trace:
320  https://developer.android.com/ndk/guides/ndk-stack
321 
322 If you want to go through the process manually, you can use addr2line to convert the
323 addresses in the stack trace to lines in your code.
324 
325 For example, if your crash looks like this:
326 
327  I/DEBUG ( 31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
328  I/DEBUG ( 31): r0 00000000 r1 00001000 r2 00000003 r3 400085d4
329  I/DEBUG ( 31): r4 400085d0 r5 40008000 r6 afd41504 r7 436c6a7c
330  I/DEBUG ( 31): r8 436c6b30 r9 435c6fb0 10 435c6f9c fp 4168d82c
331  I/DEBUG ( 31): ip 8346aff0 sp 436c6a60 lr afd1c8ff pc afd1c902 cpsr 60000030
332  I/DEBUG ( 31): #00 pc 0001c902 /system/lib/libc.so
333  I/DEBUG ( 31): #01 pc 0001ccf6 /system/lib/libc.so
334  I/DEBUG ( 31): #02 pc 000014bc /data/data/org.libsdl.app/lib/libmain.so
335  I/DEBUG ( 31): #03 pc 00001506 /data/data/org.libsdl.app/lib/libmain.so
336 
337 You can see that there's a crash in the C library being called from the main code.
338 I run addr2line with the debug version of my code:
339 
340  arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
341 
342 and then paste in the number after "pc" in the call stack, from the line that I care about:
343 000014bc
344 
345 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
346 
347 You can add logging to your code to help show what's happening:
348 
349  #include <android/log.h>
350 
351  __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
352 
353 If you need to build without optimization turned on, you can create a file called
354 "Application.mk" in the jni directory, with the following line in it:
355 
356  APP_OPTIM := debug
357 
358 
359 Memory debugging
360 ================================================================================
361 
362 The best (and slowest) way to debug memory issues on Android is valgrind.
363 Valgrind has support for Android out of the box, just grab code using:
364 
365  svn co svn://svn.valgrind.org/valgrind/trunk valgrind
366 
367 ... and follow the instructions in the file README.android to build it.
368 
369 One thing I needed to do on Mac OS X was change the path to the toolchain,
370 and add ranlib to the environment variables:
371 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
372 
373 Once valgrind is built, you can create a wrapper script to launch your
374 application with it, changing org.libsdl.app to your package identifier:
375 
376  --- start_valgrind_app -------------------
377  #!/system/bin/sh
378  export TMPDIR=/data/data/org.libsdl.app
379  exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
380  ------------------------------------------
381 
382 Then push it to the device:
383 
384  adb push start_valgrind_app /data/local
385 
386 and make it executable:
387 
388  adb shell chmod 755 /data/local/start_valgrind_app
389 
390 and tell Android to use the script to launch your application:
391 
392  adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
393 
394 If the setprop command says "could not set property", it's likely that
395 your package name is too long and you should make it shorter by changing
396 AndroidManifest.xml and the path to your class file in android-project/src
397 
398 You can then launch your application normally and waaaaaaaiiittt for it.
399 You can monitor the startup process with the logcat command above, and
400 when it's done (or even while it's running) you can grab the valgrind
401 output file:
402 
403  adb pull /sdcard/valgrind.log
404 
405 When you're done instrumenting with valgrind, you can disable the wrapper:
406 
407  adb shell setprop wrap.org.libsdl.app ""
408 
409 
410 Graphics debugging
411 ================================================================================
412 
413 If you are developing on a compatible Tegra-based tablet, NVidia provides
414 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
415 and GLES libraries, you must follow their instructions for installing the
416 interposer library on a rooted device. The non-rooted instructions are not
417 compatible with applications that use SDL2 for video.
418 
419 The Tegra Graphics Debugger is available from NVidia here:
420 https://developer.nvidia.com/tegra-graphics-debugger
421 
422 
423 Why is API level 16 the minimum required?
424 ================================================================================
425 
426 The latest NDK toolchain doesn't support targeting earlier than API level 16.
427 As of this writing, according to https://developer.android.com/about/dashboards/index.html
428 about 99% of the Android devices accessing Google Play support API level 16 or
429 higher (January 2018).
430 
431 
432 A note regarding the use of the "dirty rectangles" rendering technique
433 ================================================================================
434 
435 If your app uses a variation of the "dirty rectangles" rendering technique,
436 where you only update a portion of the screen on each frame, you may notice a
437 variety of visual glitches on Android, that are not present on other platforms.
438 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
439 contexts, in particular the use of the eglSwapBuffers function. As stated in the
440 documentation for the function "The contents of ancillary buffers are always
441 undefined after calling eglSwapBuffers".
442 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
443 is not possible for SDL as it requires EGL 1.4, available only on the API level
444 17+, so the only workaround available on this platform is to redraw the entire
445 screen each frame.
446 
447 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
448 
449 
450 Ending your application
451 ================================================================================
452 
453 Two legitimate ways:
454 
455 - return from your main() function. Java side will automatically terminate the
456 Activity by calling Activity.finish().
457 
458 - Android OS can decide to terminate your application by calling onDestroy()
459 (see Activity life cycle). Your application will receive a SDL_QUIT event you
460 can handle to save things and quit.
461 
462 Don't call exit() as it stops the activity badly.
463 
464 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
465 SDLK_AC_BACK, for any purpose.
466 
467 Known issues
468 ================================================================================
469 
470 - The number of buttons reported for each joystick is hardcoded to be 36, which
471 is the current maximum number of buttons Android can report.
472