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 ================================================================================
14  Requirements
15 ================================================================================
16 
17 Android SDK (version 26 or later)
18 https://developer.android.com/sdk/index.html
19 
20 Android NDK r15c or later
21 https://developer.android.com/tools/sdk/ndk/index.html
22 
23 Minimum API level supported by SDL: 16 (Android 4.1)
24 
25 
26 ================================================================================
27  How the port works
28 ================================================================================
29 
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
32  the SDL library
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
36 
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
39 
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
43 
44 
45 ================================================================================
46  Building an app
47 ================================================================================
48 
49 For simple projects you can use the script located at build-scripts/androidbuild.sh
50 
51 There's two ways of using it:
52 
53  androidbuild.sh com.yourcompany.yourapp < sources.list
54  androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
55 
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
59 run:
60 
61  ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
62 
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.
65 
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.
69 
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!
72 
73 
74 For more complex projects, follow these instructions:
75 
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
80 
81 4a. If you want to use Android Studio, simply open your <project> directory and start building.
82 
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
84 
85 
86 If you already have a project that uses CMake, the instructions change somewhat:
87 
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.
96 
97 If you wish to use Android Studio, you can skip the last step.
98 
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
101 
102 Here's an explanation of the files in the Android project, so you can customize them:
103 
104  android-project/app
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.
121 
122 
123 ================================================================================
124  Customizing your application name
125 ================================================================================
126 
127 To customize your application name, edit AndroidManifest.xml and replace
128 "org.libsdl.app" with an identifier for your product package.
129 
130 Then create a Java class extending SDLActivity and place it in a directory
131 under src matching your package, e.g.
132 
133  src/com/gamemaker/game/MyGame.java
134 
135 Here's an example of a minimal class file:
136 
137  --- MyGame.java --------------------------
138  package com.gamemaker.game;
139 
140  import org.libsdl.app.SDLActivity;
141 
142  /**
143  * A sample wrapper class that just calls SDLActivity
144  */
145 
146  public class MyGame extends SDLActivity { }
147 
148  ------------------------------------------
149 
150 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
151 class, .e.g. "MyGame"
152 
153 
154 ================================================================================
155  Customizing your application icon
156 ================================================================================
157 
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.
161 
162 
163 ================================================================================
164  Loading assets
165 ================================================================================
166 
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.
170 
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()
176 
177 See SDL_system.h for more details on these functions.
178 
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
185 files are involved.
186 For more information on which extensions get compressed by default and how to
187 disable this behaviour, see for example:
188 
189 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
190 
191 
192 ================================================================================
193  Pause / Resume behaviour
194 ================================================================================
195 
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).
201 
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.
205 
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)
211 
212 
213 ================================================================================
214  Threads and the Java VM
215 ================================================================================
216 
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
219 
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
226 detach it.
227 
228 
229 ================================================================================
230  Using STL
231 ================================================================================
232 
233 You can use STL in your project by creating an Application.mk file in the jni
234 folder and adding the following line:
235 
236  APP_STL := c++_shared
237 
238 For more information go here:
239  https://developer.android.com/ndk/guides/cpp-support
240 
241 
242 ================================================================================
243  Using the emulator
244 ================================================================================
245 
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
248 
249 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
250 
251 Notice that this software emulator is incredibly slow and needs a lot of disk space.
252 Using a real device works better.
253 
254 
255 ================================================================================
256  Troubleshooting
257 ================================================================================
258 
259 You can see if adb can see any devices with the following command:
260 
261  adb devices
262 
263 You can see the output of log messages on the default device with:
264 
265  adb logcat
266 
267 You can push files to the device with:
268 
269  adb push local_file remote_path_and_file
270 
271 You can push files to the SD Card at /sdcard, for example:
272 
273  adb push moose.dat /sdcard/moose.dat
274 
275 You can see the files on the SD card with a shell command:
276 
277  adb shell ls /sdcard/
278 
279 You can start a command shell on the default device with:
280 
281  adb shell
282 
283 You can remove the library files of your project (and not the SDL lib files) with:
284 
285  ndk-build clean
286 
287 You can do a build with the following command:
288 
289  ndk-build
290 
291 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
292 
293  ndk-build V=1
294 
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
297 
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.
300 
301 For example, if your crash looks like this:
302 
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
312 
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:
315 
316  arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
317 
318 and then paste in the number after "pc" in the call stack, from the line that I care about:
319 000014bc
320 
321 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
322 
323 You can add logging to your code to help show what's happening:
324 
325  #include <android/log.h>
326 
327  __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
328 
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:
331 
332  APP_OPTIM := debug
333 
334 
335 ================================================================================
336  Memory debugging
337 ================================================================================
338 
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:
341 
342  svn co svn://svn.valgrind.org/valgrind/trunk valgrind
343 
344 ... and follow the instructions in the file README.android to build it.
345 
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
349 
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:
352 
353  --- start_valgrind_app -------------------
354  #!/system/bin/sh
355  export TMPDIR=/data/data/org.libsdl.app
356  exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
357  ------------------------------------------
358 
359 Then push it to the device:
360 
361  adb push start_valgrind_app /data/local
362 
363 and make it executable:
364 
365  adb shell chmod 755 /data/local/start_valgrind_app
366 
367 and tell Android to use the script to launch your application:
368 
369  adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
370 
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
374 
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
378 output file:
379 
380  adb pull /sdcard/valgrind.log
381 
382 When you're done instrumenting with valgrind, you can disable the wrapper:
383 
384  adb shell setprop wrap.org.libsdl.app ""
385 
386 
387 ================================================================================
388  Graphics debugging
389 ================================================================================
390 
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.
396 
397 The Tegra Graphics Debugger is available from NVidia here:
398 https://developer.nvidia.com/tegra-graphics-debugger
399 
400 
401 ================================================================================
402  Why is API level 16 the minimum required?
403 ================================================================================
404 
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).
409 
410 
411 ================================================================================
412  A note regarding the use of the "dirty rectangles" rendering technique
413 ================================================================================
414 
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
425 screen each frame.
426 
427 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
428 
429 
430 ================================================================================
431  Ending your application
432 ================================================================================
433 
434 Two legitimate ways:
435 
436 - return from your main() function. Java side will automatically terminate the
437 Activity by calling Activity.finish().
438 
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.
442 
443 Don't call exit() as it stops the activity badly.
444 
445 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
446 SDLK_AC_BACK, for any purpose.
447 
448 ================================================================================
449  Known issues
450 ================================================================================
451 
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.
454