SDL  2.0
docs/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 19 or later)
18 https://developer.android.com/sdk/index.html
19 
20 Android NDK r10e or later
21 https://developer.android.com/tools/sdk/ndk/index.html
22 
23 Minimum API level supported by SDL: 14 (Android 4.0.1)
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 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
81 
82 If you want to use Android Studio (recommended), skip to the Android Studio section below.
83 
84 5. 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
85 
86 Here's an explanation of the files in the Android project, so you can customize them:
87 
88  android-project/app
89  build.gradle - build info including the application version and SDK
90  src/main/AndroidManifest.xml - package manifest. Among others, it contains the class name
91  of the main Activity and the package name of the application.
92  jni/ - directory holding native code
93  jni/Application.mk - Application JNI settings, including target platform and STL library
94  jni/Android.mk - Android makefile that can call recursively the Android.mk files in all subdirectories
95  jni/SDL/ - (symlink to) directory holding the SDL library files
96  jni/SDL/Android.mk - Android makefile for creating the SDL shared library
97  jni/src/ - directory holding your C/C++ source
98  jni/src/Android.mk - Android makefile that you should customize to include your source code and any library references
99  src/main/assets/ - directory holding asset files for your application
100  src/main/res/ - directory holding resources for your application
101  src/main/res/mipmap-* - directories holding icons for different phone hardware
102  src/main/res/values/strings.xml - strings used in your application, including the application name
103  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.
104 
105 
106 ================================================================================
107  Customizing your application name
108 ================================================================================
109 
110 To customize your application name, edit AndroidManifest.xml and replace
111 "org.libsdl.app" with an identifier for your product package.
112 
113 Then create a Java class extending SDLActivity and place it in a directory
114 under src matching your package, e.g.
115 
116  src/com/gamemaker/game/MyGame.java
117 
118 Here's an example of a minimal class file:
119 
120  --- MyGame.java --------------------------
121  package com.gamemaker.game;
122 
123  import org.libsdl.app.SDLActivity;
124 
125  /**
126  * A sample wrapper class that just calls SDLActivity
127  */
128 
129  public class MyGame extends SDLActivity { }
130 
131  ------------------------------------------
132 
133 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
134 class, .e.g. "MyGame"
135 
136 
137 ================================================================================
138  Customizing your application icon
139 ================================================================================
140 
141 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
142 the drawable directories under the res directory. There are several directories
143 for different screen sizes.
144 
145 
146 ================================================================================
147  Loading assets
148 ================================================================================
149 
150 Any files you put in the "app/src/main/assets" directory of your project
151 directory will get bundled into the application package and you can load
152 them using the standard functions in SDL_rwops.h.
153 
154 There are also a few Android specific functions that allow you to get other
155 useful paths for saving and loading data:
156 * SDL_AndroidGetInternalStoragePath()
157 * SDL_AndroidGetExternalStorageState()
158 * SDL_AndroidGetExternalStoragePath()
159 
160 See SDL_system.h for more details on these functions.
161 
162 The asset packaging system will, by default, compress certain file extensions.
163 SDL includes two asset file access mechanisms, the preferred one is the so
164 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
165 GC, but given this method does not work on compressed assets, there is also the
166 "Input Stream" method, which is automatically used as a fall back by SDL. You
167 may want to keep this fact in mind when building your APK, specially when large
168 files are involved.
169 For more information on which extensions get compressed by default and how to
170 disable this behaviour, see for example:
171 
172 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
173 
174 
175 ================================================================================
176  Pause / Resume behaviour
177 ================================================================================
178 
179 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
180 the event loop will block itself when the app is paused (ie, when the user
181 returns to the main Android dashboard). Blocking is better in terms of battery
182 use, and it allows your app to spring back to life instantaneously after resume
183 (versus polling for a resume message).
184 
185 Upon resume, SDL will attempt to restore the GL context automatically.
186 In modern devices (Android 3.0 and up) this will most likely succeed and your
187 app can continue to operate as it was.
188 
189 However, there's a chance (on older hardware, or on systems under heavy load),
190 where the GL context can not be restored. In that case you have to listen for
191 a specific message, (which is not yet implemented!) and restore your textures
192 manually or quit the app (which is actually the kind of behaviour you'll see
193 under iOS, if the OS can not restore your GL context it will just kill your app)
194 
195 
196 ================================================================================
197  Threads and the Java VM
198 ================================================================================
199 
200 For a quick tour on how Linux native threads interoperate with the Java VM, take
201 a look here: https://developer.android.com/guide/practices/jni.html
202 
203 If you want to use threads in your SDL app, it's strongly recommended that you
204 do so by creating them using SDL functions. This way, the required attach/detach
205 handling is managed by SDL automagically. If you have threads created by other
206 means and they make calls to SDL functions, make sure that you call
207 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
208 your thread automatically anyway (when you make an SDL call), but it'll never
209 detach it.
210 
211 
212 ================================================================================
213  Using STL
214 ================================================================================
215 
216 You can use STL in your project by creating an Application.mk file in the jni
217 folder and adding the following line:
218 
219  APP_STL := stlport_static
220 
221 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
222 
223 
224 ================================================================================
225  Additional documentation
226 ================================================================================
227 
228 The documentation in the NDK docs directory is very helpful in understanding the
229 build process and how to work with native code on the Android platform.
230 
231 The best place to start is with docs/OVERVIEW.TXT
232 
233 
234 ================================================================================
235  Using Android Studio
236 ================================================================================
237 
238 You can open your project directory with Android Studio and run it normally.
239 
240 
241 ================================================================================
242  Using the emulator
243 ================================================================================
244 
245 There are some good tips and tricks for getting the most out of the
246 emulator here: https://developer.android.com/tools/devices/emulator.html
247 
248 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
249 
250 Notice that this software emulator is incredibly slow and needs a lot of disk space.
251 Using a real device works better.
252 
253 
254 ================================================================================
255  Troubleshooting
256 ================================================================================
257 
258 You can see if adb can see any devices with the following command:
259 
260  adb devices
261 
262 You can see the output of log messages on the default device with:
263 
264  adb logcat
265 
266 You can push files to the device with:
267 
268  adb push local_file remote_path_and_file
269 
270 You can push files to the SD Card at /sdcard, for example:
271 
272  adb push moose.dat /sdcard/moose.dat
273 
274 You can see the files on the SD card with a shell command:
275 
276  adb shell ls /sdcard/
277 
278 You can start a command shell on the default device with:
279 
280  adb shell
281 
282 You can remove the library files of your project (and not the SDL lib files) with:
283 
284  ndk-build clean
285 
286 You can do a build with the following command:
287 
288  ndk-build
289 
290 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
291 
292  ndk-build V=1
293 
294 If your application crashes in native code, you can use addr2line to convert the
295 addresses in the stack trace to lines in your code.
296 
297 For example, if your crash looks like this:
298 
299  I/DEBUG ( 31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
300  I/DEBUG ( 31): r0 00000000 r1 00001000 r2 00000003 r3 400085d4
301  I/DEBUG ( 31): r4 400085d0 r5 40008000 r6 afd41504 r7 436c6a7c
302  I/DEBUG ( 31): r8 436c6b30 r9 435c6fb0 10 435c6f9c fp 4168d82c
303  I/DEBUG ( 31): ip 8346aff0 sp 436c6a60 lr afd1c8ff pc afd1c902 cpsr 60000030
304  I/DEBUG ( 31): #00 pc 0001c902 /system/lib/libc.so
305  I/DEBUG ( 31): #01 pc 0001ccf6 /system/lib/libc.so
306  I/DEBUG ( 31): #02 pc 000014bc /data/data/org.libsdl.app/lib/libmain.so
307  I/DEBUG ( 31): #03 pc 00001506 /data/data/org.libsdl.app/lib/libmain.so
308 
309 You can see that there's a crash in the C library being called from the main code.
310 I run addr2line with the debug version of my code:
311 
312  arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
313 
314 and then paste in the number after "pc" in the call stack, from the line that I care about:
315 000014bc
316 
317 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
318 
319 You can add logging to your code to help show what's happening:
320 
321  #include <android/log.h>
322 
323  __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
324 
325 If you need to build without optimization turned on, you can create a file called
326 "Application.mk" in the jni directory, with the following line in it:
327 
328  APP_OPTIM := debug
329 
330 
331 ================================================================================
332  Memory debugging
333 ================================================================================
334 
335 The best (and slowest) way to debug memory issues on Android is valgrind.
336 Valgrind has support for Android out of the box, just grab code using:
337 
338  svn co svn://svn.valgrind.org/valgrind/trunk valgrind
339 
340 ... and follow the instructions in the file README.android to build it.
341 
342 One thing I needed to do on Mac OS X was change the path to the toolchain,
343 and add ranlib to the environment variables:
344 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
345 
346 Once valgrind is built, you can create a wrapper script to launch your
347 application with it, changing org.libsdl.app to your package identifier:
348 
349  --- start_valgrind_app -------------------
350  #!/system/bin/sh
351  export TMPDIR=/data/data/org.libsdl.app
352  exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
353  ------------------------------------------
354 
355 Then push it to the device:
356 
357  adb push start_valgrind_app /data/local
358 
359 and make it executable:
360 
361  adb shell chmod 755 /data/local/start_valgrind_app
362 
363 and tell Android to use the script to launch your application:
364 
365  adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
366 
367 If the setprop command says "could not set property", it's likely that
368 your package name is too long and you should make it shorter by changing
369 AndroidManifest.xml and the path to your class file in android-project/src
370 
371 You can then launch your application normally and waaaaaaaiiittt for it.
372 You can monitor the startup process with the logcat command above, and
373 when it's done (or even while it's running) you can grab the valgrind
374 output file:
375 
376  adb pull /sdcard/valgrind.log
377 
378 When you're done instrumenting with valgrind, you can disable the wrapper:
379 
380  adb shell setprop wrap.org.libsdl.app ""
381 
382 
383 ================================================================================
384  Graphics debugging
385 ================================================================================
386 
387 If you are developing on a compatible Tegra-based tablet, NVidia provides
388 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
389 and GLES libraries, you must follow their instructions for installing the
390 interposer library on a rooted device. The non-rooted instructions are not
391 compatible with applications that use SDL2 for video.
392 
393 The Tegra Graphics Debugger is available from NVidia here:
394 https://developer.nvidia.com/tegra-graphics-debugger
395 
396 
397 ================================================================================
398  Why is API level 14 the minimum required?
399 ================================================================================
400 
401 The latest NDK toolchain doesn't support targeting earlier than API level 14.
402 As of this writing, according to https://developer.android.com/about/dashboards/index.html
403 about 99% of the Android devices accessing Google Play support API level 14 or
404 higher (October 2017).
405 
406 
407 ================================================================================
408  A note regarding the use of the "dirty rectangles" rendering technique
409 ================================================================================
410 
411 If your app uses a variation of the "dirty rectangles" rendering technique,
412 where you only update a portion of the screen on each frame, you may notice a
413 variety of visual glitches on Android, that are not present on other platforms.
414 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
415 contexts, in particular the use of the eglSwapBuffers function. As stated in the
416 documentation for the function "The contents of ancillary buffers are always
417 undefined after calling eglSwapBuffers".
418 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
419 is not possible for SDL as it requires EGL 1.4, available only on the API level
420 17+, so the only workaround available on this platform is to redraw the entire
421 screen each frame.
422 
423 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
424 
425 
426 ================================================================================
427  Known issues
428 ================================================================================
429 
430 - The number of buttons reported for each joystick is hardcoded to be 36, which
431 is the current maximum number of buttons Android can report.
432