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