SDL  2.0
docs/README-android.md
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1 Android
2 ================================================================================
3 
4 Requirements:
5 
6 Android SDK (version 12 or later)
7 http://developer.android.com/sdk/index.html
8 
9 Android NDK r7 or later
10 http://developer.android.com/tools/sdk/ndk/index.html
11 
12 Minimum API level supported by SDL: 10 (Android 2.3.3)
13 Joystick support is available for API level >=12 devices.
14 
15 ================================================================================
16  How the port works
17 ================================================================================
18 
19 - Android applications are Java-based, optionally with parts written in C
20 - As SDL apps are C-based, we use a small Java shim that uses JNI to talk to
21  the SDL library
22 - This means that your application C code must be placed inside an Android
23  Java project, along with some C support code that communicates with Java
24 - This eventually produces a standard Android .apk package
25 
26 The Android Java code implements an "Activity" and can be found in:
27 android-project/src/org/libsdl/app/SDLActivity.java
28 
29 The Java code loads your game code, the SDL shared library, and
30 dispatches to native functions implemented in the SDL library:
31 src/core/android/SDL_android.c
32 
33 Your project must include some glue code that starts your main() routine:
34 src/main/android/SDL_android_main.c
35 
36 
37 ================================================================================
38  Building an app
39 ================================================================================
40 
41 For simple projects you can use the script located at build-scripts/androidbuild.sh
42 
43 There's two ways of using it:
44 
45  androidbuild.sh com.yourcompany.yourapp < sources.list
46  androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
47 
48 sources.list should be a text file with a source file name in each line
49 Filenames should be specified relative to the current directory, for example if
50 you are in the build-scripts directory and want to create the testgles.c test, you'll
51 run:
52 
53  ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
54 
55 One limitation of this script is that all sources provided will be aggregated into
56 a single directory, thus all your source files should have a unique name.
57 
58 Once the project is complete the script will tell you where the debug APK is located.
59 If you want to create a signed release APK, you can use the project created by this
60 utility to generate it.
61 
62 Finally, a word of caution: re running androidbuild.sh wipes any changes you may have
63 done in the build directory for the app!
64 
65 
66 For more complex projects, follow these instructions:
67 
68 1. Copy the android-project directory wherever you want to keep your projects
69  and rename it to the name of your project.
70 2. Move or symlink this SDL directory into the "<project>/jni" directory
71 3. Edit "<project>/jni/src/Android.mk" to include your source files
72 4. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
73 
74 If you want to use the Eclipse IDE, skip to the Eclipse section below.
75 
76 5. Create "<project>/local.properties" and use that to point to the Android SDK directory, by writing a line with the following form:
77 
78  sdk.dir=PATH_TO_ANDROID_SDK
79 
80 6. Run 'ant debug' in android/project. This compiles the .java and eventually
81  creates a .apk with the native code embedded
82 7. 'ant debug install' will push the apk to the device or emulator (if connected)
83 
84 Here's an explanation of the files in the Android project, so you can customize them:
85 
86  android-project/
87  AndroidManifest.xml - package manifest. Among others, it contains the class name
88  of the main Activity and the package name of the application.
89  build.properties - empty
90  build.xml - build description file, used by ant. The actual application name
91  is specified here.
92  default.properties - holds the target ABI for the application, android-10 and up
93  project.properties - holds the target ABI for the application, android-10 and up
94  local.properties - holds the SDK path, you should change this to the path to your SDK
95  jni/ - directory holding native code
96  jni/Android.mk - Android makefile that can call recursively the Android.mk files
97  in all subdirectories
98  jni/SDL/ - (symlink to) directory holding the SDL library files
99  jni/SDL/Android.mk - Android makefile for creating the SDL shared library
100  jni/src/ - directory holding your C/C++ source
101  jni/src/Android.mk - Android makefile that you should customize to include your
102  source code and any library references
103  res/ - directory holding resources for your application
104  res/drawable-* - directories holding icons for different phone hardware. Could be
105  one dir called "drawable".
106  res/layout/main.xml - Usually contains a file main.xml, which declares the screen layout.
107  We don't need it because we use the SDL video output.
108  res/values/strings.xml - strings used in your application, including the application name
109  shown on the phone.
110  src/org/libsdl/app/SDLActivity.java - the Java class handling the initialization and binding
111  to SDL. Be very careful changing this, as the SDL library relies
112  on this implementation.
113 
114 
115 ================================================================================
116  Build an app with static linking of libSDL
117 ================================================================================
118 
119 This build uses the Android NDK module system.
120 
121 Instructions:
122 1. Copy the android-project directory wherever you want to keep your projects
123  and rename it to the name of your project.
124 2. Rename "<project>/jni/src/Android_static.mk" to "<project>/jni/src/Android.mk"
125  (overwrite the existing one)
126 3. Edit "<project>/jni/src/Android.mk" to include your source files
127 4. create and export an environment variable named NDK_MODULE_PATH that points
128  to the parent directory of this SDL directory. e.g.:
129 
130  export NDK_MODULE_PATH="$PWD"/..
131 
132 5. Edit "<project>/src/org/libsdl/app/SDLActivity.java" and remove the call to
133  System.loadLibrary("SDL2").
134 6. Run 'ndk-build' (a script provided by the NDK). This compiles the C source
135 
136 
137 ================================================================================
138  Customizing your application name
139 ================================================================================
140 
141 To customize your application name, edit AndroidManifest.xml and replace
142 "org.libsdl.app" with an identifier for your product package.
143 
144 Then create a Java class extending SDLActivity and place it in a directory
145 under src matching your package, e.g.
146 
147  src/com/gamemaker/game/MyGame.java
148 
149 Here's an example of a minimal class file:
150 
151  --- MyGame.java --------------------------
152  package com.gamemaker.game;
153 
154  import org.libsdl.app.SDLActivity;
155 
156  /**
157  * A sample wrapper class that just calls SDLActivity
158  */
159 
160  public class MyGame extends SDLActivity { }
161 
162  ------------------------------------------
163 
164 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
165 class, .e.g. "MyGame"
166 
167 ================================================================================
168  Customizing your application icon
169 ================================================================================
170 
171 Conceptually changing your icon is just replacing the "ic_launcher.png" files in
172 the drawable directories under the res directory. There are four directories for
173 different screen sizes. These can be replaced with one dir called "drawable",
174 containing an icon file "ic_launcher.png" with dimensions 48x48 or 72x72.
175 
176 You may need to change the name of your icon in AndroidManifest.xml to match
177 this icon filename.
178 
179 ================================================================================
180  Loading assets
181 ================================================================================
182 
183 Any files you put in the "assets" directory of your android-project directory
184 will get bundled into the application package and you can load them using the
185 standard functions in SDL_rwops.h.
186 
187 There are also a few Android specific functions that allow you to get other
188 useful paths for saving and loading data:
189 * SDL_AndroidGetInternalStoragePath()
190 * SDL_AndroidGetExternalStorageState()
191 * SDL_AndroidGetExternalStoragePath()
192 
193 See SDL_system.h for more details on these functions.
194 
195 The asset packaging system will, by default, compress certain file extensions.
196 SDL includes two asset file access mechanisms, the preferred one is the so
197 called "File Descriptor" method, which is faster and doesn't involve the Dalvik
198 GC, but given this method does not work on compressed assets, there is also the
199 "Input Stream" method, which is automatically used as a fall back by SDL. You
200 may want to keep this fact in mind when building your APK, specially when large
201 files are involved.
202 For more information on which extensions get compressed by default and how to
203 disable this behaviour, see for example:
204 
205 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
206 
207 ================================================================================
208  Pause / Resume behaviour
209 ================================================================================
210 
211 If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default),
212 the event loop will block itself when the app is paused (ie, when the user
213 returns to the main Android dashboard). Blocking is better in terms of battery
214 use, and it allows your app to spring back to life instantaneously after resume
215 (versus polling for a resume message).
216 
217 Upon resume, SDL will attempt to restore the GL context automatically.
218 In modern devices (Android 3.0 and up) this will most likely succeed and your
219 app can continue to operate as it was.
220 
221 However, there's a chance (on older hardware, or on systems under heavy load),
222 where the GL context can not be restored. In that case you have to listen for
223 a specific message, (which is not yet implemented!) and restore your textures
224 manually or quit the app (which is actually the kind of behaviour you'll see
225 under iOS, if the OS can not restore your GL context it will just kill your app)
226 
227 ================================================================================
228  Threads and the Java VM
229 ================================================================================
230 
231 For a quick tour on how Linux native threads interoperate with the Java VM, take
232 a look here: http://developer.android.com/guide/practices/jni.html
233 
234 If you want to use threads in your SDL app, it's strongly recommended that you
235 do so by creating them using SDL functions. This way, the required attach/detach
236 handling is managed by SDL automagically. If you have threads created by other
237 means and they make calls to SDL functions, make sure that you call
238 Android_JNI_SetupThread() before doing anything else otherwise SDL will attach
239 your thread automatically anyway (when you make an SDL call), but it'll never
240 detach it.
241 
242 ================================================================================
243  Using STL
244 ================================================================================
245 
246 You can use STL in your project by creating an Application.mk file in the jni
247 folder and adding the following line:
248 
249  APP_STL := stlport_static
250 
251 For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation.
252 
253 ================================================================================
254  Additional documentation
255 ================================================================================
256 
257 The documentation in the NDK docs directory is very helpful in understanding the
258 build process and how to work with native code on the Android platform.
259 
260 The best place to start is with docs/OVERVIEW.TXT
261 
262 
263 ================================================================================
264  Using Eclipse
265 ================================================================================
266 
267 First make sure that you've installed Eclipse and the Android extensions as described here:
268  http://developer.android.com/tools/sdk/eclipse-adt.html
269 
270 Once you've copied the SDL android project and customized it, you can create an Eclipse project from it:
271  * File -> New -> Other
272  * Select the Android -> Android Project wizard and click Next
273  * Enter the name you'd like your project to have
274  * Select "Create project from existing source" and browse for your project directory
275  * Make sure the Build Target is set to Android 3.1 (API 12)
276  * Click Finish
277 
278 
279 ================================================================================
280  Using the emulator
281 ================================================================================
282 
283 There are some good tips and tricks for getting the most out of the
284 emulator here: http://developer.android.com/tools/devices/emulator.html
285 
286 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
287 
288 Notice that this software emulator is incredibly slow and needs a lot of disk space.
289 Using a real device works better.
290 
291 ================================================================================
292  Troubleshooting
293 ================================================================================
294 
295 You can create and run an emulator from the Eclipse IDE:
296  * Window -> Android SDK and AVD Manager
297 
298 You can see if adb can see any devices with the following command:
299 
300  adb devices
301 
302 You can see the output of log messages on the default device with:
303 
304  adb logcat
305 
306 You can push files to the device with:
307 
308  adb push local_file remote_path_and_file
309 
310 You can push files to the SD Card at /sdcard, for example:
311 
312  adb push moose.dat /sdcard/moose.dat
313 
314 You can see the files on the SD card with a shell command:
315 
316  adb shell ls /sdcard/
317 
318 You can start a command shell on the default device with:
319 
320  adb shell
321 
322 You can remove the library files of your project (and not the SDL lib files) with:
323 
324  ndk-build clean
325 
326 You can do a build with the following command:
327 
328  ndk-build
329 
330 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
331 
332  ndk-build V=1
333 
334 If your application crashes in native code, you can use addr2line to convert the
335 addresses in the stack trace to lines in your code.
336 
337 For example, if your crash looks like this:
338 
339  I/DEBUG ( 31): signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 400085d0
340  I/DEBUG ( 31): r0 00000000 r1 00001000 r2 00000003 r3 400085d4
341  I/DEBUG ( 31): r4 400085d0 r5 40008000 r6 afd41504 r7 436c6a7c
342  I/DEBUG ( 31): r8 436c6b30 r9 435c6fb0 10 435c6f9c fp 4168d82c
343  I/DEBUG ( 31): ip 8346aff0 sp 436c6a60 lr afd1c8ff pc afd1c902 cpsr 60000030
344  I/DEBUG ( 31): #00 pc 0001c902 /system/lib/libc.so
345  I/DEBUG ( 31): #01 pc 0001ccf6 /system/lib/libc.so
346  I/DEBUG ( 31): #02 pc 000014bc /data/data/org.libsdl.app/lib/libmain.so
347  I/DEBUG ( 31): #03 pc 00001506 /data/data/org.libsdl.app/lib/libmain.so
348 
349 You can see that there's a crash in the C library being called from the main code.
350 I run addr2line with the debug version of my code:
351 
352  arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
353 
354 and then paste in the number after "pc" in the call stack, from the line that I care about:
355 000014bc
356 
357 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
358 
359 You can add logging to your code to help show what's happening:
360 
361  #include <android/log.h>
362 
363  __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
364 
365 If you need to build without optimization turned on, you can create a file called
366 "Application.mk" in the jni directory, with the following line in it:
367 
368  APP_OPTIM := debug
369 
370 
371 ================================================================================
372  Memory debugging
373 ================================================================================
374 
375 The best (and slowest) way to debug memory issues on Android is valgrind.
376 Valgrind has support for Android out of the box, just grab code using:
377 
378  svn co svn://svn.valgrind.org/valgrind/trunk valgrind
379 
380 ... and follow the instructions in the file README.android to build it.
381 
382 One thing I needed to do on Mac OS X was change the path to the toolchain,
383 and add ranlib to the environment variables:
384 export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib
385 
386 Once valgrind is built, you can create a wrapper script to launch your
387 application with it, changing org.libsdl.app to your package identifier:
388 
389  --- start_valgrind_app -------------------
390  #!/system/bin/sh
391  export TMPDIR=/data/data/org.libsdl.app
392  exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
393  ------------------------------------------
394 
395 Then push it to the device:
396 
397  adb push start_valgrind_app /data/local
398 
399 and make it executable:
400 
401  adb shell chmod 755 /data/local/start_valgrind_app
402 
403 and tell Android to use the script to launch your application:
404 
405  adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
406 
407 If the setprop command says "could not set property", it's likely that
408 your package name is too long and you should make it shorter by changing
409 AndroidManifest.xml and the path to your class file in android-project/src
410 
411 You can then launch your application normally and waaaaaaaiiittt for it.
412 You can monitor the startup process with the logcat command above, and
413 when it's done (or even while it's running) you can grab the valgrind
414 output file:
415 
416  adb pull /sdcard/valgrind.log
417 
418 When you're done instrumenting with valgrind, you can disable the wrapper:
419 
420  adb shell setprop wrap.org.libsdl.app ""
421 
422 ================================================================================
423  Graphics debugging
424 ================================================================================
425 
426 If you are developing on a compatible Tegra-based tablet, NVidia provides
427 Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL
428 and GLES libraries, you must follow their instructions for installing the
429 interposer library on a rooted device. The non-rooted instructions are not
430 compatible with applications that use SDL2 for video.
431 
432 The Tegra Graphics Debugger is available from NVidia here:
433 https://developer.nvidia.com/tegra-graphics-debugger
434 
435 ================================================================================
436  Why is API level 10 the minimum required?
437 ================================================================================
438 
439 API level 10 is the minimum required level at runtime (that is, on the device)
440 because SDL requires some functionality for running not
441 available on older devices. Since the incorporation of joystick support into SDL,
442 the minimum SDK required to *build* SDL is version 12. Devices running API levels
443 10-11 are still supported, only with the joystick functionality disabled.
444 
445 Support for native OpenGL ES and ES2 applications was introduced in the NDK for
446 API level 4 and 8. EGL was made a stable API in the NDK for API level 9, which
447 has since then been obsoleted, with the recommendation to developers to bump the
448 required API level to 10.
449 As of this writing, according to http://developer.android.com/about/dashboards/index.html
450 about 90% of the Android devices accessing Google Play support API level 10 or
451 higher (March 2013).
452 
453 ================================================================================
454  A note regarding the use of the "dirty rectangles" rendering technique
455 ================================================================================
456 
457 If your app uses a variation of the "dirty rectangles" rendering technique,
458 where you only update a portion of the screen on each frame, you may notice a
459 variety of visual glitches on Android, that are not present on other platforms.
460 This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2
461 contexts, in particular the use of the eglSwapBuffers function. As stated in the
462 documentation for the function "The contents of ancillary buffers are always
463 undefined after calling eglSwapBuffers".
464 Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED
465 is not possible for SDL as it requires EGL 1.4, available only on the API level
466 17+, so the only workaround available on this platform is to redraw the entire
467 screen each frame.
468 
469 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
470 
471 ================================================================================
472  Known issues
473 ================================================================================
474 
475 - The number of buttons reported for each joystick is hardcoded to be 36, which
476 is the current maximum number of buttons Android can report.
477