2 ================================================================================
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
7 The rest of this README covers the Android gradle style build process.
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.
13 ================================================================================
15 ================================================================================
17 Android SDK (version 26 or later)
18 https://developer.android.com/sdk/index.html
20 Android NDK r15c or later
21 https://developer.android.com/tools/sdk/ndk/index.html
23 Minimum API level supported by SDL: 16 (Android 4.1)
26 ================================================================================
28 ================================================================================
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
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
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
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
45 ================================================================================
47 ================================================================================
49 For simple projects you can use the script located at build-scripts/androidbuild.sh
51 There's two ways of using it:
53 androidbuild.sh com.yourcompany.yourapp < sources.list
54 androidbuild.sh com.yourcompany.yourapp source1.c source2.c ...sourceN.c
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
61 ./androidbuild.sh org.libsdl.testgles ../test/testgles.c
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.
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.
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!
74 For more complex projects, follow these instructions:
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
81 4a. If you want to use Android Studio, simply open your <project> directory and start building.
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
85 Here's an explanation of the files in the Android project, so you can customize them:
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.
104 ================================================================================
105 Customizing your application name
106 ================================================================================
108 To customize your application name, edit AndroidManifest.xml and replace
109 "org.libsdl.app" with an identifier for your product package.
111 Then create a Java class extending SDLActivity and place it in a directory
112 under src matching your package, e.g.
114 src/com/gamemaker/game/MyGame.java
116 Here's an example of a minimal class file:
118 --- MyGame.java --------------------------
119 package com.gamemaker.game;
121 import org.libsdl.app.SDLActivity;
124 * A sample wrapper class that just calls SDLActivity
127 public class MyGame extends SDLActivity { }
129 ------------------------------------------
131 Then replace "SDLActivity" in AndroidManifest.xml with the name of your
132 class, .e.g. "MyGame"
135 ================================================================================
136 Customizing your application icon
137 ================================================================================
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.
144 ================================================================================
146 ================================================================================
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.
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()
158 See SDL_system.h for more details on these functions.
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
167 For more information on which extensions get compressed by default and how to
168 disable this behaviour, see for example:
170 http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/
173 ================================================================================
174 Pause / Resume behaviour
175 ================================================================================
177 If SDL_HINT_ANDROID_BLOCK_ON_PAUSE hint is set (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).
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.
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)
194 ================================================================================
195 Threads and the Java VM
196 ================================================================================
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
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
210 ================================================================================
212 ================================================================================
214 You can use STL in your project by creating an Application.mk file in the jni
215 folder and adding the following line:
217 APP_STL := c++_shared
219 For more information go here:
220 https://developer.android.com/ndk/guides/cpp-support
223 ================================================================================
225 ================================================================================
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
230 Especially useful is the info on setting up OpenGL ES 2.0 emulation.
232 Notice that this software emulator is incredibly slow and needs a lot of disk space.
233 Using a real device works better.
236 ================================================================================
238 ================================================================================
240 You can see if adb can see any devices with the following command:
244 You can see the output of log messages on the default device with:
248 You can push files to the device with:
250 adb push local_file remote_path_and_file
252 You can push files to the SD Card at /sdcard, for example:
254 adb push moose.dat /sdcard/moose.dat
256 You can see the files on the SD card with a shell command:
258 adb shell ls /sdcard/
260 You can start a command shell on the default device with:
264 You can remove the library files of your project (and not the SDL lib files) with:
268 You can do a build with the following command:
272 You can see the complete command line that ndk-build is using by passing V=1 on the command line:
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
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.
282 For example, if your crash looks like this:
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
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:
297 arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so
299 and then paste in the number after "pc" in the call stack, from the line that I care about:
302 I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23.
304 You can add logging to your code to help show what's happening:
306 #include <android/log.h>
308 __android_log_print(ANDROID_LOG_INFO, "foo", "Something happened! x = %d", x);
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:
316 ================================================================================
318 ================================================================================
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:
323 svn co svn://svn.valgrind.org/valgrind/trunk valgrind
325 ... and follow the instructions in the file README.android to build it.
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
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:
334 --- start_valgrind_app -------------------
336 export TMPDIR=/data/data/org.libsdl.app
337 exec /data/local/Inst/bin/valgrind --log-file=/sdcard/valgrind.log --error-limit=no $*
338 ------------------------------------------
340 Then push it to the device:
342 adb push start_valgrind_app /data/local
344 and make it executable:
346 adb shell chmod 755 /data/local/start_valgrind_app
348 and tell Android to use the script to launch your application:
350 adb shell setprop wrap.org.libsdl.app "logwrapper /data/local/start_valgrind_app"
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
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
361 adb pull /sdcard/valgrind.log
363 When you're done instrumenting with valgrind, you can disable the wrapper:
365 adb shell setprop wrap.org.libsdl.app ""
368 ================================================================================
370 ================================================================================
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.
378 The Tegra Graphics Debugger is available from NVidia here:
379 https://developer.nvidia.com/tegra-graphics-debugger
382 ================================================================================
383 Why is API level 16 the minimum required?
384 ================================================================================
386 The latest NDK toolchain doesn't support targeting earlier than API level 16.
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 16 or
389 higher (January 2018).
392 ================================================================================
393 A note regarding the use of the "dirty rectangles" rendering technique
394 ================================================================================
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
408 Reference: http://www.khronos.org/registry/egl/specs/EGLTechNote0001.html
411 ================================================================================
412 Ending your application
413 ================================================================================
417 - return from your main() function. Java side will automatically terminate the
418 Activity by calling Activity.finish().
420 - Android OS can decide to terminate your application by calling onDestroy()
421 (see Activity life cycle). Your application will receive a SDL_QUIT event you
422 can handle to save things and quit.
424 Don't call exit() as it stops the activity badly.
426 NB: "Back button" can be handled as a SDL_KEYDOWN/UP events, with Keycode
427 SDLK_AC_BACK, for any purpose.
429 ================================================================================
431 ================================================================================
433 - The number of buttons reported for each joystick is hardcoded to be 36, which
434 is the current maximum number of buttons Android can report.