1Android 2================================================================================ 3 4Matt Styles wrote a tutorial on building SDL for Android with Visual Studio: 5http://trederia.blogspot.de/2017/03/building-sdl2-for-android-with-visual.html 6 7The rest of this README covers the Android gradle style build process. 8 9If you are using the older ant build process, it is no longer officially 10supported, but you can use the "android-project-ant" directory as a template. 11 12 13================================================================================ 14 Requirements 15================================================================================ 16 17Android SDK (version 19 or later) 18https://developer.android.com/sdk/index.html 19 20Android NDK r10e or later 21https://developer.android.com/tools/sdk/ndk/index.html 22 23Minimum 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 37The Android Java code implements an "Activity" and can be found in: 38android-project/app/src/main/java/org/libsdl/app/SDLActivity.java 39 40The Java code loads your game code, the SDL shared library, and 41dispatches to native functions implemented in the SDL library: 42src/core/android/SDL_android.c 43 44 45================================================================================ 46 Building an app 47================================================================================ 48 49For simple projects you can use the script located at build-scripts/androidbuild.sh 50 51There'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 56sources.list should be a text file with a source file name in each line 57Filenames should be specified relative to the current directory, for example if 58you are in the build-scripts directory and want to create the testgles.c test, you'll 59run: 60 61 ./androidbuild.sh org.libsdl.testgles ../test/testgles.c 62 63One limitation of this script is that all sources provided will be aggregated into 64a single directory, thus all your source files should have a unique name. 65 66Once the project is complete the script will tell you where the debug APK is located. 67If you want to create a signed release APK, you can use the project created by this 68utility to generate it. 69 70Finally, a word of caution: re running androidbuild.sh wipes any changes you may have 71done in the build directory for the app! 72 73 74For more complex projects, follow these instructions: 75 761. Copy the android-project directory wherever you want to keep your projects 77 and rename it to the name of your project. 782. Move or symlink this SDL directory into the "<project>/app/jni" directory 793. Edit "<project>/app/jni/src/Android.mk" to include your source files 804. Run 'ndk-build' (a script provided by the NDK). This compiles the C source 81 82If you want to use Android Studio (recommended), skip to the Android Studio section below. 83 845. 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 86Here'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 110To customize your application name, edit AndroidManifest.xml and replace 111"org.libsdl.app" with an identifier for your product package. 112 113Then create a Java class extending SDLActivity and place it in a directory 114under src matching your package, e.g. 115 116 src/com/gamemaker/game/MyGame.java 117 118Here'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 133Then replace "SDLActivity" in AndroidManifest.xml with the name of your 134class, .e.g. "MyGame" 135 136 137================================================================================ 138 Customizing your application icon 139================================================================================ 140 141Conceptually changing your icon is just replacing the "ic_launcher.png" files in 142the drawable directories under the res directory. There are several directories 143for different screen sizes. 144 145 146================================================================================ 147 Loading assets 148================================================================================ 149 150Any files you put in the "app/src/main/assets" directory of your project 151directory will get bundled into the application package and you can load 152them using the standard functions in SDL_rwops.h. 153 154There are also a few Android specific functions that allow you to get other 155useful paths for saving and loading data: 156* SDL_AndroidGetInternalStoragePath() 157* SDL_AndroidGetExternalStorageState() 158* SDL_AndroidGetExternalStoragePath() 159 160See SDL_system.h for more details on these functions. 161 162The asset packaging system will, by default, compress certain file extensions. 163SDL includes two asset file access mechanisms, the preferred one is the so 164called "File Descriptor" method, which is faster and doesn't involve the Dalvik 165GC, 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 167may want to keep this fact in mind when building your APK, specially when large 168files are involved. 169For more information on which extensions get compressed by default and how to 170disable this behaviour, see for example: 171 172http://ponystyle.com/blog/2010/03/26/dealing-with-asset-compression-in-android-apps/ 173 174 175================================================================================ 176 Pause / Resume behaviour 177================================================================================ 178 179If SDL is compiled with SDL_ANDROID_BLOCK_ON_PAUSE defined (the default), 180the event loop will block itself when the app is paused (ie, when the user 181returns to the main Android dashboard). Blocking is better in terms of battery 182use, and it allows your app to spring back to life instantaneously after resume 183(versus polling for a resume message). 184 185Upon resume, SDL will attempt to restore the GL context automatically. 186In modern devices (Android 3.0 and up) this will most likely succeed and your 187app can continue to operate as it was. 188 189However, there's a chance (on older hardware, or on systems under heavy load), 190where the GL context can not be restored. In that case you have to listen for 191a specific message, (which is not yet implemented!) and restore your textures 192manually or quit the app (which is actually the kind of behaviour you'll see 193under 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 200For a quick tour on how Linux native threads interoperate with the Java VM, take 201a look here: https://developer.android.com/guide/practices/jni.html 202 203If you want to use threads in your SDL app, it's strongly recommended that you 204do so by creating them using SDL functions. This way, the required attach/detach 205handling is managed by SDL automagically. If you have threads created by other 206means and they make calls to SDL functions, make sure that you call 207Android_JNI_SetupThread() before doing anything else otherwise SDL will attach 208your thread automatically anyway (when you make an SDL call), but it'll never 209detach it. 210 211 212================================================================================ 213 Using STL 214================================================================================ 215 216You can use STL in your project by creating an Application.mk file in the jni 217folder and adding the following line: 218 219 APP_STL := stlport_static 220 221For more information check out CPLUSPLUS-SUPPORT.html in the NDK documentation. 222 223 224================================================================================ 225 Additional documentation 226================================================================================ 227 228The documentation in the NDK docs directory is very helpful in understanding the 229build process and how to work with native code on the Android platform. 230 231The best place to start is with docs/OVERVIEW.TXT 232 233 234================================================================================ 235 Using Android Studio 236================================================================================ 237 238You can open your project directory with Android Studio and run it normally. 239 240 241================================================================================ 242 Using the emulator 243================================================================================ 244 245There are some good tips and tricks for getting the most out of the 246emulator here: https://developer.android.com/tools/devices/emulator.html 247 248Especially useful is the info on setting up OpenGL ES 2.0 emulation. 249 250Notice that this software emulator is incredibly slow and needs a lot of disk space. 251Using a real device works better. 252 253 254================================================================================ 255 Troubleshooting 256================================================================================ 257 258You can see if adb can see any devices with the following command: 259 260 adb devices 261 262You can see the output of log messages on the default device with: 263 264 adb logcat 265 266You can push files to the device with: 267 268 adb push local_file remote_path_and_file 269 270You can push files to the SD Card at /sdcard, for example: 271 272 adb push moose.dat /sdcard/moose.dat 273 274You can see the files on the SD card with a shell command: 275 276 adb shell ls /sdcard/ 277 278You can start a command shell on the default device with: 279 280 adb shell 281 282You can remove the library files of your project (and not the SDL lib files) with: 283 284 ndk-build clean 285 286You can do a build with the following command: 287 288 ndk-build 289 290You 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 294If your application crashes in native code, you can use addr2line to convert the 295addresses in the stack trace to lines in your code. 296 297For 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 309You can see that there's a crash in the C library being called from the main code. 310I run addr2line with the debug version of my code: 311 312 arm-eabi-addr2line -C -f -e obj/local/armeabi/libmain.so 313 314and then paste in the number after "pc" in the call stack, from the line that I care about: 315000014bc 316 317I get output from addr2line showing that it's in the quit function, in testspriteminimal.c, on line 23. 318 319You 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 325If 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 335The best (and slowest) way to debug memory issues on Android is valgrind. 336Valgrind 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 342One thing I needed to do on Mac OS X was change the path to the toolchain, 343and add ranlib to the environment variables: 344export RANLIB=$NDKROOT/toolchains/arm-linux-androideabi-4.4.3/prebuilt/darwin-x86/bin/arm-linux-androideabi-ranlib 345 346Once valgrind is built, you can create a wrapper script to launch your 347application 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 355Then push it to the device: 356 357 adb push start_valgrind_app /data/local 358 359and make it executable: 360 361 adb shell chmod 755 /data/local/start_valgrind_app 362 363and 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 367If the setprop command says "could not set property", it's likely that 368your package name is too long and you should make it shorter by changing 369AndroidManifest.xml and the path to your class file in android-project/src 370 371You can then launch your application normally and waaaaaaaiiittt for it. 372You can monitor the startup process with the logcat command above, and 373when it's done (or even while it's running) you can grab the valgrind 374output file: 375 376 adb pull /sdcard/valgrind.log 377 378When 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 387If you are developing on a compatible Tegra-based tablet, NVidia provides 388Tegra Graphics Debugger at their website. Because SDL2 dynamically loads EGL 389and GLES libraries, you must follow their instructions for installing the 390interposer library on a rooted device. The non-rooted instructions are not 391compatible with applications that use SDL2 for video. 392 393The Tegra Graphics Debugger is available from NVidia here: 394https://developer.nvidia.com/tegra-graphics-debugger 395 396 397================================================================================ 398 Why is API level 14 the minimum required? 399================================================================================ 400 401The latest NDK toolchain doesn't support targeting earlier than API level 14. 402As of this writing, according to https://developer.android.com/about/dashboards/index.html 403about 99% of the Android devices accessing Google Play support API level 14 or 404higher (October 2017). 405 406 407================================================================================ 408 A note regarding the use of the "dirty rectangles" rendering technique 409================================================================================ 410 411If your app uses a variation of the "dirty rectangles" rendering technique, 412where you only update a portion of the screen on each frame, you may notice a 413variety of visual glitches on Android, that are not present on other platforms. 414This is caused by SDL's use of EGL as the support system to handle OpenGL ES/ES2 415contexts, in particular the use of the eglSwapBuffers function. As stated in the 416documentation for the function "The contents of ancillary buffers are always 417undefined after calling eglSwapBuffers". 418Setting the EGL_SWAP_BEHAVIOR attribute of the surface to EGL_BUFFER_PRESERVED 419is not possible for SDL as it requires EGL 1.4, available only on the API level 42017+, so the only workaround available on this platform is to redraw the entire 421screen each frame. 422 423Reference: 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 431is the current maximum number of buttons Android can report. 432 433
