Porting and Maintaining your C++ Game on Android without losing your mind
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This document provides a comprehensive guide on porting and maintaining C++ games on Android, highlighting the advantages of using C++ for cross-platform support and existing codebases. It discusses the NDK setup, challenges faced, such as data duplication and compression issues, and offers solutions for managing file and library integration between C++ and Java. Additionally, it covers specific coding practices for JNI interactions and architectural compilation for various platforms.
![Excluded file extensions
Source: Android Asset Packaging Tool
/* these formats are already compressed, or don't
compress well */
static const char* kNoCompressExt[] = { ".jpg",
".jpeg", ".png", ".gif", ".wav", ".mp2",
".mp3", ".ogg", ".aac", ".mpg", ".mpeg",
".mid", ".midi", ".smf", ".jet", ".rtttl",
".imy", ".xmf", ".mp4", ".m4a", ".m4v", ".3gp",
".3gpp", ".3g2", ".3gpp2", ".amr", ".awb",
".wma", ".wmv" };](https://image.slidesharecdn.com/portingandmaintainingyourcgame-140305115319-phpapp01/85/Porting-and-Maintaining-your-C-Game-on-Android-without-losing-your-mind-21-320.jpg)
Porting and Maintaining your C++ Game on Android without losing your mind
- 1. Porting and Maintaining Your C++ Game on Android (without losing your mind)
- 3. Why C++ Cross-Platform support (Some lesser platforms don’t have a JVM) Don’t want to use Unity, etc Existing C++ Codebase
- 4. Overview NDK recap What goes where? C++ vs Java Streamlining packaged app data Eliminating Data Duplication Compiling multiple architectures Other quirks we’ve run into Some downloads info about our apps
- 5. NDK Application.mk APP_PROJECT_PATH := $(call my-dir) APP_BUILD_SCRIPT := $(call my-dir)/Android.mk APP_MODULES := GHEngine APP_OPTIM := release APP_STL := stlport_static APP_PLATFORM := android-8
- 6. NDK (static lib) Android.mk LOCAL_PATH := $(call my-dir) LOCAL_CFLAGS := -Wno-psabi LOCAL_CFLAGS += -D ANDROID LOCAL_MODULE := GHEngine LOCAL_MODULE_FILENAME := libGHEngine LOCAL_C_INCLUDES += $(LOCAL_PATH)/../../../../Base LOCAL_SRC_FILES += ../../../../Base/GHAppRunner.cpp include $(BUILD_STATIC_LIBRARY)
- 7. NDK Android.mk (shared lib – loaded by java) LOCAL_MODULE := libGHEngine LOCAL_SRC_FILES := ../../GHEngine/obj/local/armeabi/libGHEngine.a include $(PREBUILT_STATIC_LIBRARY) LOCAL_STATIC_LIBRARIES += libGHEngine include $(BUILD_SHARED_LIBRARY) $(shell cp libs/armeabi/libGHBowling.so ../../../GHBowlingBase/libs/armeabi)
- 8. NDK JNI Loading the C++ Library public class GHBowlingBaseActivity extends Activity { static { System.loadLibrary("GHBowling"); } } Loads the file named libGHBowling.so
- 9. NDK JNI Java (calling C++) public class GHEngineInterface { public native void runNativeFrame(); public native void launchNativeApp(int windowWidth, int windowHeight, String externalStoragePath, int isTablet,int iapIsOn); //resizeWindow, handleTouchStart, handleTouchEnd, handleTouchPos //handleAcceleration, handleJavaPause, handleJavaResume, //handleJavaShutdown,handleBackPressed, calculatePublicKey, //onInterstitialRewardGranted,onRewardInterstitialAvailabilityChange, //onInterstitialDismiss, loadFile,handleTextureLoadConfirmed, //onAdActivation, onAdDeactivation, onIAPPurchase }
- 10. NDK JNI C++ (called by Java) static jobject globalEngineInterface = 0; extern "C“ __attribute__((visibility("default"))) void Java_goldenhammer_ghbowlingbase_GHEngineInterface_launchNativeApp (JNIEnv* env, jobject engineInterface, jint windowWidth, jint windowHeight, jstring jExternalStoragePath, jint isTablet, jint useIAP) { globalEngineInterface = env->NewGlobalRef(engineInterface); //Engine/Game Initialization goes here. } When you shut down: env->DeleteGlobalRef(globalEngineInterface);
- 11. NDK JNI Java (called by C++) public class GHEngineInterface { public void showInterstitialAd() { if (mInterstitialHandler != null) { mInterstitialHandler.showInterstitial(); } else { onInterstitialDismiss(); } } };
- 12. NDK JNI C++ (calling Java) GHAndroidInterstitialAd class declaration: JNIEnv& mJNIEnv; jobject mEngineInterface; jmethodID mShowAdMethod; GHAndroidInterstitialAd ctor: jclass cls = mJNIEnv.GetObjectClass(mEngineInterface); mShowAdMethod = mJNIEnv.GetMethodID(cls, "showInterstitialAd", "()V"); GHAndroidInterstitialAd::activate: mJNIEnv.CallVoidMethod(mJavaObj, mShowAdMethod);
- 13. What goes Where? C++ or Java C++ Java All your platform-independent/pre-existing code Bare minimum wrapper for Android implementation of platform services Typical Android platform code Middleware integration Can swap middleware vendors of the same service without touching C++ Exceptions: OpenGL (initialization in Java, most code in C++ or GLSL) File I/O (mix of Java, C++)
- 14. What Goes Where Java OpenGL initialization Sound through SoundPool File handle loading through AssetManager Image loading through BitmapFactory Google Play, In-App Billing, etc Ads and other middleware integration AdMob, AdColony, Chartboost, PlayHaven, Facebook, etc Input Handling (touches, accelerometer, buttons/gamepad)
- 15. What Goes Where C++ All your game code OpenGL rendering code Ideally 90% of your app Need to handle reinit after lost device fopen using file handle from Java Thin wrapper over JNI calls for everything else
- 16. What Goes Where Our code distribution. 2800 lines Java 1600 in base project 1200 in master project Includes middleware integration 50k-150k lines C++ Varies depending on game 6400 Android-specific C++
- 17. Eliminating Data Duplication Problem Eclipse wants all data underneath project We want to reuse data (between projects) in our own directory structure We hate maintaining multiple copies of the same data files.
- 18. Eliminating Data Duplication Solution Batch file/shell script to copy data On Mac cp ../../../../../data/GHBowling/ballrollloop.wav ../../../GHBowling/assets/ballrollloop.wav cp ../../../../../data/Bowling/GHBowlingAndroid/backwall.jpg ../. ./../GHBowling/assets/backwall.jpg On Windows copy ..........dataGHBowlingballrollloop.wav ......GHBowlingassetsballrollloop.wav copy ..........dataBowlingGHBowlingAndroidbackwall.jpg ... ...GHBowlingassetsbackwall.jpg
- 19. Eliminating Data Duplication Batch File Generation Tool for initial generation Looks through set of directories with a specified order of preference Some files are different per-platform We may have Android-specific files We may not, but we prefer iOS-specific to generic Downside: some unnecessary files get copied Maintenance usually done by hand
- 20. Packaged App Data Problem Data is packaged through Android build process All files except those with certain excluded file extensions (precompressed file types) are automatically compressed. Platform-agnostic file reading code doesn’t know to uncompress: sees garbage
- 21. Excluded file extensions Source: Android Asset Packaging Tool /* these formats are already compressed, or don't compress well */ static const char* kNoCompressExt[] = { ".jpg", ".jpeg", ".png", ".gif", ".wav", ".mp2", ".mp3", ".ogg", ".aac", ".mpg", ".mpeg", ".mid", ".midi", ".smf", ".jet", ".rtttl", ".imy", ".xmf", ".mp4", ".m4a", ".m4v", ".3gp", ".3gpp", ".3g2", ".3gpp2", ".amr", ".awb", ".wma", ".wmv" };
- 22. App Data Compression Solution One option: forgo Eclipse and pass –0 to the AAPT via command line (universally or for certain extensions) What we do cp ../../../../../data/GHBowlingiOS/arrowpixel.glsl ../ ../../GHBowling/assets/arrowpixel.glsl.mp3
- 23. Compiling for x86 (or other architectures) In Application.mk: APP_ABI := x86 armeabi Supported values: armeabi armeabi-v7a x86 mips all
- 24. Compiling for x86 Problem Shared library Android.mk needs to include the correct static library for each architecture For arm: /armeabi/libGHEngine.a For x86: /x86/libGHEngine.a
- 25. Compiling for x86 Solution include $(CLEAR_VARS) LOCAL_MODULE := libGHEngine LOCAL_SRC_FILES := ../../GHEngine/obj/local/$(TARGET_ARCH_ABI)/libGHEngine.a include $(PREBUILT_STATIC_LIBRARY)
- 26. Building on Windows Problem We really like verbose filenames GHBowlingYellowBallThrowWith190Degre eSpinTransitionXMLLoaderTransition.cpp Our GHEngine project has lots of files Linker includes all of those filenames in one shell command Exceeds maximum line length on Windows cmd (8191 characters)
- 27. Building on Windows Problem We really like verbose filenames Ok, more like GHGUIPopTransitionXMLLoader.cpp Our GHEngine project has lots of files Linker includes all of those filenames in one shell command Exceeds maximum line length on Windows cmd (8191 characters)
- 28. Building on Windows Solution In Android.mk: LOCAL_SHORT_COMMANDS := true Build system generates intermediate list file and then invokes it with a much shorter command line Downside: slower compiles Can use only in projects that need it.