Presentation from David Wingrove & Katie Merrill from Golden Hammer Software http://www.goldenhammersoftware.com/ From the Barcelona Android User Group meetup: http://www.meetup.com/Barcelona-Android-User-Group/events/166734982/

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.