Talk at DroidCon 2013 titled "Lessons learned from porting Roloengine from iOS to Android"

1. Porting from iOS to Android
Lessons Learned
Manish Mathai
Game Programmer@Rolocule

2. roloengine iOS Games
Touch Squash (2009)
Super Badminton (2010)
Flick Tennis (2011)
Motion Tennis (2013)

3. roloengine Android Games
Flick Tennis (2013)
…..
More coming soon

4. roloengine iOS Internals
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Written in Obj-C
OpenGL ES 2.0 for rendering
OpenAL for audio
Custom Physics engine
Custom Animation engine
Custom asset format for models, animations

5. Decision time
Completely Native
vs
Hybrid approach
NDK provided “NativeActivity”
Standard UI combined with
C/C++ code invoked via JNI
Pros :● Almost Ultimate control over
memory management
● Faster (?)
Pros :● Easy access to java APIs
● Leverage standard UI
Cons :● No UI support
● Many APIs not available via NDK
Cons :● Adds GC overhead on UI
● UI communication a hassle

6. roloengine iOS Android Internals
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•
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Written in Obj-C C++ (NDK) & Java (UI)
OpenGL ES 2.0 for rendering
OpenAL-soft for audio
Custom Physics engine
Custom Animation engine
Custom asset format for models, animations

7. Rendering
• Competent OpenGL ES 2.0 implementations
from Android 2.3 onwards.
• DO NOT MIX OpenGL 1.0 & 2.0 calls.
• Recreate glBegin() / glEnd(), glPushMatrix() /
glPopMatrix semantics in 2.0 if needed.

8. OpenGL context creation
Pure Native a.k.a the hard way
static int engine_init_display(struct engine* engine) {
const EGLint attribs[] = {
EGL_SURFACE_TYPE, EGL_WINDOW_BIT, EGL_BLUE_SIZE, 8,
EGL_GREEN_SIZE, 8, EGL_RED_SIZE, 8, EGL_NONE
};
EGLint w, h, dummy, format;
EGLint numConfigs;
EGLConfig config;
EGLSurface surface;
EGLContext context;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);

9. OpenGL context creation
eglInitialize(display, 0, 0);
eglChooseConfig(display, attribs, &config, 1, &numConfigs);
eglGetConfigAttrib(display, config, EGL_NATIVE_VISUAL_ID, &format);
surface = eglCreateWindowSurface(display, config, engine->app->window, NULL);
context = eglCreateContext(display, config, NULL, NULL);
if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE) {
LOGW("Unable to eglMakeCurrent");
return -1;
}
return 0;
}

10. OpenGL context creation
Context creation in Java
GLSurfaceView mGLView = new GLSurfaceView(this);
mGLView.setRenderer(new GLRenderer());
class GLRenderer implements GLSurfaceView.Renderer {
…
public native void native_render();
public void onDrawFrame(GL10 gl) {
native_render();
}
}

11. OpenGL context creation
Rendering via JNI calls to C/C++
JNIEXPORT void JNICALL Java_com_example_package_native_render(JNIEnv *env_,
jobject obj_) {
// Drawing code goes here
}

12. OpenGL Tips
• All OpenGL calls on render thread. All UI
changes in UI thread.
• Avoid touching Java heap during the game
loop.
• Block OpenGL thread on application pause.

13. Audio
• Java APIs (SoundPool & Media Player) vs
Native API OpenSL ES
• OpenSL ES has a horrible & convoluted API
• OpenAL-soft - Software impl of OpenAL with
OpenEL ES as the backend
https://github.com/AerialX/openal-soft-android

14. C++ utils & tools
• Boost - surprisingly easy to build
https://github.com/MysticTreeGames/Boost-for-Android
Boost::Bind, Boost::IO
• tinyxml2 - small and efficient XML parser
https://github.com/leethomason/tinyxml2
• libpng + libzip for compressed textures

15. UI
• Android is stingy with memory (16-24MB)
• Easy to hit OOM with large bitmaps.
• Modern phones (1 GB+ RAM) too
Solution :BitmapFactory.Options options = new BitmapFactory.Options();
options.inPurgeable = true;
options.inInputShareable = true;

16. UI
• Layouts for all screen sizes a must, for
consistent UI placement.
• Stock android fonts are limited.

17. Thank You !
manish.mathai@rolocule.com