3D Shooters Episode I: Wolfenstein 3D for Android - Pro Android Games - page 202

listener.OnStartSound(idx);
}

// Fires when music is played in the C layer.
private static void OnStartMusic(int idx) {
if (listener != null)
listener.OnStartMusic(idx);
}

// Sends a key event to the native layer
// type : one of Natives.EV_KEYDOWN or Natives.EV_KEYUP
// sym: PC scan code
public static void sendNativeKeyEvent(int type, int sym) {
try {
if (type == Natives.EV_KEYDOWN)
Natives.keyPress(sym);
else
Natives.keyRelease(sym);
} catch (UnsatisfiedLinkError e) {
Log.e(TAG, e.toString());
}
}
}

In order for the game activity ( WolfLauncher ) to receive native callbacks, such as when a video
update occurs or a sound must be played, it must implement the interface Natives . EventListener . This
interface provides the critical notifications at the core of the game:

OnMessage(String text) : This event sends a message from the native layer for
information purposes.

•

•

OnInitGraphics(int w, int h) : This event gets called when the video graphics
gets initialized. It returns the width and height of the video buffer.

OnImageUpdate(int[] pixels, int x, int y, int w, int h) : This is perhaps the
most important method out there. It gets called when a video update occurs and
returns an Android ARGB packed array of pixels to be displayed on the device. It
also returns the X and Y coordinates of the top left pixel and the width and height
of the video buffer.

•

OnSysError(String text) : This event fires when a fatal error occurs. The client
should display the incoming message and terminate; otherwise, the application
will certainly crash.

•

• OnStartSound(int idx) : This event fires when a sound must be played. idx
represents the native sound ID.
• OnStartMusic(int idx) : This event fires when background music must be played.
idx represents the native music ID.
Now, let's look at some of the native code where all the magic occurs.