Writing a Match-3 Game - Android NDK Game Development - page 227

4. All the work our new SendMotion() JNI callback has to do is pack the touch event

parameters into the queue:

Java_com_packtpub_ndkcookbook_game1_Game1Activity_SendMotion(
JNIEnv * env, jobject obj, int PointerID, int x, int y,
bool Pressed, int Flag)
{
sSendMotionData M;
M.ContactID = PointerID;
M.Flag = (eMotionFlag)Flag;
M.Pos = LVector2( (float)x / (float)g_Width,
(float)y / (float)g_Height );
M.Pressed = Pressed;
LMutex Lock( &g_MotionEventsQueueMutex );
g_MotionEventsQueue.push_back( M );
}

We can now process the touch events whenever we like.

How it works…

To handle the touch events in the queue, we extend the implementation of the DrawFrame()
JNI callback:

Java_com_packtpub_ndkcookbook_game1_Game1Activity_DrawFrame(
JNIEnv* env, jobject obj )
{

Note the scope of the Lock variable inside the additional {} . We need it because the mutex
variable must be unlocked to prevent deadlocks, before proceeding with the game logic:

{
LMutex Lock(&g_MotionEventsQueueMutex );
for( auto m : g_MotionEventsQueue )
{
GestureHandler_SendMotion( m.ContactID, m.Flag,
m.Pos, m.Pressed );
}
g_MotionEventsQueue.clear();
}
GenerateTicks();
}

See the jni/Wrappers.cpp ile from the example 1_Game for
the complete implementation, which can be retrieved from www.
packtpub.com/support .