Cross-platform UI and Input Systems - Android NDK Game Development - page 197

3. The Event_PointerChanged() and Event_PointerMoved() methods are called

to indicate the changes in individual touches:
virtual void Event_PointerChanged(int PtrID,
const vec2& Pnt, bool Pressed) {}
virtual void Event_PointerMoved(int PtrID, const vec2&
const vec2& Pnt){}

4. The information about decoded gestures is sent to the iGestureResponder

instance. When the ling/swipe event inishes, the Event_Fling() method is called:
virtual void Event_Fling( const sTouchPoint& Down,
const sTouchPoint& Up ) {}

5. Using the timestamps in the Up and Down points, the responder may estimate the

speed of the inger movement and decide if the gesture succeeds. The Event_
Drag() method is called when the inger is dragged across the screen:
virtual void Event_Drag( const sTouchPoint& Down,
const sTouchPoint& Current ) {}

6. The pinch-zoom event is handled using three methods. The Event_PinchStart()

method is called when the gesture starts, Event_PinchStop() is called at the end
of the gesture, and the Event_Pinch() method is called on each update of two
touch points:
virtual void Event_PinchStart( const sTouchPoint& Initial1,
const sTouchPoint& Initial2 ) {}
virtual void Event_Pinch( const sTouchPoint& Initial1,
const sTouchPoint& Initial2,
const sTouchPoint& Current1,
const sTouchPoint& Current2 ) {}
virtual void Event_PinchStop( const sTouchPoint& Initial1,
const sTouchPoint& Initial2,
const sTouchPoint& Current1,
const sTouchPoint& Current2 ) {};
};

7. Let's get to the mid-level routines to decode gestures. First, declare an instance

of iGestureResponder which is used later:
iGestureResponder* g_Responder;

8. We introduce the sMotionData structure, which describes the current gesture

state. Individual touch point features are accessed with the Get* functions. The
AddTouchPoint() function ensures no points with duplicate IDs are added:
struct sMotionData
{
sMotionData(): FTouchPoints() {};
void Clear() { FTouchPoints.clear(); };