使用 IGameInput 建置原生觸控介面

struct TouchPoint
{
    // GameInputTouchState.touchId corresponding to this point
    uint64_t Id = 0;    

    // X pixel being touched
    uint32_t X = 0;

    // Y pixel being touched
    uint32_t Y = 0;

    // Is this entry in the array of touch points currently being used to track a touch
    bool IsInUse = false;

    // Is this TouchPoint tracking a finger which is currently touching the screen
    bool IsTouchActive = false;
};

// Touch points currently being tracked
std::array<TouchPoint, 10> g_touchPoints = {};

extern IGameInput* g_gameInput;
extern uint32_t g_frameWidth;
extern uint32_t g_frameHeight;

void TouchPointPressed(const TouchPoint& touchPoint);
void TouchPointMoved(const TouchPoint& touchPoint);
void TouchPointReleased(const TouchPoint& touchPoint);


void ProcessTouchInput()
{
    // Reset the active touch state from the previous frame
    for (TouchPoint& touchPoint : g_touchPoints)
    {
        touchPoint.IsTouchActive = false;
    }

    // Process any new touch points for this frame
    Microsoft::WRL::ComPtr<IGameInputReading> reading = nullptr;
    if (SUCCEEDED(g_gameInput->GetCurrentReading(GameInputKindTouch, nullptr, &reading)))
    {
        uint32_t touchCount = reading->GetTouchCount();
        if (touchCount > 0)
        {
            std::vector<GameInputTouchState> touchStates(touchCount);
            touchCount = reading->GetTouchState(touchCount, touchStates.data());

            for (const GameInputTouchState& touchState : touchStates)
            {
                const uint32_t x = static_cast<uint32_t>(touchState.positionX * g_frameWidth);
                const uint32_t y = static_cast<uint32_t>(touchState.positionY * g_frameHeight);

                // Check to see if we are already tracking this touch point
                auto existingPoint = std::find_if(std::begin(g_touchPoints), std::end(g_touchPoints), [id = touchState.touchId](const TouchPoint& point)
                {
                    return point.IsInUse && point.Id == id;
                });

                if (existingPoint != g_touchPoints.end())
                {
                    // We were already tracking the point - it is still alive this frame, but it may have
                    // also moved position.
                    existingPoint->IsTouchActive = true;
                    if (existingPoint->X != x || existingPoint->Y != y)
                    {
                        existingPoint->X = x;
                        existingPoint->Y = y;
                        TouchPointMoved(*existingPoint);
                    }
                }
                else
                {
                    // This is a new touch point. Start tracking it and treat it as a press
                    auto insertPoint = std::find_if(std::begin(g_touchPoints), std::end(g_touchPoints), [](const TouchPoint& point)
                    {
                        return !point.IsInUse;
                    });

                    if (insertPoint != std::end(g_touchPoints))
                    {
                        insertPoint->Id = touchState.touchId;
                        insertPoint->X = x;
                        insertPoint->Y = y;
                        insertPoint->IsInUse = true;
                        insertPoint->IsTouchActive = true;

                        TouchPointPressed(*insertPoint);
                    }
                }
            }
        }

        // Look for any points which were pressed last frame but are no longer pressed this frame
        // and treat those as touch releases
        for (TouchPoint& touchPoint : g_touchPoints)
        {
            if (touchPoint.IsInUse && !touchPoint.IsTouchActive)
            {
                TouchPointReleased(touchPoint);
                touchPoint = TouchPoint{};
            }
        }
    }
}