no route to host Chromium网页输入事件捕捉和手势检测过程分析(9)

这个GestureListenerImpl对象负责检测参数event描写叙述的Touch事件是否产生滑动手势操作。这是通过调用它的成员函数OnTouchEvent实现的。

GestureProvider类的成员变量scale_gesture_listener_指向的是一个ScaleGestureListenerImpl对象。

这个ScaleGestureListenerImpl对象负责检测参数event描写叙述的Touch事件是否产生捏合手势操作。

这是通过调用它的成员函数OnTouchEvent实现的。

接下来，我们就分别分析GestureListenerImpl类和ScaleGestureListenerImpl类的成员函数OnTouchEvent的实现，以便了解滑动和捏合手势操作的检测过程。

GestureListenerImpl类的成员函数OnTouchEvent的实现例如以下所看到的：

class GestureProvider::GestureListenerImpl
    : public GestureDetector::GestureListener,
      public GestureDetector::DoubleTapListener {
 public:
  ......

  bool OnTouchEvent(const MotionEvent& e,
                    bool is_scale_gesture_detection_in_progress) {
    ......

    return gesture_detector_.OnTouchEvent(e);
  }

 private:
  ......

  GestureDetector gesture_detector_;
  
  ......
};

这个函数定义在文件external/chromium_org/ui/events/gesture_detection/gesture_provider.cc中。

GestureListenerImpl类的成员函数OnTouchEvent通过调用成员变量gesture_detector_描写叙述的一个GestureDetector对象的成员函数OnTouchEvent检测测参数e描写叙述的Touch事件是否产生了滑动手势操作。

GestureDetector类的成员函数OnTouchEvent的实现例如以下所看到的：

bool GestureDetector::OnTouchEvent(const MotionEvent& ev) {
  const MotionEvent::Action action = ev.GetAction();

  ......

  const bool pointer_up = action == MotionEvent::ACTION_POINTER_UP;
  const int skip_index = pointer_up ?
 ev.GetActionIndex() : -1;

  // Determine focal point.
  float sum_x = 0, sum_y = 0;
  const int count = static_cast<int>(ev.GetPointerCount());
  for (int i = 0; i < count; i++) {
    if (skip_index == i)
      continue;
    sum_x += ev.GetX(i);
    sum_y += ev.GetY(i);
  }
  const int div = pointer_up ? count - 1 : count;
  const float focus_x = sum_x / div;
  const float focus_y = sum_y / div;

  bool handled = false;

  switch (action) {
    ......

    case MotionEvent::ACTION_MOVE:
      {
        const float scroll_x = last_focus_x_ - focus_x;
        const float scroll_y = last_focus_y_ - focus_y;
        if (is_double_tapping_) {
          // Give the move events of the double-tap.
          DCHECK(double_tap_listener_);
          handled |= double_tap_listener_->OnDoubleTapEvent(ev);
        } else if (always_in_tap_region_) {
          const float delta_x = focus_x - down_focus_x_;
          const float delta_y = focus_y - down_focus_y_;
          const float distance_square = delta_x * delta_x + delta_y * delta_y;
          if (distance_square > touch_slop_square_) {
            handled = listener_->OnScroll(
                *current_down_event_, ev, scroll_x, scroll_y);
            last_focus_x_ = focus_x;
            last_focus_y_ = focus_y;
            always_in_tap_region_ = false;
            ......
          }
          ......
        } else if (std::abs(scroll_x) > kScrollEpsilon ||
                   std::abs(scroll_y) > kScrollEpsilon) {
          handled =
              listener_->OnScroll(*current_down_event_, ev, scroll_x, scroll_y);
          last_focus_x_ = focus_x;
          last_focus_y_ = focus_y;
        }

      ......

      break;

    ......
  }

  return handled;
}

这个函数定义在文件external/chromium_org/ui/events/gesture_detection/gesture_detector.cc中。

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