no route to host Chromium网页输入事件捕捉和手势检测过程分析(21)

这一步运行完毕后，Browser进程就将检测到的手势操作发送给Render进程了。回到前面分析的RenderWidgetHostViewAndroid类的成员函数OnTouchEvent中，它接下来再调用函数CreateWebTouchEventFromMotionEvent将原始的Touch事件封装在一个blink::WebTouchEvent对象中。例如以下所看到的：

blink::WebTouchEvent CreateWebTouchEventFromMotionEvent(
    const ui::MotionEvent& event) {
  blink::WebTouchEvent result;

  WebTouchEventTraits::ResetType(
      ToWebInputEventType(event.GetAction()),
      (event.GetEventTime() - base::TimeTicks()).InSecondsF(),
      &result);

  result.touchesLength =
      std::min(event.GetPointerCount(),
               static_cast<size_t>(WebTouchEvent::touchesLengthCap));
  DCHECK_GT(result.touchesLength, 0U);

  for (size_t i = 0; i < result.touchesLength; ++i)
    result.touches[i] = CreateWebTouchPoint(event, i);

  return result;
}

这个函数定义在文件external/chromium_org/content/browser/renderer_host/input/web_input_event_util.cc中。

函数CreateWebTouchEventFromMotionEvent首先调用函数ToWebInputEventType获得接下来要创建的blink::WebTouchEvent对象的类型，例如以下所看到的：

WebInputEvent::Type ToWebInputEventType(MotionEvent::Action action) {
  switch (action) {
    case MotionEvent::ACTION_DOWN:
      return WebInputEvent::TouchStart;
    case MotionEvent::ACTION_MOVE:
      return WebInputEvent::TouchMove;
    case MotionEvent::ACTION_UP:
      return WebInputEvent::TouchEnd;
    case MotionEvent::ACTION_CANCEL:
      return WebInputEvent::TouchCancel;
    case MotionEvent::ACTION_POINTER_DOWN:
      return WebInputEvent::TouchStart;
    case MotionEvent::ACTION_POINTER_UP:
      return WebInputEvent::TouchEnd;
  }
  NOTREACHED() << "Invalid MotionEvent::Action.";
  return WebInputEvent::Undefined;
}

这个函数定义在文件external/chromium_org/content/browser/renderer_host/input/web_input_event_util.cc中。

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