Extract TouchEventEmitter from ViewEventEmitter

Summary: In the future, we may want some components (like Virtual Text) to handle only touch events. Therefore, I've extracted `TouchEventEmitter` from `ViewEventEmitter`.

Reviewed By: shergin

Differential Revision: D9696903

fbshipit-source-id: f6acc90d8ff53b5e6badaa472a5e099fb7cf03ff

ReactCommon/fabric/components/view/TouchEventEmitter.cpp

@@ -0,0 +1,63 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include "TouchEventEmitter.h"
+
+namespace facebook {
+namespace react {
+  
+#pragma mark - Touches
+  
+static folly::dynamic touchPayload(const Touch &touch) {
+  folly::dynamic object = folly::dynamic::object();
+  object["locationX"] = touch.offsetPoint.x;
+  object["locationY"] = touch.offsetPoint.x;
+  object["pageX"] = touch.pagePoint.x;
+  object["pageY"] = touch.pagePoint.x;
+  object["screenX"] = touch.screenPoint.x;
+  object["screenY"] = touch.screenPoint.x;
+  object["identifier"] = touch.identifier;
+  object["target"] = touch.target;
+  object["timestamp"] = touch.timestamp * 1000;
+  object["force"] = touch.force;
+  return object;
+}
+
+static folly::dynamic touchesPayload(const Touches &touches) {
+  folly::dynamic array = folly::dynamic::array();
+  for (const auto &touch : touches) {
+    array.push_back(touchPayload(touch));
+  }
+  return array;
+}
+
+static folly::dynamic touchEventPayload(const TouchEvent &event) {
+  folly::dynamic object = folly::dynamic::object();
+  object["touches"] = touchesPayload(event.touches);
+  object["changedTouches"] = touchesPayload(event.changedTouches);
+  object["targetTouches"] = touchesPayload(event.targetTouches);
+  return object;
+}
+
+void TouchEventEmitter::onTouchStart(const TouchEvent &event) const {
+  dispatchEvent("touchStart", touchEventPayload(event), EventPriority::SynchronousUnbatched);
+}
+
+void TouchEventEmitter::onTouchMove(const TouchEvent &event) const {
+  dispatchEvent("touchMove", touchEventPayload(event), EventPriority::SynchronousBatched);
+}
+
+void TouchEventEmitter::onTouchEnd(const TouchEvent &event) const {
+  dispatchEvent("touchEnd", touchEventPayload(event), EventPriority::SynchronousBatched);
+}
+
+void TouchEventEmitter::onTouchCancel(const TouchEvent &event) const {
+  dispatchEvent("touchCancel", touchEventPayload(event), EventPriority::SynchronousBatched);
+}
+  
+} // namespace react
+} // namespace facebook