From d01290dd34c0274f49adcd75b7488c90fe70f562 Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Fri, 8 Jun 2018 20:16:17 -0700
Subject: [PATCH] Fabric: Data model of Touch Events

Summary: The data model of Touch events and payload serialization. The implementation mimics W3C standard and current React Native implementation.

Reviewed By: fkgozali

Differential Revision: D8246711

fbshipit-source-id: 955b2068674f290d8bdb82da1ebfb796dd32971b
---
 ReactCommon/fabric/view/ViewEventHandlers.cpp | 49 ++++++++++
 ReactCommon/fabric/view/ViewEventHandlers.h   | 90 +++++++++++++++++++
 2 files changed, 139 insertions(+)

diff --git a/ReactCommon/fabric/view/ViewEventHandlers.cpp b/ReactCommon/fabric/view/ViewEventHandlers.cpp
index e673d077ef..3cdadd3527 100644
--- a/ReactCommon/fabric/view/ViewEventHandlers.cpp
+++ b/ReactCommon/fabric/view/ViewEventHandlers.cpp
@@ -38,5 +38,54 @@ void ViewEventHandlers::onLayout(const LayoutMetrics &layoutMetrics) const {
   dispatchEvent("layout", payload);
 }
 
+#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 (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 ViewEventHandlers::onTouchStart(const TouchEvent &event) const {
+  dispatchEvent("touchStart", touchEventPayload(event));
+}
+
+void ViewEventHandlers::onTouchMove(const TouchEvent &event) const {
+  dispatchEvent("touchMove", touchEventPayload(event));
+}
+
+void ViewEventHandlers::onTouchEnd(const TouchEvent &event) const {
+  dispatchEvent("touchEnd", touchEventPayload(event));
+}
+
+void ViewEventHandlers::onTouchCancel(const TouchEvent &event) const {
+  dispatchEvent("touchCancel", touchEventPayload(event));
+}
+
 } // namespace react
 } // namespace facebook
diff --git a/ReactCommon/fabric/view/ViewEventHandlers.h b/ReactCommon/fabric/view/ViewEventHandlers.h
index e72e41f345..654649ed38 100644
--- a/ReactCommon/fabric/view/ViewEventHandlers.h
+++ b/ReactCommon/fabric/view/ViewEventHandlers.h
@@ -10,10 +10,93 @@
 
 #include <fabric/core/EventHandlers.h>
 #include <fabric/core/LayoutMetrics.h>
+#include <fabric/core/ReactPrimitives.h>
 
 namespace facebook {
 namespace react {
 
+/*
+ * Describes an individual touch point for a touch event.
+ * See https://www.w3.org/TR/touch-events/ for more details.
+ */
+struct Touch {
+  /*
+   * The coordinate of point relative to the root component in points.
+   */
+  Point pagePoint;
+
+  /*
+   * The coordinate of point relative to the target component in points.
+   */
+  Point offsetPoint;
+
+  /*
+   * The coordinate of point relative to the screen component in points.
+   */
+  Point screenPoint;
+
+  /*
+   * An identification number for each touch point.
+   */
+  int identifier;
+
+  /*
+   * The tag of a component on which the touch point started when it was first placed on the surface,
+   * even if the touch point has since moved outside the interactive area of that element.
+   */
+  Tag target;
+
+  /*
+   * The force of the touch.
+   */
+  Float force;
+
+  /*
+   * The time in seconds when the touch occurred or when it was last mutated.
+   */
+  Float timestamp;
+
+  /*
+   * The particular implementation of `Hasher` and (especially) `Comparator`
+   * make sense only when `Touch` object is used as a *key* in indexed collections.
+   * Because of that they are expressed as separate classes.
+   */
+  struct Hasher {
+    size_t operator()(const Touch &touch) const {
+      return std::hash<decltype(touch.identifier)>()(touch.identifier);
+    }
+  };
+
+  struct Comparator {
+    bool operator()(const Touch &lhs, const Touch &rhs) const {
+      return lhs.identifier == rhs.identifier;
+    }
+  };
+};
+
+using Touches = std::unordered_set<Touch, Touch::Hasher, Touch::Comparator>;
+
+/*
+ * Defines the `touchstart`, `touchend`, `touchmove`, and `touchcancel` event types.
+ */
+struct TouchEvent {
+  /*
+   * A list of Touches for every point of contact currently touching the surface.
+   */
+  Touches touches;
+
+  /*
+   * A list of Touches for every point of contact which contributed to the event.
+   */
+  Touches changedTouches;
+
+  /*
+   * A list of Touches for every point of contact that is touching the surface
+   * and started on the element that is the target of the current event.
+   */
+  Touches targetTouches;
+};
+
 class ViewEventHandlers;
 
 using SharedViewEventHandlers = std::shared_ptr<const ViewEventHandlers>;
@@ -34,6 +117,13 @@ public:
 #pragma mark - Layout
 
   void onLayout(const LayoutMetrics &layoutMetrics) const;
+
+#pragma mark - Touches
+
+  void onTouchStart(const TouchEvent &event) const;
+  void onTouchMove(const TouchEvent &event) const;
+  void onTouchEnd(const TouchEvent &event) const;
+  void onTouchCancel(const TouchEvent &event) const;
 };
 
 } // namespace react