Add initial Pointer Capture API implementation (facebook#38505)

Summary:
Pull Request resolved: facebook#38505

Changelog: [Internal] - Add initial Pointer Capture API implementation

This diff introduces the first baseline implementation of pointer capturing through intercepting/modifying Pointer Events in flight through the `PointerEventsProcessor` class.

Firstly: This adds and exposes the imperative methods `setPointerCapture`, `releasePointerCapture`, and `hasPointerCapture` which is added to the host `ReadOnlyElement` ref API. These methods are used to manage/query the `pendingPointerCaptureTargetOverrides_` map as [defined in the spec](https://www.w3.org/TR/pointerevents/#setting-pointer-capture).

The code is fairly self-explainatory when it comes to retargeting the events in `PointerEventsProcessor::interceptPointerEvent` but when it comes to firing the `gotPointerCapture` and `lostPointerCapture` events those are handled in `PointerEventsProcessor::processPendingPointerCapture` and is a fairly direct implementation of [the spec's pseudocode](https://www.w3.org/TR/pointerevents/#process-pending-pointer-capture).

Finally at the end of `interceptPointerEvent` I've included the basics of implicit pointer capture *release* as per [the spec](https://www.w3.org/TR/pointerevents/#implicit-release-of-pointer-capture) (note that implicit pointer capture is not yet implemented).

Differential Revision: D47533366

fbshipit-source-id: f30f4ec292897ad7aa7ab13a19b40ee81749f517

packages/react-native/Libraries/DOM/Nodes/ReadOnlyElement.js

@@ -170,6 +170,34 @@ export default class ReadOnlyElement extends ReadOnlyNode {
   getClientRects(): DOMRectList {
     throw new TypeError('Unimplemented');
   }
+
+  /**
+   * Pointer Capture APIs
+   */
+  hasPointerCapture(pointerId: number): boolean {
+    const node = getShadowNode(this);
+    if (node != null) {
+      return nullthrows(getFabricUIManager()).hasPointerCapture(
+        node,
+        pointerId,
+      );
+    }
+    return false;
+  }
+
+  setPointerCapture(pointerId: number): void {
+    const node = getShadowNode(this);
+    if (node != null) {
+      nullthrows(getFabricUIManager()).setPointerCapture(node, pointerId);
+    }
+  }
+
+  releasePointerCapture(pointerId: number): void {
+    const node = getShadowNode(this);
+    if (node != null) {
+      nullthrows(getFabricUIManager()).releasePointerCapture(node, pointerId);
+    }
+  }
 }
 
 function getChildElements(node: ReadOnlyNode): $ReadOnlyArray<ReadOnlyElement> {

packages/react-native/Libraries/ReactNative/FabricUIManager.js

@@ -91,6 +91,13 @@ export interface Spec {
   +getScrollPosition: (
     node: Node,
   ) => ?[/* scrollLeft: */ number, /* scrollTop: */ number];
+
+  /**
+   * Support methods for the Pointer Capture APIs.
+   */
+  +hasPointerCapture: (node: Node, pointerId: number) => boolean;
+  +setPointerCapture: (node: Node, pointerId: number) => void;
+  +releasePointerCapture: (node: Node, pointerId: number) => void;
 }
 
 let nativeFabricUIManagerProxy: ?Spec;

packages/react-native/Libraries/ReactNative/__mocks__/FabricUIManager.js

@@ -312,6 +312,9 @@ const FabricUIManagerMock: IFabricUIManagerMock = {
       return [x, y, width, height];
     },
   ),
+  hasPointerCapture: jest.fn((node: Node, pointerId: number): boolean => false),
+  setPointerCapture: jest.fn((node: Node, pointerId: number): void => {}),
+  releasePointerCapture: jest.fn((node: Node, pointerId: number): void => {}),
   setNativeProps: jest.fn((node: Node, newProps: NodeProps): void => {}),
   dispatchCommand: jest.fn(
     (node: Node, commandName: string, args: Array<mixed>): void => {},

packages/react-native/ReactCommon/react/renderer/core/EventEmitter.cpp

@@ -150,4 +150,8 @@ void EventEmitter::setEnabled(bool enabled) const {
   }
 }
 
+const SharedEventTarget &EventEmitter::getEventTarget() const {
+  return eventTarget_;
+}
+
 } // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/core/EventEmitter.h

@@ -56,6 +56,8 @@ class EventEmitter {
    */
   void setEnabled(bool enabled) const;
 
+  SharedEventTarget const &getEventTarget() const;
+
  protected:
 #ifdef ANDROID
   // We need this temporarily due to lack of Java-counterparts for particular

packages/react-native/ReactCommon/react/renderer/core/EventTarget.cpp

@@ -26,7 +26,10 @@ void EventTarget::retain(jsi::Runtime &runtime) const {
     return;
   }
 
-  strongInstanceHandle_ = instanceHandle_->getInstanceHandle(runtime);
+  if (retainCount_ == 0) {
+    strongInstanceHandle_ = instanceHandle_->getInstanceHandle(runtime);
+  }
+  retainCount_ += 1;
 
   // Having a `null` or `undefined` object here indicates that
   // `weakInstanceHandle_` was already deallocated. This should *not* happen by
@@ -44,7 +47,12 @@ void EventTarget::release(jsi::Runtime & /*runtime*/) const {
   // The method does not use `jsi::Runtime` reference.
   // It takes it only to ensure thread-safety (if the caller has the reference,
   // we are on a proper thread).
-  strongInstanceHandle_ = jsi::Value::null();
+  if (retainCount_ > 0) {
+    retainCount_ -= 1;
+    if (retainCount_ == 0) {
+      strongInstanceHandle_ = jsi::Value::null();
+    }
+  }
 }
 
 jsi::Value EventTarget::getInstanceHandle(jsi::Runtime &runtime) const {

packages/react-native/ReactCommon/react/renderer/core/EventTarget.h

@@ -68,6 +68,7 @@ class EventTarget {
   const InstanceHandle::Shared instanceHandle_;
   mutable bool enabled_{false}; // Protected by `EventEmitter::DispatchMutex()`.
   mutable jsi::Value strongInstanceHandle_; // Protected by `jsi::Runtime &`.
+  mutable int retainCount_{0}; // Protected by `jsi::Runtime &`.
 };
 
 using SharedEventTarget = std::shared_ptr<const EventTarget>;

packages/react-native/ReactCommon/react/renderer/uimanager/PointerEventsProcessor.cpp

@@ -9,15 +9,182 @@
 
 namespace facebook::react {
 
+static PointerEventTarget retargetPointerEvent(
+    PointerEvent const &event,
+    ShadowNode const &nodeToTarget,
+    UIManager const &uiManager) {
+  PointerEvent retargetedEvent(event);
+
+  // TODO: is dereferencing latestNodeToTarget without null checking safe?
+  auto latestNodeToTarget = uiManager.getNewestCloneOfShadowNode(nodeToTarget);
+
+  // Adjust offsetX/Y to be relative to the retargeted node
+  // HACK: This is a basic/incomplete implementation which simply subtracts
+  // the retargeted node's origin from the original event's client coordinates.
+  // More work will be needed to properly take non-trival transforms into
+  // account.
+  auto layoutMetrics = uiManager.getRelativeLayoutMetrics(
+      *latestNodeToTarget, nullptr, {/* .includeTransform */ true});
+  retargetedEvent.offsetPoint = {
+      event.clientPoint.x - layoutMetrics.frame.origin.x,
+      event.clientPoint.y - layoutMetrics.frame.origin.y,
+  };
+
+  // Retrieve the event target of the retargeted node
+  auto retargetedEventTarget =
+      latestNodeToTarget->getEventEmitter()->getEventTarget();
+
+  PointerEventTarget result = {};
+  result.event = retargetedEvent;
+  result.target = retargetedEventTarget;
+  return result;
+}
+
+static ShadowNode::Shared getCaptureTargetOverride(
+    PointerIdentifier pointerId,
+    CaptureTargetOverrideRegistry &registry) {
+  auto pendingPointerItr = registry.find(pointerId);
+  if (pendingPointerItr == registry.end()) {
+    return nullptr;
+  }
+
+  ShadowNode::Weak maybeTarget = pendingPointerItr->second;
+  if (maybeTarget.expired()) {
+    // target has expired so it should functionally behave the same as if it
+    // was removed from the override list.
+    registry.erase(pointerId);
+    return nullptr;
+  }
+
+  return maybeTarget.lock();
+}
+
 void PointerEventsProcessor::interceptPointerEvent(
     jsi::Runtime &runtime,
-    EventTarget const *eventTarget,
+    EventTarget const *target,
     std::string const &type,
     ReactEventPriority priority,
     PointerEvent const &event,
-    DispatchEvent const &eventDispatcher) {
-  // TODO: implement pointer capture redirection
-  eventDispatcher(runtime, eventTarget, type, priority, event);
+    DispatchEvent const &eventDispatcher,
+    UIManager const &uiManager) {
+  // Process all pending pointer capture assignments
+  processPendingPointerCapture(event, runtime, eventDispatcher, uiManager);
+
+  PointerEvent pointerEvent(event);
+  EventTarget const *eventTarget = target;
+
+  // Retarget the event if it has a pointer capture override target
+  auto overrideTarget = getCaptureTargetOverride(
+      pointerEvent.pointerId, pendingPointerCaptureTargetOverrides_);
+  if (overrideTarget != nullptr &&
+      overrideTarget->getTag() != eventTarget->getTag()) {
+    auto retargeted = retargetPointerEvent(pointerEvent, *overrideTarget, uiManager);
+
+    pointerEvent = retargeted.event;
+    eventTarget = retargeted.target.get();
+  }
+
+  eventTarget->retain(runtime);
+  eventDispatcher(runtime, eventTarget, type, priority, pointerEvent);
+  eventTarget->release(runtime);
+
+  // Implicit pointer capture release
+  if (overrideTarget != nullptr &&
+      (type == "topPointerUp" || type == "topPointerCancel")) {
+    releasePointerCapture(pointerEvent.pointerId, overrideTarget.get());
+    processPendingPointerCapture(
+        pointerEvent, runtime, eventDispatcher, uiManager);
+  }
+}
+
+void PointerEventsProcessor::setPointerCapture(
+    PointerIdentifier pointerId,
+    ShadowNode::Shared const &shadowNode) {
+  // TODO: Throw DOMException with name "NotFoundError" when pointerId does not
+  // match any of the active pointers
+  pendingPointerCaptureTargetOverrides_[pointerId] = shadowNode;
+}
+
+void PointerEventsProcessor::releasePointerCapture(
+    PointerIdentifier pointerId,
+    ShadowNode const *shadowNode) {
+  // TODO: Throw DOMException with name "NotFoundError" when pointerId does not
+  // match any of the active pointers
+
+  // We only clear the pointer's capture target override if release was called
+  // on the shadowNode which has the capture override, otherwise the result
+  // should no-op
+  auto pendingTarget = getCaptureTargetOverride(
+      pointerId, pendingPointerCaptureTargetOverrides_);
+  if (pendingTarget != nullptr &&
+      pendingTarget->getTag() == shadowNode->getTag()) {
+    pendingPointerCaptureTargetOverrides_.erase(pointerId);
+  }
+}
+
+bool PointerEventsProcessor::hasPointerCapture(
+    PointerIdentifier pointerId,
+    ShadowNode const *shadowNode) {
+  ShadowNode::Shared pendingTarget = getCaptureTargetOverride(
+      pointerId, pendingPointerCaptureTargetOverrides_);
+  if (pendingTarget != nullptr) {
+    return pendingTarget->getTag() == shadowNode->getTag();
+  }
+  return false;
+}
+
+void PointerEventsProcessor::processPendingPointerCapture(
+    PointerEvent const &event,
+    jsi::Runtime &runtime,
+    DispatchEvent const &eventDispatcher,
+    UIManager const &uiManager) {
+  auto pendingOverride = getCaptureTargetOverride(
+      event.pointerId, pendingPointerCaptureTargetOverrides_);
+  bool hasPendingOverride = pendingOverride != nullptr;
+
+  auto activeOverride = getCaptureTargetOverride(
+      event.pointerId, activePointerCaptureTargetOverrides_);
+  bool hasActiveOverride = activeOverride != nullptr;
+
+  if (!hasPendingOverride && !hasActiveOverride) {
+    return;
+  }
+
+  auto pendingOverrideTag =
+      (hasPendingOverride) ? pendingOverride->getTag() : -1;
+  auto activeOverrideTag = (hasActiveOverride) ? activeOverride->getTag() : -1;
+
+  if (hasActiveOverride && activeOverrideTag != pendingOverrideTag) {
+    auto retargeted = retargetPointerEvent(event, *activeOverride, uiManager);
+
+    retargeted.target->retain(runtime);
+    eventDispatcher(
+        runtime,
+        retargeted.target.get(),
+        "topLostPointerCapture",
+        ReactEventPriority::Discrete,
+        retargeted.event);
+    retargeted.target->release(runtime);
+  }
+
+  if (hasPendingOverride && activeOverrideTag != pendingOverrideTag) {
+    auto retargeted = retargetPointerEvent(event, *pendingOverride, uiManager);
+
+    retargeted.target->retain(runtime);
+    eventDispatcher(
+        runtime,
+        retargeted.target.get(),
+        "topGotPointerCapture",
+        ReactEventPriority::Discrete,
+        retargeted.event);
+    retargeted.target->release(runtime);
+  }
+
+  if (!hasPendingOverride) {
+    activePointerCaptureTargetOverrides_.erase(event.pointerId);
+  } else {
+    activePointerCaptureTargetOverrides_[event.pointerId] = pendingOverride;
+  }
 }
 
 } // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/uimanager/PointerEventsProcessor.h

@@ -22,6 +22,16 @@ using DispatchEvent = std::function<void(
     ReactEventPriority priority,
     const EventPayload &payload)>;
 
+using PointerIdentifier = int;
+using CaptureTargetOverrideRegistry =
+    std::unordered_map<PointerIdentifier, ShadowNode::Weak>;
+
+// Helper struct to package a PointerEvent and SharedEventTarget together
+struct PointerEventTarget {
+  PointerEvent event;
+  SharedEventTarget target;
+};
+
 class PointerEventsProcessor final {
  public:
   void interceptPointerEvent(
@@ -30,7 +40,28 @@ class PointerEventsProcessor final {
       std::string const &type,
       ReactEventPriority priority,
       PointerEvent const &event,
-      DispatchEvent const &eventDispatcher);
+      DispatchEvent const &eventDispatcher,
+      UIManager const &uiManager);
+
+  void setPointerCapture(
+      PointerIdentifier pointerId,
+      ShadowNode::Shared const &shadowNode);
+  void releasePointerCapture(
+      PointerIdentifier pointerId,
+      ShadowNode const *shadowNode);
+  bool hasPointerCapture(
+      PointerIdentifier pointerId,
+      ShadowNode const *shadowNode);
+
+ private:
+  void processPendingPointerCapture(
+      PointerEvent const &event,
+      jsi::Runtime &runtime,
+      DispatchEvent const &eventDispatcher,
+      UIManager const &uiManager);
+
+  CaptureTargetOverrideRegistry pendingPointerCaptureTargetOverrides_;
+  CaptureTargetOverrideRegistry activePointerCaptureTargetOverrides_;
 };
 
 } // namespace facebook::react