react-native/React/Fabric/RCTSurfaceTouchHandler.mm

/**
 * 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.
 */

#import "RCTSurfaceTouchHandler.h"

#import <UIKit/UIGestureRecognizerSubclass.h>
#import <fabric/view/ViewEventEmitter.h>
#import <React/RCTUtils.h>
#import <React/RCTViewComponentView.h>

#import "RCTConversions.h"

using namespace facebook::react;

template <size_t size>
class IdentifierPool {
public:

  void enqueue(int index) {
    usage[index] = false;
  }

  int dequeue() {
    while (true) {
      if (!usage[lastIndex]) {
        usage[lastIndex] = true;
        return lastIndex;
      }
      lastIndex = (lastIndex + 1) % size;
    }
  }

  void reset() {
    for (int i = 0; i < size; i++) {
      usage[i] = false;
    }
  }

private:

  bool usage[size];
  int lastIndex;
};

@protocol RCTTouchableComponentViewProtocol <NSObject>
  - (SharedViewEventEmitter)touchEventEmitter;
@end

typedef NS_ENUM(NSInteger, RCTTouchEventType) {
  RCTTouchEventTypeTouchStart,
  RCTTouchEventTypeTouchMove,
  RCTTouchEventTypeTouchEnd,
  RCTTouchEventTypeTouchCancel,
};

struct ActiveTouch {
  Touch touch;
  SharedViewEventEmitter eventEmitter;

  struct Hasher {
    size_t operator()(const ActiveTouch &activeTouch) const {
      return std::hash<decltype(activeTouch.touch.identifier)>()(activeTouch.touch.identifier);
    }
  };

  struct Comparator {
    bool operator()(const ActiveTouch &lhs, const ActiveTouch &rhs) const {
      return lhs.touch.identifier == rhs.touch.identifier;
    }
  };
};

static void UpdateActiveTouchWithUITouch(ActiveTouch &activeTouch, UITouch *uiTouch, UIView *rootComponentView) {
  CGPoint offsetPoint = [uiTouch locationInView:uiTouch.view];
  CGPoint screenPoint = [uiTouch locationInView:uiTouch.window];
  CGPoint pagePoint = [uiTouch locationInView:rootComponentView];

  activeTouch.touch.offsetPoint = RCTPointFromCGPoint(offsetPoint);
  activeTouch.touch.screenPoint = RCTPointFromCGPoint(screenPoint);
  activeTouch.touch.pagePoint = RCTPointFromCGPoint(pagePoint);

  activeTouch.touch.timestamp = uiTouch.timestamp;

  if (RCTForceTouchAvailable()) {
    activeTouch.touch.force = uiTouch.force / uiTouch.maximumPossibleForce;
  }
}

static ActiveTouch CreateTouchWithUITouch(UITouch *uiTouch, UIView *rootComponentView) {
  UIView *componentView = uiTouch.view;

  ActiveTouch activeTouch = {};

  if ([componentView respondsToSelector:@selector(touchEventEmitter)]) {
    activeTouch.eventEmitter = [(id<RCTTouchableComponentViewProtocol>)componentView touchEventEmitter];
    activeTouch.touch.target = (Tag)componentView.tag;
  }

  UpdateActiveTouchWithUITouch(activeTouch, uiTouch, rootComponentView);
  return activeTouch;
}

static BOOL AllTouchesAreCancelledOrEnded(NSSet<UITouch *> *touches) {
  for (UITouch *touch in touches) {
    if (touch.phase == UITouchPhaseBegan ||
        touch.phase == UITouchPhaseMoved ||
        touch.phase == UITouchPhaseStationary) {
      return NO;
    }
  }
  return YES;
}

static BOOL AnyTouchesChanged(NSSet<UITouch *> *touches) {
  for (UITouch *touch in touches) {
    if (touch.phase == UITouchPhaseBegan ||
        touch.phase == UITouchPhaseMoved) {
      return YES;
    }
  }
  return NO;
}

/**
 * Surprisingly, `__unsafe_unretained id` pointers are not regular pointers
 * and `std::hash<>` cannot hash them.
 * This is quite trivial but decent implementation of hasher function
 * inspired by this research: https://stackoverflow.com/a/21062520/496389.
 */
template<typename PointerT>
struct PointerHasher {
  constexpr std::size_t operator()(const PointerT &value) const {
    return reinterpret_cast<size_t>(&value);
  }
};

@interface RCTSurfaceTouchHandler () <UIGestureRecognizerDelegate>
@end

@implementation RCTSurfaceTouchHandler {
  std::unordered_map<
    __unsafe_unretained UITouch *,
    ActiveTouch,
    PointerHasher<__unsafe_unretained UITouch *>
  > _activeTouches;

  UIView *_rootComponentView;
  IdentifierPool<11> _identifierPool;
}

- (instancetype)init
{
  if (self = [super initWithTarget:nil action:nil]) {
    // `cancelsTouchesInView` and `delaysTouches*` are needed in order
    // to be used as a top level event delegated recognizer.
    // Otherwise, lower-level components not built using React Native,
    // will fail to recognize gestures.
    self.cancelsTouchesInView = NO;
    self.delaysTouchesBegan = NO; // This is default value.
    self.delaysTouchesEnded = NO;

    self.delegate = self;
  }

  return self;
}

RCT_NOT_IMPLEMENTED(- (instancetype)initWithTarget:(id)target action:(SEL)action)

- (void)attachToView:(UIView *)view
{
  RCTAssert(self.view == nil, @"RCTTouchHandler already has attached view.");

  [view addGestureRecognizer:self];
  _rootComponentView = view;
}

- (void)detachFromView:(UIView *)view
{
  RCTAssertParam(view);
  RCTAssert(self.view == view, @"RCTTouchHandler attached to another view.");

  [view removeGestureRecognizer:self];
  _rootComponentView = nil;
}

- (void)_registerTouches:(NSSet<UITouch *> *)touches
{
  for (UITouch *touch in touches) {
    auto activeTouch = CreateTouchWithUITouch(touch, _rootComponentView);
    activeTouch.touch.identifier = _identifierPool.dequeue();
    _activeTouches.emplace(touch, activeTouch);
  }
}

- (void)_updateTouches:(NSSet<UITouch *> *)touches
{
  for (UITouch *touch in touches) {
    UpdateActiveTouchWithUITouch(_activeTouches[touch], touch, _rootComponentView);
  }
}

- (void)_unregisterTouches:(NSSet<UITouch *> *)touches
{
  for (UITouch *touch in touches) {
    const auto &activeTouch = _activeTouches[touch];
    _identifierPool.enqueue(activeTouch.touch.identifier);
    _activeTouches.erase(touch);
  }
}

- (void)_dispatchTouches:(NSSet<UITouch *> *)touches eventType:(RCTTouchEventType)eventType
{
  TouchEvent event = {};
  std::unordered_set<ActiveTouch, ActiveTouch::Hasher, ActiveTouch::Comparator> changedActiveTouches = {};
  std::unordered_set<SharedViewEventEmitter> uniqueEventEmitter = {};
  BOOL isEndishEventType = eventType == RCTTouchEventTypeTouchEnd || eventType == RCTTouchEventTypeTouchCancel;

  for (UITouch *touch in touches) {
    const auto &activeTouch = _activeTouches[touch];

    if (!activeTouch.eventEmitter) {
      continue;
    }

    changedActiveTouches.insert(activeTouch);
    event.changedTouches.insert(activeTouch.touch);
    uniqueEventEmitter.insert(activeTouch.eventEmitter);
  }

  for (const auto &pair : _activeTouches) {
    if (!pair.second.eventEmitter) {
      continue;
    }

    if (
        isEndishEventType &&
        event.changedTouches.find(pair.second.touch) != event.changedTouches.end()
    ) {
      continue;
    }

    event.touches.insert(pair.second.touch);
  }

  for (const auto &eventEmitter : uniqueEventEmitter) {
    event.targetTouches.clear();

    for (const auto &pair : _activeTouches) {
      if (pair.second.eventEmitter == eventEmitter) {
        event.targetTouches.insert(pair.second.touch);
      }
    }

    switch (eventType) {
      case RCTTouchEventTypeTouchStart:
        eventEmitter->onTouchStart(event);
        break;
      case RCTTouchEventTypeTouchMove:
        eventEmitter->onTouchMove(event);
        break;
      case RCTTouchEventTypeTouchEnd:
        eventEmitter->onTouchEnd(event);
        break;
      case RCTTouchEventTypeTouchCancel:
        eventEmitter->onTouchCancel(event);
        break;
    }
  }
}

#pragma mark - `UIResponder`-ish touch-delivery methods

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  [super touchesBegan:touches withEvent:event];

  [self _registerTouches:touches];
  [self _dispatchTouches:touches eventType:RCTTouchEventTypeTouchStart];

  if (self.state == UIGestureRecognizerStatePossible) {
    self.state = UIGestureRecognizerStateBegan;
  } else if (self.state == UIGestureRecognizerStateBegan) {
    self.state = UIGestureRecognizerStateChanged;
  }
}

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  [super touchesMoved:touches withEvent:event];

  [self _updateTouches:touches];
  [self _dispatchTouches:touches eventType:RCTTouchEventTypeTouchMove];

  self.state = UIGestureRecognizerStateChanged;
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  [super touchesEnded:touches withEvent:event];

  [self _updateTouches:touches];
  [self _dispatchTouches:touches eventType:RCTTouchEventTypeTouchEnd];
  [self _unregisterTouches:touches];

  if (AllTouchesAreCancelledOrEnded(event.allTouches)) {
    self.state = UIGestureRecognizerStateEnded;
  } else if (AnyTouchesChanged(event.allTouches)) {
    self.state = UIGestureRecognizerStateChanged;
  }
}

- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  [super touchesCancelled:touches withEvent:event];

  [self _updateTouches:touches];
  [self _dispatchTouches:touches eventType:RCTTouchEventTypeTouchCancel];
  [self _unregisterTouches:touches];

  if (AllTouchesAreCancelledOrEnded(event.allTouches)) {
    self.state = UIGestureRecognizerStateCancelled;
  } else if (AnyTouchesChanged(event.allTouches)) {
    self.state = UIGestureRecognizerStateChanged;
  }
}

- (void)reset
{
  // Technically, `_activeTouches` must be already empty at this point,
  // but just to be sure, we clear it explicitly.
  _activeTouches.clear();
  _identifierPool.reset();
}

- (BOOL)canPreventGestureRecognizer:(__unused UIGestureRecognizer *)preventedGestureRecognizer
{
  return NO;
}

- (BOOL)canBePreventedByGestureRecognizer:(UIGestureRecognizer *)preventingGestureRecognizer
{
  // We fail in favour of other external gesture recognizers.
  // iOS will ask `delegate`'s opinion about this gesture recognizer little bit later.
  return ![preventingGestureRecognizer.view isDescendantOfView:self.view];
}

#pragma mark - UIGestureRecognizerDelegate

- (BOOL)gestureRecognizer:(__unused UIGestureRecognizer *)gestureRecognizer shouldRequireFailureOfGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
  // Same condition for `failure of` as for `be prevented by`.
  return [self canBePreventedByGestureRecognizer:otherGestureRecognizer];
}

@end