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diff --git a/gfx/layers/apz/src/InputBlockState.h b/gfx/layers/apz/src/InputBlockState.h
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+++ b/gfx/layers/apz/src/InputBlockState.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_InputBlockState_h
+#define mozilla_layers_InputBlockState_h
+
+#include "InputData.h"           // for MultiTouchInput
+#include "mozilla/RefCounted.h"  // for RefCounted
+#include "mozilla/RefPtr.h"      // for RefPtr
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/gfx/Matrix.h"  // for Matrix4x4
+#include "mozilla/layers/APZUtils.h"
+#include "mozilla/layers/LayersTypes.h"  // for TouchBehaviorFlags
+#include "mozilla/layers/AsyncDragMetrics.h"
+#include "mozilla/layers/TouchCounter.h"
+#include "mozilla/TimeStamp.h"  // for TimeStamp
+#include "nsTArray.h"           // for nsTArray
+
+namespace mozilla {
+namespace layers {
+
+class AsyncPanZoomController;
+class OverscrollHandoffChain;
+class CancelableBlockState;
+class TouchBlockState;
+class WheelBlockState;
+class DragBlockState;
+class PanGestureBlockState;
+class PinchGestureBlockState;
+class KeyboardBlockState;
+enum class BrowserGestureResponse : bool;
+
+/**
+ * A base class that stores state common to various input blocks.
+ * Note that the InputBlockState constructor acquires the tree lock, so callers
+ * from inside AsyncPanZoomController should ensure that the APZC lock is not
+ * held.
+ */
+class InputBlockState : public RefCounted<InputBlockState> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(InputBlockState)
+
+  static const uint64_t NO_BLOCK_ID = 0;
+
+  enum class TargetConfirmationState : uint8_t {
+    eUnconfirmed,
+    eTimedOut,
+    eTimedOutAndMainThreadResponded,
+    eConfirmed
+  };
+
+  InputBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                  TargetConfirmationFlags aFlags);
+  virtual ~InputBlockState() = default;
+
+  virtual CancelableBlockState* AsCancelableBlock() { return nullptr; }
+  virtual TouchBlockState* AsTouchBlock() { return nullptr; }
+  virtual WheelBlockState* AsWheelBlock() { return nullptr; }
+  virtual DragBlockState* AsDragBlock() { return nullptr; }
+  virtual PanGestureBlockState* AsPanGestureBlock() { return nullptr; }
+  virtual PinchGestureBlockState* AsPinchGestureBlock() { return nullptr; }
+  virtual KeyboardBlockState* AsKeyboardBlock() { return nullptr; }
+
+  virtual bool SetConfirmedTargetApzc(
+      const RefPtr<AsyncPanZoomController>& aTargetApzc,
+      TargetConfirmationState aState, InputData* aFirstInput,
+      bool aForScrollbarDrag);
+  const RefPtr<AsyncPanZoomController>& GetTargetApzc() const;
+  const RefPtr<const OverscrollHandoffChain>& GetOverscrollHandoffChain() const;
+  uint64_t GetBlockId() const;
+
+  bool IsTargetConfirmed() const;
+  bool HasReceivedRealConfirmedTarget() const;
+
+  virtual bool ShouldDropEvents() const;
+
+  void SetScrolledApzc(AsyncPanZoomController* aApzc);
+  AsyncPanZoomController* GetScrolledApzc() const;
+  bool IsDownchainOfScrolledApzc(AsyncPanZoomController* aApzc) const;
+
+  /**
+   * Dispatch the event to the target APZC. Mostly this is a hook for
+   * subclasses to do any per-event processing they need to.
+   */
+  virtual void DispatchEvent(const InputData& aEvent) const;
+
+  /**
+   * Return true if this input block must stay active if it would otherwise
+   * be removed as the last item in the pending queue.
+   */
+  virtual bool MustStayActive() = 0;
+
+ protected:
+  virtual void UpdateTargetApzc(
+      const RefPtr<AsyncPanZoomController>& aTargetApzc);
+
+ private:
+  // Checks whether |aA| is an ancestor of |aB| (or the same as |aB|) in
+  // |mOverscrollHandoffChain|.
+  bool IsDownchainOf(AsyncPanZoomController* aA,
+                     AsyncPanZoomController* aB) const;
+
+ private:
+  RefPtr<AsyncPanZoomController> mTargetApzc;
+  TargetConfirmationState mTargetConfirmed;
+  bool mRequiresTargetConfirmation;
+  const uint64_t mBlockId;
+
+  // The APZC that was actually scrolled by events in this input block.
+  // This is used in configurations where a single input block is only
+  // allowed to scroll a single APZC (configurations where
+  // StaticPrefs::apz_allow_immediate_handoff() is false). Set the first time an
+  // input event in this block scrolls an APZC.
+  RefPtr<AsyncPanZoomController> mScrolledApzc;
+
+ protected:
+  RefPtr<const OverscrollHandoffChain> mOverscrollHandoffChain;
+
+  // Used to transform events from global screen space to |mTargetApzc|'s
+  // screen space. It's cached at the beginning of the input block so that
+  // all events in the block are in the same coordinate space.
+  ScreenToParentLayerMatrix4x4 mTransformToApzc;
+};
+
+/**
+ * This class represents a set of events that can be cancelled by web content
+ * via event listeners.
+ *
+ * Each cancelable input block can be cancelled by web content, and
+ * this information is stored in the mPreventDefault flag. Because web
+ * content runs on the Gecko main thread, we cannot always wait for web
+ * content's response. Instead, there is a timeout that sets this flag in the
+ * case where web content doesn't respond in time. The mContentResponded and
+ * mContentResponseTimerExpired flags indicate which of these scenarios
+ * occurred.
+ */
+class CancelableBlockState : public InputBlockState {
+ public:
+  CancelableBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                       TargetConfirmationFlags aFlags);
+
+  CancelableBlockState* AsCancelableBlock() override { return this; }
+
+  /**
+   * Record whether or not content cancelled this block of events.
+   * @param aPreventDefault true iff the block is cancelled.
+   * @return false if this block has already received a response from
+   *         web content, true if not.
+   */
+  virtual bool SetContentResponse(bool aPreventDefault);
+
+  /**
+   * Record that content didn't respond in time.
+   * @return false if this block already timed out, true if not.
+   */
+  virtual bool TimeoutContentResponse();
+
+  /**
+   * Checks if the content response timer has already expired.
+   */
+  bool IsContentResponseTimerExpired() const;
+
+  /**
+   * @return true iff web content cancelled this block of events.
+   */
+  bool IsDefaultPrevented() const;
+
+  /**
+   * @return true iff this block has received all the information needed
+   *         to properly dispatch the events in the block.
+   */
+  virtual bool IsReadyForHandling() const;
+
+  /**
+   * Return a descriptive name for the block kind.
+   */
+  virtual const char* Type() = 0;
+
+  bool ShouldDropEvents() const override;
+
+ private:
+  bool mPreventDefault;
+  bool mContentResponded;
+  bool mContentResponseTimerExpired;
+};
+
+/**
+ * A single block of wheel events.
+ */
+class WheelBlockState : public CancelableBlockState {
+ public:
+  WheelBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                  TargetConfirmationFlags aFlags,
+                  const ScrollWheelInput& aEvent);
+
+  bool SetContentResponse(bool aPreventDefault) override;
+  bool MustStayActive() override;
+  const char* Type() override;
+  bool SetConfirmedTargetApzc(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                              TargetConfirmationState aState,
+                              InputData* aFirstInput,
+                              bool aForScrollbarDrag) override;
+
+  WheelBlockState* AsWheelBlock() override { return this; }
+
+  /**
+   * Determine whether this wheel block is accepting new events.
+   */
+  bool ShouldAcceptNewEvent() const;
+
+  /**
+   * Call to check whether a wheel event will cause the current transaction to
+   * timeout.
+   */
+  bool MaybeTimeout(const ScrollWheelInput& aEvent);
+
+  /**
+   * Called from APZCTM when a mouse move or drag+drop event occurs, before
+   * the event has been processed.
+   */
+  void OnMouseMove(const ScreenIntPoint& aPoint,
+                   const Maybe<ScrollableLayerGuid>& aTargetGuid);
+
+  /**
+   * Returns whether or not the block is participating in a wheel transaction.
+   * This means that the block is the most recent input block to be created,
+   * and no events have occurred that would require scrolling a different
+   * frame.
+   *
+   * @return True if in a transaction, false otherwise.
+   */
+  bool InTransaction() const;
+
+  /**
+   * Mark the block as no longer participating in a wheel transaction. This
+   * will force future wheel events to begin a new input block.
+   */
+  void EndTransaction();
+
+  /**
+   * @return Whether or not overscrolling is prevented for this wheel block.
+   */
+  bool AllowScrollHandoff() const;
+
+  /**
+   * Called to check and possibly end the transaction due to a timeout.
+   *
+   * @return True if the transaction ended, false otherwise.
+   */
+  bool MaybeTimeout(const TimeStamp& aTimeStamp);
+
+  /**
+   * Update the wheel transaction state for a new event.
+   */
+  void Update(ScrollWheelInput& aEvent);
+
+  ScrollDirections GetAllowedScrollDirections() const {
+    return mAllowedScrollDirections;
+  }
+
+ protected:
+  void UpdateTargetApzc(
+      const RefPtr<AsyncPanZoomController>& aTargetApzc) override;
+
+ private:
+  TimeStamp mLastEventTime;
+  TimeStamp mLastMouseMove;
+  uint32_t mScrollSeriesCounter;
+  bool mTransactionEnded;
+  bool mIsScrollable = true;
+  ScrollDirections mAllowedScrollDirections;
+};
+
+/**
+ * A block of mouse events that are part of a drag
+ */
+class DragBlockState : public CancelableBlockState {
+ public:
+  DragBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                 TargetConfirmationFlags aFlags, const MouseInput& aEvent);
+
+  bool MustStayActive() override;
+  const char* Type() override;
+
+  bool HasReceivedMouseUp();
+  void MarkMouseUpReceived();
+
+  DragBlockState* AsDragBlock() override { return this; }
+
+  void SetInitialThumbPos(OuterCSSCoord aThumbPos);
+  void SetDragMetrics(const AsyncDragMetrics& aDragMetrics);
+
+  void DispatchEvent(const InputData& aEvent) const override;
+
+ private:
+  AsyncDragMetrics mDragMetrics;
+  OuterCSSCoord mInitialThumbPos;
+  bool mReceivedMouseUp;
+};
+
+/**
+ * A single block of pan gesture events.
+ */
+class PanGestureBlockState : public CancelableBlockState {
+ public:
+  PanGestureBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                       TargetConfirmationFlags aFlags,
+                       const PanGestureInput& aEvent);
+
+  bool SetContentResponse(bool aPreventDefault) override;
+  bool IsReadyForHandling() const override;
+  bool MustStayActive() override;
+  const char* Type() override;
+  bool SetConfirmedTargetApzc(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                              TargetConfirmationState aState,
+                              InputData* aFirstInput,
+                              bool aForScrollbarDrag) override;
+
+  PanGestureBlockState* AsPanGestureBlock() override { return this; }
+
+  bool ShouldDropEvents() const override;
+
+  bool TimeoutContentResponse() override;
+
+  /**
+   * @return Whether or not overscrolling is prevented for this block.
+   */
+  bool AllowScrollHandoff() const;
+
+  bool WasInterrupted() const { return mInterrupted; }
+
+  void SetNeedsToWaitForContentResponse(bool aWaitForContentResponse);
+  void SetNeedsToWaitForBrowserGestureResponse(
+      bool aWaitForBrowserGestureResponse);
+  void SetBrowserGestureResponse(BrowserGestureResponse aResponse);
+
+  ScrollDirections GetAllowedScrollDirections() const {
+    return mAllowedScrollDirections;
+  }
+
+ private:
+  bool mInterrupted;
+  bool mWaitingForContentResponse;
+  // A pan gesture may be used for browser's swipe gestures so APZ needs to wait
+  // for the response from the browser whether the gesture has been used for
+  // swipe or not. This `mWaitingForBrowserGestureResponse` flag represents the
+  // waiting state. And below `mStartedBrowserGesture` represents the response
+  // from the browser.
+  bool mWaitingForBrowserGestureResponse;
+  bool mStartedBrowserGesture;
+  ScrollDirections mAllowedScrollDirections;
+};
+
+/**
+ * A single block of pinch gesture events.
+ */
+class PinchGestureBlockState : public CancelableBlockState {
+ public:
+  PinchGestureBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                         TargetConfirmationFlags aFlags);
+
+  bool SetContentResponse(bool aPreventDefault) override;
+  bool IsReadyForHandling() const override;
+  bool MustStayActive() override;
+  const char* Type() override;
+
+  PinchGestureBlockState* AsPinchGestureBlock() override { return this; }
+
+  bool WasInterrupted() const { return mInterrupted; }
+
+  void SetNeedsToWaitForContentResponse(bool aWaitForContentResponse);
+
+ private:
+  bool mInterrupted;
+  bool mWaitingForContentResponse;
+};
+
+/**
+ * This class represents a single touch block. A touch block is
+ * a set of touch events that can be cancelled by web content via
+ * touch event listeners.
+ *
+ * Every touch-start event creates a new touch block. In this case, the
+ * touch block consists of the touch-start, followed by all touch events
+ * up to but not including the next touch-start (except in the case where
+ * a long-tap happens, see below). Note that in particular we cannot know
+ * when a touch block ends until the next one is started. Most touch
+ * blocks are created by receipt of a touch-start event.
+ *
+ * Every long-tap event also creates a new touch block, since it can also
+ * be consumed by web content. In this case, when the long-tap event is
+ * dispatched to web content, a new touch block is started to hold the remaining
+ * touch events, up to but not including the next touch start (or long-tap).
+ *
+ * Additionally, if touch-action is enabled, each touch block should
+ * have a set of allowed touch behavior flags; one for each touch point.
+ * This also requires running code on the Gecko main thread, and so may
+ * be populated with some latency. The mAllowedTouchBehaviorSet and
+ * mAllowedTouchBehaviors variables track this information.
+ */
+class TouchBlockState : public CancelableBlockState {
+ public:
+  explicit TouchBlockState(const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                           TargetConfirmationFlags aFlags,
+                           TouchCounter& aTouchCounter);
+
+  TouchBlockState* AsTouchBlock() override { return this; }
+
+  /**
+   * Set the allowed touch behavior flags for this block.
+   * @return false if this block already has these flags set, true if not.
+   */
+  bool SetAllowedTouchBehaviors(const nsTArray<TouchBehaviorFlags>& aBehaviors);
+  /**
+   * If the allowed touch behaviors have been set, populate them into
+   * |aOutBehaviors| and return true. Else, return false.
+   */
+  bool GetAllowedTouchBehaviors(
+      nsTArray<TouchBehaviorFlags>& aOutBehaviors) const;
+
+  /**
+   * Returns true if the allowed touch behaviours have been set, or if touch
+   * action is disabled.
+   */
+  bool HasAllowedTouchBehaviors() const;
+
+  /**
+   * Copy various properties from another block.
+   */
+  void CopyPropertiesFrom(const TouchBlockState& aOther);
+
+  /**
+   * @return true iff this block has received all the information needed
+   *         to properly dispatch the events in the block.
+   */
+  bool IsReadyForHandling() const override;
+
+  /**
+   * Sets a flag that indicates this input block occurred while the APZ was
+   * in a state of fast flinging. This affects gestures that may be produced
+   * from input events in this block.
+   */
+  void SetDuringFastFling();
+  /**
+   * @return true iff SetDuringFastFling was called on this block.
+   */
+  bool IsDuringFastFling() const;
+  /**
+   * Set the single-tap-occurred flag that indicates that this touch block
+   * triggered a single tap event.
+   */
+  void SetSingleTapOccurred();
+  /**
+   * @return true iff the single-tap-occurred flag is set on this block.
+   */
+  bool SingleTapOccurred() const;
+
+  /**
+   * @return false iff touch-action is enabled and the allowed touch behaviors
+   * for this touch block do not allow pinch-zooming.
+   */
+  bool TouchActionAllowsPinchZoom() const;
+  /**
+   * @return false iff touch-action is enabled and the allowed touch behaviors
+   * for this touch block do not allow double-tap zooming.
+   */
+  bool TouchActionAllowsDoubleTapZoom() const;
+  /**
+   * @return false iff touch-action is enabled and the allowed touch behaviors
+   *         for the first touch point do not allow panning in the specified
+   *         direction(s).
+   */
+  bool TouchActionAllowsPanningX() const;
+  bool TouchActionAllowsPanningY() const;
+  bool TouchActionAllowsPanningXY() const;
+
+  /**
+   * Notifies the input block of an incoming touch event so that the block can
+   * update its internal slop state. "Slop" refers to the area around the
+   * initial touchstart where we drop touchmove events so that content doesn't
+   * see them. The |aApzcCanConsumeEvents| parameter is factored into how large
+   * the slop area is - if this is true the slop area is larger.
+   * @return true iff the provided event is a touchmove in the slop area and
+   *         so should not be sent to content.
+   */
+  bool UpdateSlopState(const MultiTouchInput& aInput,
+                       bool aApzcCanConsumeEvents);
+  bool IsInSlop() const;
+
+  /**
+   * Based on the slop origin and the given input event, return a best guess
+   * as to the pan direction of this touch block. Returns Nothing() if no guess
+   * can be made.
+   */
+  Maybe<ScrollDirection> GetBestGuessPanDirection(
+      const MultiTouchInput& aInput);
+
+  /**
+   * Returns the number of touch points currently active.
+   */
+  uint32_t GetActiveTouchCount() const;
+
+  void DispatchEvent(const InputData& aEvent) const override;
+  bool MustStayActive() override;
+  const char* Type() override;
+  TimeDuration GetTimeSinceBlockStart() const;
+
+ private:
+  nsTArray<TouchBehaviorFlags> mAllowedTouchBehaviors;
+  bool mAllowedTouchBehaviorSet;
+  bool mDuringFastFling;
+  bool mSingleTapOccurred;
+  bool mInSlop;
+  ScreenIntPoint mSlopOrigin;
+  // A reference to the InputQueue's touch counter
+  TouchCounter& mTouchCounter;
+  TimeStamp mStartTime;
+};
+
+/**
+ * This class represents a set of keyboard inputs targeted at the same Apzc.
+ */
+class KeyboardBlockState : public InputBlockState {
+ public:
+  explicit KeyboardBlockState(
+      const RefPtr<AsyncPanZoomController>& aTargetApzc);
+
+  KeyboardBlockState* AsKeyboardBlock() override { return this; }
+
+  bool MustStayActive() override { return false; }
+
+  /**
+   * @return Whether or not overscrolling is prevented for this keyboard block.
+   */
+  bool AllowScrollHandoff() const { return false; }
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_InputBlockState_h