tor-browser

ScrollContainerFrame.h (61869B)

---

/* -*- 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/. */

/* rendering object to wrap rendering objects that should be scrollable */

#ifndef mozilla_ScrollContainerFrame_h_
#define mozilla_ScrollContainerFrame_h_

#include "FrameMetrics.h"
#include "ScrollVelocityQueue.h"
#include "mozilla/Attributes.h"
#include "mozilla/ScrollOrigin.h"
#include "mozilla/ScrollTypes.h"
#include "mozilla/dom/WindowBinding.h"  // for mozilla::dom::ScrollBehavior
#include "mozilla/layout/ScrollAnchorContainer.h"
#include "nsContainerFrame.h"
#include "nsExpirationTracker.h"
#include "nsIAnonymousContentCreator.h"
#include "nsIReflowCallback.h"
#include "nsIScrollbarMediator.h"
#include "nsIStatefulFrame.h"
#include "nsQueryFrame.h"
#include "nsThreadUtils.h"

class nsPresContext;
class nsIContent;
class nsAtom;
class AutoContainsBlendModeCapturer;

namespace mozilla {
struct nsDisplayListCollection;
class PresShell;
class PresState;
enum class PhysicalAxis : uint8_t;
enum class StyleScrollbarWidth : uint8_t;
class ScrollContainerFrame;
class ScrollPositionUpdate;
class StickyScrollContainer;
struct ScrollReflowInput;
struct ScrollStyles;
struct StyleScrollSnapAlign;
namespace layers {
class Layer;
class WebRenderLayerManager;
}  // namespace layers
namespace layout {
class ScrollbarActivity;
}  // namespace layout

}  // namespace mozilla

mozilla::ScrollContainerFrame* NS_NewScrollContainerFrame(
   mozilla::PresShell* aPresShell, mozilla::ComputedStyle* aStyle,
   bool aIsRoot);

namespace mozilla {

/**
* The scroll frame creates and manages the scrolling view
*
* It only supports having a single child frame that typically is an area
* frame, but doesn't have to be. The child frame must have a view, though
*
* Scroll frames don't support incremental changes, i.e. you can't replace
* or remove the scrolled frame
*/
class ScrollContainerFrame : public nsContainerFrame,
                            public nsIScrollbarMediator,
                            public nsIAnonymousContentCreator,
                            public nsIReflowCallback,
                            public nsIStatefulFrame {
public:
 using CSSPoint = mozilla::CSSPoint;
 using Element = dom::Element;
 using ScrollAnchorContainer = layout::ScrollAnchorContainer;
 using SnapTargetSet = nsTHashSet<RefPtr<nsIContent>>;

 friend ScrollContainerFrame* ::NS_NewScrollContainerFrame(
     mozilla::PresShell* aPresShell, ComputedStyle* aStyle, bool aIsRoot);
 friend class layout::ScrollAnchorContainer;

 NS_DECL_QUERYFRAME
 NS_DECL_FRAMEARENA_HELPERS(ScrollContainerFrame)

 void BuildDisplayList(nsDisplayListBuilder* aBuilder,
                       const nsDisplayListSet& aLists) override;

 // Return the sum of inline-size of the scrollbar gutters (if any) at the
 // inline-start and inline-end edges of the scroll frame (for a potential
 // scrollbar that scrolls in the block axis).
 nscoord IntrinsicScrollbarGutterSizeAtInlineEdges() const;

 // Return the size of space created by scrollbar-gutter or actual scrollbars,
 // assuming that the content is *not* overflowing the container. In other
 // words, this space is created by stable scrollbar-gutter or by scrollbars
 // due to "overflow: scroll".
 nsMargin IntrinsicScrollbarGutterSize() const;

 // Compute stable scrollbar-gutter from scrollbar-width and scrollbar-gutter
 // properties.
 //
 // Note: this method doesn't consider overflow property and the space created
 // by the actual scrollbars. That is, if scrollbar-gutter is 'auto', this
 // method just returns empty result.
 nsMargin ComputeStableScrollbarGutter(
     const StyleScrollbarWidth& aStyleScrollbarWidth,
     const StyleScrollbarGutter& aStyleScrollbarGutter) const;

 bool GetBorderRadii(const nsSize& aFrameSize, const nsSize& aBorderArea,
                     nsIFrame::Sides aSkipSides,
                     nsRectCornerRadii&) const final;

 nscoord IntrinsicISize(const IntrinsicSizeInput& aInput,
                        IntrinsicISizeType aType) override;

 void Reflow(nsPresContext* aPresContext, ReflowOutput& aDesiredSize,
             const ReflowInput& aReflowInput,
             nsReflowStatus& aStatus) override;
 void DidReflow(nsPresContext* aPresContext,
                const ReflowInput* aReflowInput) override;

 bool ComputeCustomOverflow(OverflowAreas& aOverflowAreas) final;

 BaselineSharingGroup GetDefaultBaselineSharingGroup() const override;
 nscoord SynthesizeFallbackBaseline(
     WritingMode aWM, BaselineSharingGroup aBaselineGroup) const override;
 Maybe<nscoord> GetNaturalBaselineBOffset(
     WritingMode aWM, BaselineSharingGroup aBaselineGroup,
     BaselineExportContext aExportContext) const override;

 StickyScrollContainer* GetStickyContainer() const {
   return mStickyContainer.get();
 }
 StickyScrollContainer& EnsureStickyContainer();

 // Recomputes the scrollable overflow area we store in the helper to take
 // children that are affected by perpsective set on the outer frame and scroll
 // at different rates.
 void AdjustForPerspective(nsRect& aScrollableOverflow);

 // Called to set the child frames. We typically have three: the scroll area,
 // the vertical scrollbar, and the horizontal scrollbar.
 void SetInitialChildList(ChildListID aListID,
                          nsFrameList&& aChildList) override;
 void AppendFrames(ChildListID aListID, nsFrameList&& aFrameList) final;
 void InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
                   const nsLineList::iterator* aPrevFrameLine,
                   nsFrameList&& aFrameList) final;
 void RemoveFrame(DestroyContext&, ChildListID, nsIFrame*) final;

 void DidSetComputedStyle(ComputedStyle* aOldComputedStyle) final;

 void Destroy(DestroyContext&) override;

 ScrollContainerFrame* GetScrollTargetFrame() const final {
   return const_cast<ScrollContainerFrame*>(this);
 }

 nsContainerFrame* GetContentInsertionFrame() override {
   return GetScrolledFrame()->GetContentInsertionFrame();
 }

 nsPoint GetPositionOfChildIgnoringScrolling(const nsIFrame* aChild) final {
   nsPoint pt = aChild->GetPosition();
   if (aChild == GetScrolledFrame()) {
     pt += GetScrollPosition();
   }
   return pt;
 }

 // nsIAnonymousContentCreator
 nsresult CreateAnonymousContent(nsTArray<ContentInfo>&) final;
 void AppendAnonymousContentTo(nsTArray<nsIContent*>&, uint32_t aFilter) final;

 /**
  * Get the frame for the content that we are scrolling within
  * this scrollable frame.
  */
 nsIFrame* GetScrolledFrame() const { return mScrolledFrame; }

 /**
  * Get the overflow styles (StyleOverflow::Scroll, StyleOverflow::Hidden, or
  * StyleOverflow::Auto) governing the horizontal and vertical scrollbars for
  * this frame.
  *
  * This is special because they can be propagated from the <body> element,
  * unlike other styles.
  */
 ScrollStyles GetScrollStyles() const;

 /**
  * Returns whether we already have anonymous content nodes for all our needed
  * scrollbar parts (or a superset thereof).
  */
 bool HasAllNeededScrollbars() const {
   return GetCurrentAnonymousContent().contains(GetNeededAnonymousContent());
 }

 struct PerAxisScrollDirections {
   bool mToRight = false;
   bool mToBottom = false;
 };

 static PerAxisScrollDirections ComputePerAxisScrollDirections(
     const nsIFrame* aScrolledFrame);

 /**
  * Get the overscroll-behavior styles.
  */
 layers::OverscrollBehaviorInfo GetOverscrollBehaviorInfo() const;

 /**
  * Return the scrollbars which are visible. It's OK to call this during reflow
  * of the scrolled contents, in which case it will reflect the current
  * assumptions about scrollbar visibility.
  */
 layers::ScrollDirections GetScrollbarVisibility() const {
   layers::ScrollDirections result;
   if (mHasHorizontalScrollbar) {
     result += layers::ScrollDirection::eHorizontal;
   }
   if (mHasVerticalScrollbar) {
     result += layers::ScrollDirection::eVertical;
   }
   return result;
 }

 /**
  * Returns the directions in which scrolling is allowed (if the scroll range
  * is at least one device pixel in that direction).
  */
 layers::ScrollDirections GetAvailableScrollingDirections() const;

 /**
  * Returns the directions in which scrolling is allowed when taking into
  * account the visual viewport size and overflow hidden. (An (apz) zoomed in
  * overflow hidden scrollframe is actually user scrollable.)
  */
 layers::ScrollDirections GetAvailableScrollingDirectionsForUserInputEvents()
     const;

 /**
  * Return the actual sizes of all possible scrollbars. Returns 0 for scrollbar
  * positions that don't have a scrollbar or where the scrollbar is not
  * visible. Do not call this while this frame's descendants are being
  * reflowed, it won't be accurate.
  * INCLUDE_VISUAL_VIEWPORT_SCROLLBARS means we include the size of layout
  * scrollbars that are only visible to scroll the visual viewport inside the
  * layout viewport (ie the layout viewport cannot be scrolled) even though
  * there is no layout space set aside for these scrollbars.
  */
 enum class ScrollbarSizesOptions { NONE, INCLUDE_VISUAL_VIEWPORT_SCROLLBARS };
 nsMargin GetActualScrollbarSizes(
     ScrollbarSizesOptions aOptions = ScrollbarSizesOptions::NONE) const;

 /**
  * Return the sizes of all scrollbars assuming that any scrollbars that could
  * be visible due to overflowing content, are. This can be called during
  * reflow of the scrolled contents.
  */
 nsMargin GetDesiredScrollbarSizes() const;

 /**
  * Get the layout size of this frame.
  * Note that this is a value which is not expanded by the minimum scale size.
  * For scroll frames other than the root content document's scroll frame, this
  * value will be the same as GetScrollPortRect().Size().
  *
  * This value is used for Element.clientWidth and clientHeight.
  */
 nsSize GetLayoutSize() const {
   if (mIsUsingMinimumScaleSize) {
     return mICBSize;
   }
   return mScrollPort.Size();
 }

 /**
  * Get the size used for window.innerWidth or innerHeight.
  * This works only for the root scroll container.
  */
 nsSize GetSizeForWindowInnerSize() const;

 /**
  * GetScrolledRect is designed to encapsulate deciding which
  * directions of overflow should be reachable by scrolling and which
  * should not.  Callers should NOT depend on it having any particular
  * behavior.
  *
  * This should only be called when the scrolled frame has been
  * reflowed with the scroll port size given in mScrollPort.
  *
  * Currently it allows scrolling down and to the right for
  * ScrollContainerFrames with LTR directionality, and allows scrolling down
  * and to the left for ScrollContainerFrames with RTL directionality.
  */
 nsRect GetScrolledRect() const;

 /**
  * Get the area of the scrollport relative to the origin of this frame's
  * border-box.
  * This is the area of this frame minus border and scrollbars.
  */
 nsRect GetScrollPortRect() const { return mScrollPort; }
 nsRect GetScrollPortRectAccountingForDynamicToolbar() const {
   auto rect = mScrollPort;
   if (mIsRoot) {
     rect.height += PresContext()->GetBimodalDynamicToolbarHeightInAppUnits();
   }
   return rect;
 }
 nsRect GetScrollPortRectAccountingForMaxDynamicToolbar() const;

 nsSize GetScrolledFrameSizeAccountingForDynamicToolbar() const {
   auto size = mScrolledFrame->GetContentRectRelativeToSelf().Size();
   if (mIsRoot) {
     size.height += PresContext()->GetBimodalDynamicToolbarHeightInAppUnits();
   }
   return size;
 }

 /**
  * Get the offset of the scrollport origin relative to the scrolled
  * frame origin. Typically the position will be non-negative.
  * This will always be a multiple of device pixels.
  */
 nsPoint GetScrollPosition() const {
   return mScrollPort.TopLeft() - mScrolledFrame->GetPosition();
 }

 /**
  * For LTR frames, the logical scroll position is the offset of the top left
  * corner of the frame from the top left corner of the scroll port (same as
  * GetScrollPosition).
  * For RTL frames, it is the offset of the top right corner of the frame from
  * the top right corner of the scroll port.
  */
 nsPoint GetLogicalScrollPosition() const {
   nsPoint pt;
   pt.x = IsPhysicalLTR()
              ? mScrollPort.x - mScrolledFrame->GetPosition().x
              : mScrollPort.XMost() - mScrolledFrame->GetRect().XMost();
   pt.y = mScrollPort.y - mScrolledFrame->GetPosition().y;
   return pt;
 }

 /**
  * Get the area that must contain the scroll position. Typically
  * (but not always, e.g. for RTL content) x and y will be 0, and
  * width or height will be nonzero if the content can be scrolled in
  * that direction. Since scroll positions must be a multiple of
  * device pixels, the range extrema will also be a multiple of
  * device pixels.
  */
 nsRect GetScrollRange() const { return GetLayoutScrollRange(); }

 /**
  * Get the size of the view port to use when clamping the scroll
  * position.
  */
 nsSize GetVisualViewportSize() const;

 /**
  * Returns the offset of the visual viewport relative to
  * the origin of the scrolled content. Note that only the RCD-RSF
  * has a distinct visual viewport; for other scroll frames, the
  * visual viewport always coincides with the layout viewport, and
  * consequently the offset this function returns is equal to
  * GetScrollPosition().
  */
 nsPoint GetVisualViewportOffset() const;

 /**
  * Set the visual viewport offset associated with a root scroll frame. This is
  * only valid when called on a root scroll frame and will assert otherwise.
  * aRepaint indicates if we need to ask for a main thread paint if this
  * changes scrollbar positions or not. For example, if the compositor has
  * already put the scrollbars at this position then they don't need to move so
  * we can skip the repaint. Returns true if the offset changed and the scroll
  * frame is still alive after this call.
  */
 bool SetVisualViewportOffset(const nsPoint& aOffset, bool aRepaint);
 /**
  * Get the area that must contain the visual viewport offset.
  */
 nsRect GetVisualScrollRange() const;

 /**
  * Like GetVisualScrollRange but also takes into account overflow: hidden.
  */
 nsRect GetScrollRangeForUserInputEvents() const;

 /**
  * Return how much we would try to scroll by in each direction if
  * asked to scroll by one "line" vertically and horizontally.
  */
 nsSize GetLineScrollAmount() const;
 /**
  * Return how much we would try to scroll by in each direction if
  * asked to scroll by one "page" vertically and horizontally.
  */
 nsSize GetPageScrollAmount() const;

 /**
  * Return scroll-padding value of this frame.
  */
 nsMargin GetScrollPadding() const;

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Clamps aScrollPosition to GetScrollRange and sets the scroll position
  * to that value.
  * @param aRange If non-null, specifies area which contains aScrollPosition
  * and can be used for choosing a performance-optimized scroll position.
  * Any point within this area can be chosen.
  * The choosen point will be as close as possible to aScrollPosition.
  */
 void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
               const nsRect* aRange = nullptr,
               ScrollSnapFlags aSnapFlags = ScrollSnapFlags::Disabled,
               ScrollTriggeredByScript aTriggeredByScript =
                   ScrollTriggeredByScript::No) {
   return ScrollToInternal(aScrollPosition, aMode, ScrollOrigin::Other, aRange,
                           aSnapFlags, aTriggeredByScript);
 }

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Scrolls to a particular position in integer CSS pixels.
  * Keeps the exact current horizontal or vertical position if the current
  * position, rounded to CSS pixels, matches aScrollPosition. If
  * aScrollPosition.x/y is different from the current CSS pixel position,
  * makes sure we only move in the direction given by the difference.
  *
  * When aMode is SMOOTH, INSTANT, or NORMAL, GetRoundedScrollPositionCSSPixels
  * (the scroll position after rounding to CSS pixels) will be exactly
  * aScrollPosition at the end of the scroll animation.
  *
  * When aMode is SMOOTH_MSD, intermediate animation frames may be outside the
  * range and / or moving in any direction; GetRoundedScrollPositionCSSPixels
  * will be exactly aScrollPosition at the end of the scroll animation unless
  * the SMOOTH_MSD animation is interrupted.
  */
 void ScrollToCSSPixels(const CSSPoint& aScrollPosition,
                        ScrollMode aMode = ScrollMode::Instant);

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Scrolls to a particular position in float CSS pixels.
  * This does not guarantee that GetRoundedScrollPositionCSSPixels equals
  * aScrollPosition afterward. It tries to scroll as close to
  * aScrollPosition as possible while scrolling by an integer
  * number of layer pixels (so the operation is fast and looks clean).
  */
 void ScrollToCSSPixelsForApz(const CSSPoint& aScrollPosition,
                              ScrollSnapTargetIds&& aLastSnapTargetIds);

 /**
  * Returns the scroll position in integer CSS pixels, rounded to the nearest
  * pixel.
  */
 CSSIntPoint GetRoundedScrollPositionCSSPixels();

 /**
  * Returns the scroll position in CSS pixels.
  */
 CSSPoint GetScrollPositionCSSPixels() const {
   return CSSPoint::FromAppUnits(GetScrollPosition());
 }

 /**
  * Some platforms (OSX) may generate additional scrolling events even
  * after the user has stopped scrolling, simulating a momentum scrolling
  * effect resulting from fling gestures.
  * SYNTHESIZED_MOMENTUM_EVENT indicates that the scrolling is being requested
  * by such a synthesized event and may be ignored if another scroll has
  * been started since the last actual user input.
  */
 enum ScrollMomentum { NOT_MOMENTUM, SYNTHESIZED_MOMENTUM_EVENT };

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Modifies the current scroll position by aDelta units given by aUnit,
  * clamping it to GetScrollRange. If WHOLE is specified as the unit,
  * content is scrolled all the way in the direction(s) given by aDelta.
  * @param aOverflow if non-null, returns the amount that scrolling
  * was clamped by in each direction (how far we moved the scroll position
  * to bring it back into the legal range). This is never negative. The
  * values are in device pixels.
  */
 void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
               nsIntPoint* aOverflow = nullptr,
               ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
               ScrollMomentum aMomentum = NOT_MOMENTUM,
               ScrollSnapFlags aSnapFlags = ScrollSnapFlags::Disabled);

 void ScrollByCSSPixels(const CSSPoint& aDelta,
                        ScrollMode aMode = ScrollMode::Instant) {
   return ScrollByCSSPixelsInternal(aDelta, aMode);
 }

 /**
  * Perform scroll snapping, possibly resulting in a smooth scroll to
  * maintain the scroll snap position constraints.  Velocity sampled from
  * main thread scrolling is used to determine best matching snap point
  * when called after a fling gesture on a trackpad or mouse wheel.
  */
 void ScrollSnap() { return ScrollSnap(ScrollMode::SmoothMsd); }

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * This tells the scroll frame to try scrolling to the scroll
  * position that was restored from the history. This must be called
  * at least once after state has been restored. It is called by the
  * scrolled frame itself during reflow, but sometimes state can be
  * restored after reflows are done...
  * XXX should we take an aMode parameter here? Currently it's instant.
  */
 void ScrollToRestoredPosition();

 bool NeedRestorePosition() const {
   return mRestorePos.y != -1 && mLastPos.x != -1 && mLastPos.y != -1;
 }

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Internal method used by scrollbars to notify their scrolling
  * container of changes.
  */
 void ScrollbarCurPosChanged(bool aDoScroll = true);

 /**
  * Allows the docshell to request that the scroll frame post an event
  * after being restored from history.
  */
 NS_IMETHOD PostScrolledAreaEventForCurrentArea() final {
   PostScrolledAreaEvent();
   return NS_OK;
 }

 /**
  * Returns true if this scrollframe is being "actively scrolled".
  * This basically means that we should allocate resources in the
  * expectation that scrolling is going to happen.
  */
 bool IsScrollingActive() const;

 /**
  * Returns true if this scroll frame might be scrolled
  * asynchronously by the compositor.
  */
 bool IsMaybeAsynchronouslyScrolled() const {
   // If this is true, then we'll build an ASR, and that's what we want
   // to know I think.
   return mWillBuildScrollableLayer;
 }

 /**
  * Was the current presentation state for this frame restored from history?
  */
 bool DidHistoryRestore() const { return mDidHistoryRestore; }

 /**
  * Clear the flag so that DidHistoryRestore() returns false until the next
  * RestoreState call.
  * @see nsIStatefulFrame::RestoreState
  */
 void ClearDidHistoryRestore() { mDidHistoryRestore = false; }

 /**
  * Mark the frame as having been scrolled at least once, so that it remains
  * active and we can also start storing its scroll position when saving state.
  */
 void MarkEverScrolled();

 /**
  * Determine if the passed in rect is nearly visible according to the frame
  * visibility heuristics for how close it is to the visible scrollport.
  */
 bool IsRectNearlyVisible(const nsRect& aRect) const;

 /**
  * Expand the given rect taking into account which directions we can scroll
  * and how far we want to expand for frame visibility purposes.
  */
 nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const;

 /**
  * Returns the origin that triggered the last instant scroll. Will equal
  * ScrollOrigin::Apz when the compositor's replica frame metrics includes the
  * latest instant scroll.
  */
 ScrollOrigin LastScrollOrigin() const { return mLastScrollOrigin; }

 /**
  * Gets the async scroll animation state of this scroll frame.
  *
  * There are five possible kinds that can overlap.
  * MainThread means async scroll animated by the main thread.
  * APZ scroll animations that are requested from the main thread go through
  * three states: 1) pending, when the main thread has recorded that it wants
  * apz to do a scroll animation, 2) requested, when the main thread has sent
  * the request to the compositor (but it hasn't necessarily arrived yet), and
  * 3) in progress, after apz has responded to the main thread that it got the
  * request.
  * TriggeredByScript means that the async scroll animation was triggered by
  * script, e.g. Element.scrollTo().
  */
 enum class AnimationState {
   MainThread,        // mAsyncScroll || mAsyncSmoothMSDScroll
   APZPending,        // mScrollUpdates.LastElement() is Smooth or SmoothMsd
   APZRequested,      // mApzAnimationRequested
   APZInProgress,     // mCurrentAPZScrollAnimationType !=
                      // APZScrollAniationType::No
   TriggeredByScript  // The animation was triggered with
                      // ScrollTriggeredByScript::Yes
 };
 EnumSet<AnimationState> ScrollAnimationState() const;

 /**
  * Returns the current generation counter for the scrollframe. This counter
  * increments every time the scroll position is set.
  */
 MainThreadScrollGeneration CurrentScrollGeneration() const {
   return mScrollGeneration;
 }

 /**
  * The APZ scroll generation associated with the last APZ scroll offset for
  * which we processed a repaint request.
  */
 APZScrollGeneration ScrollGenerationOnApz() const {
   return mScrollGenerationOnApz;
 }

 /**
  * LastScrollDestination returns the destination of the most recently
  * requested smooth scroll animation.
  */
 nsPoint LastScrollDestination() { return mDestination; }

 /**
  * Returns the list of scroll position updates since the last call to
  * NotifyApzTransaction().
  */
 nsTArray<ScrollPositionUpdate> GetScrollUpdates() const;

 /**
  * Returns true if the scroll frame has any scroll position updates since
  * the last call to NotifyApzTransaction().
  */
 bool HasScrollUpdates() const { return !mScrollUpdates.IsEmpty(); }

 /**
  * Clears the "origin of last scroll" property stored in this frame, if
  * the generation counter passed in matches the current scroll generation
  * counter, and clears the "origin of last smooth scroll" property if the
  * generation counter matches. It also resets whether there's an ongoing apz
  * animation.
  */
 enum class InScrollingGesture : bool { No, Yes };
 void ResetScrollInfoIfNeeded(const MainThreadScrollGeneration& aGeneration,
                              const APZScrollGeneration& aGenerationOnApz,
                              APZScrollAnimationType aAPZScrollAnimationType,
                              InScrollingGesture aInScrollingGesture);

 /**
  * Determine whether it is desirable to be able to asynchronously scroll this
  * scroll frame.
  */
 bool WantAsyncScroll() const;

 /**
  * Returns the ScrollMetadata contributed by this frame, if there is one.
  */
 Maybe<layers::ScrollMetadata> ComputeScrollMetadata(
     layers::WebRenderLayerManager* aLayerManager, const nsIFrame* aItemFrame,
     const nsPoint& aOffsetToReferenceFrame) const;

 /**
  * Mark the scrollbar frames for reflow.
  */
 void MarkScrollbarsDirtyForReflow() const;

 /**
  * Invalidate the scrollbar after the marks have been changed.
  */
 void InvalidateScrollbars() const;

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * Update scrollbar to reflect current scroll position
  */
 void UpdateScrollbarPosition();

 void SetTransformingByAPZ(bool aTransforming);
 bool IsTransformingByAPZ() const { return mTransformingByAPZ; }

 /**
  * Notify this scroll frame that it can be scrolled by APZ. In particular,
  * this is called *after* the APZ code has created an APZC for this scroll
  * frame and verified that it is not a scrollinfo layer. Therefore, setting an
  * async transform on it is actually user visible.
  */
 void SetScrollableByAPZ(bool aScrollable);

 /**
  * Notify this scroll frame that it can be zoomed by APZ.
  */
 void SetZoomableByAPZ(bool aZoomable);

 /**
  * Mark this scroll frame as having out-of-flow content inside a CSS filter.
  * Such content will move incorrectly during async-scrolling; to mitigate
  * this, paint skipping is disabled for such scroll frames.
  */
 void SetHasOutOfFlowContentInsideFilter();

 /**
  * Determine if we should build a scrollable layer for this scroll frame and
  * return the result. It will also record this result on the scroll frame.
  * Pass the visible rect in aVisibleRect. On return it will be set to the
  * displayport if there is one.
  * Pass the dirty rect in aDirtyRect. On return it will be set to the
  * dirty rect inside the displayport (ie the dirty rect that should be used).
  * This function will set the display port base rect if aSetBase is true.
  * aSetBase is only allowed to be false if there has been a call with it
  * set to true before on the same paint.
  */
 bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
                            nsRect* aVisibleRect, nsRect* aDirtyRect,
                            bool aSetBase) {
   return DecideScrollableLayer(aBuilder, aVisibleRect, aDirtyRect, aSetBase,
                                nullptr);
 }

 /**
  * Like DecideScrollableLayer but skips computing dirty/visible rects and
  * setting the base rect. In addition, this always ensures a display port is
  * set if this scroll frame could async scroll. DecideScrollableLayer only
  * sets a display port in that situation if ShouldActivateAllScrollFrames
  * returns true. However you should only call this function is
  * ShouldActivateAllScrollFrames returns true anyways.
  * */
 bool DecideScrollableLayerEnsureDisplayport(nsDisplayListBuilder* aBuilder);

 /**
  * Notify the scrollframe that the current scroll offset and origin have been
  * sent over in a layers transaction.
  *
  * This sets a flag on the scrollframe that indicates subsequent changes
  * to the scroll position by "weaker" origins are permitted to overwrite the
  * the scroll origin. Scroll origins that
  * nsLayoutUtils::CanScrollOriginClobberApz returns false for are considered
  * "weaker" than scroll origins for which that function returns true.
  *
  * This function must be called for a scrollframe after all calls to
  * ComputeScrollMetadata in a layers transaction have been completed.
  *
  */
 void NotifyApzTransaction();

 /**
  * Notification that this scroll frame is getting its frame visibility
  * updated. aIgnoreDisplayPort indicates that the display port was ignored
  * (because there was no suitable base rect)
  */
 void NotifyApproximateFrameVisibilityUpdate(bool aIgnoreDisplayPort);

 /**
  * Returns true if this scroll frame had a display port at the last frame
  * visibility update and fills in aDisplayPort with that displayport. Returns
  * false otherwise, and doesn't touch aDisplayPort.
  */
 bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
     nsRect* aDisplayPort);

 /**
  * This is called when a descendant scrollframe's has its displayport expired.
  * This function will check to see if this scrollframe may safely expire its
  * own displayport and schedule a timer to do that if it is safe.
  */
 void TriggerDisplayPortExpiration();

 /**
  * Returns information required to determine where to snap to after a scroll.
  */
 ScrollSnapInfo GetScrollSnapInfo();

 void TryResnap();

 /**
  * Post a pending re-snap request if the given |aFrame| is one of the snap
  * points on the last scroll operation.
  */
 void PostPendingResnapIfNeeded(const nsIFrame* aFrame);
 void PostPendingResnap();

 /**
  * Returns a pair of the scroll-snap-align property value both on X and Y axes
  * for the given |aFrame| considering the scroll-snap-type of this scroll
  * container. For example, if the scroll-snap-type is `none`, the pair of
  * scroll-snap-align is also `none none`.
  */
 using PhysicalScrollSnapAlign =
     std::pair<StyleScrollSnapAlignKeyword, StyleScrollSnapAlignKeyword>;
 PhysicalScrollSnapAlign GetScrollSnapAlignFor(const nsIFrame* aFrame) const;

 /**
  * Given the drag event aEvent, determine whether the mouse is near the edge
  * of the scrollable area, and scroll the view in the direction of that edge
  * if so. If scrolling occurred, true is returned. When false is returned, the
  * caller should look for an ancestor to scroll.
  */
 bool DragScroll(WidgetEvent* aEvent);

 void AsyncScrollbarDragInitiated(uint64_t aDragBlockId,
                                  layers::ScrollDirection aDirection);
 void AsyncScrollbarDragRejected();

 /**
  * Returns whether this scroll frame is the root scroll frame of the document
  * that it is in. Note that some documents don't have root scroll frames at
  * all (ie XUL documents) even though they may contain other scroll frames.
  */
 bool IsRootScrollFrameOfDocument() const { return mIsRoot; }

 /**
  * Returns the paint sequence number if this scroll frame was the first
  * scrollable frame for the paint.
  */
 Maybe<uint32_t> IsFirstScrollableFrameSequenceNumber() const {
   return mIsFirstScrollableFrameSequenceNumber;
 }

 /**
  * Set the paint sequence number for the paint in which this was the first
  * scrollable frame that was encountered.
  */
 void SetIsFirstScrollableFrameSequenceNumber(Maybe<uint32_t> aValue) {
   mIsFirstScrollableFrameSequenceNumber = aValue;
 }

 /**
  * Returns the scroll anchor associated with this scrollable frame. This is
  * never null.
  */
 const ScrollAnchorContainer* Anchor() const { return &mAnchor; }
 ScrollAnchorContainer* Anchor() { return &mAnchor; }

 bool SmoothScrollVisual(
     const nsPoint& aVisualViewportOffset,
     layers::FrameMetrics::ScrollOffsetUpdateType aUpdateType,
     ScrollMode aMode);

 /**
  * Returns true if this scroll frame should perform smooth scroll with the
  * given |aBehavior|.
  */
 bool IsSmoothScroll(
     dom::ScrollBehavior aBehavior = dom::ScrollBehavior::Auto) const;

 /**
  * Returns the ScrollMode that this scroll frame should use for a
  * programmatic scroll governed by CSSOM-View `scroll-behavior`.
  * This includes most programmatic scrolls but not scroll snapping.
  */
 ScrollMode ScrollModeForScrollBehavior(
     dom::ScrollBehavior aBehavior = dom::ScrollBehavior::Auto) const;

 static nscoord GetNonOverlayScrollbarSize(const nsPresContext*,
                                           StyleScrollbarWidth);

 void ScrollByCSSPixelsInternal(
     const CSSPoint& aDelta, ScrollMode aMode = ScrollMode::Instant,
     // This ScrollByCSSPixels is mainly used for Element.scrollBy and
     // Window.scrollBy. An exception is the transmogrification of
     // ScrollToCSSPixels.
     ScrollSnapFlags aSnapFlags = ScrollSnapFlags::IntendedDirection |
                                  ScrollSnapFlags::IntendedEndPosition);

 // nsIReflowCallback
 bool ReflowFinished() override;
 void ReflowCallbackCanceled() final;

 // nsIStatefulFrame
 UniquePtr<PresState> SaveState() final;
 NS_IMETHOD RestoreState(PresState* aState) final;

 // nsIScrollbarMediator
 void ScrollByPage(
     nsScrollbarFrame* aScrollbar, int32_t aDirection,
     ScrollSnapFlags aSnapFlags = ScrollSnapFlags::Disabled) final;
 void ScrollByWhole(
     nsScrollbarFrame* aScrollbar, int32_t aDirection,
     ScrollSnapFlags aSnapFlags = ScrollSnapFlags::Disabled) final;
 void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
                   ScrollSnapFlags = ScrollSnapFlags::Disabled) final;
 void ScrollByUnit(nsScrollbarFrame* aScrollbar, ScrollMode aMode,
                   int32_t aDirection, ScrollUnit aUnit,
                   ScrollSnapFlags = ScrollSnapFlags::Disabled) final;
 void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) final;
 void ThumbMoved(nsScrollbarFrame* aScrollbar, nscoord aOldPos,
                 nscoord aNewPos) final;
 void ScrollbarReleased(nsScrollbarFrame* aScrollbar) final;
 void VisibilityChanged(bool aVisible) final {}
 nsScrollbarFrame* GetScrollbarBox(bool aVertical) final {
   return aVertical ? mVScrollbarBox : mHScrollbarBox;
 }
 void ScrollbarActivityStarted() const final;
 void ScrollbarActivityStopped() const final;
 bool IsScrollbarOnRight() const final;
 bool ShouldSuppressScrollbarRepaints() const final {
   return mSuppressScrollbarRepaints;
 }

 // Return the scrolled frame.
 void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) final {
   aResult.AppendElement(OwnedAnonBox(GetScrolledFrame()));
 }

#ifdef DEBUG_FRAME_DUMP
 nsresult GetFrameName(nsAString& aResult) const override;
#endif

#ifdef ACCESSIBILITY
 a11y::AccType AccessibleType() override;
#endif

 static void AsyncScrollCallback(ScrollContainerFrame* aInstance,
                                 TimeStamp aTime);
 static void AsyncSmoothMSDScrollCallback(ScrollContainerFrame* aInstance,
                                          TimeDuration aDeltaTime);
 /**
  * @note This method might destroy the frame, pres shell and other objects.
  * aRange is the range of allowable scroll positions around the desired
  * aScrollPosition. Null means only aScrollPosition is allowed.
  * This is a closed-ended range --- aRange.XMost()/aRange.YMost() are allowed.
  */
 void ScrollToInternal(
     nsPoint aScrollPosition, ScrollMode aMode,
     ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
     const nsRect* aRange = nullptr,
     ScrollSnapFlags aSnapFlags = ScrollSnapFlags::Disabled,
     ScrollTriggeredByScript aTriggeredByScript = ScrollTriggeredByScript::No);
 /**
  * @note This method might destroy the frame, pres shell and other objects.
  */
 void ScrollToImpl(
     nsPoint aPt, const nsRect& aRange,
     ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
     ScrollTriggeredByScript aTriggeredByScript = ScrollTriggeredByScript::No);
 void ScrollVisual();

 enum class LoadingState { Loading, Stopped, Loaded };

 LoadingState GetPageLoadingState();

 /**
  * GetSnapPointForDestination determines which point to snap to after
  * scrolling. aStartPos gives the position before scrolling and aDestination
  * gives the position after scrolling, with no snapping. Behaviour is
  * dependent on the value of aUnit.
  * Returns true if a suitable snap point could be found and aDestination has
  * been updated to a valid snapping position.
  */
 Maybe<SnapDestination> GetSnapPointForDestination(
     ScrollUnit aUnit, ScrollSnapFlags aFlags, const nsPoint& aStartPos,
     const nsPoint& aDestination);

 Maybe<SnapDestination> GetSnapPointForResnap();
 bool NeedsResnap();

 void SetLastSnapTargetIds(UniquePtr<ScrollSnapTargetIds> aId);

 static void SetScrollbarVisibility(nsIFrame* aScrollbar, bool aVisible);

 /**
  * GetUnsnappedScrolledRectInternal is designed to encapsulate deciding which
  * directions of overflow should be reachable by scrolling and which
  * should not.  Callers should NOT depend on it having any particular
  * behavior.
  *
  * Currently it allows scrolling down and to the right for
  * ScrollContainerFrames with LTR directionality, and allows scrolling down
  * and to the left for ScrollContainerFrames with RTL directionality.
  */
 nsRect GetUnsnappedScrolledRectInternal(const nsRect& aScrolledOverflowArea,
                                         const nsSize& aScrollPortSize) const;

 bool IsPhysicalLTR() const { return GetWritingMode().IsPhysicalLTR(); }
 bool IsBidiLTR() const { return GetWritingMode().IsBidiLTR(); }

 bool IsAlwaysActive() const;
 void MarkRecentlyScrolled();
 void MarkNotRecentlyScrolled();
 nsExpirationState* GetExpirationState() { return &mActivityExpirationState; }

 bool UsesOverlayScrollbars() const;
 bool IsLastSnappedTarget(const nsIFrame* aFrame) const;

 // If aBuilder is non-null, returns the value cached on aBuilder. Pass null
 // for aBuilder to get the correct value to cache on a new builder or new
 // frame of painting, or if you need the correct value outside of paint time.
 static bool ShouldActivateAllScrollFrames(nsDisplayListBuilder* aBuilder,
                                           nsIFrame* aFrame);
 nsRect RestrictToRootDisplayPort(const nsRect& aDisplayportBase);
 bool DecideScrollableLayer(nsDisplayListBuilder* aBuilder,
                            nsRect* aVisibleRect, nsRect* aDirtyRect,
                            bool aSetBase, bool* aDirtyRectHasBeenOverriden);
 bool AllowDisplayPortExpiration();
 void ResetDisplayPortExpiryTimer();

 void ScheduleSyntheticMouseMove();
 static void ScrollActivityCallback(nsITimer* aTimer, void* anInstance);

 void HandleScrollbarStyleSwitching();

 bool IsApzAnimationInProgress() const {
   return mCurrentAPZScrollAnimationType != APZScrollAnimationType::No;
 }
 nsPoint LastScrollDestination() const { return mDestination; }

 bool IsLastScrollUpdateAnimating() const;
 bool IsLastScrollUpdateTriggeredByScriptAnimating() const;

 // Update minimum-scale size.  The minimum-scale size will be set/used only
 // if there is overflow-x:hidden region.
 void UpdateMinimumScaleSize(const nsRect& aScrollableOverflow,
                             const nsSize& aICBSize);

 // Return the scroll frame's "true outer size".
 // This is GetSize(), except when we've been sized to reflect a virtual
 // (layout) viewport in which case this returns the outer size used to size
 // the physical (visual) viewport.
 nsSize TrueOuterSize(nsDisplayListBuilder* aBuilder) const;

 already_AddRefed<Element> MakeScrollbar(dom::NodeInfo* aNodeInfo,
                                         bool aVertical,
                                         AnonymousContentKey& aKey);

 void AppendScrollUpdate(const ScrollPositionUpdate& aUpdate);

 bool HasBeenScrolled() const { return mHasBeenScrolled; }

protected:
 ScrollContainerFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
                      bool aIsRoot)
     : ScrollContainerFrame(aStyle, aPresContext, kClassID, aIsRoot) {}
 ScrollContainerFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
                      nsIFrame::ClassID aID, bool aIsRoot);
 ~ScrollContainerFrame();
 bool GuessHScrollbarNeeded(const ScrollReflowInput& aState);
 bool GuessVScrollbarNeeded(const ScrollReflowInput& aState);

 // Return whether we're in an "initial" reflow.  Some reflows with
 // NS_FRAME_FIRST_REFLOW set are NOT "initial" as far as we're concerned.
 bool InInitialReflow() const;

 bool TryLayout(ScrollReflowInput& aState, ReflowOutput* aKidMetrics,
                bool aAssumeHScroll, bool aAssumeVScroll, bool aForce);

 // Return true if ReflowScrolledFrame is going to do something different based
 // on the presence of a horizontal scrollbar in a horizontal writing mode or a
 // vertical scrollbar in a vertical writing mode.
 bool ScrolledContentDependsOnBSize(const ScrollReflowInput& aState) const;

 void ReflowScrolledFrame(ScrollReflowInput& aState, bool aAssumeHScroll,
                          bool aAssumeVScroll, ReflowOutput* aMetrics);
 void ReflowContents(ScrollReflowInput& aState,
                     const ReflowOutput& aDesiredSize);
 void PlaceScrollArea(ScrollReflowInput& aState,
                      const nsPoint& aScrollPosition);

 void UpdateSticky();
 void UpdatePrevScrolledRect();

 // adjust the scrollbar rectangle aRect to account for any visible resizer.
 // aHasResizer specifies if there is a content resizer, however this method
 // will also check if a widget resizer is present as well.
 void AdjustScrollbarRectForResizer(nsIFrame* aFrame,
                                    nsPresContext* aPresContext, nsRect& aRect,
                                    bool aHasResizer,
                                    layers::ScrollDirection aDirection);
 void LayoutScrollbars(ScrollReflowInput& aState,
                       const nsRect& aInsideBorderArea,
                       const nsRect& aOldScrollPort);

 void LayoutScrollbarPartAtRect(const ScrollReflowInput&,
                                ReflowInput& aKidReflowInput, const nsRect&);

 /**
  * Override this to return false if computed bsize/min-bsize/max-bsize
  * should NOT be propagated to child content.
  * nsListControlFrame uses this.
  */
 virtual bool ShouldPropagateComputedBSizeToScrolledContent() const {
   return true;
 }

 PhysicalAxes GetOverflowAxes() const;

 MOZ_CAN_RUN_SCRIPT nsresult FireScrollPortEvent();
 void PostScrollEndEvent();
 MOZ_CAN_RUN_SCRIPT void FireScrollEndEvent();
 void PostOverflowEvent();

 // Add display items for the top-layer (which includes things like
 // the fullscreen element, its backdrop, and text selection carets)
 // to |aLists|.
 // This is a no-op for scroll frames other than the viewport's
 // root scroll frame.
 // This should be called with an nsDisplayListSet that will be
 // wrapped in the async zoom container, if we're building one.
 // It should not be called with an ASR setter on the stack, as the
 // top-layer items handle setting up their own ASRs.
 void MaybeCreateTopLayerAndWrapRootItems(
     nsDisplayListBuilder*, nsDisplayListCollection&, bool aCreateAsyncZoom,
     bool aCapturedByViewTransition,
     AutoContainsBlendModeCapturer* aAsyncZoomBlendCapture,
     const nsRect& aAsyncZoomClipRect, const nsRectCornerRadii* aRadii);

 void AppendScrollPartsTo(nsDisplayListBuilder* aBuilder,
                          const nsDisplayListSet& aLists, bool aCreateLayer,
                          bool aPositioned);

 void PostScrollEvent();
 MOZ_CAN_RUN_SCRIPT void FireScrollEvent();
 void PostScrolledAreaEvent();
 MOZ_CAN_RUN_SCRIPT void FireScrolledAreaEvent();

 void FinishReflowForScrollbar(nsScrollbarFrame*, nscoord aMinXY,
                               nscoord aMaxXY, nscoord aCurPosXY,
                               nscoord aPageIncrement);
 void ActivityOccurred();

 nsRect GetLayoutScrollRange() const;
 // Get the scroll range assuming the viewport has size (aWidth, aHeight).
 nsRect GetScrollRange(nscoord aWidth, nscoord aHeight) const;

 const nsRect& ScrollPort() const { return mScrollPort; }
 void SetScrollPort(const nsRect& aNewScrollPort) {
   if (!mScrollPort.IsEqualEdges(aNewScrollPort)) {
     mMayScheduleScrollAnimations = true;
   }
   mScrollPort = aNewScrollPort;
 }

 /**
  * Return the 'optimal viewing region' as a rect suitable for use by
  * scroll anchoring. This rect is in the same coordinate space as
  * 'GetScrollPortRect', and accounts for 'scroll-padding' as defined by:
  *
  * https://drafts.csswg.org/css-scroll-snap-1/#optimal-viewing-region
  */
 nsRect GetVisualOptimalViewingRect() const;

 /**
  * For LTR frames, this is the same as GetVisualViewportOffset().
  * For RTL frames, we take the offset from the top right corner of the frame
  * to the top right corner of the visual viewport.
  */
 nsPoint GetLogicalVisualViewportOffset() const {
   nsPoint pt = GetVisualViewportOffset();
   if (!IsPhysicalLTR()) {
     pt.x += GetVisualViewportSize().width - mScrolledFrame->GetRect().width;
   }
   return pt;
 }
 void ScrollSnap(ScrollMode aMode);
 void ScrollSnap(const nsPoint& aDestination,
                 ScrollMode aMode = ScrollMode::SmoothMsd);

 bool HasPendingScrollRestoration() const {
   return mRestorePos != nsPoint(-1, -1);
 }

 bool IsProcessingScrollEvent() const { return mProcessingScrollEvent; }

 class AutoScrollbarRepaintSuppression;
 friend class AutoScrollbarRepaintSuppression;
 class AutoScrollbarRepaintSuppression {
  public:
   AutoScrollbarRepaintSuppression(ScrollContainerFrame* aFrame,
                                   AutoWeakFrame& aWeakOuter, bool aSuppress)
       : mFrame(aFrame),
         mWeakOuter(aWeakOuter),
         mOldSuppressValue(aFrame->mSuppressScrollbarRepaints) {
     mFrame->mSuppressScrollbarRepaints = aSuppress;
   }

   ~AutoScrollbarRepaintSuppression() {
     if (mWeakOuter.IsAlive()) {
       mFrame->mSuppressScrollbarRepaints = mOldSuppressValue;
     }
   }

  private:
   ScrollContainerFrame* mFrame;
   AutoWeakFrame& mWeakOuter;
   bool mOldSuppressValue;
 };

 struct ScrollOperationParams {
   ScrollOperationParams(const ScrollOperationParams&) = delete;
   ScrollOperationParams(ScrollMode aMode, ScrollOrigin aOrigin)
       : mMode(aMode), mOrigin(aOrigin) {}
   ScrollOperationParams(ScrollMode aMode, ScrollOrigin aOrigin,
                         ScrollSnapTargetIds&& aSnapTargetIds)
       : ScrollOperationParams(aMode, aOrigin) {
     mTargetIds = std::move(aSnapTargetIds);
   }
   ScrollOperationParams(ScrollMode aMode, ScrollOrigin aOrigin,
                         ScrollSnapFlags aSnapFlags,
                         ScrollTriggeredByScript aTriggeredByScript)
       : ScrollOperationParams(aMode, aOrigin) {
     mSnapFlags = aSnapFlags;
     mTriggeredByScript = aTriggeredByScript;
   }

   ScrollMode mMode;
   ScrollOrigin mOrigin;
   ScrollSnapFlags mSnapFlags = ScrollSnapFlags::Disabled;
   ScrollTriggeredByScript mTriggeredByScript = ScrollTriggeredByScript::No;
   ScrollSnapTargetIds mTargetIds;

   bool IsInstant() const { return mMode == ScrollMode::Instant; }
   bool IsSmoothMsd() const { return mMode == ScrollMode::SmoothMsd; }
   bool IsSmooth() const { return mMode == ScrollMode::Smooth; }
   bool IsScrollSnapDisabled() const {
     return mSnapFlags == ScrollSnapFlags::Disabled;
   }
 };

 /**
  * @note This method might destroy the frame, pres shell and other objects.
  *
  * A caller can ask this ScrollToWithOrigin() function to perform snapping by
  * passing in aParams.mSnapFlags != ScrollSnapFlags::Disabled. Alternatively,
  * a caller may want to do its own snapping, in which case it should pass
  * ScrollSnapFlags::Disabled and populate aParams.mTargetIds based on the
  * result of the snapping.
  */
 void ScrollToWithOrigin(nsPoint aScrollPosition, const nsRect* aRange,
                         ScrollOperationParams&& aParams);

 void CompleteAsyncScroll(const nsPoint& aStartPosition, const nsRect& aRange,
                          UniquePtr<ScrollSnapTargetIds> aSnapTargetIds,
                          ScrollOrigin aOrigin = ScrollOrigin::NotSpecified);

 bool HasPerspective() const { return ChildrenHavePerspective(); }
 bool HasBgAttachmentLocal() const;
 StyleDirection GetScrolledFrameDir() const;
 static StyleDirection GetScrolledFrameDir(const nsIFrame*);

 // Ask APZ to smooth scroll to |aDestination|.
 // This method does not clamp the destination; callers should clamp it to
 // either the layout or the visual scroll range (APZ will happily smooth
 // scroll to either).
 void ApzSmoothScrollTo(const nsPoint& aDestination, ScrollMode, ScrollOrigin,
                        ScrollTriggeredByScript,
                        UniquePtr<ScrollSnapTargetIds> aSnapTargetIds,
                        ViewportType aViewportToScroll);

 // Check whether APZ can scroll in the provided directions, keeping in mind
 // that APZ currently cannot scroll along axes which are overflow:hidden.
 bool CanApzScrollInTheseDirections(layers::ScrollDirections aDirections);

 // Removes any RefreshDriver observers we might have registered.
 void RemoveObservers();

private:
 class AsyncScroll;
 class AsyncSmoothMSDScroll;
 class AutoMinimumScaleSizeChangeDetector;

 enum class AnonymousContentType {
   VerticalScrollbar,
   HorizontalScrollbar,
   Resizer,
 };
 EnumSet<AnonymousContentType> GetNeededAnonymousContent() const;
 EnumSet<AnonymousContentType> GetCurrentAnonymousContent() const;

 // If a child frame was added or removed on the scrollframe,
 // reload our child frame list.
 // We need this if a scrollbar frame is recreated.
 void ReloadChildFrames();

 // NOTE: Use GetScrollStyles() if you want `overflow` property info.
 nsIFrame* GetFrameForStyle() const;

 // Compute all scroll snap related information and store eash snap target
 // element in |mSnapTargets|.
 ScrollSnapInfo ComputeScrollSnapInfo();

 bool NeedsScrollSnap() const;

 // Returns the snapport size of this scroll container.
 // https://drafts.csswg.org/css-scroll-snap/#scroll-snapport
 nsSize GetSnapportSize() const;

 // Schedule the scroll-driven animations.
 void ScheduleScrollAnimations();
 void TryScheduleScrollAnimations() {
   if (!mMayScheduleScrollAnimations) {
     return;
   }
   ScheduleScrollAnimations();
   mMayScheduleScrollAnimations = false;
 }

 static void RemoveDisplayPortCallback(nsITimer* aTimer, void* aClosure);

 // owning references to the nsIAnonymousContentCreator-built content
 nsCOMPtr<Element> mHScrollbarContent;
 nsCOMPtr<Element> mVScrollbarContent;
 nsCOMPtr<Element> mScrollCornerContent;
 nsCOMPtr<Element> mResizerContent;

 class ScrollEvent;
 class ScrollEndEvent;
 class AsyncScrollPortEvent;
 class ScrolledAreaEvent;

 RefPtr<ScrollEvent> mScrollEvent;
 RefPtr<ScrollEndEvent> mScrollEndEvent;
 nsRevocableEventPtr<AsyncScrollPortEvent> mAsyncScrollPortEvent;
 nsRevocableEventPtr<ScrolledAreaEvent> mScrolledAreaEvent;
 nsScrollbarFrame* mHScrollbarBox;
 nsScrollbarFrame* mVScrollbarBox;
 nsIFrame* mScrolledFrame;
 nsIFrame* mScrollCornerBox;
 nsIFrame* mResizerBox;
 const nsIFrame* mReferenceFrameDuringPainting;
 RefPtr<AsyncScroll> mAsyncScroll;
 RefPtr<AsyncSmoothMSDScroll> mAsyncSmoothMSDScroll;
 RefPtr<layout::ScrollbarActivity> mScrollbarActivity;
 ScrollOrigin mLastScrollOrigin;
 Maybe<nsPoint> mApzSmoothScrollDestination;
 MainThreadScrollGeneration mScrollGeneration;
 APZScrollGeneration mScrollGenerationOnApz;

 nsTArray<ScrollPositionUpdate> mScrollUpdates;

 // The minimum-scale size, this is specific to mobile environments where the
 // initial-scale can be less than 1.0.
 // See
 // https://github.com/bokand/bokand.github.io/blob/master/web_viewports_explainer.md#minimum-scale
 // for details.
 nsSize mMinimumScaleSize;

 // Stores the ICB size for the root document if this frame is using the
 // minimum scale size for |mScrollPort|.
 nsSize mICBSize;

 // Where we're currently scrolling to, if we're scrolling asynchronously.
 // If we're not in the middle of an asynchronous scroll then this is
 // just the current scroll position. ScrollBy will choose its
 // destination based on this value.
 nsPoint mDestination;

 // A goal position to try to scroll to as content loads. As long as mLastPos
 // matches the current logical scroll position, we try to scroll to
 // mRestorePos after every reflow --- because after each time content is
 // loaded/added to the scrollable element, there will be a reflow.
 // Note that for frames where layout and visual viewport aren't one and the
 // same thing, this scroll position will be the logical scroll position of
 // the *visual* viewport, as its position will be more relevant to the user.
 nsPoint mRestorePos;
 // The last logical position we scrolled to while trying to restore
 // mRestorePos, or 0,0 when this is a new frame. Set to -1,-1 once we've
 // scrolled for any reason other than trying to restore mRestorePos.
 // Just as with mRestorePos, this position will be the logical position of
 // the *visual* viewport where available.
 nsPoint mLastPos;

 // The latest scroll position we've sent or received from APZ. This
 // represents the main thread's best knowledge of the APZ scroll position,
 // and is used to calculate relative scroll offset updates.
 nsPoint mApzScrollPos;

 nsExpirationState mActivityExpirationState;

 nsCOMPtr<nsITimer> mScrollActivityTimer;

 // The scroll position where we last updated frame visibility.
 nsPoint mLastUpdateFramesPos;
 nsRect mDisplayPortAtLastFrameUpdate;

 nsRect mPrevScrolledRect;

 layers::ScrollableLayerGuid::ViewID mScrollParentID;

 // Timer to remove the displayport some time after scrolling has stopped
 nsCOMPtr<nsITimer> mDisplayPortExpiryTimer;

 ScrollAnchorContainer mAnchor;

 // We keep holding a strong reference for each snap target element until the
 // next snapping happens so that it avoids using the same nsIContent* pointer
 // for newly created contents in this scroll container. Otherwise we will try
 // to match different nsIContent(s) generated at the same address during
 // re-snapping.
 SnapTargetSet mSnapTargets;

 // Representing there's an APZ animation is in progress and what caused the
 // animation. Note that this is only set when repainted via APZ, which means
 // that there may be a request for an APZ animation in flight for example,
 // while this is still `No`. In order to answer "is an APZ animation in the
 // process of starting or in progress" you need to check mScrollUpdates,
 // mApzAnimationRequested, and this type.
 APZScrollAnimationType mCurrentAPZScrollAnimationType;

 // The paint sequence number if the scroll frame is the first scrollable frame
 // encountered.
 Maybe<uint32_t> mIsFirstScrollableFrameSequenceNumber;

 // Representing whether the APZC corresponding to this frame is now in the
 // middle of handling a gesture (e.g. a pan gesture).
 InScrollingGesture mInScrollingGesture : 1;

 bool mAllowScrollOriginDowngrade : 1;
 bool mHadDisplayPortAtLastFrameUpdate : 1;

 // True if the most recent reflow of the scroll container frame has
 // the vertical scrollbar shown.
 bool mHasVerticalScrollbar : 1;
 // True if the most recent reflow of the scroll container frame has the
 // horizontal scrollbar shown.
 bool mHasHorizontalScrollbar : 1;

 // If mHas(Vertical|Horizontal)Scrollbar is true then
 // mOnlyNeed(V|H)ScrollbarToScrollVVInsideLV indicates if the only reason we
 // need that scrollbar is to scroll the visual viewport inside the layout
 // viewport. These scrollbars are special in that even if they are layout
 // scrollbars they do not take up any layout space.
 bool mOnlyNeedVScrollbarToScrollVVInsideLV : 1;
 bool mOnlyNeedHScrollbarToScrollVVInsideLV : 1;
 bool mFrameIsUpdatingScrollbar : 1;
 bool mDidHistoryRestore : 1;
 // Is this the scrollframe for the document's viewport?
 bool mIsRoot : 1;
 // If true, we skipped a scrollbar layout due to mSuppressScrollbarUpdate
 // being set at some point.  That means we should lay out scrollbars even if
 // it might not strictly be needed next time mSuppressScrollbarUpdate is
 // false.
 bool mSkippedScrollbarLayout : 1;

 bool mHadNonInitialReflow : 1;
 // Initially true; first call to ReflowFinished() sets it to false.
 bool mFirstReflow : 1;
 // State used only by PostScrollEvents so we know
 // which overflow states have changed.
 bool mHorizontalOverflow : 1;
 bool mVerticalOverflow : 1;
 bool mPostedReflowCallback : 1;
 bool mMayHaveDirtyFixedChildren : 1;
 // If true, need to actually update our scrollbar attributes in the
 // reflow callback.
 bool mUpdateScrollbarAttributes : 1;
 // If true, we should be prepared to scroll using this scrollframe
 // by placing descendant content into its own layer(s)
 bool mHasBeenScrolledRecently : 1;

 // If true, the scroll frame should always be active because we always build
 // a scrollable layer. Used for asynchronous scrolling.
 bool mWillBuildScrollableLayer : 1;

 // If true, the scroll frame is an ancestor of other "active" scrolling
 // frames, where "active" means has a non-minimal display port if
 // ShouldActivateAllScrollFrames is true, or has a display port if
 // ShouldActivateAllScrollFrames is false. And this means that we shouldn't
 // expire the display port (if ShouldActivateAllScrollFrames is true then
 // expiring a display port means making it minimal, otherwise it means
 // removing the display port). If those descendant scrollframes have their
 // display ports removed or made minimal, then we expire our display port.
 bool mIsParentToActiveScrollFrames : 1;

 // True if this frame has been scrolled at least once
 bool mHasBeenScrolled : 1;

 // True if the events synthesized by OSX to produce momentum scrolling should
 // be ignored.  Reset when the next real, non-synthesized scroll event occurs.
 bool mIgnoreMomentumScroll : 1;

 // True if the APZ is in the process of async-transforming this scrollframe,
 // (as best as we can tell on the main thread, anyway).
 bool mTransformingByAPZ : 1;

 // True if APZ can scroll this frame asynchronously (i.e. it has an APZC
 // set up for this frame and it's not a scrollinfo layer).
 bool mScrollableByAPZ : 1;

 // True if the APZ is allowed to zoom this scrollframe.
 bool mZoomableByAPZ : 1;

 // True if the scroll frame contains out-of-flow content and is inside
 // a CSS filter.
 bool mHasOutOfFlowContentInsideFilter : 1;

 // True if we don't want the scrollbar to repaint itself right now.
 bool mSuppressScrollbarRepaints : 1;

 // True if we are using the minimum scale size instead of ICB for scroll port.
 bool mIsUsingMinimumScaleSize : 1;

 // True if the minimum scale size has been changed since the last reflow.
 bool mMinimumScaleSizeChanged : 1;

 // True if we're processing an scroll event.
 bool mProcessingScrollEvent : 1;

 // This is true from the time a scroll animation is requested of APZ to the
 // time that APZ responds with an up-to-date repaint request. More precisely,
 // this is flipped to true if a repaint request is dispatched to APZ where
 // the most recent scroll request is a smooth scroll, and it is cleared when
 // mApzAnimationInProgress is updated.
 bool mApzAnimationRequested : 1;

 // Similar to above mApzAnimationRequested but the request came from script,
 // e.g., scrollBy().
 bool mApzAnimationTriggeredByScriptRequested : 1;

 // Whether we need to reclamp the visual viewport offset in ReflowFinished.
 bool mReclampVVOffsetInReflowFinished : 1;

 // Whether we need to schedule the scroll-driven animations.
 bool mMayScheduleScrollAnimations : 1;

#ifdef MOZ_WIDGET_ANDROID
 // True if this scrollable frame was vertically overflowed on the last reflow.
 bool mHasVerticalOverflowForDynamicToolbar : 1;
#endif

 layout::ScrollVelocityQueue mVelocityQueue;

 // NOTE: On mobile this value might be factoring into overflow:hidden region
 // in the case of the top level document.
 nsRect mScrollPort;
 UniquePtr<ScrollSnapTargetIds> mLastSnapTargetIds;
 // Lazily created on demand, see StickyScrollContainer::GetOrCreateForFrame.
 UniquePtr<StickyScrollContainer> mStickyContainer;
};

}  // namespace mozilla

#endif /* mozilla_ScrollContainerFrame_h_ */