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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/. */
+
+/*
+ * interface that provides scroll APIs implemented by scrollable frames
+ */
+
+#ifndef nsIScrollFrame_h___
+#define nsIScrollFrame_h___
+
+#include "nsCoord.h"
+#include "mozilla/dom/WindowBinding.h" // for mozilla::dom::ScrollBehavior
+#include "mozilla/Maybe.h"
+#include "mozilla/ScrollOrigin.h"
+#include "mozilla/ScrollPositionUpdate.h"
+#include "mozilla/ScrollStyles.h"
+#include "mozilla/ScrollTypes.h"
+#include "mozilla/gfx/Point.h"
+#include "nsIScrollbarMediator.h"
+#include "Units.h"
+#include "FrameMetrics.h"
+
+class gfxContext;
+class nsIScrollPositionListener;
+class nsIFrame;
+class nsPresContext;
+class nsIContent;
+
+namespace mozilla {
+class DisplayItemClip;
+class nsDisplayListBuilder;
+enum class StyleScrollSnapAlignKeyword : uint8_t;
+
+namespace layers {
+struct ScrollMetadata;
+class Layer;
+class WebRenderLayerManager;
+} // namespace layers
+namespace layout {
+class ScrollAnchorContainer;
+} // namespace layout
+} // namespace mozilla
+
+/**
+ * Interface for frames that are scrollable. This interface exposes
+ * APIs for examining scroll state, observing changes to scroll state,
+ * and triggering scrolling.
+ */
+class nsIScrollableFrame : public nsIScrollbarMediator {
+ public:
+ using CSSIntPoint = mozilla::CSSIntPoint;
+ using ScrollSnapInfo = mozilla::layers::ScrollSnapInfo;
+ using ScrollAnchorContainer = mozilla::layout::ScrollAnchorContainer;
+ using ScrollMode = mozilla::ScrollMode;
+ using ScrollOrigin = mozilla::ScrollOrigin;
+ using PhysicalScrollSnapAlign =
+ std::pair<mozilla::StyleScrollSnapAlignKeyword,
+ mozilla::StyleScrollSnapAlignKeyword>;
+
+ NS_DECL_QUERYFRAME_TARGET(nsIScrollableFrame)
+
+ /**
+ * Get the frame for the content that we are scrolling within
+ * this scrollable frame.
+ */
+ virtual nsIFrame* GetScrolledFrame() const = 0;
+
+ /**
+ * 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.
+ */
+ virtual mozilla::ScrollStyles GetScrollStyles() const = 0;
+
+ /**
+ * Returns whether this scroll frame is for a text control element with no
+ * scrollbars (for <input>, basically).
+ */
+ virtual bool IsForTextControlWithNoScrollbars() const = 0;
+
+ /**
+ * Returns whether we already have anonymous content nodes for all our needed
+ * scrollbar parts (or a superset thereof).
+ */
+ virtual bool HasAllNeededScrollbars() const = 0;
+
+ /**
+ * Get the overscroll-behavior styles.
+ */
+ virtual mozilla::layers::OverscrollBehaviorInfo GetOverscrollBehaviorInfo()
+ const = 0;
+
+ /**
+ * 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.
+ */
+ virtual mozilla::layers::ScrollDirections GetScrollbarVisibility() const = 0;
+ /**
+ * Returns the directions in which scrolling is allowed (if the scroll range
+ * is at least one device pixel in that direction).
+ */
+ mozilla::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.)
+ */
+ virtual mozilla::layers::ScrollDirections
+ GetAvailableScrollingDirectionsForUserInputEvents() const = 0;
+ /**
+ * 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 };
+ virtual nsMargin GetActualScrollbarSizes(
+ ScrollbarSizesOptions aOptions = ScrollbarSizesOptions::NONE) const = 0;
+ /**
+ * 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.
+ */
+ virtual nsMargin GetDesiredScrollbarSizes() const = 0;
+ /**
+ * Return the width for non-disappearing scrollbars.
+ */
+ static nscoord GetNondisappearingScrollbarWidth(nsPresContext*,
+ mozilla::WritingMode);
+ /**
+ * 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.
+ */
+ virtual nsSize GetLayoutSize() const = 0;
+ /**
+ * 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 (although nsXULScrollFrame currently does).
+ *
+ * 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
+ * nsHTMLScrollFrames with LTR directionality and for all
+ * nsXULScrollFrames, and allows scrolling down and to the left for
+ * nsHTMLScrollFrames with RTL directionality.
+ */
+ virtual nsRect GetScrolledRect() const = 0;
+ /**
+ * 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.
+ */
+ virtual nsRect GetScrollPortRect() const = 0;
+ /**
+ * 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.
+ */
+ virtual nsPoint GetScrollPosition() const = 0;
+ /**
+ * As GetScrollPosition(), but uses the top-right as origin for RTL frames.
+ */
+ virtual nsPoint GetLogicalScrollPosition() const = 0;
+
+ /**
+ * 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.
+ */
+ virtual nsRect GetScrollRange() const = 0;
+ /**
+ * Get the size of the view port to use when clamping the scroll
+ * position.
+ */
+ virtual nsSize GetVisualViewportSize() const = 0;
+ /**
+ * 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().
+ */
+ virtual nsPoint GetVisualViewportOffset() const = 0;
+ /**
+ * 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.
+ */
+ virtual bool SetVisualViewportOffset(const nsPoint& aOffset,
+ bool aRepaint) = 0;
+ /**
+ * Get the area that must contain the visual viewport offset.
+ */
+ virtual nsRect GetVisualScrollRange() const = 0;
+ /**
+ * Like GetVisualScrollRange but also takes into account overflow: hidden.
+ */
+ virtual nsRect GetScrollRangeForUserInputEvents() const = 0;
+ /**
+ * Return how much we would try to scroll by in each direction if
+ * asked to scroll by one "line" vertically and horizontally.
+ */
+ virtual nsSize GetLineScrollAmount() const = 0;
+ /**
+ * Return how much we would try to scroll by in each direction if
+ * asked to scroll by one "page" vertically and horizontally.
+ */
+ virtual nsSize GetPageScrollAmount() const = 0;
+
+ /**
+ * Return scroll-padding value of this frame.
+ */
+ virtual nsMargin GetScrollPadding() const = 0;
+ /**
+ * 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.
+ * 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.
+ */
+ virtual void ScrollTo(
+ nsPoint aScrollPosition, ScrollMode aMode, const nsRect* aRange = nullptr,
+ mozilla::ScrollSnapFlags aSnapFlags = mozilla::ScrollSnapFlags::Disabled,
+ mozilla::ScrollTriggeredByScript aTriggeredByScript =
+ mozilla::ScrollTriggeredByScript::No) = 0;
+ /**
+ * @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, GetScrollPositionCSSPixels (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; GetScrollPositionCSSPixels will be
+ * exactly aScrollPosition at the end of the scroll animation unless the
+ * SMOOTH_MSD animation is interrupted.
+ */
+ virtual void ScrollToCSSPixels(const CSSIntPoint& aScrollPosition,
+ ScrollMode aMode = ScrollMode::Instant) = 0;
+ /**
+ * @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 GetScrollPositionCSSPixels 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).
+ */
+ virtual void ScrollToCSSPixelsForApz(
+ const mozilla::CSSPoint& aScrollPosition,
+ mozilla::ScrollSnapTargetIds&& aLastSnapTargetIds) = 0;
+
+ /**
+ * Returns the scroll position in integer CSS pixels, rounded to the nearest
+ * pixel.
+ */
+ virtual CSSIntPoint GetScrollPositionCSSPixels() = 0;
+ /**
+ * @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.
+ */
+ virtual void ScrollBy(nsIntPoint aDelta, mozilla::ScrollUnit aUnit,
+ ScrollMode aMode, nsIntPoint* aOverflow = nullptr,
+ ScrollOrigin aOrigin = ScrollOrigin::NotSpecified,
+ ScrollMomentum aMomentum = NOT_MOMENTUM,
+ mozilla::ScrollSnapFlags aSnapFlags =
+ mozilla::ScrollSnapFlags::Disabled) = 0;
+
+ virtual void ScrollByCSSPixels(const CSSIntPoint& aDelta,
+ ScrollMode aMode = ScrollMode::Instant) = 0;
+
+ /**
+ * 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.
+ */
+ virtual void ScrollSnap() = 0;
+
+ /**
+ * @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.
+ */
+ virtual void ScrollToRestoredPosition() = 0;
+
+ /**
+ * Add a scroll position listener. This listener must be removed
+ * before it is destroyed.
+ */
+ virtual void AddScrollPositionListener(
+ nsIScrollPositionListener* aListener) = 0;
+ /**
+ * Remove a scroll position listener.
+ */
+ virtual void RemoveScrollPositionListener(
+ nsIScrollPositionListener* aListener) = 0;
+
+ /**
+ * Internal method used by scrollbars to notify their scrolling
+ * container of changes.
+ */
+ virtual void CurPosAttributeChanged(nsIContent* aChild) = 0;
+
+ /**
+ * Allows the docshell to request that the scroll frame post an event
+ * after being restored from history.
+ */
+ NS_IMETHOD PostScrolledAreaEventForCurrentArea() = 0;
+
+ /**
+ * 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.
+ */
+ virtual bool IsScrollingActive() const = 0;
+
+ /**
+ * Returns true if this scroll frame might be scrolled
+ * asynchronously by the compositor.
+ */
+ virtual bool IsMaybeAsynchronouslyScrolled() const = 0;
+
+ /**
+ * Was the current presentation state for this frame restored from history?
+ */
+ virtual bool DidHistoryRestore() const = 0;
+ /**
+ * Clear the flag so that DidHistoryRestore() returns false until the next
+ * RestoreState call.
+ * @see nsIStatefulFrame::RestoreState
+ */
+ virtual void ClearDidHistoryRestore() = 0;
+ /**
+ * 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.
+ */
+ virtual void MarkEverScrolled() = 0;
+ /**
+ * Determine if the passed in rect is nearly visible according to the frame
+ * visibility heuristics for how close it is to the visible scrollport.
+ */
+ virtual bool IsRectNearlyVisible(const nsRect& aRect) const = 0;
+ /**
+ * Expand the given rect taking into account which directions we can scroll
+ * and how far we want to expand for frame visibility purposes.
+ */
+ virtual nsRect ExpandRectToNearlyVisible(const nsRect& aRect) const = 0;
+ /**
+ * 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.
+ */
+ virtual ScrollOrigin LastScrollOrigin() const = 0;
+
+ /**
+ * 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
+ };
+ virtual mozilla::EnumSet<AnimationState> ScrollAnimationState() const = 0;
+
+ /**
+ * Returns the current generation counter for the scrollframe. This counter
+ * increments every time the scroll position is set.
+ */
+ virtual mozilla::MainThreadScrollGeneration CurrentScrollGeneration()
+ const = 0;
+ /**
+ * The APZ scroll generation associated with the last APZ scroll offset for
+ * which we processed a repaint request.
+ */
+ virtual mozilla::APZScrollGeneration ScrollGenerationOnApz() const = 0;
+ /**
+ * LastScrollDestination returns the destination of the most recently
+ * requested smooth scroll animation.
+ */
+ virtual nsPoint LastScrollDestination() = 0;
+ /**
+ * Returns the list of scroll position updates since the last call to
+ * NotifyApzTransaction().
+ */
+ virtual nsTArray<mozilla::ScrollPositionUpdate> GetScrollUpdates() const = 0;
+ /**
+ * Returns true if the scroll frame has any scroll position updates since
+ * the last call to NotifyApzTransaction().
+ */
+ virtual bool HasScrollUpdates() const = 0;
+
+ enum class InScrollingGesture : bool { No, Yes };
+ /**
+ * 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.
+ */
+ virtual void ResetScrollInfoIfNeeded(
+ const mozilla::MainThreadScrollGeneration& aGeneration,
+ const mozilla::APZScrollGeneration& aGenerationOnApz,
+ mozilla::APZScrollAnimationType aAPZScrollAnimationType,
+ InScrollingGesture aInScrollingGesture) = 0;
+ /**
+ * Determine whether it is desirable to be able to asynchronously scroll this
+ * scroll frame.
+ */
+ virtual bool WantAsyncScroll() const = 0;
+ /**
+ * Returns the ScrollMetadata contributed by this frame, if there is one.
+ */
+ virtual mozilla::Maybe<mozilla::layers::ScrollMetadata> ComputeScrollMetadata(
+ mozilla::layers::WebRenderLayerManager* aLayerManager,
+ const nsIFrame* aItemFrame,
+ const nsPoint& aOffsetToReferenceFrame) const = 0;
+
+ /**
+ * Mark the scrollbar frames for reflow.
+ */
+ virtual void MarkScrollbarsDirtyForReflow() const = 0;
+
+ /**
+ * Invalidate the scrollbar after the marks have been changed.
+ */
+ virtual void InvalidateScrollbars() const = 0;
+
+ virtual void UpdateScrollbarPosition() = 0;
+
+ virtual void SetTransformingByAPZ(bool aTransforming) = 0;
+ virtual bool IsTransformingByAPZ() const = 0;
+
+ /**
+ * 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.
+ */
+ virtual void SetScrollableByAPZ(bool aScrollable) = 0;
+
+ /**
+ * Notify this scroll frame that it can be zoomed by APZ.
+ */
+ virtual void SetZoomableByAPZ(bool aZoomable) = 0;
+
+ /**
+ * 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.
+ */
+ virtual void SetHasOutOfFlowContentInsideFilter() = 0;
+
+ /**
+ * 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.
+ */
+ virtual bool DecideScrollableLayer(mozilla::nsDisplayListBuilder* aBuilder,
+ nsRect* aVisibleRect, nsRect* aDirtyRect,
+ bool aSetBase) = 0;
+
+ /**
+ * 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.
+ *
+ */
+ virtual void NotifyApzTransaction() = 0;
+
+ /**
+ * 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)
+ */
+ virtual void NotifyApproximateFrameVisibilityUpdate(
+ bool aIgnoreDisplayPort) = 0;
+
+ /**
+ * 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.
+ */
+ virtual bool GetDisplayPortAtLastApproximateFrameVisibilityUpdate(
+ nsRect* aDisplayPort) = 0;
+
+ /**
+ * 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.
+ */
+ virtual void TriggerDisplayPortExpiration() = 0;
+
+ /**
+ * Returns information required to determine where to snap to after a scroll.
+ */
+ virtual ScrollSnapInfo GetScrollSnapInfo() = 0;
+
+ virtual void TryResnap() = 0;
+ /**
+ * Post a pending re-snap request if the given |aFrame| is one of the snap
+ * points on the last scroll operation.
+ */
+ virtual void PostPendingResnapIfNeeded(const nsIFrame* aFrame) = 0;
+ virtual void PostPendingResnap() = 0;
+
+ /**
+ * 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`.
+ */
+ virtual PhysicalScrollSnapAlign GetScrollSnapAlignFor(
+ const nsIFrame* aFrame) const = 0;
+
+ /**
+ * 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.
+ */
+ virtual bool DragScroll(mozilla::WidgetEvent* aEvent) = 0;
+
+ virtual void AsyncScrollbarDragInitiated(
+ uint64_t aDragBlockId, mozilla::layers::ScrollDirection aDirection) = 0;
+ virtual void AsyncScrollbarDragRejected() = 0;
+
+ /**
+ * 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.
+ */
+ virtual bool IsRootScrollFrameOfDocument() const = 0;
+
+ /**
+ * Returns the paint sequence number if this scroll frame was the first
+ * scrollable frame for the paint.
+ */
+ virtual mozilla::Maybe<uint32_t> IsFirstScrollableFrameSequenceNumber()
+ const = 0;
+
+ /**
+ * Set the paint sequence number for the paint in which this was the first
+ * scrollable frame that was encountered.
+ */
+ virtual void SetIsFirstScrollableFrameSequenceNumber(
+ mozilla::Maybe<uint32_t> aValue) = 0;
+
+ /**
+ * Returns the scroll anchor associated with this scrollable frame. This is
+ * never null.
+ */
+ virtual const ScrollAnchorContainer* Anchor() const = 0;
+ virtual ScrollAnchorContainer* Anchor() = 0;
+
+ virtual bool SmoothScrollVisual(
+ const nsPoint& aVisualViewportOffset,
+ mozilla::layers::FrameMetrics::ScrollOffsetUpdateType aUpdateType) = 0;
+
+ /**
+ * Returns true if this scroll frame should perform smooth scroll with the
+ * given |aBehavior|.
+ */
+ virtual bool IsSmoothScroll(mozilla::dom::ScrollBehavior aBehavior =
+ mozilla::dom::ScrollBehavior::Auto) const = 0;
+};
+
+#endif