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6fb1b72c6e
If we always align the new scroll position with the previous scroll position, we can accumulate error and gradually drift out of alignment with the layer pixels until we exceed the tolerance and are forced to rerender everything.
215 lines
8.1 KiB
C++
215 lines
8.1 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* interface that provides scroll APIs implemented by scrollable frames
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*/
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#ifndef nsIScrollFrame_h___
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#define nsIScrollFrame_h___
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#include "nsISupports.h"
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#include "nsCoord.h"
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#include "nsPresContext.h"
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#define NS_DEFAULT_VERTICAL_SCROLL_DISTANCE 3
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class nsBoxLayoutState;
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class nsIScrollPositionListener;
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class nsIFrame;
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/**
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* Interface for frames that are scrollable. This interface exposes
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* APIs for examining scroll state, observing changes to scroll state,
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* and triggering scrolling.
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*/
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class nsIScrollableFrame : public nsQueryFrame {
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public:
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NS_DECL_QUERYFRAME_TARGET(nsIScrollableFrame)
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/**
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* Get the frame for the content that we are scrolling within
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* this scrollable frame.
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*/
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virtual nsIFrame* GetScrolledFrame() const = 0;
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typedef nsPresContext::ScrollbarStyles ScrollbarStyles;
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/**
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* Get the styles (NS_STYLE_OVERFLOW_SCROLL, NS_STYLE_OVERFLOW_HIDDEN,
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* or NS_STYLE_OVERFLOW_AUTO) governing the horizontal and vertical
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* scrollbars for this frame.
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*/
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virtual ScrollbarStyles GetScrollbarStyles() const = 0;
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enum { HORIZONTAL = 0x01, VERTICAL = 0x02 };
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/**
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* Return the scrollbars which are visible. It's OK to call this during reflow
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* of the scrolled contents, in which case it will reflect the current
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* assumptions about scrollbar visibility.
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*/
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virtual uint32_t GetScrollbarVisibility() const = 0;
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/**
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* Return the actual sizes of all possible scrollbars. Returns 0 for scrollbar
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* positions that don't have a scrollbar or where the scrollbar is not visible.
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* Do not call this while this frame's descendants are being reflowed, it won't be
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* accurate.
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*/
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virtual nsMargin GetActualScrollbarSizes() const = 0;
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/**
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* Return the sizes of all scrollbars assuming that any scrollbars that could
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* be visible due to overflowing content, are. This can be called during reflow
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* of the scrolled contents.
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*/
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virtual nsMargin GetDesiredScrollbarSizes(nsBoxLayoutState* aState) = 0;
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/**
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* Return the sizes of all scrollbars assuming that any scrollbars that could
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* be visible due to overflowing content, are. This can be called during reflow
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* of the scrolled contents.
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*/
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virtual nsMargin GetDesiredScrollbarSizes(nsPresContext* aPresContext,
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nsRenderingContext* aRC) = 0;
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/**
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* Get the area of the scrollport relative to the origin of this frame's
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* border-box.
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* This is the area of this frame minus border and scrollbars.
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*/
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virtual nsRect GetScrollPortRect() const = 0;
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/**
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* Get the offset of the scrollport origin relative to the scrolled
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* frame origin. Typically the position will be non-negative.
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* This will always be a multiple of device pixels.
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*/
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virtual nsPoint GetScrollPosition() const = 0;
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/**
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* Get the area that must contain the scroll position. Typically
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* (but not always, e.g. for RTL content) x and y will be 0, and
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* width or height will be nonzero if the content can be scrolled in
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* that direction. Since scroll positions must be a multiple of
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* device pixels, the range extrema will also be a multiple of
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* device pixels.
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*/
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virtual nsRect GetScrollRange() const = 0;
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/**
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* Get the size of the scroll port to use when clamping the scroll
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* position.
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*/
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virtual nsSize GetScrollPositionClampingScrollPortSize() const = 0;
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/**
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* Return how much we would try to scroll by in each direction if
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* asked to scroll by one "line" vertically and horizontally.
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*/
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virtual nsSize GetLineScrollAmount() const = 0;
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/**
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* Return how much we would try to scroll by in each direction if
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* asked to scroll by one "page" vertically and horizontally.
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*/
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virtual nsSize GetPageScrollAmount() const = 0;
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/**
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* When a scroll operation is requested, we ask for instant, smooth or normal
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* scrolling. SMOOTH will only be smooth if smooth scrolling is actually
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* enabled. INSTANT is always synchronous, NORMAL can be asynchronous.
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* If an INSTANT request happens while a smooth or async scroll is already in
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* progress, the async scroll is interrupted and we instantly scroll to the
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* destination.
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*/
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enum ScrollMode { INSTANT, SMOOTH, NORMAL };
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/**
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* Clamps aScrollPosition to GetScrollRange and sets the scroll position
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* to that value.
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* @param aRange If non-null, specifies area which contains aScrollPosition
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* and can be used for choosing a performance-optimized scroll position.
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* Any point within this area can be chosen.
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* The choosen point will be as close as possible to aScrollPosition.
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*/
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virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
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const nsRect* aRange = nullptr) = 0;
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/**
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* Scrolls to a particular position in integer CSS pixels.
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* Keeps the exact current horizontal or vertical position if the current
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* position, rounded to CSS pixels, matches aScrollPosition. If
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* aScrollPosition.x/y is different from the current CSS pixel position,
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* makes sure we only move in the direction given by the difference.
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* The scroll mode is INSTANT.
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*/
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virtual void ScrollToCSSPixels(nsIntPoint aScrollPosition) = 0;
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/**
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* Returns the scroll position in integer CSS pixels, rounded to the nearest
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* pixel.
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*/
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virtual nsIntPoint GetScrollPositionCSSPixels() = 0;
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/**
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* When scrolling by a relative amount, we can choose various units.
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*/
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enum ScrollUnit { DEVICE_PIXELS, LINES, PAGES, WHOLE };
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/**
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* Modifies the current scroll position by aDelta units given by aUnit,
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* clamping it to GetScrollRange. If WHOLE is specified as the unit,
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* content is scrolled all the way in the direction(s) given by aDelta.
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* @param aOverflow if non-null, returns the amount that scrolling
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* was clamped by in each direction (how far we moved the scroll position
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* to bring it back into the legal range). This is never negative. The
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* values are in device pixels.
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*/
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virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
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nsIntPoint* aOverflow = nullptr, nsIAtom *aOrigin = nullptr) = 0;
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/**
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* This tells the scroll frame to try scrolling to the scroll
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* position that was restored from the history. This must be called
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* at least once after state has been restored. It is called by the
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* scrolled frame itself during reflow, but sometimes state can be
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* restored after reflows are done...
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* XXX should we take an aMode parameter here? Currently it's instant.
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*/
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virtual void ScrollToRestoredPosition() = 0;
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/**
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* Add a scroll position listener. This listener must be removed
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* before it is destroyed.
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*/
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virtual void AddScrollPositionListener(nsIScrollPositionListener* aListener) = 0;
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/**
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* Remove a scroll position listener.
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*/
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virtual void RemoveScrollPositionListener(nsIScrollPositionListener* aListener) = 0;
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/**
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* Obtain the XUL box for the horizontal or vertical scrollbar, or null
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* if there is no such box. Avoid using this, but may be useful for
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* setting up a scrollbar mediator if you want to redirect scrollbar
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* input.
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*/
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virtual nsIFrame* GetScrollbarBox(bool aVertical) = 0;
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/**
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* Internal method used by scrollbars to notify their scrolling
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* container of changes.
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*/
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virtual void CurPosAttributeChanged(nsIContent* aChild) = 0;
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/**
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* Allows the docshell to request that the scroll frame post an event
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* after being restored from history.
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*/
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NS_IMETHOD PostScrolledAreaEventForCurrentArea() = 0;
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/**
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* Returns true if this scrollframe is being "actively scrolled".
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* This basically means that we should allocate resources in the
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* expectation that scrolling is going to happen.
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*/
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virtual bool IsScrollingActive() = 0;
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/**
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* Call this when the layer(s) induced by active scrolling are being
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* completely redrawn.
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*/
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virtual void ResetScrollPositionForLayerPixelAlignment() = 0;
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};
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#endif
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