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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 */
#ifndef mozilla_layout_ScrollSnap_h_
#define mozilla_layout_ScrollSnap_h_
#include <memory>
#include "mozilla/ScrollTypes.h"
#include "mozilla/ScrollSnapTargetId.h"
#include "mozilla/Maybe.h"
class nsIContent;
class nsIFrame;
struct nsPoint;
struct nsRect;
struct nsSize;
namespace mozilla {
namespace layers {
struct ScrollSnapInfo;
struct ScrollSnapUtils {
* 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|.
* |aSnapInfo| and |aScrollRange| are characteristics of the scroll frame for
* which snapping is being performed.
* If a suitable snap point could be found, it is returned. Otherwise, an
* empty Maybe is returned.
* IMPORTANT NOTE: This function is designed to be called both on and off
* the main thread. If modifying its implementation, be sure
* not to touch main-thread-only data structures without
* appropriate locking.
static Maybe<SnapTarget> GetSnapPointForDestination(
const layers::ScrollSnapInfo& aSnapInfo, ScrollUnit aUnit,
ScrollSnapFlags aSnapFlags, const nsRect& aScrollRange,
const nsPoint& aStartPos, const nsPoint& aDestination);
* Similar to above GetSnapPointForDestination but for re-snapping.
* |aCurrentPosition| are the snap point(s) last time when we scrolled.
* |aLastSnapTargetIds| are the snap point(s) last time when we scrolled if
* exists.
* |aFocusedContent| is the focused content in the document if exists.
* Other parameters are same as GetSnapPointForDestination.
static mozilla::Maybe<mozilla::SnapTarget> GetSnapPointForResnap(
const layers::ScrollSnapInfo& aSnapInfo, const nsRect& aScrollRange,
const nsPoint& aCurrentPosition,
const UniquePtr<ScrollSnapTargetIds>& aLastSnapTargetIds,
const nsIContent* aFocusedContent);
static ScrollSnapTargetId GetTargetIdFor(const nsIFrame* aFrame);
// Post a pending re-snap request if the given |aFrame| is one of the snap
// points on the last scroll operation.
static void PostPendingResnapIfNeededFor(nsIFrame* aFrame);
// Similar to above PostPendingResnapIfNeededFor but post a pending re-snap
// request even if the given |aFrame| is not one of the last snap point.
// This is basically used for cases there was no valid snap point on the last
// scroll operation but the given |aFrame| might be a valid snap point now,
// e.g changing the scroll-snap-align property from `none` to something.
static void PostPendingResnapFor(nsIFrame* aFrame);
// Returns true if the writing-mode of the snap target element needs to be
// respected to resolve scroll-snap-align property.
// Note that usually the scroll container's writing-mode is used for resolving
// the property but there's a special case defined in the CSS scroll snap
// spec.
static bool NeedsToRespectTargetWritingMode(const nsSize& aSnapAreaSize,
const nsSize& aSnapportSize);
// Returns the scroll snap area for the snap target frame |aFrame| inside the
// nearest scroll container |aScrolledFrame| and its scrolled rect
// |aScrolledRect|.
static nsRect GetSnapAreaFor(const nsIFrame* aFrame,
const nsIFrame* aScrolledFrame,
const nsRect& aScrolledRect);
} // namespace mozilla
#endif // mozilla_layout_ScrollSnap_h_