ScrollSnap.h - mozsearch

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_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 {

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<SnapDestination> GetSnapPointForDestination(

      const 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<SnapDestination> GetSnapPointForResnap(

      const 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_