layout/generic/ScrollSnap.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_layout_ScrollSnap_h_
   8 #define mozilla_layout_ScrollSnap_h_
   9
  10 #include <memory>
  11 #include "mozilla/ScrollTypes.h"
  12 #include "mozilla/ScrollSnapTargetId.h"
  13 #include "mozilla/Maybe.h"
  14
  15 class nsIContent;
  16 class nsIFrame;
  17 struct nsPoint;
  18 struct nsRect;
  19 struct nsSize;
  20
  21 namespace mozilla {
  22
  23 struct ScrollSnapInfo;
  24
  25 struct ScrollSnapUtils {
  26   /**
  27    * GetSnapPointForDestination determines which point to snap to after
  28    * scrolling. |aStartPos| gives the position before scrolling and
  29    * |aDestination| gives the position after scrolling, with no snapping.
  30    * Behaviour is dependent on the value of |aUnit|.
  31    * |aSnapInfo| and |aScrollRange| are characteristics of the scroll frame for
  32    * which snapping is being performed.
  33    * If a suitable snap point could be found, it is returned. Otherwise, an
  34    * empty Maybe is returned.
  35    * IMPORTANT NOTE: This function is designed to be called both on and off
  36    *                 the main thread. If modifying its implementation, be sure
  37    *                 not to touch main-thread-only data structures without
  38    *                 appropriate locking.
  39    */
  40   static Maybe<SnapDestination> GetSnapPointForDestination(
  41       const ScrollSnapInfo& aSnapInfo, ScrollUnit aUnit,
  42       ScrollSnapFlags aSnapFlags, const nsRect& aScrollRange,
  43       const nsPoint& aStartPos, const nsPoint& aDestination);
  44
  45   /**
  46    * Similar to above GetSnapPointForDestination but for re-snapping.
  47    *
  48    * |aCurrentPosition| are the snap point(s) last time when we scrolled.
  49    * |aLastSnapTargetIds| are the snap point(s) last time when we scrolled if
  50    * exists.
  51    * |aFocusedContent| is the focused content in the document if exists.
  52    * Other parameters are same as GetSnapPointForDestination.
  53    */
  54
  55   static mozilla::Maybe<SnapDestination> GetSnapPointForResnap(
  56       const ScrollSnapInfo& aSnapInfo, const nsRect& aScrollRange,
  57       const nsPoint& aCurrentPosition,
  58       const UniquePtr<ScrollSnapTargetIds>& aLastSnapTargetIds,
  59       const nsIContent* aFocusedContent);
  60
  61   static ScrollSnapTargetId GetTargetIdFor(const nsIFrame* aFrame);
  62
  63   // Post a pending re-snap request if the given |aFrame| is one of the snap
  64   // points on the last scroll operation.
  65   static void PostPendingResnapIfNeededFor(nsIFrame* aFrame);
  66
  67   // Similar to above PostPendingResnapIfNeededFor but post a pending re-snap
  68   // request even if the given |aFrame| is not one of the last snap point.
  69   // This is basically used for cases there was no valid snap point on the last
  70   // scroll operation but the given |aFrame| might be a valid snap point now,
  71   // e.g changing the scroll-snap-align property from `none` to something.
  72   static void PostPendingResnapFor(nsIFrame* aFrame);
  73
  74   // Returns true if the writing-mode of the snap target element needs to be
  75   // respected to resolve scroll-snap-align property.
  76   // Note that usually the scroll container's writing-mode is used for resolving
  77   // the property but there's a special case defined in the CSS scroll snap
  78   // spec.
  79   static bool NeedsToRespectTargetWritingMode(const nsSize& aSnapAreaSize,
  80                                               const nsSize& aSnapportSize);
  81
  82   // Returns the scroll snap area for the snap target frame |aFrame| inside the
  83   // nearest scroll container |aScrolledFrame| and its scrolled rect
  84   // |aScrolledRect|.
  85   static nsRect GetSnapAreaFor(const nsIFrame* aFrame,
  86                                const nsIFrame* aScrolledFrame,
  87                                const nsRect& aScrolledRect);
  88 };
  89
  90 }  // namespace mozilla
  91
  92 #endif  // mozilla_layout_ScrollSnap_h_