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 "mozilla/ScrollTypes.h"
  11 #include "mozilla/Maybe.h"
  12
  13 struct nsPoint;
  14 struct nsRect;
  15
  16 namespace mozilla {
  17
  18 namespace layers {
  19 struct ScrollSnapInfo;
  20 }
  21
  22 struct ScrollSnapUtils {
  23   /**
  24    * GetSnapPointForDestination determines which point to snap to after
  25    * scrolling. |aStartPos| gives the position before scrolling and
  26    * |aDestination| gives the position after scrolling, with no snapping.
  27    * Behaviour is dependent on the value of |aUnit|.
  28    * |aSnapInfo| and |aScrollRange| are characteristics of the scroll frame for
  29    * which snapping is being performed.
  30    * If a suitable snap point could be found, it is returned. Otherwise, an
  31    * empty Maybe is returned.
  32    * IMPORTANT NOTE: This function is designed to be called both on and off
  33    *                 the main thread. If modifying its implementation, be sure
  34    *                 not to touch main-thread-only data structures without
  35    *                 appropriate locking.
  36    */
  37   static mozilla::Maybe<nsPoint> GetSnapPointForDestination(
  38       const layers::ScrollSnapInfo& aSnapInfo, ScrollUnit aUnit,
  39       const nsRect& aScrollRange, const nsPoint& aStartPos,
  40       const nsPoint& aDestination);
  41 };
  42
  43 }  // namespace mozilla
  44
  45 #endif  // mozilla_layout_ScrollSnap_h_