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_
46