layout/generic/Visibility.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 /**
   8  * Declares visibility-related types. @Visibility is an enumeration of the
   9  * possible visibility states of a frame. @OnNonvisible is an enumeration that
  10  * allows callers to request a specific action when a frame transitions from
  11  * visible to nonvisible.
  12  */
  13
  14 #ifndef mozilla_layout_generic_Visibility_h
  15 #define mozilla_layout_generic_Visibility_h
  16
  17 namespace mozilla {
  18
  19 // Visibility states for frames.
  20 enum class Visibility : uint8_t {
  21   // Indicates that we're not tracking visibility for this frame.
  22   Untracked,
  23
  24   // Indicates that the frame is probably nonvisible. Visible frames *may* be
  25   // ApproximatelyNonVisible because approximate visibility is not updated
  26   // synchronously. Some truly nonvisible frames may be marked
  27   // ApproximatelyVisible instead if our heuristics lead us to think they may
  28   // be visible soon.
  29   ApproximatelyNonVisible,
  30
  31   // Indicates that the frame is either visible now or is likely to be visible
  32   // soon according to our heuristics. As with ApproximatelyNonVisible , it's
  33   // important to note that approximately visibility is not updated
  34   // synchronously, so this information may be out of date.
  35   ApproximatelyVisible,
  36 };
  37
  38 // Requested actions when frames transition to the nonvisible state.
  39 enum class OnNonvisible : uint8_t {
  40   DiscardImages  // Discard images associated with the frame.
  41 };
  42
  43 }  // namespace mozilla
  44
  45 #endif  // mozilla_layout_generic_Visibility_h