layout/base/RelativeTo.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_RelativeTo_h
   8 #define mozilla_RelativeTo_h
   9
  10 #include <ostream>
  11
  12 class nsIFrame;
  13
  14 namespace mozilla {
  15
  16 // A flag that can be used to annotate a frame to distinguish coordinates
  17 // relative to the viewport frame as being in layout or visual coordinates.
  18 enum class ViewportType { Layout, Visual };
  19
  20 // A struct that combines a frame with a ViewportType annotation. The
  21 // combination completely describes what a set of coordinates is "relative to".
  22 // Notes on expected usage:
  23 //  - The boundary between visual and layout coordinates is approximately
  24 //    at the root content document (RCD)'s ViewportFrame, which we'll
  25 //    call "RCD-VF".
  26 //  - Coordinates relative to the RCD-VF's descendants (other than the
  27 //    RCD's viewport scrollbar frames) should be in layout coordinates.
  28 //  - Coordinates relative to the RCD-VF's ancestors should be in visual
  29 //    coordinates (note that in an e10s setup, the RCD-VF doesn't
  30 //    typically have in-process ancestors).
  31 //  - Coordinates relative to the RCD-VF itself can be in either layout
  32 //    or visual coordinates.
  33 struct RelativeTo {
  34   const nsIFrame* mFrame = nullptr;
  35   // Choose ViewportType::Layout as the default as this is what the vast
  36   // majority of layout code deals with.
  37   ViewportType mViewportType = ViewportType::Layout;
  38   bool operator==(const RelativeTo& aOther) const {
  39     return mFrame == aOther.mFrame && mViewportType == aOther.mViewportType;
  40   }
  41   friend std::ostream& operator<<(std::ostream& aOs, const RelativeTo& aR) {
  42     return aOs << "{" << aR.mFrame << ", "
  43                << (aR.mViewportType == ViewportType::Visual ? "visual"
  44                                                             : "layout")
  45                << "}";
  46   }
  47 };
  48
  49 }  // namespace mozilla
  50
  51 #endif  // mozilla_RelativeTo_h