layout/generic/ScrollPositionUpdate.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_ScrollPositionUpdate_h_
   6 #define mozilla_ScrollPositionUpdate_h_
   7
   8 #include <cstdint>
   9 #include <iosfwd>
  10
  11 #include "nsPoint.h"
  12 #include "mozilla/ScrollGeneration.h"
  13 #include "mozilla/ScrollOrigin.h"
  14 #include "mozilla/ScrollSnapTargetId.h"
  15 #include "mozilla/ScrollTypes.h"
  16 #include "Units.h"
  17
  18 namespace IPC {
  19 template <typename T>
  20 struct ParamTraits;
  21 }  // namespace IPC
  22
  23 namespace mozilla {
  24
  25 enum class ScrollUpdateType {
  26   // A scroll update to a specific destination, regardless of the current
  27   // scroll position.
  28   Absolute,
  29   // A scroll update by a specific amount, based off a given starting scroll
  30   // position. XXX Fold this into PureRelative, it should be relatively
  31   // straightforward after bug 1655733.
  32   Relative,
  33   // A scroll update by a specific amount, where only the delta is provided.
  34   // The delta should be applied to whatever the current scroll position is
  35   // on the receiver side.
  36   PureRelative,
  37   // Similar to |Absolute|, but even if there's an active async scroll animation
  38   // the position update will NOT cancel the async scroll animation.
  39   MergeableAbsolute,
  40 };
  41
  42 enum class ScrollTriggeredByScript : bool { No, Yes };
  43
  44 /**
  45  * This class represents an update to the scroll position that is initiated by
  46  * something on the main thread. A list of these classes is accumulated by
  47  * scrollframes on the main thread, and the list is sent over as part of a
  48  * paint transaction to the compositor. The compositor can then iterate through
  49  * the scroll updates and apply/merge them with scrolling that has already
  50  * occurred independently on the compositor side.
  51  */
  52 class ScrollPositionUpdate {
  53   friend struct IPC::ParamTraits<mozilla::ScrollPositionUpdate>;
  54
  55  public:
  56   // Constructor for IPC use only.
  57   explicit ScrollPositionUpdate();
  58
  59   // Create a ScrollPositionUpdate for a newly created (or reconstructed)
  60   // scrollframe.
  61   static ScrollPositionUpdate NewScrollframe(nsPoint aInitialPosition);
  62   // Create a ScrollPositionUpdate for a new absolute/instant scroll, to
  63   // the given destination.
  64   static ScrollPositionUpdate NewScroll(ScrollOrigin aOrigin,
  65                                         nsPoint aDestination);
  66   // Create a ScrollPositionUpdate for a new relative/instant scroll, with
  67   // the given source/destination.
  68   static ScrollPositionUpdate NewRelativeScroll(nsPoint aSource,
  69                                                 nsPoint aDestination);
  70   // Create a ScrollPositionUpdate for a new absolute/smooth scroll, which
  71   // animates smoothly to the given destination from whatever the current
  72   // scroll position is in the receiver.
  73   // If the smooth operation involves snapping to |aDestination|,
  74   // |aSnapTargetIds| has snap-target-ids for snapping. Once after this smooth
  75   // scroll finished on the target APZC, the ids will be reported back to the
  76   // main-thread as the last snap target ids which will be used for re-snapping
  77   // to the same snapped element(s).
  78   static ScrollPositionUpdate NewSmoothScroll(
  79       ScrollMode aMode, ScrollOrigin aOrigin, nsPoint aDestination,
  80       ScrollTriggeredByScript aTriggeredByScript,
  81       UniquePtr<ScrollSnapTargetIds> aSnapTargetIds);
  82   // Create a ScrollPositionUpdate for a new pure-relative scroll. The
  83   // aMode parameter controls whether or not this is a smooth animation or
  84   // instantaneous scroll.
  85   static ScrollPositionUpdate NewPureRelativeScroll(ScrollOrigin aOrigin,
  86                                                     ScrollMode aMode,
  87                                                     const nsPoint& aDelta);
  88
  89   static ScrollPositionUpdate NewMergeableScroll(ScrollOrigin aOrigin,
  90                                                  nsPoint aDestination);
  91
  92   bool operator==(const ScrollPositionUpdate& aOther) const;
  93
  94   MainThreadScrollGeneration GetGeneration() const;
  95   ScrollUpdateType GetType() const;
  96   ScrollMode GetMode() const;
  97   ScrollOrigin GetOrigin() const;
  98   // GetDestination is only valid for Absolute and Relative types; it asserts
  99   // otherwise.
 100   CSSPoint GetDestination() const;
 101   // GetSource is only valid for the Relative type; it asserts otherwise.
 102   CSSPoint GetSource() const;
 103   // GetDelta is only valid for the PureRelative type; it asserts otherwise.
 104   CSSPoint GetDelta() const;
 105
 106   ScrollTriggeredByScript GetScrollTriggeredByScript() const {
 107     return mTriggeredByScript;
 108   }
 109   bool WasTriggeredByScript() const {
 110     return mTriggeredByScript == ScrollTriggeredByScript::Yes;
 111   }
 112   const ScrollSnapTargetIds& GetSnapTargetIds() const { return mSnapTargetIds; }
 113
 114   friend std::ostream& operator<<(std::ostream& aStream,
 115                                   const ScrollPositionUpdate& aUpdate);
 116
 117  private:
 118   MainThreadScrollGeneration mScrollGeneration;
 119   // Refer to the ScrollUpdateType documentation for what the types mean.
 120   // All fields are populated for all types, except as noted below.
 121   ScrollUpdateType mType;
 122   ScrollMode mScrollMode;
 123   ScrollOrigin mScrollOrigin;
 124   // mDestination is not populated when mType == PureRelative.
 125   CSSPoint mDestination;
 126   // mSource is not populated when mType == Absolute || mType == PureRelative.
 127   CSSPoint mSource;
 128   // mDelta is not populated when mType == Absolute || mType == Relative.
 129   CSSPoint mDelta;
 130   ScrollTriggeredByScript mTriggeredByScript;
 131   ScrollSnapTargetIds mSnapTargetIds;
 132 };
 133
 134 }  // namespace mozilla
 135
 136 #endif  // mozilla_ScrollPositionUpdate_h_