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 };
  38
  39 enum class ScrollTriggeredByScript : bool { No, Yes };
  40
  41 /**
  42  * This class represents an update to the scroll position that is initiated by
  43  * something on the main thread. A list of these classes is accumulated by
  44  * scrollframes on the main thread, and the list is sent over as part of a
  45  * paint transaction to the compositor. The compositor can then iterate through
  46  * the scroll updates and apply/merge them with scrolling that has already
  47  * occurred independently on the compositor side.
  48  */
  49 class ScrollPositionUpdate {
  50   friend struct IPC::ParamTraits<mozilla::ScrollPositionUpdate>;
  51
  52  public:
  53   // Constructor for IPC use only.
  54   explicit ScrollPositionUpdate();
  55
  56   // Create a ScrollPositionUpdate for a newly created (or reconstructed)
  57   // scrollframe.
  58   static ScrollPositionUpdate NewScrollframe(nsPoint aInitialPosition);
  59   // Create a ScrollPositionUpdate for a new absolute/instant scroll, to
  60   // the given destination.
  61   static ScrollPositionUpdate NewScroll(ScrollOrigin aOrigin,
  62                                         nsPoint aDestination);
  63   // Create a ScrollPositionUpdate for a new relative/instant scroll, with
  64   // the given source/destination.
  65   static ScrollPositionUpdate NewRelativeScroll(nsPoint aSource,
  66                                                 nsPoint aDestination);
  67   // Create a ScrollPositionUpdate for a new absolute/smooth scroll, which
  68   // animates smoothly to the given destination from whatever the current
  69   // scroll position is in the receiver.
  70   // If the smooth operation involves snapping to |aDestination|,
  71   // |aSnapTargetIds| has snap-target-ids for snapping. Once after this smooth
  72   // scroll finished on the target APZC, the ids will be reported back to the
  73   // main-thread as the last snap target ids which will be used for re-snapping
  74   // to the same snapped element(s).
  75   static ScrollPositionUpdate NewSmoothScroll(
  76       ScrollMode aMode, ScrollOrigin aOrigin, nsPoint aDestination,
  77       ScrollTriggeredByScript aTriggeredByScript,
  78       UniquePtr<ScrollSnapTargetIds> aSnapTargetIds);
  79   // Create a ScrollPositionUpdate for a new pure-relative scroll. The
  80   // aMode parameter controls whether or not this is a smooth animation or
  81   // instantaneous scroll.
  82   static ScrollPositionUpdate NewPureRelativeScroll(ScrollOrigin aOrigin,
  83                                                     ScrollMode aMode,
  84                                                     const nsPoint& aDelta);
  85
  86   bool operator==(const ScrollPositionUpdate& aOther) const;
  87
  88   MainThreadScrollGeneration GetGeneration() const;
  89   ScrollUpdateType GetType() const;
  90   ScrollMode GetMode() const;
  91   ScrollOrigin GetOrigin() const;
  92   // GetDestination is only valid for Absolute and Relative types; it asserts
  93   // otherwise.
  94   CSSPoint GetDestination() const;
  95   // GetSource is only valid for the Relative type; it asserts otherwise.
  96   CSSPoint GetSource() const;
  97   // GetDelta is only valid for the PureRelative type; it asserts otherwise.
  98   CSSPoint GetDelta() const;
  99
 100   ScrollTriggeredByScript GetScrollTriggeredByScript() const {
 101     return mTriggeredByScript;
 102   }
 103   bool WasTriggeredByScript() const {
 104     return mTriggeredByScript == ScrollTriggeredByScript::Yes;
 105   }
 106   const ScrollSnapTargetIds& GetSnapTargetIds() const { return mSnapTargetIds; }
 107
 108   friend std::ostream& operator<<(std::ostream& aStream,
 109                                   const ScrollPositionUpdate& aUpdate);
 110
 111  private:
 112   MainThreadScrollGeneration mScrollGeneration;
 113   // Refer to the ScrollUpdateType documentation for what the types mean.
 114   // All fields are populated for all types, except as noted below.
 115   ScrollUpdateType mType;
 116   ScrollMode mScrollMode;
 117   ScrollOrigin mScrollOrigin;
 118   // mDestination is not populated when mType == PureRelative.
 119   CSSPoint mDestination;
 120   // mSource is not populated when mType == Absolute || mType == PureRelative.
 121   CSSPoint mSource;
 122   // mDelta is not populated when mType == Absolute || mType == Relative.
 123   CSSPoint mDelta;
 124   ScrollTriggeredByScript mTriggeredByScript;
 125   ScrollSnapTargetIds mSnapTargetIds;
 126 };
 127
 128 }  // namespace mozilla
 129
 130 #endif  // mozilla_ScrollPositionUpdate_h_