ScrollPositionUpdate.h

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/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_ScrollPositionUpdate_h_

#define mozilla_ScrollPositionUpdate_h_

#include <cstdint>

#include <iosfwd>

#include "nsPoint.h"

#include "mozilla/ScrollGeneration.h"

#include "mozilla/ScrollOrigin.h"

#include "mozilla/ScrollSnapTargetId.h"

#include "mozilla/ScrollTypes.h"

#include "Units.h"

namespace IPC {

template <typename T>

struct ParamTraits;

}  // namespace IPC

namespace mozilla {

enum class ScrollUpdateType {

  // A scroll update to a specific destination, regardless of the current

  // scroll position.

  Absolute,

  // A scroll update by a specific amount, based off a given starting scroll

  // position. XXX Fold this into PureRelative, it should be relatively

  // straightforward after bug 1655733.

  Relative,

  // A scroll update by a specific amount, where only the delta is provided.

  // The delta should be applied to whatever the current scroll position is

  // on the receiver side.

  PureRelative,

};

enum class ScrollTriggeredByScript : bool { No, Yes };

/**

 * This class represents an update to the scroll position that is initiated by

 * something on the main thread. A list of these classes is accumulated by

 * scrollframes on the main thread, and the list is sent over as part of a

 * paint transaction to the compositor. The compositor can then iterate through

 * the scroll updates and apply/merge them with scrolling that has already

 * occurred independently on the compositor side.

*/

class ScrollPositionUpdate {

  friend struct IPC::ParamTraits<mozilla::ScrollPositionUpdate>;

 public:

  // Constructor for IPC use only.

  explicit ScrollPositionUpdate();

  // Create a ScrollPositionUpdate for a newly created (or reconstructed)

  // scrollframe.

  static ScrollPositionUpdate NewScrollframe(nsPoint aInitialPosition);

  // Create a ScrollPositionUpdate for a new absolute/instant scroll, to

  // the given destination.

  static ScrollPositionUpdate NewScroll(ScrollOrigin aOrigin,

                                        nsPoint aDestination);

  // Create a ScrollPositionUpdate for a new relative/instant scroll, with

  // the given source/destination.

  static ScrollPositionUpdate NewRelativeScroll(nsPoint aSource,

                                                nsPoint aDestination);

  // Create a ScrollPositionUpdate for a new absolute/smooth scroll, which

  // animates smoothly to the given destination from whatever the current

  // scroll position is in the receiver.

  // If the smooth operation involves snapping to |aDestination|,

  // |aSnapTargetIds| has snap-target-ids for snapping. Once after this smooth

  // scroll finished on the target APZC, the ids will be reported back to the

  // main-thread as the last snap target ids which will be used for re-snapping

  // to the same snapped element(s).

  static ScrollPositionUpdate NewSmoothScroll(

      ScrollMode aMode, ScrollOrigin aOrigin, nsPoint aDestination,

      ScrollTriggeredByScript aTriggeredByScript,

      UniquePtr<ScrollSnapTargetIds> aSnapTargetIds);

  // Create a ScrollPositionUpdate for a new pure-relative scroll. The

  // aMode parameter controls whether or not this is a smooth animation or

  // instantaneous scroll.

  static ScrollPositionUpdate NewPureRelativeScroll(ScrollOrigin aOrigin,

                                                    ScrollMode aMode,

                                                    const nsPoint& aDelta);

  bool operator==(const ScrollPositionUpdate& aOther) const;

  MainThreadScrollGeneration GetGeneration() const;

  ScrollUpdateType GetType() const;

  ScrollMode GetMode() const;

  ScrollOrigin GetOrigin() const;

  // GetDestination is only valid for Absolute and Relative types; it asserts

  // otherwise.

  CSSPoint GetDestination() const;

  // GetSource is only valid for the Relative type; it asserts otherwise.

  CSSPoint GetSource() const;

  // GetDelta is only valid for the PureRelative type; it asserts otherwise.

  CSSPoint GetDelta() const;

  ScrollTriggeredByScript GetScrollTriggeredByScript() const {

    return mTriggeredByScript;

  bool WasTriggeredByScript() const {

    return mTriggeredByScript == ScrollTriggeredByScript::Yes;

  const ScrollSnapTargetIds& GetSnapTargetIds() const { return mSnapTargetIds; }

  friend std::ostream& operator<<(std::ostream& aStream,

                                  const ScrollPositionUpdate& aUpdate);

 private:

  MainThreadScrollGeneration mScrollGeneration;

  // Refer to the ScrollUpdateType documentation for what the types mean.

  // All fields are populated for all types, except as noted below.

  ScrollUpdateType mType;

  ScrollMode mScrollMode;

  ScrollOrigin mScrollOrigin;

  // mDestination is not populated when mType == PureRelative.

  CSSPoint mDestination;

  // mSource is not populated when mType == Absolute || mType == PureRelative.

  CSSPoint mSource;

  // mDelta is not populated when mType == Absolute || mType == Relative.

  CSSPoint mDelta;

  ScrollTriggeredByScript mTriggeredByScript;

  ScrollSnapTargetIds mSnapTargetIds;

};

}  // namespace mozilla

#endif  // mozilla_ScrollPositionUpdate_h_