1 files changed, 130 insertions, 0 deletions
diff --git a/layout/generic/ScrollPositionUpdate.h b/layout/generic/ScrollPositionUpdate.h
new file mode 100644
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+++ b/layout/generic/ScrollPositionUpdate.h
@@ -0,0 +1,130 @@
+/* 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(
+      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_