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diff --git a/gfx/layers/AnimationHelper.h b/gfx/layers/AnimationHelper.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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_layers_AnimationHelper_h
+#define mozilla_layers_AnimationHelper_h
+
+#include "mozilla/dom/Nullable.h"
+#include "mozilla/layers/AnimationStorageData.h"
+#include "mozilla/layers/LayersMessages.h"     // for TransformData, etc
+#include "mozilla/webrender/WebRenderTypes.h"  // for RenderRoot
+#include "mozilla/TimeStamp.h"                 // for TimeStamp
+#include "mozilla/TimingParams.h"
+#include "mozilla/Types.h"  // for SideBits
+#include "X11UndefineNone.h"
+#include <unordered_map>
+
+namespace mozilla::layers {
+class Animation;
+class APZSampler;
+class CompositorAnimationStorage;
+struct AnimatedValue;
+
+typedef nsTArray<layers::Animation> AnimationArray;
+
+/**
+ * This utility class allows reusing code between the webrender and
+ * non-webrender compositor-side implementations. It provides
+ * utility functions for sampling animations at particular timestamps.
+ */
+class AnimationHelper {
+ public:
+  struct SampleResult {
+    enum class Type : uint8_t { None, Skipped, Sampled };
+    enum class Reason : uint8_t { None, ScrollToDelayPhase };
+    Type mType = Type::None;
+    Reason mReason = Reason::None;
+
+    SampleResult() = default;
+    SampleResult(Type aType, Reason aReason) : mType(aType), mReason(aReason) {}
+
+    static SampleResult Skipped() { return {Type::Skipped, Reason::None}; }
+    static SampleResult Sampled() { return {Type::Sampled, Reason::None}; }
+
+    bool IsNone() { return mType == Type::None; }
+    bool IsSkipped() { return mType == Type::Skipped; }
+    bool IsSampled() { return mType == Type::Sampled; }
+  };
+
+  /**
+   * Sample animations based on a given time stamp for a element(layer) with
+   * its animation data.
+   * Generally |aPreviousFrameTime| is used for the sampling if it's
+   * supplied to make the animation more in sync with other animations on the
+   * main-thread.  But in the case where the animation just started at the time
+   * when the animation was sent to the compositor, |aCurrentFrameTime| is used
+   * for sampling instead to avoid flicker.
+   *
+   * Returns SampleResult::None if none of the animations are producing a result
+   * (e.g. they are in the delay phase with no backwards fill),
+   * SampleResult::Skipped if the animation output did not change since the last
+   * call of this function,
+   * SampleResult::Sampled if the animation output was updated.
+   *
+   * The only exception is the scroll-driven animation. When the user move the
+   * scrollbar to make the animations go from active phase to delay phase, this
+   * returns SampleResult::None but sets its |mReason| to
+   * Reason::ScrollToDelayPhase. The caller can check this flag so we can store
+   * the base style into the hash table to make sure we have the correct
+   * rendering result. The base style stays in the hash table until we sync with
+   * main thread.
+   *
+   * Using the same example from ExtractAnimations (below):
+   *
+   * Input |aPropertyAnimationGroups| (ignoring the base animation style):
+   *
+   * [
+   *   Group A: [ { rotate, Animation A }, { rotate, Animation B } ],
+   *   Group B: [ { scale, Animation B } ],
+   *   Group C: [ { transform, Animation A }, { transform, Animation B } ],
+   * ]
+   *
+   * For each property group, this function interpolates each animation in turn,
+   * using the result of interpolating one animation as input for the next such
+   * that it reduces each property group to a single output value:
+   *
+   * [
+   *   { rotate, StyleAnimationValue },
+   *   { scale, StyleAnimationValue },
+   *   { transform, StyleAnimationValue },
+   * ]
+   *
+   * For transform animations, the caller (SampleAnimations) will combine the
+   * result of the various transform properties into a final matrix.
+   */
+  static SampleResult SampleAnimationForEachNode(
+      const APZSampler* aAPZSampler, const LayersId& aLayersId,
+      const MutexAutoLock& aProofOfMapLock, TimeStamp aPreviousFrameTime,
+      TimeStamp aCurrentFrameTime, const AnimatedValue* aPreviousValue,
+      nsTArray<PropertyAnimationGroup>& aPropertyAnimationGroups,
+      nsTArray<RefPtr<StyleAnimationValue>>& aAnimationValues);
+
+  /**
+   * Extract organized animation data by property into an array of
+   * PropertyAnimationGroup objects.
+   *
+   * For example, suppose we have the following animations:
+   *
+   *   Animation A: [ transform, rotate ]
+   *   Animation B: [ rotate, scale ]
+   *   Animation C: [ transform ]
+   *   Animation D: [ opacity ]
+   *
+   * When we go to send transform-like properties to the compositor, we
+   * sort them as follows:
+   *
+   *   [
+   *     { rotate: Animation A (rotate segments only) },
+   *     { rotate: Animation B ( " " ) },
+   *     { scale: Animation B (scale segments only) },
+   *     { transform: Animation A (transform segments only) },
+   *     { transform: Animation C ( " " ) },
+   *   ]
+   *
+   * In this function, we group these animations together by property producing
+   * output such as the following:
+   *
+   *   [
+   *     [ { rotate, Animation A }, { rotate, Animation B } ],
+   *     [ { scale, Animation B } ],
+   *     [ { transform, Animation A }, { transform, Animation B } ],
+   *   ]
+   *
+   * In the process of grouping these animations, we also convert their values
+   * from the rather compact representation we use for transferring across the
+   * IPC boundary into something we can readily use for sampling.
+   *
+   * Note: the animation groups:
+   * 1. transform-like properties: transfrom, translate, rotate, scale,
+   *                               offset-*.
+   * 2. opacity property: opacity.
+   * 3. background color property: background-color.
+   */
+  static AnimationStorageData ExtractAnimations(
+      const LayersId& aLayersId, const AnimationArray& aAnimations);
+
+  /**
+   * Get a unique id to represent the compositor animation between child
+   * and parent side. This id will be used as a key to store animation
+   * data in the CompositorAnimationStorage per compositor.
+   * Each layer on the content side calls this when it gets new animation
+   * data.
+   */
+  static uint64_t GetNextCompositorAnimationsId();
+
+  /**
+   * Convert an array of animation values into a matrix given the corresponding
+   * transform parameters. |aValue| must be a transform-like value
+   * (e.g. transform, translate etc.).
+   */
+  static gfx::Matrix4x4 ServoAnimationValueToMatrix4x4(
+      const nsTArray<RefPtr<StyleAnimationValue>>& aValue,
+      const TransformData& aTransformData, gfx::Path* aCachedMotionPath);
+
+  /**
+   * Returns true if |aPrerenderedRect| transformed by |aTransform| were
+   * composited in |aClipRect| there appears area which wasn't pre-rendered
+   * on the main-thread. I.e. checkerboarding.
+   */
+  static bool ShouldBeJank(const LayoutDeviceRect& aPrerenderedRect,
+                           SideBits aOverflowedSides,
+                           const gfx::Matrix4x4& aTransform,
+                           const ParentLayerRect& aClipRect);
+};
+
+}  // namespace mozilla::layers
+
+#endif  // mozilla_layers_AnimationHelper_h