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diff --git a/gfx/layers/apz/src/APZUtils.h b/gfx/layers/apz/src/APZUtils.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_APZUtils_h
+#define mozilla_layers_APZUtils_h
+
+// This file is for APZ-related utilities that are used by code in gfx/layers
+// only. For APZ-related utilities used by the Rest of the World (widget/,
+// layout/, dom/, IPDL protocols, etc.), use APZPublicUtils.h.
+// Do not include this header from source files outside of gfx/layers.
+
+#include <stdint.h>  // for uint32_t
+#include <type_traits>
+#include "gfxTypes.h"
+#include "FrameMetrics.h"
+#include "LayersTypes.h"
+#include "UnitTransforms.h"
+#include "mozilla/gfx/CompositorHitTestInfo.h"
+#include "mozilla/gfx/Point.h"
+#include "mozilla/DefineEnum.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/FloatingPoint.h"
+
+namespace mozilla {
+
+namespace layers {
+
+enum CancelAnimationFlags : uint32_t {
+  Default = 0x0,             /* Cancel all animations */
+  ExcludeOverscroll = 0x1,   /* Don't clear overscroll */
+  ScrollSnap = 0x2,          /* Snap to snap points */
+  ExcludeWheel = 0x4,        /* Don't stop wheel smooth-scroll animations */
+  TriggeredExternally = 0x8, /* Cancellation was not triggered by APZ in
+                                response to an input event */
+};
+
+inline CancelAnimationFlags operator|(CancelAnimationFlags a,
+                                      CancelAnimationFlags b) {
+  return static_cast<CancelAnimationFlags>(static_cast<int>(a) |
+                                           static_cast<int>(b));
+}
+
+// clang-format off
+enum class ScrollSource {
+  // Touch-screen.
+  Touchscreen,
+
+  // Touchpad with gesture support.
+  Touchpad,
+
+  // Mouse wheel.
+  Wheel,
+
+  // Keyboard
+  Keyboard,
+};
+// clang-format on
+
+inline bool ScrollSourceRespectsDisregardedDirections(ScrollSource aSource) {
+  return aSource == ScrollSource::Wheel || aSource == ScrollSource::Touchpad;
+}
+
+inline bool ScrollSourceAllowsOverscroll(ScrollSource aSource) {
+  return aSource == ScrollSource::Touchpad ||
+         aSource == ScrollSource::Touchscreen;
+}
+
+// Epsilon to be used when comparing 'float' coordinate values
+// with FuzzyEqualsAdditive. The rationale is that 'float' has 7 decimal
+// digits of precision, and coordinate values should be no larger than in the
+// ten thousands. Note also that the smallest legitimate difference in page
+// coordinates is 1 app unit, which is 1/60 of a (CSS pixel), so this epsilon
+// isn't too large.
+const CSSCoord COORDINATE_EPSILON = 0.01f;
+
+inline bool IsZero(const CSSPoint& aPoint) {
+  return FuzzyEqualsAdditive(aPoint.x, CSSCoord(), COORDINATE_EPSILON) &&
+         FuzzyEqualsAdditive(aPoint.y, CSSCoord(), COORDINATE_EPSILON);
+}
+
+// Represents async transforms consisting of a scale and a translation.
+struct AsyncTransform {
+  explicit AsyncTransform(
+      LayerToParentLayerScale aScale = LayerToParentLayerScale(),
+      ParentLayerPoint aTranslation = ParentLayerPoint())
+      : mScale(aScale), mTranslation(aTranslation) {}
+
+  operator AsyncTransformComponentMatrix() const {
+    return AsyncTransformComponentMatrix::Scaling(mScale.scale, mScale.scale, 1)
+        .PostTranslate(mTranslation.x, mTranslation.y, 0);
+  }
+
+  bool operator==(const AsyncTransform& rhs) const {
+    return mTranslation == rhs.mTranslation && mScale == rhs.mScale;
+  }
+
+  bool operator!=(const AsyncTransform& rhs) const { return !(*this == rhs); }
+
+  LayerToParentLayerScale mScale;
+  ParentLayerPoint mTranslation;
+};
+
+// Deem an AsyncTransformComponentMatrix (obtained by multiplying together
+// one or more AsyncTransformComponentMatrix objects) as constituting a
+// complete async transform.
+inline AsyncTransformMatrix CompleteAsyncTransform(
+    const AsyncTransformComponentMatrix& aMatrix) {
+  return ViewAs<AsyncTransformMatrix>(
+      aMatrix, PixelCastJustification::MultipleAsyncTransforms);
+}
+
+struct TargetConfirmationFlags final {
+  explicit TargetConfirmationFlags(bool aTargetConfirmed)
+      : mTargetConfirmed(aTargetConfirmed),
+        mRequiresTargetConfirmation(false),
+        mHitScrollbar(false),
+        mHitScrollThumb(false),
+        mDispatchToContent(false) {}
+
+  explicit TargetConfirmationFlags(
+      const gfx::CompositorHitTestInfo& aHitTestInfo)
+      : mTargetConfirmed(
+            (aHitTestInfo != gfx::CompositorHitTestInvisibleToHit) &&
+            (aHitTestInfo & gfx::CompositorHitTestDispatchToContent).isEmpty()),
+        mRequiresTargetConfirmation(aHitTestInfo.contains(
+            gfx::CompositorHitTestFlags::eRequiresTargetConfirmation)),
+        mHitScrollbar(
+            aHitTestInfo.contains(gfx::CompositorHitTestFlags::eScrollbar)),
+        mHitScrollThumb(aHitTestInfo.contains(
+            gfx::CompositorHitTestFlags::eScrollbarThumb)),
+        mDispatchToContent(
+            !(aHitTestInfo & gfx::CompositorHitTestDispatchToContent)
+                 .isEmpty()) {}
+
+  bool mTargetConfirmed : 1;
+  bool mRequiresTargetConfirmation : 1;
+  bool mHitScrollbar : 1;
+  bool mHitScrollThumb : 1;
+  bool mDispatchToContent : 1;
+};
+
+enum class AsyncTransformComponent { eLayout, eVisual };
+
+using AsyncTransformComponents = EnumSet<AsyncTransformComponent>;
+
+constexpr AsyncTransformComponents LayoutAndVisual(
+    AsyncTransformComponent::eLayout, AsyncTransformComponent::eVisual);
+
+/**
+ * Allows consumers of async transforms to specify for what purpose they are
+ * using the async transform:
+ *
+ *   |eForEventHandling| is intended for event handling and other uses that
+ *                       need the most up-to-date transform, reflecting all
+ *                       events that have been processed so far, even if the
+ *                       transform is not yet reflected visually.
+ *   |eForCompositing| is intended for the transform that should be reflected
+ *                     visually.
+ *
+ * For example, if an APZC has metrics with the mForceDisableApz flag set,
+ * then the |eForCompositing| async transform will be empty, while the
+ * |eForEventHandling| async transform will reflect processed input events
+ * regardless of mForceDisableApz.
+ */
+enum class AsyncTransformConsumer {
+  eForEventHandling,
+  eForCompositing,
+};
+
+/**
+ * Metrics that GeckoView wants to know at every composite.
+ * These are the effective visual scroll offset and zoom level of
+ * the root content APZC at composition time.
+ */
+struct GeckoViewMetrics {
+  CSSPoint mVisualScrollOffset;
+  CSSToParentLayerScale mZoom;
+};
+
+namespace apz {
+
+/**
+ * Is aAngle within the given threshold of the horizontal axis?
+ * @param aAngle an angle in radians in the range [0, pi]
+ * @param aThreshold an angle in radians in the range [0, pi/2]
+ */
+bool IsCloseToHorizontal(float aAngle, float aThreshold);
+
+// As above, but for the vertical axis.
+bool IsCloseToVertical(float aAngle, float aThreshold);
+
+// Returns true if a sticky layer with async translation |aTranslation| is
+// stuck with a bottom margin. The inner/outer ranges are produced by the main
+// thread at the last paint, and so |aTranslation| only needs to be the
+// async translation from the last paint.
+bool IsStuckAtBottom(gfxFloat aTranslation,
+                     const LayerRectAbsolute& aInnerRange,
+                     const LayerRectAbsolute& aOuterRange);
+
+// Returns true if a sticky layer with async translation |aTranslation| is
+// stuck with a top margin.
+bool IsStuckAtTop(gfxFloat aTranslation, const LayerRectAbsolute& aInnerRange,
+                  const LayerRectAbsolute& aOuterRange);
+
+/**
+ * Compute the translation that should be applied to a layer that's fixed
+ * at |eFixedSides|, to respect the fixed layer margins |aFixedMargins|.
+ */
+ScreenPoint ComputeFixedMarginsOffset(
+    const ScreenMargin& aCompositorFixedLayerMargins, SideBits aFixedSides,
+    const ScreenMargin& aGeckoFixedLayerMargins);
+
+/**
+ * Takes the visible rect from the compositor metrics, adds a pref-based
+ * margin around it, and checks to see if it is contained inside the painted
+ * rect from the painted metrics. Returns true if it is contained, or false
+ * if not. Returning false means that a (relatively) small amount of async
+ * scrolling/zooming can result in the visible area going outside the painted
+ * area and resulting in visual checkerboarding.
+ * Note that this may return false positives for cases where the scrollframe
+ * in question is nested inside other scrollframes, as the composition bounds
+ * used to determine the visible rect may in fact be clipped by enclosing
+ * scrollframes, but that is not accounted for in this function.
+ */
+bool AboutToCheckerboard(const FrameMetrics& aPaintedMetrics,
+                         const FrameMetrics& aCompositorMetrics);
+
+/**
+ * Returns SideBits where the given |aOverscrollAmount| overscrolls.
+ */
+SideBits GetOverscrollSideBits(const ParentLayerPoint& aOverscrollAmount);
+
+}  // namespace apz
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_APZUtils_h