1 files changed, 733 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/Axis.cpp b/gfx/layers/apz/src/Axis.cpp
new file mode 100644
index 0000000000..ddc1e09691
--- /dev/null
+++ b/gfx/layers/apz/src/Axis.cpp
@@ -0,0 +1,733 @@
+/* -*- 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/. */
+
+#include "Axis.h"
+
+#include <math.h>     // for fabsf, pow, powf
+#include <algorithm>  // for max
+
+#include "APZCTreeManager.h"                // for APZCTreeManager
+#include "AsyncPanZoomController.h"         // for AsyncPanZoomController
+#include "FrameMetrics.h"                   // for FrameMetrics
+#include "SimpleVelocityTracker.h"          // for FrameMetrics
+#include "mozilla/Attributes.h"             // for final
+#include "mozilla/Preferences.h"            // for Preferences
+#include "mozilla/gfx/Rect.h"               // for RoundedIn
+#include "mozilla/layers/APZThreadUtils.h"  // for AssertOnControllerThread
+#include "mozilla/mozalloc.h"               // for operator new
+#include "nsMathUtils.h"                    // for NS_lround
+#include "nsPrintfCString.h"                // for nsPrintfCString
+#include "nsThreadUtils.h"                  // for NS_DispatchToMainThread, etc
+#include "nscore.h"                         // for NS_IMETHOD
+
+static mozilla::LazyLogModule sApzAxsLog("apz.axis");
+#define AXIS_LOG(...) MOZ_LOG(sApzAxsLog, LogLevel::Debug, (__VA_ARGS__))
+
+namespace mozilla {
+namespace layers {
+
+bool FuzzyEqualsCoordinate(CSSCoord aValue1, CSSCoord aValue2) {
+  return FuzzyEqualsAdditive(aValue1, aValue2, COORDINATE_EPSILON) ||
+         FuzzyEqualsMultiplicative(aValue1, aValue2);
+}
+
+Axis::Axis(AsyncPanZoomController* aAsyncPanZoomController)
+    : mPos(0),
+      mVelocity(0.0f, "Axis::mVelocity"),
+      mAxisLocked(false),
+      mAsyncPanZoomController(aAsyncPanZoomController),
+      mOverscroll(0),
+      mMSDModel(0.0, 0.0, 0.0, StaticPrefs::apz_overscroll_spring_stiffness(),
+                StaticPrefs::apz_overscroll_damping()),
+      mVelocityTracker(mAsyncPanZoomController->GetPlatformSpecificState()
+                           ->CreateVelocityTracker(this)) {}
+
+float Axis::ToLocalVelocity(float aVelocityInchesPerMs) const {
+  ScreenPoint velocity =
+      MakePoint(aVelocityInchesPerMs * mAsyncPanZoomController->GetDPI());
+  // Use ToScreenCoordinates() to convert a point rather than a vector by
+  // treating the point as a vector, and using (0, 0) as the anchor.
+  ScreenPoint panStart = mAsyncPanZoomController->ToScreenCoordinates(
+      mAsyncPanZoomController->PanStart(), ParentLayerPoint());
+  ParentLayerPoint localVelocity =
+      mAsyncPanZoomController->ToParentLayerCoordinates(velocity, panStart);
+  return localVelocity.Length();
+}
+
+void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos,
+                                        TimeStamp aTimestamp) {
+  // mVelocityTracker is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  mPos = aPos;
+
+  AXIS_LOG("%p|%s got position %f\n", mAsyncPanZoomController, Name(),
+           mPos.value);
+  if (Maybe<float> newVelocity =
+          mVelocityTracker->AddPosition(aPos, aTimestamp)) {
+    DoSetVelocity(mAxisLocked ? 0 : *newVelocity);
+    AXIS_LOG("%p|%s velocity from tracker is %f%s\n", mAsyncPanZoomController,
+             Name(), *newVelocity,
+             mAxisLocked ? ", but we are axis locked" : "");
+  }
+}
+
+void Axis::StartTouch(ParentLayerCoord aPos, TimeStamp aTimestamp) {
+  mStartPos = aPos;
+  mPos = aPos;
+  mVelocityTracker->StartTracking(aPos, aTimestamp);
+  mAxisLocked = false;
+}
+
+bool Axis::AdjustDisplacement(ParentLayerCoord aDisplacement,
+                              ParentLayerCoord& aDisplacementOut,
+                              ParentLayerCoord& aOverscrollAmountOut,
+                              bool aForceOverscroll /* = false */) {
+  if (mAxisLocked) {
+    aOverscrollAmountOut = 0;
+    aDisplacementOut = 0;
+    return false;
+  }
+  if (aForceOverscroll) {
+    aOverscrollAmountOut = aDisplacement;
+    aDisplacementOut = 0;
+    return false;
+  }
+
+  ParentLayerCoord displacement = aDisplacement;
+
+  // First consume any overscroll in the opposite direction along this axis.
+  ParentLayerCoord consumedOverscroll = 0;
+  if (mOverscroll > 0 && aDisplacement < 0) {
+    consumedOverscroll = std::min(mOverscroll, -aDisplacement);
+  } else if (mOverscroll < 0 && aDisplacement > 0) {
+    consumedOverscroll = 0.f - std::min(-mOverscroll, aDisplacement);
+  }
+  mOverscroll -= consumedOverscroll;
+  displacement += consumedOverscroll;
+
+  if (consumedOverscroll != 0.0f) {
+    AXIS_LOG("%p|%s changed overscroll amount to %f\n", mAsyncPanZoomController,
+             Name(), mOverscroll.value);
+  }
+
+  // Split the requested displacement into an allowed displacement that does
+  // not overscroll, and an overscroll amount.
+  aOverscrollAmountOut = DisplacementWillOverscrollAmount(displacement);
+  if (aOverscrollAmountOut != 0.0f) {
+    // No need to have a velocity along this axis anymore; it won't take us
+    // anywhere, so we're just spinning needlessly.
+    AXIS_LOG("%p|%s has overscrolled, clearing velocity\n",
+             mAsyncPanZoomController, Name());
+    DoSetVelocity(0.0f);
+    displacement -= aOverscrollAmountOut;
+  }
+  aDisplacementOut = displacement;
+  return fabsf(consumedOverscroll) > EPSILON;
+}
+
+ParentLayerCoord Axis::ApplyResistance(
+    ParentLayerCoord aRequestedOverscroll) const {
+  // 'resistanceFactor' is a value between 0 and 1/16, which:
+  //   - tends to 1/16 as the existing overscroll tends to 0
+  //   - tends to 0 as the existing overscroll tends to the composition length
+  // The actual overscroll is the requested overscroll multiplied by this
+  // factor.
+  float resistanceFactor =
+      (1 - fabsf(GetOverscroll()) / GetCompositionLength()) / 16;
+  float result = resistanceFactor < 0 ? ParentLayerCoord(0)
+                                      : aRequestedOverscroll * resistanceFactor;
+  result = clamped(result, -8.0f, 8.0f);
+  return result;
+}
+
+void Axis::OverscrollBy(ParentLayerCoord aOverscroll) {
+  MOZ_ASSERT(CanScroll());
+  // We can get some spurious calls to OverscrollBy() with near-zero values
+  // due to rounding error. Ignore those (they might trip the asserts below.)
+  if (mAsyncPanZoomController->IsZero(aOverscroll)) {
+    return;
+  }
+  EndOverscrollAnimation();
+  aOverscroll = ApplyResistance(aOverscroll);
+  if (aOverscroll > 0) {
+#ifdef DEBUG
+    if (!IsScrolledToEnd()) {
+      nsPrintfCString message(
+          "composition end (%f) is not equal (within error) to page end (%f)\n",
+          GetCompositionEnd().value, GetPageEnd().value);
+      NS_ASSERTION(false, message.get());
+      MOZ_CRASH("GFX: Overscroll issue > 0");
+    }
+#endif
+    MOZ_ASSERT(mOverscroll >= 0);
+  } else if (aOverscroll < 0) {
+#ifdef DEBUG
+    if (!IsScrolledToStart()) {
+      nsPrintfCString message(
+          "composition origin (%f) is not equal (within error) to page origin "
+          "(%f)\n",
+          GetOrigin().value, GetPageStart().value);
+      NS_ASSERTION(false, message.get());
+      MOZ_CRASH("GFX: Overscroll issue < 0");
+    }
+#endif
+    MOZ_ASSERT(mOverscroll <= 0);
+  }
+  mOverscroll += aOverscroll;
+
+  AXIS_LOG("%p|%s changed overscroll amount to %f\n", mAsyncPanZoomController,
+           Name(), mOverscroll.value);
+}
+
+ParentLayerCoord Axis::GetOverscroll() const { return mOverscroll; }
+
+void Axis::RestoreOverscroll(ParentLayerCoord aOverscroll) {
+  mOverscroll = aOverscroll;
+}
+
+void Axis::StartOverscrollAnimation(float aVelocity) {
+  const float maxVelocity = StaticPrefs::apz_overscroll_max_velocity();
+  aVelocity = clamped(aVelocity / 2.0f, -maxVelocity, maxVelocity);
+  SetVelocity(aVelocity);
+  mMSDModel.SetPosition(mOverscroll);
+  // Convert velocity from ParentLayerCoords/millisecond to
+  // ParentLayerCoords/second.
+  mMSDModel.SetVelocity(DoGetVelocity() * 1000.0);
+
+  AXIS_LOG(
+      "%p|%s beginning overscroll animation with amount %f and velocity %f\n",
+      mAsyncPanZoomController, Name(), mOverscroll.value, DoGetVelocity());
+}
+
+void Axis::EndOverscrollAnimation() {
+  mMSDModel.SetPosition(0.0);
+  mMSDModel.SetVelocity(0.0);
+}
+
+bool Axis::SampleOverscrollAnimation(const TimeDuration& aDelta,
+                                     SideBits aOverscrollSideBits) {
+  mMSDModel.Simulate(aDelta);
+  mOverscroll = mMSDModel.GetPosition();
+
+  if (((aOverscrollSideBits & (SideBits::eTop | SideBits::eLeft)) &&
+       mOverscroll > 0) ||
+      ((aOverscrollSideBits & (SideBits::eBottom | SideBits::eRight)) &&
+       mOverscroll < 0)) {
+    // Stop the overscroll model immediately if it's going to get across the
+    // boundary.
+    mMSDModel.SetPosition(0.0);
+    mMSDModel.SetVelocity(0.0);
+  }
+
+  AXIS_LOG("%p|%s changed overscroll amount to %f\n", mAsyncPanZoomController,
+           Name(), mOverscroll.value);
+
+  if (mMSDModel.IsFinished(1.0)) {
+    // "Jump" to the at-rest state. The jump shouldn't be noticeable as the
+    // velocity and overscroll are already low.
+    AXIS_LOG("%p|%s oscillation dropped below threshold, going to rest\n",
+             mAsyncPanZoomController, Name());
+    ClearOverscroll();
+    DoSetVelocity(0);
+    return false;
+  }
+
+  // Otherwise, continue the animation.
+  return true;
+}
+
+bool Axis::IsOverscrollAnimationRunning() const {
+  return !mMSDModel.IsFinished(1.0);
+}
+
+bool Axis::IsOverscrollAnimationAlive() const {
+  // Unlike IsOverscrollAnimationRunning, check the position and the velocity to
+  // be sure that the animation has started but hasn't yet finished.
+  return mMSDModel.GetPosition() != 0.0 || mMSDModel.GetVelocity() != 0.0;
+}
+
+bool Axis::IsOverscrolled() const { return mOverscroll != 0.f; }
+
+bool Axis::IsScrolledToStart() const {
+  const auto zoom = GetFrameMetrics().GetZoom();
+
+  if (zoom == CSSToParentLayerScale(0)) {
+    return true;
+  }
+
+  return FuzzyEqualsCoordinate(GetOrigin() / zoom, GetPageStart() / zoom);
+}
+
+bool Axis::IsScrolledToEnd() const {
+  const auto zoom = GetFrameMetrics().GetZoom();
+
+  if (zoom == CSSToParentLayerScale(0)) {
+    return true;
+  }
+
+  return FuzzyEqualsCoordinate(GetCompositionEnd() / zoom, GetPageEnd() / zoom);
+}
+
+bool Axis::IsInInvalidOverscroll() const {
+  if (mOverscroll > 0) {
+    return !IsScrolledToEnd();
+  } else if (mOverscroll < 0) {
+    return !IsScrolledToStart();
+  }
+  return false;
+}
+
+void Axis::ClearOverscroll() {
+  EndOverscrollAnimation();
+  mOverscroll = 0;
+}
+
+ParentLayerCoord Axis::PanStart() const { return mStartPos; }
+
+ParentLayerCoord Axis::PanDistance() const { return fabs(mPos - mStartPos); }
+
+ParentLayerCoord Axis::PanDistance(ParentLayerCoord aPos) const {
+  return fabs(aPos - mStartPos);
+}
+
+void Axis::EndTouch(TimeStamp aTimestamp, ClearAxisLock aClearAxisLock) {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  // If the velocity tracker wasn't able to compute a velocity, zero out
+  // the velocity to make sure we don't get a fling based on some old and
+  // no-longer-relevant value of mVelocity. Also if the axis is locked then
+  // just reset the velocity to 0 since we don't need any velocity to carry
+  // into the fling.
+  if (mAxisLocked) {
+    DoSetVelocity(0);
+  } else if (Maybe<float> velocity =
+                 mVelocityTracker->ComputeVelocity(aTimestamp)) {
+    DoSetVelocity(*velocity);
+  } else {
+    DoSetVelocity(0);
+  }
+  if (aClearAxisLock == ClearAxisLock::Yes) {
+    mAxisLocked = false;
+  }
+  AXIS_LOG("%p|%s ending touch, computed velocity %f\n",
+           mAsyncPanZoomController, Name(), DoGetVelocity());
+}
+
+void Axis::CancelGesture() {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  AXIS_LOG("%p|%s cancelling touch, clearing velocity queue\n",
+           mAsyncPanZoomController, Name());
+  DoSetVelocity(0.0f);
+  mVelocityTracker->Clear();
+  SetAxisLocked(false);
+}
+
+bool Axis::CanScroll() const {
+  return mAsyncPanZoomController->FuzzyGreater(GetPageLength(),
+                                               GetCompositionLength());
+}
+
+bool Axis::CanScroll(CSSCoord aDelta) const {
+  return CanScroll(aDelta * GetFrameMetrics().GetZoom());
+}
+
+bool Axis::CanScroll(ParentLayerCoord aDelta) const {
+  if (!CanScroll()) {
+    return false;
+  }
+
+  const auto zoom = GetFrameMetrics().GetZoom();
+  CSSCoord availableToScroll = 0;
+
+  if (zoom != CSSToParentLayerScale(0)) {
+    availableToScroll =
+        ParentLayerCoord(
+            fabs(DisplacementWillOverscrollAmount(aDelta) - aDelta)) /
+        zoom;
+  }
+
+  return availableToScroll > COORDINATE_EPSILON;
+}
+
+CSSCoord Axis::ClampOriginToScrollableRect(CSSCoord aOrigin) const {
+  CSSToParentLayerScale zoom = GetFrameMetrics().GetZoom();
+  ParentLayerCoord origin = aOrigin * zoom;
+  ParentLayerCoord result;
+  if (origin < GetPageStart()) {
+    result = GetPageStart();
+  } else if (origin + GetCompositionLength() > GetPageEnd()) {
+    result = GetPageEnd() - GetCompositionLength();
+  } else {
+    return aOrigin;
+  }
+  if (zoom == CSSToParentLayerScale(0)) {
+    return aOrigin;
+  }
+  return result / zoom;
+}
+
+bool Axis::CanScrollNow() const { return !mAxisLocked && CanScroll(); }
+
+ParentLayerCoord Axis::DisplacementWillOverscrollAmount(
+    ParentLayerCoord aDisplacement) const {
+  ParentLayerCoord newOrigin = GetOrigin() + aDisplacement;
+  ParentLayerCoord newCompositionEnd = GetCompositionEnd() + aDisplacement;
+  // If the current pan plus a displacement takes the window to the left of or
+  // above the current page rect.
+  bool minus = newOrigin < GetPageStart();
+  // If the current pan plus a displacement takes the window to the right of or
+  // below the current page rect.
+  bool plus = newCompositionEnd > GetPageEnd();
+  if (minus && plus) {
+    // Don't handle overscrolled in both directions; a displacement can't cause
+    // this, it must have already been zoomed out too far.
+    return 0;
+  }
+  if (minus) {
+    return newOrigin - GetPageStart();
+  }
+  if (plus) {
+    return newCompositionEnd - GetPageEnd();
+  }
+  return 0;
+}
+
+CSSCoord Axis::ScaleWillOverscrollAmount(float aScale, CSSCoord aFocus) const {
+  // Internally, do computations in ParentLayer coordinates *before* the scale
+  // is applied.
+  CSSToParentLayerScale zoom = GetFrameMetrics().GetZoom();
+  ParentLayerCoord focus = aFocus * zoom;
+  ParentLayerCoord originAfterScale = (GetOrigin() + focus) - (focus / aScale);
+
+  bool both = ScaleWillOverscrollBothSides(aScale);
+  bool minus = GetPageStart() - originAfterScale > COORDINATE_EPSILON;
+  bool plus =
+      (originAfterScale + (GetCompositionLength() / aScale)) - GetPageEnd() >
+      COORDINATE_EPSILON;
+
+  if ((minus && plus) || both) {
+    // If we ever reach here it's a bug in the client code.
+    MOZ_ASSERT(false,
+               "In an OVERSCROLL_BOTH condition in ScaleWillOverscrollAmount");
+    return 0;
+  }
+  if (minus && zoom != CSSToParentLayerScale(0)) {
+    return (originAfterScale - GetPageStart()) / zoom;
+  }
+  if (plus && zoom != CSSToParentLayerScale(0)) {
+    return (originAfterScale + (GetCompositionLength() / aScale) -
+            GetPageEnd()) /
+           zoom;
+  }
+  return 0;
+}
+
+bool Axis::IsAxisLocked() const { return mAxisLocked; }
+
+float Axis::GetVelocity() const { return mAxisLocked ? 0 : DoGetVelocity(); }
+
+void Axis::SetVelocity(float aVelocity) {
+  AXIS_LOG("%p|%s direct-setting velocity to %f\n", mAsyncPanZoomController,
+           Name(), aVelocity);
+  DoSetVelocity(aVelocity);
+}
+
+ParentLayerCoord Axis::GetCompositionEnd() const {
+  return GetOrigin() + GetCompositionLength();
+}
+
+ParentLayerCoord Axis::GetPageEnd() const {
+  return GetPageStart() + GetPageLength();
+}
+
+ParentLayerCoord Axis::GetScrollRangeEnd() const {
+  return GetPageEnd() - GetCompositionLength();
+}
+
+ParentLayerCoord Axis::GetOrigin() const {
+  ParentLayerPoint origin =
+      GetFrameMetrics().GetVisualScrollOffset() * GetFrameMetrics().GetZoom();
+  return GetPointOffset(origin);
+}
+
+ParentLayerCoord Axis::GetCompositionLength() const {
+  return GetRectLength(GetFrameMetrics().GetCompositionBounds());
+}
+
+ParentLayerCoord Axis::GetPageStart() const {
+  ParentLayerRect pageRect = GetFrameMetrics().GetExpandedScrollableRect() *
+                             GetFrameMetrics().GetZoom();
+  return GetRectOffset(pageRect);
+}
+
+ParentLayerCoord Axis::GetPageLength() const {
+  ParentLayerRect pageRect = GetFrameMetrics().GetExpandedScrollableRect() *
+                             GetFrameMetrics().GetZoom();
+  return GetRectLength(pageRect);
+}
+
+bool Axis::ScaleWillOverscrollBothSides(float aScale) const {
+  const FrameMetrics& metrics = GetFrameMetrics();
+  ParentLayerRect screenCompositionBounds =
+      metrics.GetCompositionBounds() / ParentLayerToParentLayerScale(aScale);
+  return GetRectLength(screenCompositionBounds) - GetPageLength() >
+         COORDINATE_EPSILON;
+}
+
+float Axis::DoGetVelocity() const {
+  auto velocity = mVelocity.Lock();
+  return velocity.ref();
+}
+void Axis::DoSetVelocity(float aVelocity) {
+  auto velocity = mVelocity.Lock();
+  velocity.ref() = aVelocity;
+}
+
+const FrameMetrics& Axis::GetFrameMetrics() const {
+  return mAsyncPanZoomController->GetFrameMetrics();
+}
+
+const ScrollMetadata& Axis::GetScrollMetadata() const {
+  return mAsyncPanZoomController->GetScrollMetadata();
+}
+
+bool Axis::OverscrollBehaviorAllowsHandoff() const {
+  // Scroll handoff is a "non-local" overscroll behavior, so it's allowed
+  // with "auto" and disallowed with "contain" and "none".
+  return GetOverscrollBehavior() == OverscrollBehavior::Auto;
+}
+
+bool Axis::OverscrollBehaviorAllowsOverscrollEffect() const {
+  // An overscroll effect is a "local" overscroll behavior, so it's allowed
+  // with "auto" and "contain" and disallowed with "none".
+  return GetOverscrollBehavior() != OverscrollBehavior::None;
+}
+
+AxisX::AxisX(AsyncPanZoomController* aAsyncPanZoomController)
+    : Axis(aAsyncPanZoomController) {}
+
+CSSCoord AxisX::GetPointOffset(const CSSPoint& aPoint) const {
+  return aPoint.x;
+}
+
+OuterCSSCoord AxisX::GetPointOffset(const OuterCSSPoint& aPoint) const {
+  return aPoint.x;
+}
+
+ParentLayerCoord AxisX::GetPointOffset(const ParentLayerPoint& aPoint) const {
+  return aPoint.x;
+}
+
+CSSToParentLayerScale AxisX::GetAxisScale(
+    const CSSToParentLayerScale2D& aScale) const {
+  return CSSToParentLayerScale(aScale.xScale);
+}
+
+ParentLayerCoord AxisX::GetRectLength(const ParentLayerRect& aRect) const {
+  return aRect.Width();
+}
+
+CSSCoord AxisX::GetRectLength(const CSSRect& aRect) const {
+  return aRect.Width();
+}
+
+ParentLayerCoord AxisX::GetRectOffset(const ParentLayerRect& aRect) const {
+  return aRect.X();
+}
+
+CSSCoord AxisX::GetRectOffset(const CSSRect& aRect) const { return aRect.X(); }
+
+float AxisX::GetTransformScale(
+    const AsyncTransformComponentMatrix& aMatrix) const {
+  return aMatrix._11;
+}
+
+ParentLayerCoord AxisX::GetTransformTranslation(
+    const AsyncTransformComponentMatrix& aMatrix) const {
+  return aMatrix._41;
+}
+
+void AxisX::PostScale(AsyncTransformComponentMatrix& aMatrix,
+                      float aScale) const {
+  aMatrix.PostScale(aScale, 1.f, 1.f);
+}
+
+void AxisX::PostTranslate(AsyncTransformComponentMatrix& aMatrix,
+                          ParentLayerCoord aTranslation) const {
+  aMatrix.PostTranslate(aTranslation, 0, 0);
+}
+
+ScreenPoint AxisX::MakePoint(ScreenCoord aCoord) const {
+  return ScreenPoint(aCoord, 0);
+}
+
+const char* AxisX::Name() const { return "X"; }
+
+bool AxisX::CanScrollTo(Side aSide) const {
+  switch (aSide) {
+    case eSideLeft:
+      return CanScroll(CSSCoord(-COORDINATE_EPSILON * 2));
+    case eSideRight:
+      return CanScroll(CSSCoord(COORDINATE_EPSILON * 2));
+    default:
+      MOZ_ASSERT_UNREACHABLE("aSide is out of valid values");
+      return false;
+  }
+}
+
+SideBits AxisX::ScrollableDirections() const {
+  SideBits directions = SideBits::eNone;
+
+  if (CanScrollTo(eSideLeft)) {
+    directions |= SideBits::eLeft;
+  }
+  if (CanScrollTo(eSideRight)) {
+    directions |= SideBits::eRight;
+  }
+
+  return directions;
+}
+
+OverscrollBehavior AxisX::GetOverscrollBehavior() const {
+  return GetScrollMetadata().GetOverscrollBehavior().mBehaviorX;
+}
+
+AxisY::AxisY(AsyncPanZoomController* aAsyncPanZoomController)
+    : Axis(aAsyncPanZoomController) {}
+
+CSSCoord AxisY::GetPointOffset(const CSSPoint& aPoint) const {
+  return aPoint.y;
+}
+
+OuterCSSCoord AxisY::GetPointOffset(const OuterCSSPoint& aPoint) const {
+  return aPoint.y;
+}
+
+ParentLayerCoord AxisY::GetPointOffset(const ParentLayerPoint& aPoint) const {
+  return aPoint.y;
+}
+
+CSSToParentLayerScale AxisY::GetAxisScale(
+    const CSSToParentLayerScale2D& aScale) const {
+  return CSSToParentLayerScale(aScale.yScale);
+}
+
+ParentLayerCoord AxisY::GetRectLength(const ParentLayerRect& aRect) const {
+  return aRect.Height();
+}
+
+CSSCoord AxisY::GetRectLength(const CSSRect& aRect) const {
+  return aRect.Height();
+}
+
+ParentLayerCoord AxisY::GetRectOffset(const ParentLayerRect& aRect) const {
+  return aRect.Y();
+}
+
+CSSCoord AxisY::GetRectOffset(const CSSRect& aRect) const { return aRect.Y(); }
+
+float AxisY::GetTransformScale(
+    const AsyncTransformComponentMatrix& aMatrix) const {
+  return aMatrix._22;
+}
+
+ParentLayerCoord AxisY::GetTransformTranslation(
+    const AsyncTransformComponentMatrix& aMatrix) const {
+  return aMatrix._42;
+}
+
+void AxisY::PostScale(AsyncTransformComponentMatrix& aMatrix,
+                      float aScale) const {
+  aMatrix.PostScale(1.f, aScale, 1.f);
+}
+
+void AxisY::PostTranslate(AsyncTransformComponentMatrix& aMatrix,
+                          ParentLayerCoord aTranslation) const {
+  aMatrix.PostTranslate(0, aTranslation, 0);
+}
+
+ScreenPoint AxisY::MakePoint(ScreenCoord aCoord) const {
+  return ScreenPoint(0, aCoord);
+}
+
+const char* AxisY::Name() const { return "Y"; }
+
+bool AxisY::CanScrollTo(Side aSide) const {
+  switch (aSide) {
+    case eSideTop:
+      return CanScroll(CSSCoord(-COORDINATE_EPSILON * 2));
+    case eSideBottom:
+      return CanScroll(CSSCoord(COORDINATE_EPSILON * 2));
+    default:
+      MOZ_ASSERT_UNREACHABLE("aSide is out of valid values");
+      return false;
+  }
+}
+
+SideBits AxisY::ScrollableDirections() const {
+  SideBits directions = SideBits::eNone;
+
+  if (CanScrollTo(eSideTop)) {
+    directions |= SideBits::eTop;
+  }
+  if (CanScrollTo(eSideBottom)) {
+    directions |= SideBits::eBottom;
+  }
+
+  return directions;
+}
+
+bool AxisY::HasDynamicToolbar() const {
+  return GetCompositionLengthWithoutDynamicToolbar() != ParentLayerCoord(0);
+}
+
+SideBits AxisY::ScrollableDirectionsWithDynamicToolbar(
+    const ScreenMargin& aFixedLayerMargins) const {
+  MOZ_ASSERT(mAsyncPanZoomController->IsRootContent());
+
+  SideBits directions = ScrollableDirections();
+
+  if (HasDynamicToolbar()) {
+    ParentLayerCoord toolbarHeight =
+        GetCompositionLength() - GetCompositionLengthWithoutDynamicToolbar();
+
+    ParentLayerMargin fixedLayerMargins = ViewAs<ParentLayerPixel>(
+        aFixedLayerMargins, PixelCastJustification::ScreenIsParentLayerForRoot);
+
+    if (!mAsyncPanZoomController->IsZero(fixedLayerMargins.bottom)) {
+      directions |= SideBits::eTop;
+    }
+    if (mAsyncPanZoomController->FuzzyGreater(
+            fixedLayerMargins.bottom + toolbarHeight, 0)) {
+      directions |= SideBits::eBottom;
+    }
+  }
+
+  return directions;
+}
+
+bool AxisY::CanVerticalScrollWithDynamicToolbar() const {
+  return !HasDynamicToolbar()
+             ? CanScroll()
+             : mAsyncPanZoomController->FuzzyGreater(
+                   GetPageLength(),
+                   GetCompositionLengthWithoutDynamicToolbar());
+}
+
+OverscrollBehavior AxisY::GetOverscrollBehavior() const {
+  return GetScrollMetadata().GetOverscrollBehavior().mBehaviorY;
+}
+
+ParentLayerCoord AxisY::GetCompositionLengthWithoutDynamicToolbar() const {
+  return GetFrameMetrics().GetCompositionSizeWithoutDynamicToolbar().Height();
+}
+
+}  // namespace layers
+}  // namespace mozilla