Add m-esr52 at 52.6.0

1 files changed, 681 insertions, 0 deletions

diff --git a/gfx/layers/apz/src/Axis.cpp b/gfx/layers/apz/src/Axis.cpp
new file mode 100644
index 000000000..ddd660e0b
--- /dev/null
+++ b/gfx/layers/apz/src/Axis.cpp
@@ -0,0 +1,681 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set sw=2 ts=8 et 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 "AsyncPanZoomController.h"     // for AsyncPanZoomController
+#include "mozilla/layers/APZCTreeManager.h" // for APZCTreeManager
+#include "mozilla/layers/APZThreadUtils.h" // for AssertOnControllerThread
+#include "FrameMetrics.h"               // for FrameMetrics
+#include "mozilla/Attributes.h"         // for final
+#include "mozilla/ComputedTimingFunction.h" // for ComputedTimingFunction
+#include "mozilla/Preferences.h"        // for Preferences
+#include "mozilla/gfx/Rect.h"           // for RoundedIn
+#include "mozilla/mozalloc.h"           // for operator new
+#include "mozilla/FloatingPoint.h"      // for FuzzyEqualsAdditive
+#include "mozilla/StaticPtr.h"          // for StaticAutoPtr
+#include "nsMathUtils.h"                // for NS_lround
+#include "nsPrintfCString.h"            // for nsPrintfCString
+#include "nsThreadUtils.h"              // for NS_DispatchToMainThread, etc
+#include "nscore.h"                     // for NS_IMETHOD
+#include "gfxPrefs.h"                   // for the preferences
+
+#define AXIS_LOG(...)
+// #define AXIS_LOG(...) printf_stderr("AXIS: " __VA_ARGS__)
+
+namespace mozilla {
+namespace layers {
+
+// When we compute the velocity we do so by taking two input events and
+// dividing the distance delta over the time delta. In some cases the time
+// delta can be really small, which can make the velocity computation very
+// volatile. To avoid this we impose a minimum time delta below which we do
+// not recompute the velocity.
+const uint32_t MIN_VELOCITY_SAMPLE_TIME_MS = 5;
+
+bool FuzzyEqualsCoordinate(float aValue1, float aValue2)
+{
+  return FuzzyEqualsAdditive(aValue1, aValue2, COORDINATE_EPSILON)
+      || FuzzyEqualsMultiplicative(aValue1, aValue2);
+}
+
+extern StaticAutoPtr<ComputedTimingFunction> gVelocityCurveFunction;
+
+Axis::Axis(AsyncPanZoomController* aAsyncPanZoomController)
+  : mPos(0),
+    mVelocitySampleTimeMs(0),
+    mVelocitySamplePos(0),
+    mVelocity(0.0f),
+    mAxisLocked(false),
+    mAsyncPanZoomController(aAsyncPanZoomController),
+    mOverscroll(0),
+    mFirstOverscrollAnimationSample(0),
+    mLastOverscrollPeak(0),
+    mOverscrollScale(1.0f)
+{
+}
+
+float Axis::ToLocalVelocity(float aVelocityInchesPerMs) const {
+  ScreenPoint velocity = MakePoint(aVelocityInchesPerMs * APZCTreeManager::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, ParentLayerCoord aAdditionalDelta, uint32_t aTimestampMs) {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  if (aTimestampMs <= mVelocitySampleTimeMs + MIN_VELOCITY_SAMPLE_TIME_MS) {
+    // See also the comment on MIN_VELOCITY_SAMPLE_TIME_MS.
+    // We still update mPos so that the positioning is correct (and we don't run
+    // into problems like bug 1042734) but the velocity will remain where it was.
+    // In particular we don't update either mVelocitySampleTimeMs or
+    // mVelocitySamplePos so that eventually when we do get an event with the
+    // required time delta we use the corresponding distance delta as well.
+    AXIS_LOG("%p|%s skipping velocity computation for small time delta %dms\n",
+        mAsyncPanZoomController, Name(), (aTimestampMs - mVelocitySampleTimeMs));
+    mPos = aPos;
+    return;
+  }
+
+  float newVelocity = mAxisLocked ? 0.0f : (float)(mVelocitySamplePos - aPos + aAdditionalDelta) / (float)(aTimestampMs - mVelocitySampleTimeMs);
+
+  newVelocity = ApplyFlingCurveToVelocity(newVelocity);
+
+  AXIS_LOG("%p|%s updating velocity to %f with touch\n",
+    mAsyncPanZoomController, Name(), newVelocity);
+  mVelocity = newVelocity;
+  mPos = aPos;
+  mVelocitySampleTimeMs = aTimestampMs;
+  mVelocitySamplePos = aPos;
+
+  AddVelocityToQueue(aTimestampMs, mVelocity);
+}
+
+float Axis::ApplyFlingCurveToVelocity(float aVelocity) const {
+  float newVelocity = aVelocity;
+  if (gfxPrefs::APZMaxVelocity() > 0.0f) {
+    bool velocityIsNegative = (newVelocity < 0);
+    newVelocity = fabs(newVelocity);
+
+    float maxVelocity = ToLocalVelocity(gfxPrefs::APZMaxVelocity());
+    newVelocity = std::min(newVelocity, maxVelocity);
+
+    if (gfxPrefs::APZCurveThreshold() > 0.0f && gfxPrefs::APZCurveThreshold() < gfxPrefs::APZMaxVelocity()) {
+      float curveThreshold = ToLocalVelocity(gfxPrefs::APZCurveThreshold());
+      if (newVelocity > curveThreshold) {
+        // here, 0 < curveThreshold < newVelocity <= maxVelocity, so we apply the curve
+        float scale = maxVelocity - curveThreshold;
+        float funcInput = (newVelocity - curveThreshold) / scale;
+        float funcOutput =
+          gVelocityCurveFunction->GetValue(funcInput,
+            ComputedTimingFunction::BeforeFlag::Unset);
+        float curvedVelocity = (funcOutput * scale) + curveThreshold;
+        AXIS_LOG("%p|%s curving up velocity from %f to %f\n",
+          mAsyncPanZoomController, Name(), newVelocity, curvedVelocity);
+        newVelocity = curvedVelocity;
+      }
+    }
+
+    if (velocityIsNegative) {
+      newVelocity = -newVelocity;
+    }
+  }
+
+  return newVelocity;
+}
+
+void Axis::AddVelocityToQueue(uint32_t aTimestampMs, float aVelocity) {
+  mVelocityQueue.AppendElement(std::make_pair(aTimestampMs, aVelocity));
+  if (mVelocityQueue.Length() > gfxPrefs::APZMaxVelocityQueueSize()) {
+    mVelocityQueue.RemoveElementAt(0);
+  }
+}
+
+void Axis::HandleTouchVelocity(uint32_t aTimestampMs, float aSpeed) {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  mVelocity = ApplyFlingCurveToVelocity(aSpeed);
+  mVelocitySampleTimeMs = aTimestampMs;
+
+  AddVelocityToQueue(aTimestampMs, mVelocity);
+}
+
+void Axis::StartTouch(ParentLayerCoord aPos, uint32_t aTimestampMs) {
+  mStartPos = aPos;
+  mPos = aPos;
+  mVelocitySampleTimeMs = aTimestampMs;
+  mVelocitySamplePos = aPos;
+  mAxisLocked = false;
+}
+
+bool Axis::AdjustDisplacement(ParentLayerCoord aDisplacement,
+                              /* ParentLayerCoord */ float& aDisplacementOut,
+                              /* ParentLayerCoord */ float& aOverscrollAmountOut,
+                              bool aForceOverscroll /* = false */)
+{
+  if (mAxisLocked) {
+    aOverscrollAmountOut = 0;
+    aDisplacementOut = 0;
+    return false;
+  }
+  if (aForceOverscroll) {
+    aOverscrollAmountOut = aDisplacement;
+    aDisplacementOut = 0;
+    return false;
+  }
+
+  EndOverscrollAnimation();
+
+  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;
+
+  // 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());
+    mVelocity = 0.0f;
+    displacement -= aOverscrollAmountOut;
+  }
+  aDisplacementOut = displacement;
+  return fabsf(consumedOverscroll) > EPSILON;
+}
+
+ParentLayerCoord Axis::ApplyResistance(ParentLayerCoord aRequestedOverscroll) const {
+  // 'resistanceFactor' is a value between 0 and 1, which:
+  //   - tends to 1 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; this should prevent overscrolling by more than the composition
+  // length.
+  float resistanceFactor = 1 - fabsf(GetOverscroll()) / GetCompositionLength();
+  return resistanceFactor < 0 ? ParentLayerCoord(0) : aRequestedOverscroll * resistanceFactor;
+}
+
+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 (FuzzyEqualsAdditive(aOverscroll.value, 0.0f, COORDINATE_EPSILON)) {
+    return;
+  }
+  EndOverscrollAnimation();
+  aOverscroll = ApplyResistance(aOverscroll);
+  if (aOverscroll > 0) {
+#ifdef DEBUG
+    if (!FuzzyEqualsCoordinate(GetCompositionEnd().value, GetPageEnd().value)) {
+      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 (!FuzzyEqualsCoordinate(GetOrigin().value, GetPageStart().value)) {
+      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;
+}
+
+ParentLayerCoord Axis::GetOverscroll() const {
+  ParentLayerCoord result = (mOverscroll - mLastOverscrollPeak) / mOverscrollScale;
+
+  // Assert that we return overscroll in the correct direction
+#ifdef DEBUG
+  if ((result.value * mFirstOverscrollAnimationSample.value) < 0.0f) {
+    nsPrintfCString message("GetOverscroll() (%f) and first overscroll animation sample (%f) have different signs\n",
+                            result.value, mFirstOverscrollAnimationSample.value);
+    NS_ASSERTION(false, message.get());
+    MOZ_CRASH("GFX: Overscroll issue");
+  }
+#endif
+
+  return result;
+}
+
+void Axis::StartOverscrollAnimation(float aVelocity) {
+  // Make sure any state from a previous animation has been cleared.
+  MOZ_ASSERT(mFirstOverscrollAnimationSample == 0 &&
+             mLastOverscrollPeak == 0 &&
+             mOverscrollScale == 1);
+
+  SetVelocity(aVelocity);
+}
+
+void Axis::EndOverscrollAnimation() {
+  ParentLayerCoord overscroll = GetOverscroll();
+  mFirstOverscrollAnimationSample = 0;
+  mLastOverscrollPeak = 0;
+  mOverscrollScale = 1.0f;
+  mOverscroll = overscroll;
+}
+
+void Axis::StepOverscrollAnimation(double aStepDurationMilliseconds) {
+  // Apply spring physics to the overscroll as time goes on.
+  // Note: this method of sampling isn't perfectly smooth, as it assumes
+  // a constant velocity over 'aDelta', instead of an accelerating velocity.
+  // (The way we applying friction to flings has the same issue.)
+  // Hooke's law with damping:
+  //   F = -kx - bv
+  // where
+  //   k is a constant related to the stiffness of the spring
+  //     The larger the constant, the stiffer the spring.
+  //   x is the displacement of the end of the spring from its equilibrium
+  //     In our scenario, it's the amount of overscroll on the axis.
+  //   b is a constant that provides damping (friction)
+  //   v is the velocity of the point at the end of the spring
+  // See http://gafferongames.com/game-physics/spring-physics/
+  const float kSpringStiffness = gfxPrefs::APZOverscrollSpringStiffness();
+  const float kSpringFriction = gfxPrefs::APZOverscrollSpringFriction();
+
+  // Apply spring force.
+  float springForce = -1 * kSpringStiffness * mOverscroll;
+  // Assume unit mass, so force = acceleration.
+  float oldVelocity = mVelocity;
+  mVelocity += springForce * aStepDurationMilliseconds;
+
+  // Apply dampening.
+  mVelocity *= pow(double(1 - kSpringFriction), aStepDurationMilliseconds);
+  AXIS_LOG("%p|%s sampled overscroll animation, leaving velocity at %f\n",
+    mAsyncPanZoomController, Name(), mVelocity);
+
+  // At the peak of each oscillation, record new offset and scaling factors for
+  // overscroll, to ensure that GetOverscroll always returns a value of the
+  // same sign, and that this value is correctly adjusted as the spring is
+  // dampened.
+  // To handle the case where one of the velocity samples is exaclty zero,
+  // consider a sign change to have occurred when the outgoing velocity is zero.
+  bool velocitySignChange = (oldVelocity * mVelocity) < 0 || mVelocity == 0;
+  if (mFirstOverscrollAnimationSample == 0.0f) {
+    mFirstOverscrollAnimationSample = mOverscroll;
+
+    // It's possible to start sampling overscroll with velocity == 0, or
+    // velocity in the opposite direction of overscroll, so make sure we
+    // correctly record the peak in this case.
+    if (mOverscroll != 0 && ((mOverscroll > 0 ? oldVelocity : -oldVelocity) <= 0.0f)) {
+      velocitySignChange = true;
+    }
+  }
+  if (velocitySignChange) {
+    bool oddOscillation = (mOverscroll.value * mFirstOverscrollAnimationSample.value) < 0.0f;
+    mLastOverscrollPeak = oddOscillation ? mOverscroll : -mOverscroll;
+    mOverscrollScale = 2.0f;
+  }
+
+  // Adjust the amount of overscroll based on the velocity.
+  // Note that we allow for oscillations.
+  mOverscroll += (mVelocity * aStepDurationMilliseconds);
+
+  // Our mechanism for translating a set of mOverscroll values that oscillate
+  // around zero to a set of GetOverscroll() values that have the same sign
+  // (so content is always stretched, never compressed) assumes that
+  // mOverscroll does not exceed mLastOverscrollPeak in magnitude. If our
+  // calculations were exact, this would be the case, as a dampened spring
+  // should never attain a displacement greater in magnitude than a previous
+  // peak. In our approximation calculations, however, this may not hold
+  // exactly. To ensure the assumption is not violated, we clamp the magnitude
+  // of mOverscroll.
+  if (mLastOverscrollPeak != 0 && fabs(mOverscroll) > fabs(mLastOverscrollPeak)) {
+    mOverscroll = (mOverscroll >= 0) ? fabs(mLastOverscrollPeak) : -fabs(mLastOverscrollPeak);
+  }
+}
+
+bool Axis::SampleOverscrollAnimation(const TimeDuration& aDelta) {
+  // Short-circuit early rather than running through all the sampling code.
+  if (mVelocity == 0.0f && mOverscroll == 0.0f) {
+    return false;
+  }
+
+  // We approximate the curve traced out by the velocity of the spring
+  // over time by breaking up the curve into small segments over which we
+  // consider the velocity to be constant. If the animation is sampled
+  // sufficiently often, then treating |aDelta| as a single segment of this
+  // sort would be fine, but the frequency at which the animation is sampled
+  // can be affected by external factors, and as the segment size grows larger,
+  // the approximation gets worse and the approximated curve can even diverge
+  // (i.e. oscillate forever, with displacements of increasing absolute value)!
+  // To avoid this, we break up |aDelta| into smaller segments of length 1 ms
+  // each, and a segment of any remaining fractional milliseconds.
+  double milliseconds = aDelta.ToMilliseconds();
+  int wholeMilliseconds = (int) aDelta.ToMilliseconds();
+  double fractionalMilliseconds = milliseconds - wholeMilliseconds;
+  for (int i = 0; i < wholeMilliseconds; ++i) {
+    StepOverscrollAnimation(1);
+  }
+  StepOverscrollAnimation(fractionalMilliseconds);
+
+  // If both the velocity and the displacement fall below a threshold, stop
+  // the animation so we don't continue doing tiny oscillations that aren't
+  // noticeable.
+  if (fabs(mOverscroll) < gfxPrefs::APZOverscrollStopDistanceThreshold() &&
+      fabs(mVelocity) < gfxPrefs::APZOverscrollStopVelocityThreshold()) {
+    // "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();
+    mVelocity = 0;
+    return false;
+  }
+
+  // Otherwise, continue the animation.
+  return true;
+}
+
+bool Axis::IsOverscrolled() const {
+  return mOverscroll != 0.f;
+}
+
+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(uint32_t aTimestampMs) {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  mAxisLocked = false;
+  mVelocity = 0;
+  int count = 0;
+  while (!mVelocityQueue.IsEmpty()) {
+    uint32_t timeDelta = (aTimestampMs - mVelocityQueue[0].first);
+    if (timeDelta < gfxPrefs::APZVelocityRelevanceTime()) {
+      count++;
+      mVelocity += mVelocityQueue[0].second;
+    }
+    mVelocityQueue.RemoveElementAt(0);
+  }
+  if (count > 1) {
+    mVelocity /= count;
+  }
+  AXIS_LOG("%p|%s ending touch, computed velocity %f\n",
+    mAsyncPanZoomController, Name(), mVelocity);
+}
+
+void Axis::CancelGesture() {
+  // mVelocityQueue is controller-thread only
+  APZThreadUtils::AssertOnControllerThread();
+
+  AXIS_LOG("%p|%s cancelling touch, clearing velocity queue\n",
+    mAsyncPanZoomController, Name());
+  mVelocity = 0.0f;
+  while (!mVelocityQueue.IsEmpty()) {
+    mVelocityQueue.RemoveElementAt(0);
+  }
+}
+
+bool Axis::CanScroll() const {
+  return GetPageLength() - GetCompositionLength() > COORDINATE_EPSILON;
+}
+
+bool Axis::CanScroll(ParentLayerCoord aDelta) const
+{
+  if (!CanScroll() || mAxisLocked) {
+    return false;
+  }
+
+  return fabs(DisplacementWillOverscrollAmount(aDelta) - aDelta) > COORDINATE_EPSILON;
+}
+
+CSSCoord Axis::ClampOriginToScrollableRect(CSSCoord aOrigin) const
+{
+  CSSToParentLayerScale zoom = GetScaleForAxis(GetFrameMetrics().GetZoom());
+  ParentLayerCoord origin = aOrigin * zoom;
+
+  ParentLayerCoord result;
+  if (origin < GetPageStart()) {
+    result = GetPageStart();
+  } else if (origin + GetCompositionLength() > GetPageEnd()) {
+    result = GetPageEnd() - GetCompositionLength();
+  } else {
+    return aOrigin;
+  }
+
+  return result / zoom;
+}
+
+bool Axis::CanScrollNow() const {
+  return !mAxisLocked && CanScroll();
+}
+
+bool Axis::FlingApplyFrictionOrCancel(const TimeDuration& aDelta,
+                                      float aFriction,
+                                      float aThreshold) {
+  if (fabsf(mVelocity) <= aThreshold) {
+    // If the velocity is very low, just set it to 0 and stop the fling,
+    // otherwise we'll just asymptotically approach 0 and the user won't
+    // actually see any changes.
+    mVelocity = 0.0f;
+    return false;
+  } else {
+    mVelocity *= pow(1.0f - aFriction, float(aDelta.ToMilliseconds()));
+  }
+  AXIS_LOG("%p|%s reduced velocity to %f due to friction\n",
+    mAsyncPanZoomController, Name(), mVelocity);
+  return true;
+}
+
+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().ToScaleFactor();
+  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) {
+    return (originAfterScale - GetPageStart()) / zoom;
+  }
+  if (plus) {
+    return (originAfterScale + (GetCompositionLength() / aScale) - GetPageEnd()) / zoom;
+  }
+  return 0;
+}
+
+bool Axis::IsAxisLocked() const {
+  return mAxisLocked;
+}
+
+float Axis::GetVelocity() const {
+  return mAxisLocked ? 0 : mVelocity;
+}
+
+void Axis::SetVelocity(float aVelocity) {
+  AXIS_LOG("%p|%s direct-setting velocity to %f\n",
+    mAsyncPanZoomController, Name(), aVelocity);
+  mVelocity = 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().GetScrollOffset() * 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;
+}
+
+const FrameMetrics& Axis::GetFrameMetrics() const {
+  return mAsyncPanZoomController->GetFrameMetrics();
+}
+
+
+AxisX::AxisX(AsyncPanZoomController* aAsyncPanZoomController)
+  : Axis(aAsyncPanZoomController)
+{
+
+}
+
+ParentLayerCoord AxisX::GetPointOffset(const ParentLayerPoint& aPoint) const
+{
+  return aPoint.x;
+}
+
+ParentLayerCoord AxisX::GetRectLength(const ParentLayerRect& aRect) const
+{
+  return aRect.width;
+}
+
+ParentLayerCoord AxisX::GetRectOffset(const ParentLayerRect& aRect) const
+{
+  return aRect.x;
+}
+
+CSSToParentLayerScale AxisX::GetScaleForAxis(const CSSToParentLayerScale2D& aScale) const
+{
+  return CSSToParentLayerScale(aScale.xScale);
+}
+
+ScreenPoint AxisX::MakePoint(ScreenCoord aCoord) const
+{
+  return ScreenPoint(aCoord, 0);
+}
+
+const char* AxisX::Name() const
+{
+  return "X";
+}
+
+AxisY::AxisY(AsyncPanZoomController* aAsyncPanZoomController)
+  : Axis(aAsyncPanZoomController)
+{
+
+}
+
+ParentLayerCoord AxisY::GetPointOffset(const ParentLayerPoint& aPoint) const
+{
+  return aPoint.y;
+}
+
+ParentLayerCoord AxisY::GetRectLength(const ParentLayerRect& aRect) const
+{
+  return aRect.height;
+}
+
+ParentLayerCoord AxisY::GetRectOffset(const ParentLayerRect& aRect) const
+{
+  return aRect.y;
+}
+
+CSSToParentLayerScale AxisY::GetScaleForAxis(const CSSToParentLayerScale2D& aScale) const
+{
+  return CSSToParentLayerScale(aScale.yScale);
+}
+
+ScreenPoint AxisY::MakePoint(ScreenCoord aCoord) const
+{
+  return ScreenPoint(0, aCoord);
+}
+
+const char* AxisY::Name() const
+{
+  return "Y";
+}
+
+} // namespace layers
+} // namespace mozilla