gecko-dev/layout/style/StyleAnimationValue.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

/* Utilities for animation of computed style values */

#include "mozilla/ArrayUtils.h"
#include "mozilla/MathAlgorithms.h"

#include "mozilla/StyleAnimationValue.h"
#include "nsStyleTransformMatrix.h"
#include "nsCOMArray.h"
#include "nsIStyleRule.h"
#include "mozilla/css/StyleRule.h"
#include "nsString.h"
#include "nsStyleContext.h"
#include "nsStyleSet.h"
#include "nsComputedDOMStyle.h"
#include "nsCSSParser.h"
#include "mozilla/css/Declaration.h"
#include "mozilla/dom/Element.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/Likely.h"
#include "gfxMatrix.h"
#include "gfxQuaternion.h"
#include "nsIDocument.h"
#include "gfx2DGlue.h"

using namespace mozilla;
using namespace mozilla::gfx;

// HELPER METHODS
// --------------
/*
 * Given two units, this method returns a common unit that they can both be
 * converted into, if possible.  This is intended to facilitate
 * interpolation, distance-computation, and addition between "similar" units.
 *
 * The ordering of the arguments should not affect the output of this method.
 *
 * If there's no sensible common unit, this method returns eUnit_Null.
 *
 * @param   aFirstUnit One unit to resolve.
 * @param   aFirstUnit The other unit to resolve.
 * @return  A "common" unit that both source units can be converted into, or
 *          eUnit_Null if that's not possible.
 */
static
StyleAnimationValue::Unit
GetCommonUnit(nsCSSProperty aProperty,
              StyleAnimationValue::Unit aFirstUnit,
              StyleAnimationValue::Unit aSecondUnit)
{
  if (aFirstUnit != aSecondUnit) {
    if (nsCSSProps::PropHasFlags(aProperty, CSS_PROPERTY_STORES_CALC) &&
        (aFirstUnit == StyleAnimationValue::eUnit_Coord ||
         aFirstUnit == StyleAnimationValue::eUnit_Percent ||
         aFirstUnit == StyleAnimationValue::eUnit_Calc) &&
        (aSecondUnit == StyleAnimationValue::eUnit_Coord ||
         aSecondUnit == StyleAnimationValue::eUnit_Percent ||
         aSecondUnit == StyleAnimationValue::eUnit_Calc)) {
      // We can use calc() as the common unit.
      return StyleAnimationValue::eUnit_Calc;
    }
    return StyleAnimationValue::eUnit_Null;
  }
  return aFirstUnit;
}

static
nsCSSUnit
GetCommonUnit(nsCSSProperty aProperty,
              nsCSSUnit aFirstUnit,
              nsCSSUnit aSecondUnit)
{
  if (aFirstUnit != aSecondUnit) {
    if (nsCSSProps::PropHasFlags(aProperty, CSS_PROPERTY_STORES_CALC) &&
        (aFirstUnit == eCSSUnit_Pixel ||
         aFirstUnit == eCSSUnit_Percent ||
         aFirstUnit == eCSSUnit_Calc) &&
        (aSecondUnit == eCSSUnit_Pixel ||
         aSecondUnit == eCSSUnit_Percent ||
         aSecondUnit == eCSSUnit_Calc)) {
      // We can use calc() as the common unit.
      return eCSSUnit_Calc;
    }
    return eCSSUnit_Null;
  }
  return aFirstUnit;
}

static nsCSSKeyword
ToPrimitive(nsCSSKeyword aKeyword)
{
  switch (aKeyword) {
    case eCSSKeyword_translatex:
    case eCSSKeyword_translatey:
    case eCSSKeyword_translatez:
    case eCSSKeyword_translate:
      return eCSSKeyword_translate3d;
    case eCSSKeyword_scalex:
    case eCSSKeyword_scaley:
    case eCSSKeyword_scalez:
    case eCSSKeyword_scale:
      return eCSSKeyword_scale3d;
    default:
      return aKeyword;
  }
}

static already_AddRefed<nsCSSValue::Array>
AppendFunction(nsCSSKeyword aTransformFunction)
{
  uint32_t nargs;
  switch (aTransformFunction) {
    case eCSSKeyword_matrix3d:
      nargs = 16;
      break;
    case eCSSKeyword_matrix:
      nargs = 6;
      break;
    case eCSSKeyword_rotate3d:
      nargs = 4;
      break;
    case eCSSKeyword_interpolatematrix:
    case eCSSKeyword_translate3d:
    case eCSSKeyword_scale3d:
      nargs = 3;
      break;
    case eCSSKeyword_translate:
    case eCSSKeyword_skew:
    case eCSSKeyword_scale:
      nargs = 2;
      break;
    default:
      NS_ERROR("must be a transform function");
    case eCSSKeyword_translatex:
    case eCSSKeyword_translatey:
    case eCSSKeyword_translatez:
    case eCSSKeyword_scalex:
    case eCSSKeyword_scaley:
    case eCSSKeyword_scalez:
    case eCSSKeyword_skewx:
    case eCSSKeyword_skewy:
    case eCSSKeyword_rotate:
    case eCSSKeyword_rotatex:
    case eCSSKeyword_rotatey:
    case eCSSKeyword_rotatez:
    case eCSSKeyword_perspective:
      nargs = 1;
      break;
  }

  nsRefPtr<nsCSSValue::Array> arr = nsCSSValue::Array::Create(nargs + 1);
  arr->Item(0).SetIntValue(aTransformFunction, eCSSUnit_Enumerated);

  return arr.forget();
}

static already_AddRefed<nsCSSValue::Array>
ToPrimitive(nsCSSValue::Array* aArray)
{
  nsCSSKeyword tfunc = nsStyleTransformMatrix::TransformFunctionOf(aArray);
  nsCSSKeyword primitive = ToPrimitive(tfunc);
  nsRefPtr<nsCSSValue::Array> arr = AppendFunction(primitive);

  // FIXME: This would produce fewer calc() expressions if the
  // zero were of compatible type (length vs. percent) when
  // needed.

  nsCSSValue zero(0.0f, eCSSUnit_Pixel);
  nsCSSValue one(1.0f, eCSSUnit_Number);
  switch(tfunc) {
    case eCSSKeyword_translate:
    {
      MOZ_ASSERT(aArray->Count() == 2 || aArray->Count() == 3,
                 "unexpected count");
      arr->Item(1) = aArray->Item(1);
      arr->Item(2) = aArray->Count() == 3 ? aArray->Item(2) : zero;
      arr->Item(3) = zero;
      break;
    }
    case eCSSKeyword_translatex:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = aArray->Item(1);
      arr->Item(2) = zero;
      arr->Item(3) = zero;
      break;
    }
    case eCSSKeyword_translatey:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = zero;
      arr->Item(2) = aArray->Item(1);
      arr->Item(3) = zero;
      break;
    }
    case eCSSKeyword_translatez:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = zero;
      arr->Item(2) = zero;
      arr->Item(3) = aArray->Item(1);
      break;
    }
    case eCSSKeyword_scale:
    {
      MOZ_ASSERT(aArray->Count() == 2 || aArray->Count() == 3,
                 "unexpected count");
      arr->Item(1) = aArray->Item(1);
      arr->Item(2) = aArray->Count() == 3 ? aArray->Item(2) : aArray->Item(1);
      arr->Item(3) = one;
      break;
    }
    case eCSSKeyword_scalex:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = aArray->Item(1);
      arr->Item(2) = one;
      arr->Item(3) = one;
      break;
    }
    case eCSSKeyword_scaley:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = one;
      arr->Item(2) = aArray->Item(1);
      arr->Item(3) = one;
      break;
    }
    case eCSSKeyword_scalez:
    {
      MOZ_ASSERT(aArray->Count() == 2, "unexpected count");
      arr->Item(1) = one;
      arr->Item(2) = one;
      arr->Item(3) = aArray->Item(1);
      break;
    }
    default:
      arr = aArray;
  }
  return arr.forget();
}

inline void
nscoordToCSSValue(nscoord aCoord, nsCSSValue& aCSSValue)
{
  aCSSValue.SetFloatValue(nsPresContext::AppUnitsToFloatCSSPixels(aCoord),
                          eCSSUnit_Pixel);
}

static void
AppendCSSShadowValue(const nsCSSShadowItem *aShadow,
                     nsCSSValueList **&aResultTail)
{
  MOZ_ASSERT(aShadow, "shadow expected");

  // X, Y, Radius, Spread, Color, Inset
  nsRefPtr<nsCSSValue::Array> arr = nsCSSValue::Array::Create(6);
  nscoordToCSSValue(aShadow->mXOffset, arr->Item(0));
  nscoordToCSSValue(aShadow->mYOffset, arr->Item(1));
  nscoordToCSSValue(aShadow->mRadius, arr->Item(2));
  // NOTE: This code sometimes stores mSpread: 0 even when
  // the parser would be required to leave it null.
  nscoordToCSSValue(aShadow->mSpread, arr->Item(3));
  if (aShadow->mHasColor) {
    arr->Item(4).SetColorValue(aShadow->mColor);
  }
  if (aShadow->mInset) {
    arr->Item(5).SetIntValue(NS_STYLE_BOX_SHADOW_INSET,
                             eCSSUnit_Enumerated);
  }

  nsCSSValueList *resultItem = new nsCSSValueList;
  resultItem->mValue.SetArrayValue(arr, eCSSUnit_Array);
  *aResultTail = resultItem;
  aResultTail = &resultItem->mNext;
}

// Like nsStyleCoord::CalcValue, but with length in float pixels instead
// of nscoord.
struct PixelCalcValue {
  float mLength, mPercent;
  bool mHasPercent;
};

// Requires a canonical calc() value that we generated.
static PixelCalcValue
ExtractCalcValueInternal(const nsCSSValue& aValue)
{
  MOZ_ASSERT(aValue.GetUnit() == eCSSUnit_Calc, "unexpected unit");
  nsCSSValue::Array *arr = aValue.GetArrayValue();
  MOZ_ASSERT(arr->Count() == 1, "unexpected length");

  const nsCSSValue &topval = arr->Item(0);
  PixelCalcValue result;
  if (topval.GetUnit() == eCSSUnit_Pixel) {
    result.mLength = topval.GetFloatValue();
    result.mPercent = 0.0f;
    result.mHasPercent = false;
  } else {
    MOZ_ASSERT(topval.GetUnit() == eCSSUnit_Calc_Plus,
               "unexpected unit");
    nsCSSValue::Array *arr2 = topval.GetArrayValue();
    const nsCSSValue &len = arr2->Item(0);
    const nsCSSValue &pct = arr2->Item(1);
    MOZ_ASSERT(len.GetUnit() == eCSSUnit_Pixel, "unexpected unit");
    MOZ_ASSERT(pct.GetUnit() == eCSSUnit_Percent, "unexpected unit");
    result.mLength = len.GetFloatValue();
    result.mPercent = pct.GetPercentValue();
    result.mHasPercent = true;
  }

  return result;
}

// Requires a canonical calc() value that we generated.
static PixelCalcValue
ExtractCalcValue(const StyleAnimationValue& aValue)
{
  PixelCalcValue result;
  if (aValue.GetUnit() == StyleAnimationValue::eUnit_Coord) {
    result.mLength =
      nsPresContext::AppUnitsToFloatCSSPixels(aValue.GetCoordValue());
    result.mPercent = 0.0f;
    result.mHasPercent = false;
    return result;
  }
  if (aValue.GetUnit() == StyleAnimationValue::eUnit_Percent) {
    result.mLength = 0.0f;
    result.mPercent = aValue.GetPercentValue();
    result.mHasPercent = true;
    return result;
  }
  MOZ_ASSERT(aValue.GetUnit() == StyleAnimationValue::eUnit_Calc,
             "unexpected unit");
  nsCSSValue *val = aValue.GetCSSValueValue();
  return ExtractCalcValueInternal(*val);
}

static PixelCalcValue
ExtractCalcValue(const nsCSSValue& aValue)
{
  PixelCalcValue result;
  if (aValue.GetUnit() == eCSSUnit_Pixel) {
    result.mLength = aValue.GetFloatValue();
    result.mPercent = 0.0f;
    result.mHasPercent = false;
    return result;
  }
  if (aValue.GetUnit() == eCSSUnit_Percent) {
    result.mLength = 0.0f;
    result.mPercent = aValue.GetPercentValue();
    result.mHasPercent = true;
    return result;
  }
  return ExtractCalcValueInternal(aValue);
}

static void
SetCalcValue(const nsStyleCoord::CalcValue* aCalc, nsCSSValue& aValue)
{
  nsRefPtr<nsCSSValue::Array> arr = nsCSSValue::Array::Create(1);
  if (!aCalc->mHasPercent) {
    nscoordToCSSValue(aCalc->mLength, arr->Item(0));
  } else {
    nsCSSValue::Array *arr2 = nsCSSValue::Array::Create(2);
    arr->Item(0).SetArrayValue(arr2, eCSSUnit_Calc_Plus);
    nscoordToCSSValue(aCalc->mLength, arr2->Item(0));
    arr2->Item(1).SetPercentValue(aCalc->mPercent);
  }

  aValue.SetArrayValue(arr, eCSSUnit_Calc);
}

static void
SetCalcValue(const PixelCalcValue& aCalc, nsCSSValue& aValue)
{
  nsRefPtr<nsCSSValue::Array> arr = nsCSSValue::Array::Create(1);
  if (!aCalc.mHasPercent) {
    arr->Item(0).SetFloatValue(aCalc.mLength, eCSSUnit_Pixel);
  } else {
    nsCSSValue::Array *arr2 = nsCSSValue::Array::Create(2);
    arr->Item(0).SetArrayValue(arr2, eCSSUnit_Calc_Plus);
    arr2->Item(0).SetFloatValue(aCalc.mLength, eCSSUnit_Pixel);
    arr2->Item(1).SetPercentValue(aCalc.mPercent);
  }

  aValue.SetArrayValue(arr, eCSSUnit_Calc);
}

static already_AddRefed<nsStringBuffer>
GetURIAsUtf16StringBuffer(nsIURI* aUri)
{
  nsAutoCString utf8String;
  nsresult rv = aUri->GetSpec(utf8String);
  NS_ENSURE_SUCCESS(rv, nullptr);

  return nsCSSValue::BufferFromString(NS_ConvertUTF8toUTF16(utf8String));
}

double
CalcPositionSquareDistance(const nsCSSValue& aPos1,
                           const nsCSSValue& aPos2)
{
  NS_ASSERTION(aPos1.GetUnit() == eCSSUnit_Array &&
               aPos2.GetUnit() == eCSSUnit_Array,
               "Expected two arrays");

  PixelCalcValue calcVal[4];

  nsCSSValue::Array* posArray = aPos1.GetArrayValue();
  MOZ_ASSERT(posArray->Count() == 4, "Invalid position value");
  NS_ASSERTION(posArray->Item(0).GetUnit() == eCSSUnit_Null &&
               posArray->Item(2).GetUnit() == eCSSUnit_Null,
               "Invalid list used");
  for (int i = 0; i < 2; ++i) {
    MOZ_ASSERT(posArray->Item(i*2+1).GetUnit() != eCSSUnit_Null,
               "Invalid position value");
    calcVal[i] = ExtractCalcValue(posArray->Item(i*2+1));
  }

  posArray = aPos2.GetArrayValue();
  MOZ_ASSERT(posArray->Count() == 4, "Invalid position value");
  NS_ASSERTION(posArray->Item(0).GetUnit() == eCSSUnit_Null &&
               posArray->Item(2).GetUnit() == eCSSUnit_Null,
               "Invalid list used");
  for (int i = 0; i < 2; ++i) {
    MOZ_ASSERT(posArray->Item(i*2+1).GetUnit() != eCSSUnit_Null,
               "Invalid position value");
    calcVal[i+2] = ExtractCalcValue(posArray->Item(i*2+1));
  }

  double squareDistance = 0.0;
  for (int i = 0; i < 2; ++i) {
    float difflen = calcVal[i+2].mLength - calcVal[i].mLength;
    float diffpct = calcVal[i+2].mPercent - calcVal[i].mPercent;
    squareDistance += difflen * difflen + diffpct * diffpct;
  }

  return squareDistance;
}

// CLASS METHODS
// -------------

bool
StyleAnimationValue::ComputeDistance(nsCSSProperty aProperty,
                                     const StyleAnimationValue& aStartValue,
                                     const StyleAnimationValue& aEndValue,
                                     double& aDistance)
{
  Unit commonUnit =
    GetCommonUnit(aProperty, aStartValue.GetUnit(), aEndValue.GetUnit());

  switch (commonUnit) {
    case eUnit_Null:
    case eUnit_Auto:
    case eUnit_None:
    case eUnit_Normal:
    case eUnit_UnparsedString:
      return false;

    case eUnit_Enumerated:
      switch (aProperty) {
        case eCSSProperty_font_stretch: {
          // just like eUnit_Integer.
          int32_t startInt = aStartValue.GetIntValue();
          int32_t endInt = aEndValue.GetIntValue();
          aDistance = Abs(endInt - startInt);
          return true;
        }
        default:
          return false;
      }
   case eUnit_Visibility: {
      int32_t startEnum = aStartValue.GetIntValue();
      int32_t endEnum = aEndValue.GetIntValue();
      if (startEnum == endEnum) {
        aDistance = 0;
        return true;
      }
      if ((startEnum == NS_STYLE_VISIBILITY_VISIBLE) ==
          (endEnum == NS_STYLE_VISIBILITY_VISIBLE)) {
        return false;
      }
      aDistance = 1;
      return true;
    }
    case eUnit_Integer: {
      int32_t startInt = aStartValue.GetIntValue();
      int32_t endInt = aEndValue.GetIntValue();
      aDistance = Abs(double(endInt) - double(startInt));
      return true;
    }
    case eUnit_Coord: {
      nscoord startCoord = aStartValue.GetCoordValue();
      nscoord endCoord = aEndValue.GetCoordValue();
      aDistance = Abs(double(endCoord) - double(startCoord));
      return true;
    }
    case eUnit_Percent: {
      float startPct = aStartValue.GetPercentValue();
      float endPct = aEndValue.GetPercentValue();
      aDistance = Abs(double(endPct) - double(startPct));
      return true;
    }
    case eUnit_Float: {
      float startFloat = aStartValue.GetFloatValue();
      float endFloat = aEndValue.GetFloatValue();
      aDistance = Abs(double(endFloat) - double(startFloat));
      return true;
    }
    case eUnit_Color: {
      // http://www.w3.org/TR/smil-animation/#animateColorElement says
      // that we should use Euclidean RGB cube distance.  However, we
      // have to extend that to RGBA.  For now, we'll just use the
      // Euclidean distance in the (part of the) 4-cube of premultiplied
      // colors.
      // FIXME (spec): The CSS transitions spec doesn't say whether
      // colors are premultiplied, but things work better when they are,
      // so use premultiplication.  Spec issue is still open per
      // http://lists.w3.org/Archives/Public/www-style/2009Jul/0050.html
      nscolor startColor = aStartValue.GetColorValue();
      nscolor endColor = aEndValue.GetColorValue();

      // Get a color component on a 0-1 scale, which is much easier to
      // deal with when working with alpha.
      #define GET_COMPONENT(component_, color_) \
        (NS_GET_##component_(color_) * (1.0 / 255.0))

      double startA = GET_COMPONENT(A, startColor);
      double startR = GET_COMPONENT(R, startColor) * startA;
      double startG = GET_COMPONENT(G, startColor) * startA;
      double startB = GET_COMPONENT(B, startColor) * startA;
      double endA = GET_COMPONENT(A, endColor);
      double endR = GET_COMPONENT(R, endColor) * endA;
      double endG = GET_COMPONENT(G, endColor) * endA;
      double endB = GET_COMPONENT(B, endColor) * endA;

      #undef GET_COMPONENT

      double diffA = startA - endA;
      double diffR = startR - endR;
      double diffG = startG - endG;
      double diffB = startB - endB;
      aDistance = sqrt(diffA * diffA + diffR * diffR +
                       diffG * diffG + diffB * diffB);
      return true;
    }
    case eUnit_Calc: {
      PixelCalcValue v1 = ExtractCalcValue(aStartValue);
      PixelCalcValue v2 = ExtractCalcValue(aEndValue);
      float difflen = v2.mLength - v1.mLength;
      float diffpct = v2.mPercent - v1.mPercent;
      aDistance = sqrt(difflen * difflen + diffpct * diffpct);
      return true;
    }
    case eUnit_ObjectPosition: {
      const nsCSSValue* position1 = aStartValue.GetCSSValueValue();
      const nsCSSValue* position2 = aEndValue.GetCSSValueValue();
      double squareDistance =
        CalcPositionSquareDistance(*position1,
                                   *position2);
      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_CSSValuePair: {
      const nsCSSValuePair *pair1 = aStartValue.GetCSSValuePairValue();
      const nsCSSValuePair *pair2 = aEndValue.GetCSSValuePairValue();
      nsCSSUnit unit[2];
      unit[0] = GetCommonUnit(aProperty, pair1->mXValue.GetUnit(),
                              pair2->mXValue.GetUnit());
      unit[1] = GetCommonUnit(aProperty, pair1->mYValue.GetUnit(),
                              pair2->mYValue.GetUnit());
      if (unit[0] == eCSSUnit_Null || unit[1] == eCSSUnit_Null ||
          unit[0] == eCSSUnit_URL || unit[0] == eCSSUnit_Enumerated) {
        return false;
      }

      double squareDistance = 0.0;
      static nsCSSValue nsCSSValuePair::* const pairValues[2] = {
        &nsCSSValuePair::mXValue, &nsCSSValuePair::mYValue
      };
      for (uint32_t i = 0; i < 2; ++i) {
        nsCSSValue nsCSSValuePair::*member = pairValues[i];
        double diffsquared;
        switch (unit[i]) {
          case eCSSUnit_Pixel: {
            float diff = (pair1->*member).GetFloatValue() -
                         (pair2->*member).GetFloatValue();
            diffsquared = diff * diff;
            break;
          }
          case eCSSUnit_Percent: {
            float diff = (pair1->*member).GetPercentValue() -
                         (pair2->*member).GetPercentValue();
            diffsquared = diff * diff;
            break;
          }
          case eCSSUnit_Calc: {
            PixelCalcValue v1 = ExtractCalcValue(pair1->*member);
            PixelCalcValue v2 = ExtractCalcValue(pair2->*member);
            float difflen = v2.mLength - v1.mLength;
            float diffpct = v2.mPercent - v1.mPercent;
            diffsquared = difflen * difflen + diffpct * diffpct;
            break;
          }
          default:
            MOZ_ASSERT(false, "unexpected unit");
            return false;
        }
        squareDistance += diffsquared;
      }

      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_CSSValueTriplet: {
      const nsCSSValueTriplet *triplet1 = aStartValue.GetCSSValueTripletValue();
      const nsCSSValueTriplet *triplet2 = aEndValue.GetCSSValueTripletValue();
      nsCSSUnit unit[3];
      unit[0] = GetCommonUnit(aProperty, triplet1->mXValue.GetUnit(),
                              triplet2->mXValue.GetUnit());
      unit[1] = GetCommonUnit(aProperty, triplet1->mYValue.GetUnit(),
                              triplet2->mYValue.GetUnit());
      unit[2] = GetCommonUnit(aProperty, triplet1->mZValue.GetUnit(),
                              triplet2->mZValue.GetUnit());
      if (unit[0] == eCSSUnit_Null || unit[1] == eCSSUnit_Null ||
          unit[2] == eCSSUnit_Null) {
        return false;
      }

      double squareDistance = 0.0;
      static nsCSSValue nsCSSValueTriplet::* const pairValues[3] = {
        &nsCSSValueTriplet::mXValue, &nsCSSValueTriplet::mYValue, &nsCSSValueTriplet::mZValue
      };
      for (uint32_t i = 0; i < 3; ++i) {
        nsCSSValue nsCSSValueTriplet::*member = pairValues[i];
        double diffsquared;
        switch (unit[i]) {
          case eCSSUnit_Pixel: {
            float diff = (triplet1->*member).GetFloatValue() -
                         (triplet2->*member).GetFloatValue();
            diffsquared = diff * diff;
            break;
          }
          case eCSSUnit_Percent: {
            float diff = (triplet1->*member).GetPercentValue() -
                         (triplet2->*member).GetPercentValue();
             diffsquared = diff * diff;
             break;
          }
          case eCSSUnit_Calc: {
            PixelCalcValue v1 = ExtractCalcValue(triplet1->*member);
            PixelCalcValue v2 = ExtractCalcValue(triplet2->*member);
            float difflen = v2.mLength - v1.mLength;
            float diffpct = v2.mPercent - v1.mPercent;
            diffsquared = difflen * difflen + diffpct * diffpct;
            break;
          }
          case eCSSUnit_Null:
            diffsquared = 0;
            break;
          default:
            MOZ_ASSERT(false, "unexpected unit");
            return false;
        }
        squareDistance += diffsquared;
      }

      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_CSSRect: {
      const nsCSSRect *rect1 = aStartValue.GetCSSRectValue();
      const nsCSSRect *rect2 = aEndValue.GetCSSRectValue();
      if (rect1->mTop.GetUnit() != rect2->mTop.GetUnit() ||
          rect1->mRight.GetUnit() != rect2->mRight.GetUnit() ||
          rect1->mBottom.GetUnit() != rect2->mBottom.GetUnit() ||
          rect1->mLeft.GetUnit() != rect2->mLeft.GetUnit()) {
        // At least until we have calc()
        return false;
      }

      double squareDistance = 0.0;
      for (uint32_t i = 0; i < ArrayLength(nsCSSRect::sides); ++i) {
        nsCSSValue nsCSSRect::*member = nsCSSRect::sides[i];
        MOZ_ASSERT((rect1->*member).GetUnit() == (rect2->*member).GetUnit(),
                   "should have returned above");
        double diff;
        switch ((rect1->*member).GetUnit()) {
          case eCSSUnit_Pixel:
            diff = (rect1->*member).GetFloatValue() -
                   (rect2->*member).GetFloatValue();
            break;
          case eCSSUnit_Auto:
            diff = 0;
            break;
          default:
            MOZ_ASSERT(false, "unexpected unit");
            return false;
        }
        squareDistance += diff * diff;
      }

      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_Dasharray: {
      // NOTE: This produces results on substantially different scales
      // for length values and percentage values, which might even be
      // mixed in the same property value.  This means the result isn't
      // particularly useful for paced animation.

      // Call AddWeighted to make us lists of the same length.
      StyleAnimationValue normValue1, normValue2;
      if (!AddWeighted(aProperty, 1.0, aStartValue, 0.0, aEndValue,
                       normValue1) ||
          !AddWeighted(aProperty, 0.0, aStartValue, 1.0, aEndValue,
                       normValue2)) {
        return false;
      }

      double squareDistance = 0.0;
      const nsCSSValueList *list1 = normValue1.GetCSSValueListValue();
      const nsCSSValueList *list2 = normValue2.GetCSSValueListValue();

      MOZ_ASSERT(!list1 == !list2, "lists should be same length");
      while (list1) {
        const nsCSSValue &val1 = list1->mValue;
        const nsCSSValue &val2 = list2->mValue;

        MOZ_ASSERT(val1.GetUnit() == val2.GetUnit(),
                   "unit match should be assured by AddWeighted");
        double diff;
        switch (val1.GetUnit()) {
          case eCSSUnit_Percent:
            diff = val1.GetPercentValue() - val2.GetPercentValue();
            break;
          case eCSSUnit_Number:
            diff = val1.GetFloatValue() - val2.GetFloatValue();
            break;
          default:
            MOZ_ASSERT(false, "unexpected unit");
            return false;
        }
        squareDistance += diff * diff;

        list1 = list1->mNext;
        list2 = list2->mNext;
        MOZ_ASSERT(!list1 == !list2, "lists should be same length");
      }

      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_Shadow: {
      // Call AddWeighted to make us lists of the same length.
      StyleAnimationValue normValue1, normValue2;
      if (!AddWeighted(aProperty, 1.0, aStartValue, 0.0, aEndValue,
                       normValue1) ||
          !AddWeighted(aProperty, 0.0, aStartValue, 1.0, aEndValue,
                       normValue2)) {
        return false;
      }

      const nsCSSValueList *shadow1 = normValue1.GetCSSValueListValue();
      const nsCSSValueList *shadow2 = normValue2.GetCSSValueListValue();

      double squareDistance = 0.0;
      MOZ_ASSERT(!shadow1 == !shadow2, "lists should be same length");
      while (shadow1) {
        nsCSSValue::Array *array1 = shadow1->mValue.GetArrayValue();
        nsCSSValue::Array *array2 = shadow2->mValue.GetArrayValue();
        for (size_t i = 0; i < 4; ++i) {
          MOZ_ASSERT(array1->Item(i).GetUnit() == eCSSUnit_Pixel,
                     "unexpected unit");
          MOZ_ASSERT(array2->Item(i).GetUnit() == eCSSUnit_Pixel,
                     "unexpected unit");
          double diff = array1->Item(i).GetFloatValue() -
                        array2->Item(i).GetFloatValue();
          squareDistance += diff * diff;
        }

        const nsCSSValue &color1 = array1->Item(4);
        const nsCSSValue &color2 = array2->Item(4);
#ifdef DEBUG
        {
          const nsCSSValue &inset1 = array1->Item(5);
          const nsCSSValue &inset2 = array2->Item(5);
          // There are only two possible states of the inset value:
          //  (1) GetUnit() == eCSSUnit_Null
          //  (2) GetUnit() == eCSSUnit_Enumerated &&
          //      GetIntValue() == NS_STYLE_BOX_SHADOW_INSET
          MOZ_ASSERT(((color1.IsNumericColorUnit() &&
                       color2.IsNumericColorUnit()) ||
                      (color1.GetUnit() == color2.GetUnit())) &&
                     inset1 == inset2,
                     "AddWeighted should have failed");
        }
#endif

        if (color1.GetUnit() != eCSSUnit_Null) {
          StyleAnimationValue color1Value
            (color1.GetColorValue(), StyleAnimationValue::ColorConstructor);
          StyleAnimationValue color2Value
            (color2.GetColorValue(), StyleAnimationValue::ColorConstructor);
          double colorDistance;

        #ifdef DEBUG
          bool ok =
        #endif
            StyleAnimationValue::ComputeDistance(eCSSProperty_color,
                                                 color1Value, color2Value,
                                                 colorDistance);
          MOZ_ASSERT(ok, "should not fail");
          squareDistance += colorDistance * colorDistance;
        }

        shadow1 = shadow1->mNext;
        shadow2 = shadow2->mNext;
        MOZ_ASSERT(!shadow1 == !shadow2, "lists should be same length");
      }
      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_Filter:
      // FIXME: Support paced animations for filter function interpolation.
    case eUnit_Transform: {
      return false;
    }
    case eUnit_BackgroundPosition: {
      const nsCSSValueList *position1 = aStartValue.GetCSSValueListValue();
      const nsCSSValueList *position2 = aEndValue.GetCSSValueListValue();

      double squareDistance = 0.0;
      MOZ_ASSERT(!position1 == !position2, "lists should be same length");

      while (position1 && position2) {
        squareDistance += CalcPositionSquareDistance(position1->mValue,
                                                     position2->mValue);
        position1 = position1->mNext;
        position2 = position2->mNext;
      }
      // fail if lists differ in length.
      if (position1 || position2) {
        return false;
      }

      aDistance = sqrt(squareDistance);
      return true;
    }
    case eUnit_CSSValuePairList: {
      const nsCSSValuePairList *list1 = aStartValue.GetCSSValuePairListValue();
      const nsCSSValuePairList *list2 = aEndValue.GetCSSValuePairListValue();
      double squareDistance = 0.0;
      do {
        static nsCSSValue nsCSSValuePairList::* const pairListValues[] = {
          &nsCSSValuePairList::mXValue,
          &nsCSSValuePairList::mYValue,
        };
        for (uint32_t i = 0; i < ArrayLength(pairListValues); ++i) {
          const nsCSSValue &v1 = list1->*(pairListValues[i]);
          const nsCSSValue &v2 = list2->*(pairListValues[i]);
          nsCSSUnit unit =
            GetCommonUnit(aProperty, v1.GetUnit(), v2.GetUnit());
          if (unit == eCSSUnit_Null) {
            return false;
          }
          double diffsquared = 0.0;
          switch (unit) {
            case eCSSUnit_Pixel: {
              float diff = v1.GetFloatValue() - v2.GetFloatValue();
              diffsquared = diff * diff;
              break;
            }
            case eCSSUnit_Percent: {
              float diff = v1.GetPercentValue() - v2.GetPercentValue();
              diffsquared = diff * diff;
              break;
            }
            case eCSSUnit_Calc: {
              PixelCalcValue val1 = ExtractCalcValue(v1);
              PixelCalcValue val2 = ExtractCalcValue(v2);
              float difflen = val2.mLength - val1.mLength;
              float diffpct = val2.mPercent - val1.mPercent;
              diffsquared = difflen * difflen + diffpct * diffpct;
              break;
            }
            default:
              if (v1 != v2) {
                return false;
              }
              break;
          }
          squareDistance += diffsquared;
        }
        list1 = list1->mNext;
        list2 = list2->mNext;
      } while (list1 && list2);
      if (list1 || list2) {
        // We can't interpolate lists of different lengths.
        return false;
      }
      aDistance = sqrt(squareDistance);
      return true;
    }
  }

  MOZ_ASSERT(false, "Can't compute distance using the given common unit");
  return false;
}

#define MAX_PACKED_COLOR_COMPONENT 255

inline uint8_t ClampColor(double aColor)
{
  if (aColor >= MAX_PACKED_COLOR_COMPONENT)
    return MAX_PACKED_COLOR_COMPONENT;
  if (aColor <= 0.0)
    return 0;
  return NSToIntRound(aColor);
}

// Ensure that a float/double value isn't NaN by returning zero instead
// (NaN doesn't have a sign) as a general restriction for floating point
// values in RestrictValue.
template<typename T>
MOZ_ALWAYS_INLINE T
EnsureNotNan(T aValue)
{
  return aValue;
}
template<>
MOZ_ALWAYS_INLINE float
EnsureNotNan(float aValue)
{
  // This would benefit from a MOZ_FLOAT_IS_NaN if we had one.
  return MOZ_LIKELY(!mozilla::IsNaN(aValue)) ? aValue : 0;
}
template<>
MOZ_ALWAYS_INLINE double
EnsureNotNan(double aValue)
{
  return MOZ_LIKELY(!mozilla::IsNaN(aValue)) ? aValue : 0;
}

template <typename T>
T
RestrictValue(uint32_t aRestrictions, T aValue)
{
  T result = EnsureNotNan(aValue);
  switch (aRestrictions) {
    case 0:
      break;
    case CSS_PROPERTY_VALUE_NONNEGATIVE:
      if (result < 0) {
        result = 0;
      }
      break;
    case CSS_PROPERTY_VALUE_AT_LEAST_ONE:
      if (result < 1) {
        result = 1;
      }
      break;
    default:
      MOZ_ASSERT(false, "bad value restriction");
      break;
  }
  return result;
}

template <typename T>
T
RestrictValue(nsCSSProperty aProperty, T aValue)
{
  return RestrictValue(nsCSSProps::ValueRestrictions(aProperty), aValue);
}

static inline void
AddCSSValuePixel(double aCoeff1, const nsCSSValue &aValue1,
                 double aCoeff2, const nsCSSValue &aValue2,
                 nsCSSValue &aResult, uint32_t aValueRestrictions = 0)
{
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Pixel, "unexpected unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Pixel, "unexpected unit");
  aResult.SetFloatValue(RestrictValue(aValueRestrictions,
                                      aCoeff1 * aValue1.GetFloatValue() +
                                      aCoeff2 * aValue2.GetFloatValue()),
                        eCSSUnit_Pixel);
}

static inline void
AddCSSValueNumber(double aCoeff1, const nsCSSValue &aValue1,
                  double aCoeff2, const nsCSSValue &aValue2,
                  nsCSSValue &aResult, uint32_t aValueRestrictions = 0)
{
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Number, "unexpected unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Number, "unexpected unit");
  aResult.SetFloatValue(RestrictValue(aValueRestrictions,
                                      aCoeff1 * aValue1.GetFloatValue() +
                                      aCoeff2 * aValue2.GetFloatValue()),
                        eCSSUnit_Number);
}

static inline void
AddCSSValuePercent(double aCoeff1, const nsCSSValue &aValue1,
                   double aCoeff2, const nsCSSValue &aValue2,
                   nsCSSValue &aResult, uint32_t aValueRestrictions = 0)
{
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Percent, "unexpected unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Percent, "unexpected unit");
  aResult.SetPercentValue(RestrictValue(aValueRestrictions,
                                        aCoeff1 * aValue1.GetPercentValue() +
                                        aCoeff2 * aValue2.GetPercentValue()));
}

// Add two canonical-form calc values (eUnit_Calc) to make another
// canonical-form calc value.
static void
AddCSSValueCanonicalCalc(double aCoeff1, const nsCSSValue &aValue1,
                         double aCoeff2, const nsCSSValue &aValue2,
                         nsCSSValue &aResult)
{
  PixelCalcValue v1 = ExtractCalcValue(aValue1);
  PixelCalcValue v2 = ExtractCalcValue(aValue2);
  PixelCalcValue result;
  result.mLength = aCoeff1 * v1.mLength + aCoeff2 * v2.mLength;
  result.mPercent = aCoeff1 * v1.mPercent + aCoeff2 * v2.mPercent;
  result.mHasPercent = v1.mHasPercent || v2.mHasPercent;
  MOZ_ASSERT(result.mHasPercent || result.mPercent == 0.0f,
             "can't have a nonzero percentage part without having percentages");
  SetCalcValue(result, aResult);
}

static void
AddCSSValueAngle(double aCoeff1, const nsCSSValue &aValue1,
                 double aCoeff2, const nsCSSValue &aValue2,
                 nsCSSValue &aResult)
{
  if (aValue1.GetUnit() == aValue2.GetUnit()) {
    // To avoid floating point error, if the units match, maintain the unit.
    aResult.SetFloatValue(aCoeff1 * aValue1.GetFloatValue() +
                          aCoeff2 * aValue2.GetFloatValue(),
                          aValue1.GetUnit());
  } else {
    aResult.SetFloatValue(aCoeff1 * aValue1.GetAngleValueInRadians() +
                          aCoeff2 * aValue2.GetAngleValueInRadians(),
                          eCSSUnit_Radian);
  }
}

static bool
AddCSSValuePixelPercentCalc(const uint32_t aValueRestrictions,
                            const nsCSSUnit aCommonUnit,
                            double aCoeff1, const nsCSSValue &aValue1,
                            double aCoeff2, const nsCSSValue &aValue2,
                            nsCSSValue &aResult)
{
  switch (aCommonUnit) {
    case eCSSUnit_Pixel:
      AddCSSValuePixel(aCoeff1, aValue1,
                       aCoeff2, aValue2,
                       aResult, aValueRestrictions);
      break;
    case eCSSUnit_Percent:
      AddCSSValuePercent(aCoeff1, aValue1,
                         aCoeff2, aValue2,
                         aResult, aValueRestrictions);
      break;
    case eCSSUnit_Calc:
      AddCSSValueCanonicalCalc(aCoeff1, aValue1,
                               aCoeff2, aValue2,
                               aResult);
      break;
    default:
      return false;
  }

  return true;
}

static inline float
GetNumberOrPercent(const nsCSSValue &aValue)
{
  nsCSSUnit unit = aValue.GetUnit();
  MOZ_ASSERT(unit == eCSSUnit_Number || unit == eCSSUnit_Percent,
             "unexpected unit");
  return (unit == eCSSUnit_Number) ?
    aValue.GetFloatValue() : aValue.GetPercentValue();
}

static inline void
AddCSSValuePercentNumber(const uint32_t aValueRestrictions,
                         double aCoeff1, const nsCSSValue &aValue1,
                         double aCoeff2, const nsCSSValue &aValue2,
                         nsCSSValue &aResult, float aInitialVal)
{
  float n1 = GetNumberOrPercent(aValue1);
  float n2 = GetNumberOrPercent(aValue2);

  // Rather than interpolating aValue1 and aValue2 directly, we
  // interpolate their *distances from aInitialVal* (the initial value,
  // which is either 1 or 0 for "filter" functions).  This matters in
  // cases where aInitialVal is nonzero and the coefficients don't add
  // up to 1.  For example, if initialVal is 1, aCoeff1 is 0.5, and
  // aCoeff2 is 0, then we'll return the value halfway between 1 and
  // aValue1, rather than the value halfway between 0 and aValue1.
  // Note that we do something similar in AddTransformScale().
  float result = (n1 - aInitialVal) * aCoeff1 + (n2 - aInitialVal) * aCoeff2;
  aResult.SetFloatValue(RestrictValue(aValueRestrictions, result + aInitialVal),
                        eCSSUnit_Number);
}

static bool
AddShadowItems(double aCoeff1, const nsCSSValue &aValue1,
               double aCoeff2, const nsCSSValue &aValue2,
               nsCSSValueList **&aResultTail)
{
  // X, Y, Radius, Spread, Color, Inset
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Array,
             "wrong unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Array,
             "wrong unit");
  nsCSSValue::Array *array1 = aValue1.GetArrayValue();
  nsCSSValue::Array *array2 = aValue2.GetArrayValue();
  nsRefPtr<nsCSSValue::Array> resultArray = nsCSSValue::Array::Create(6);

  for (size_t i = 0; i < 4; ++i) {
    AddCSSValuePixel(aCoeff1, array1->Item(i), aCoeff2, array2->Item(i),
                     resultArray->Item(i),
                     // blur radius must be nonnegative
                     (i == 2) ? CSS_PROPERTY_VALUE_NONNEGATIVE : 0);
  }

  const nsCSSValue& color1 = array1->Item(4);
  const nsCSSValue& color2 = array2->Item(4);
  const nsCSSValue& inset1 = array1->Item(5);
  const nsCSSValue& inset2 = array2->Item(5);
  if (color1.GetUnit() != color2.GetUnit() ||
      inset1.GetUnit() != inset2.GetUnit()) {
    // We don't know how to animate between color and no-color, or
    // between inset and not-inset.
    return false;
  }

  if (color1.GetUnit() != eCSSUnit_Null) {
    StyleAnimationValue color1Value
      (color1.GetColorValue(), StyleAnimationValue::ColorConstructor);
    StyleAnimationValue color2Value
      (color2.GetColorValue(), StyleAnimationValue::ColorConstructor);
    StyleAnimationValue resultColorValue;
  #ifdef DEBUG
    bool ok =
  #endif
      StyleAnimationValue::AddWeighted(eCSSProperty_color,
                                       aCoeff1, color1Value,
                                       aCoeff2, color2Value,
                                       resultColorValue);
    MOZ_ASSERT(ok, "should not fail");
    resultArray->Item(4).SetColorValue(resultColorValue.GetColorValue());
  }

  MOZ_ASSERT(inset1 == inset2, "should match");
  resultArray->Item(5) = inset1;

  nsCSSValueList *resultItem = new nsCSSValueList;
  resultItem->mValue.SetArrayValue(resultArray, eCSSUnit_Array);
  *aResultTail = resultItem;
  aResultTail = &resultItem->mNext;
  return true;
}

static void
AddTransformTranslate(double aCoeff1, const nsCSSValue &aValue1,
                      double aCoeff2, const nsCSSValue &aValue2,
                      nsCSSValue &aResult)
{
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Percent ||
             aValue1.GetUnit() == eCSSUnit_Pixel ||
            aValue1.IsCalcUnit(),
            "unexpected unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Percent ||
             aValue2.GetUnit() == eCSSUnit_Pixel ||
             aValue2.IsCalcUnit(),
             "unexpected unit");

  if (aValue1.GetUnit() != aValue2.GetUnit() || aValue1.IsCalcUnit()) {
    // different units; create a calc() expression
    AddCSSValueCanonicalCalc(aCoeff1, aValue1, aCoeff2, aValue2, aResult);
  } else if (aValue1.GetUnit() == eCSSUnit_Percent) {
    // both percent
    AddCSSValuePercent(aCoeff1, aValue1, aCoeff2, aValue2, aResult);
  } else {
    // both pixels
    AddCSSValuePixel(aCoeff1, aValue1, aCoeff2, aValue2, aResult);
  }
}

static void
AddTransformScale(double aCoeff1, const nsCSSValue &aValue1,
                  double aCoeff2, const nsCSSValue &aValue2,
                  nsCSSValue &aResult)
{
  // Handle scale, and the two matrix components where identity is 1, by
  // subtracting 1, multiplying by the coefficients, and then adding 1
  // back.  This gets the right AddWeighted behavior and gets us the
  // interpolation-against-identity behavior for free.
  MOZ_ASSERT(aValue1.GetUnit() == eCSSUnit_Number, "unexpected unit");
  MOZ_ASSERT(aValue2.GetUnit() == eCSSUnit_Number, "unexpected unit");

  float v1 = aValue1.GetFloatValue() - 1.0f,
        v2 = aValue2.GetFloatValue() - 1.0f;
  float result = v1 * aCoeff1 + v2 * aCoeff2;
  aResult.SetFloatValue(result + 1.0f, eCSSUnit_Number);
}

/* static */ already_AddRefed<nsCSSValue::Array>
StyleAnimationValue::AppendTransformFunction(nsCSSKeyword aTransformFunction,
                                             nsCSSValueList**& aListTail)
{
  nsRefPtr<nsCSSValue::Array> arr = AppendFunction(aTransformFunction);
  nsCSSValueList *item = new nsCSSValueList;
  item->mValue.SetArrayValue(arr, eCSSUnit_Function);

  *aListTail = item;
  aListTail = &item->mNext;

  return arr.forget();
}

/*
 * The relevant section of the transitions specification:
 * http://dev.w3.org/csswg/css3-transitions/#animation-of-property-types-
 * defers all of the details to the 2-D and 3-D transforms specifications.
 * For the 2-D transforms specification (all that's relevant for us, right
 * now), the relevant section is:
 * http://dev.w3.org/csswg/css3-2d-transforms/#animation
 * This, in turn, refers to the unmatrix program in Graphics Gems,
 * available from http://tog.acm.org/resources/GraphicsGems/ , and in
 * particular as the file GraphicsGems/gemsii/unmatrix.c
 * in http://tog.acm.org/resources/GraphicsGems/AllGems.tar.gz
 *
 * The unmatrix reference is for general 3-D transform matrices (any of the
 * 16 components can have any value).
 *
 * For CSS 2-D transforms, we have a 2-D matrix with the bottom row constant:
 *
 * [ A C E ]
 * [ B D F ]
 * [ 0 0 1 ]
 *
 * For that case, I believe the algorithm in unmatrix reduces to:
 *
 *  (1) If A * D - B * C == 0, the matrix is singular.  Fail.
 *
 *  (2) Set translation components (Tx and Ty) to the translation parts of
 *      the matrix (E and F) and then ignore them for the rest of the time.
 *      (For us, E and F each actually consist of three constants:  a
 *      length, a multiplier for the width, and a multiplier for the
 *      height.  This actually requires its own decomposition, but I'll
 *      keep that separate.)
 *
 *  (3) Let the X scale (Sx) be sqrt(A^2 + B^2).  Then divide both A and B
 *      by it.
 *
 *  (4) Let the XY shear (K) be A * C + B * D.  From C, subtract A times
 *      the XY shear.  From D, subtract B times the XY shear.
 *
 *  (5) Let the Y scale (Sy) be sqrt(C^2 + D^2).  Divide C, D, and the XY
 *      shear (K) by it.
 *
 *  (6) At this point, A * D - B * C is either 1 or -1.  If it is -1,
 *      negate the XY shear (K), the X scale (Sx), and A, B, C, and D.
 *      (Alternatively, we could negate the XY shear (K) and the Y scale
 *      (Sy).)
 *
 *  (7) Let the rotation be R = atan2(B, A).
 *
 * Then the resulting decomposed transformation is:
 *
 *   translate(Tx, Ty) rotate(R) skewX(atan(K)) scale(Sx, Sy)
 *
 * An interesting result of this is that all of the simple transform
 * functions (i.e., all functions other than matrix()), in isolation,
 * decompose back to themselves except for:
 *   'skewY(φ)', which is 'matrix(1, tan(φ), 0, 1, 0, 0)', which decomposes
 *   to 'rotate(φ) skewX(φ) scale(sec(φ), cos(φ))' since (ignoring the
 *   alternate sign possibilities that would get fixed in step 6):
 *     In step 3, the X scale factor is sqrt(1+tan²(φ)) = sqrt(sec²(φ)) = sec(φ).
 *     Thus, after step 3, A = 1/sec(φ) = cos(φ) and B = tan(φ) / sec(φ) = sin(φ).
 *     In step 4, the XY shear is sin(φ).
 *     Thus, after step 4, C = -cos(φ)sin(φ) and D = 1 - sin²(φ) = cos²(φ).
 *     Thus, in step 5, the Y scale is sqrt(cos²(φ)(sin²(φ) + cos²(φ)) = cos(φ).
 *     Thus, after step 5, C = -sin(φ), D = cos(φ), and the XY shear is tan(φ).
 *     Thus, in step 6, A * D - B * C = cos²(φ) + sin²(φ) = 1.
 *     In step 7, the rotation is thus φ.
 *
 *   skew(θ, φ), which is matrix(1, tan(φ), tan(θ), 1, 0, 0), which decomposes
 *   to 'rotate(φ) skewX(θ + φ) scale(sec(φ), cos(φ))' since (ignoring
 *   the alternate sign possibilities that would get fixed in step 6):
 *     In step 3, the X scale factor is sqrt(1+tan²(φ)) = sqrt(sec²(φ)) = sec(φ).
 *     Thus, after step 3, A = 1/sec(φ) = cos(φ) and B = tan(φ) / sec(φ) = sin(φ).
 *     In step 4, the XY shear is cos(φ)tan(θ) + sin(φ).
 *     Thus, after step 4,
 *     C = tan(θ) - cos(φ)(cos(φ)tan(θ) + sin(φ)) = tan(θ)sin²(φ) - cos(φ)sin(φ)
 *     D = 1 - sin(φ)(cos(φ)tan(θ) + sin(φ)) = cos²(φ) - sin(φ)cos(φ)tan(θ)
 *     Thus, in step 5, the Y scale is sqrt(C² + D²) =
 *     sqrt(tan²(θ)(sin⁴(φ) + sin²(φ)cos²(φ)) -
 *          2 tan(θ)(sin³(φ)cos(φ) + sin(φ)cos³(φ)) +
 *          (sin²(φ)cos²(φ) + cos⁴(φ))) =
 *     sqrt(tan²(θ)sin²(φ) - 2 tan(θ)sin(φ)cos(φ) + cos²(φ)) =
 *     cos(φ) - tan(θ)sin(φ) (taking the negative of the obvious solution so
 *     we avoid flipping in step 6).
 *     After step 5, C = -sin(φ) and D = cos(φ), and the XY shear is
 *     (cos(φ)tan(θ) + sin(φ)) / (cos(φ) - tan(θ)sin(φ)) =
 *     (dividing both numerator and denominator by cos(φ))
 *     (tan(θ) + tan(φ)) / (1 - tan(θ)tan(φ)) = tan(θ + φ).
 *     (See http://en.wikipedia.org/wiki/List_of_trigonometric_identities .)
 *     Thus, in step 6, A * D - B * C = cos²(φ) + sin²(φ) = 1.
 *     In step 7, the rotation is thus φ.
 *
 *     To check this result, we can multiply things back together:
 *
 *     [ cos(φ) -sin(φ) ] [ 1 tan(θ + φ) ] [ sec(φ)    0   ]
 *     [ sin(φ)  cos(φ) ] [ 0      1     ] [   0    cos(φ) ]
 *
 *     [ cos(φ)      cos(φ)tan(θ + φ) - sin(φ) ] [ sec(φ)    0   ]
 *     [ sin(φ)      sin(φ)tan(θ + φ) + cos(φ) ] [   0    cos(φ) ]
 *
 *     but since tan(θ + φ) = (tan(θ) + tan(φ)) / (1 - tan(θ)tan(φ)),
 *     cos(φ)tan(θ + φ) - sin(φ)
 *      = cos(φ)(tan(θ) + tan(φ)) - sin(φ) + sin(φ)tan(θ)tan(φ)
 *      = cos(φ)tan(θ) + sin(φ) - sin(φ) + sin(φ)tan(θ)tan(φ)
 *      = cos(φ)tan(θ) + sin(φ)tan(θ)tan(φ)
 *      = tan(θ) (cos(φ) + sin(φ)tan(φ))
 *      = tan(θ) sec(φ) (cos²(φ) + sin²(φ))
 *      = tan(θ) sec(φ)
 *     and
 *     sin(φ)tan(θ + φ) + cos(φ)
 *      = sin(φ)(tan(θ) + tan(φ)) + cos(φ) - cos(φ)tan(θ)tan(φ)
 *      = tan(θ) (sin(φ) - sin(φ)) + sin(φ)tan(φ) + cos(φ)
 *      = sec(φ) (sin²(φ) + cos²(φ))
 *      = sec(φ)
 *     so the above is:
 *     [ cos(φ)  tan(θ) sec(φ) ] [ sec(φ)    0   ]
 *     [ sin(φ)     sec(φ)     ] [   0    cos(φ) ]
 *
 *     [    1   tan(θ) ]
 *     [ tan(φ)    1   ]
 */

/*
 * Decompose2DMatrix implements the above decomposition algorithm.
 */

#define XYSHEAR 0
#define XZSHEAR 1
#define YZSHEAR 2

static bool
Decompose2DMatrix(const gfxMatrix &aMatrix, Point3D &aScale,
                  float aShear[3], gfxQuaternion &aRotate,
                  Point3D &aTranslate)
{
  float A = aMatrix._11,
        B = aMatrix._12,
        C = aMatrix._21,
        D = aMatrix._22;
  if (A * D == B * C) {
    // singular matrix
    return false;
  }

  float scaleX = sqrt(A * A + B * B);
  A /= scaleX;
  B /= scaleX;

  float XYshear = A * C + B * D;
  C -= A * XYshear;
  D -= B * XYshear;

  float scaleY = sqrt(C * C + D * D);
  C /= scaleY;
  D /= scaleY;
  XYshear /= scaleY;

  // A*D - B*C should now be 1 or -1
  NS_ASSERTION(0.99 < Abs(A*D - B*C) && Abs(A*D - B*C) < 1.01,
               "determinant should now be 1 or -1");
  if (A * D < B * C) {
    A = -A;
    B = -B;
    C = -C;
    D = -D;
    XYshear = -XYshear;
    scaleX = -scaleX;
  }

  float rotate = atan2f(B, A);
  aRotate = gfxQuaternion(0, 0, sin(rotate/2), cos(rotate/2));
  aShear[XYSHEAR] = XYshear;
  aScale.x = scaleX;
  aScale.y = scaleY;
  aTranslate.x = aMatrix._31;
  aTranslate.y = aMatrix._32;
  return true;
}

/**
 * Implementation of the unmatrix algorithm, specified by:
 *
 * http://dev.w3.org/csswg/css3-2d-transforms/#unmatrix
 *
 * This, in turn, refers to the unmatrix program in Graphics Gems,
 * available from http://tog.acm.org/resources/GraphicsGems/ , and in
 * particular as the file GraphicsGems/gemsii/unmatrix.c
 * in http://tog.acm.org/resources/GraphicsGems/AllGems.tar.gz
 */
static bool
Decompose3DMatrix(const gfx3DMatrix &aMatrix, Point3D &aScale,
                  float aShear[3], gfxQuaternion &aRotate,
                  Point3D &aTranslate, Point4D &aPerspective)
{
  Matrix4x4 local = ToMatrix4x4(aMatrix);

  if (local[3][3] == 0) {
    return false;
  }
  /* Normalize the matrix */
  local.Normalize();

  /**
   * perspective is used to solve for perspective, but it also provides
   * an easy way to test for singularity of the upper 3x3 component.
   */
  Matrix4x4 perspective = local;
  Point4D empty(0, 0, 0, 1);
  perspective.SetTransposedVector(3, empty);

  if (perspective.Determinant() == 0.0) {
    return false;
  }

  /* First, isolate perspective. */
  if (local[0][3] != 0 || local[1][3] != 0 ||
      local[2][3] != 0) {
    /* aPerspective is the right hand side of the equation. */
    aPerspective = local.TransposedVector(3);

    /**
     * Solve the equation by inverting perspective and multiplying
     * aPerspective by the inverse.
     */
    perspective.Invert();
    aPerspective = perspective.TransposeTransform4D(aPerspective);

    /* Clear the perspective partition */
    local.SetTransposedVector(3, empty);
  } else {
    aPerspective = Point4D(0, 0, 0, 1);
  }

  /* Next take care of translation */
  for (int i = 0; i < 3; i++) {
    aTranslate[i] = local[3][i];
    local[3][i] = 0;
  }

  /* Now get scale and shear. */

  /* Compute X scale factor and normalize first row. */
  aScale.x = local[0].Length();
  local[0] /= aScale.x;

  /* Compute XY shear factor and make 2nd local orthogonal to 1st. */
  aShear[XYSHEAR] = local[0].DotProduct(local[1]);
  local[1] -= local[0] * aShear[XYSHEAR];

  /* Now, compute Y scale and normalize 2nd local. */
  aScale.y = local[1].Length();
  local[1] /= aScale.y;
  aShear[XYSHEAR] /= aScale.y;

  /* Compute XZ and YZ shears, make 3rd local orthogonal */
  aShear[XZSHEAR] = local[0].DotProduct(local[2]);
  local[2] -= local[0] * aShear[XZSHEAR];
  aShear[YZSHEAR] = local[1].DotProduct(local[2]);
  local[2] -= local[1] * aShear[YZSHEAR];

  /* Next, get Z scale and normalize 3rd local. */
  aScale.z = local[2].Length();
  local[2] /= aScale.z;

  aShear[XZSHEAR] /= aScale.z;
  aShear[YZSHEAR] /= aScale.z;

  /**
   * At this point, the matrix (in locals) is orthonormal.
   * Check for a coordinate system flip.  If the determinant
   * is -1, then negate the matrix and the scaling factors.
   */
  if (local[0].DotProduct(local[1].CrossProduct(local[2])) < 0) {
    aScale *= -1;
    for (int i = 0; i < 3; i++) {
      local[i] *= -1;
    }
  }

  /* Now, get the rotations out */
  aRotate = gfxQuaternion(local);

  return true;
}

template<typename T>
T InterpolateNumerically(const T& aOne, const T& aTwo, double aCoeff)
{
  return aOne + (aTwo - aOne) * aCoeff;
}


/* static */ gfx3DMatrix
StyleAnimationValue::InterpolateTransformMatrix(const gfx3DMatrix &aMatrix1,
                                                const gfx3DMatrix &aMatrix2,
                                                double aProgress)
{
  // Decompose both matrices

  // TODO: What do we do if one of these returns false (singular matrix)

  Point3D scale1(1, 1, 1), translate1;
  Point4D perspective1(0, 0, 0, 1);
  gfxQuaternion rotate1;
  float shear1[3] = { 0.0f, 0.0f, 0.0f};

  Point3D scale2(1, 1, 1), translate2;
  Point4D perspective2(0, 0, 0, 1);
  gfxQuaternion rotate2;
  float shear2[3] = { 0.0f, 0.0f, 0.0f};

  gfxMatrix matrix2d1, matrix2d2;
  if (aMatrix1.Is2D(&matrix2d1) && aMatrix2.Is2D(&matrix2d2)) {
    Decompose2DMatrix(matrix2d1, scale1, shear1, rotate1, translate1);
    Decompose2DMatrix(matrix2d2, scale2, shear2, rotate2, translate2);
  } else {
    Decompose3DMatrix(aMatrix1, scale1, shear1,
                      rotate1, translate1, perspective1);
    Decompose3DMatrix(aMatrix2, scale2, shear2,
                      rotate2, translate2, perspective2);
  }

  // Interpolate each of the pieces
  Matrix4x4 result;

  Point4D perspective =
    InterpolateNumerically(perspective1, perspective2, aProgress);
  result.SetTransposedVector(3, perspective);

  Point3D translate =
    InterpolateNumerically(translate1, translate2, aProgress);
  result.PreTranslate(translate.x, translate.y, translate.z);

  gfxQuaternion q3 = rotate1.Slerp(rotate2, aProgress);
  Matrix4x4 rotate = q3.ToMatrix();
  if (!rotate.IsIdentity()) {
      result = rotate * result;
  }

  // TODO: Would it be better to interpolate these as angles? How do we convert back to angles?
  float yzshear =
    InterpolateNumerically(shear1[YZSHEAR], shear2[YZSHEAR], aProgress);
  if (yzshear != 0.0) {
    result.SkewYZ(yzshear);
  }

  float xzshear =
    InterpolateNumerically(shear1[XZSHEAR], shear2[XZSHEAR], aProgress);
  if (xzshear != 0.0) {
    result.SkewXZ(xzshear);
  }

  float xyshear =
    InterpolateNumerically(shear1[XYSHEAR], shear2[XYSHEAR], aProgress);
  if (xyshear != 0.0) {
    result.SkewXY(xyshear);
  }

  Point3D scale =
    InterpolateNumerically(scale1, scale2, aProgress);
  if (scale != Point3D(1.0, 1.0, 1.0)) {
    result.PreScale(scale.x, scale.y, scale.z);
  }

  return To3DMatrix(result);
}

static nsCSSValueList*
AddDifferentTransformLists(double aCoeff1, const nsCSSValueList* aList1,
                           double aCoeff2, const nsCSSValueList* aList2)
{
  nsAutoPtr<nsCSSValueList> result;
  nsCSSValueList **resultTail = getter_Transfers(result);

  nsRefPtr<nsCSSValue::Array> arr;
  arr =
    StyleAnimationValue::AppendTransformFunction(eCSSKeyword_interpolatematrix,
                                                 resultTail);

  // FIXME: We should change the other transform code to also only
  // take a single progress value, as having values that don't
  // sum to 1 doesn't make sense for these.
  if (aList1 == aList2) {
    arr->Item(1).Reset();
  } else {
    aList1->CloneInto(arr->Item(1).SetListValue());
  }

  aList2->CloneInto(arr->Item(2).SetListValue());
  arr->Item(3).SetPercentValue(aCoeff2);

  return result.forget();
}

static bool
TransformFunctionsMatch(nsCSSKeyword func1, nsCSSKeyword func2)
{
  return ToPrimitive(func1) == ToPrimitive(func2);
}

static bool
AddFilterFunctionImpl(double aCoeff1, const nsCSSValueList* aList1,
                      double aCoeff2, const nsCSSValueList* aList2,
                      nsCSSValueList**& aResultTail)
{
  // AddFilterFunction should be our only caller, and it should ensure that both
  // args are non-null.
  MOZ_ASSERT(aList1, "expected filter list");
  MOZ_ASSERT(aList2, "expected filter list");
  MOZ_ASSERT(aList1->mValue.GetUnit() == eCSSUnit_Function,
             "expected function");
  MOZ_ASSERT(aList2->mValue.GetUnit() == eCSSUnit_Function,
             "expected function");
  nsRefPtr<nsCSSValue::Array> a1 = aList1->mValue.GetArrayValue(),
                              a2 = aList2->mValue.GetArrayValue();
  nsCSSKeyword filterFunction = a1->Item(0).GetKeywordValue();
  if (filterFunction != a2->Item(0).GetKeywordValue())
    return false; // Can't add two filters of different types.

  nsAutoPtr<nsCSSValueList> resultListEntry(new nsCSSValueList);
  nsCSSValue::Array* result =
    resultListEntry->mValue.InitFunction(filterFunction, 1);

  // "hue-rotate" is the only filter-function that accepts negative values, and
  // we don't use this "restrictions" variable in its clause below.
  const uint32_t restrictions = CSS_PROPERTY_VALUE_NONNEGATIVE;
  const nsCSSValue& funcArg1 = a1->Item(1);
  const nsCSSValue& funcArg2 = a2->Item(1);
  nsCSSValue& resultArg = result->Item(1);
  float initialVal = 1.0f;
  switch (filterFunction) {
    case eCSSKeyword_blur: {
      nsCSSUnit unit;
      if (funcArg1.GetUnit() == funcArg2.GetUnit()) {
        unit = funcArg1.GetUnit();
      } else {
        // If units differ, we'll just combine them with calc().
        unit = eCSSUnit_Calc;
      }
      if (!AddCSSValuePixelPercentCalc(restrictions,
                                       unit,
                                       aCoeff1, funcArg1,
                                       aCoeff2, funcArg2,
                                       resultArg)) {
        return false;
      }
      break;
    }
    case eCSSKeyword_grayscale:
    case eCSSKeyword_invert:
    case eCSSKeyword_sepia:
      initialVal = 0.0f;
    case eCSSKeyword_brightness:
    case eCSSKeyword_contrast:
    case eCSSKeyword_opacity:
    case eCSSKeyword_saturate:
      AddCSSValuePercentNumber(restrictions,
                               aCoeff1, funcArg1,
                               aCoeff2, funcArg2,
                               resultArg,
                               initialVal);
      break;
    case eCSSKeyword_hue_rotate:
      AddCSSValueAngle(aCoeff1, funcArg1,
                       aCoeff2, funcArg2,
                       resultArg);
      break;
    case eCSSKeyword_drop_shadow: {
      nsCSSValueList* resultShadow = resultArg.SetListValue();
      nsAutoPtr<nsCSSValueList> shadowValue;
      nsCSSValueList **shadowTail = getter_Transfers(shadowValue);
      MOZ_ASSERT(!funcArg1.GetListValue()->mNext &&
                 !funcArg2.GetListValue()->mNext,
                 "drop-shadow filter func doesn't support lists");
      if (!AddShadowItems(aCoeff1, funcArg1.GetListValue()->mValue,
                          aCoeff2, funcArg2.GetListValue()->mValue,
                          shadowTail)) {
        return false;
      }
      *resultShadow = *shadowValue;
      break;
    }
    default:
      MOZ_ASSERT(false, "unknown filter function");
      return false;
  }

  *aResultTail = resultListEntry.forget();
  aResultTail = &(*aResultTail)->mNext;

  return true;
}

static bool
AddFilterFunction(double aCoeff1, const nsCSSValueList* aList1,
                  double aCoeff2, const nsCSSValueList* aList2,
                  nsCSSValueList**& aResultTail)
{
  MOZ_ASSERT(aList1 || aList2,
             "one function list item must not be null");
  // Note that one of our arguments could be null, indicating that
  // it's the initial value. Rather than adding special null-handling
  // logic, we just check for null values and replace them with
  // 0 * the other value. That way, AddFilterFunctionImpl can assume
  // its args are non-null.
  if (!aList1) {
    return AddFilterFunctionImpl(aCoeff2, aList2, 0, aList2, aResultTail);
  }
  if (!aList2) {
    return AddFilterFunctionImpl(aCoeff1, aList1, 0, aList1, aResultTail);
  }

  return AddFilterFunctionImpl(aCoeff1, aList1, aCoeff2, aList2, aResultTail);
}

static nsCSSValueList*
AddTransformLists(double aCoeff1, const nsCSSValueList* aList1,
                  double aCoeff2, const nsCSSValueList* aList2)
{
  nsAutoPtr<nsCSSValueList> result;
  nsCSSValueList **resultTail = getter_Transfers(result);

  do {
    nsRefPtr<nsCSSValue::Array> a1 = ToPrimitive(aList1->mValue.GetArrayValue()),
                                a2 = ToPrimitive(aList2->mValue.GetArrayValue());
    MOZ_ASSERT(
      TransformFunctionsMatch(nsStyleTransformMatrix::TransformFunctionOf(a1),
                              nsStyleTransformMatrix::TransformFunctionOf(a2)),
      "transform function mismatch");
    MOZ_ASSERT(!*resultTail,
               "resultTail isn't pointing to the tail (may leak)");

    nsCSSKeyword tfunc = nsStyleTransformMatrix::TransformFunctionOf(a1);
    nsRefPtr<nsCSSValue::Array> arr;
    if (tfunc != eCSSKeyword_matrix &&
        tfunc != eCSSKeyword_matrix3d &&
        tfunc != eCSSKeyword_interpolatematrix &&
        tfunc != eCSSKeyword_rotate3d &&
        tfunc != eCSSKeyword_perspective) {
      arr = StyleAnimationValue::AppendTransformFunction(tfunc, resultTail);
    }

    switch (tfunc) {
      case eCSSKeyword_translate3d: {
          MOZ_ASSERT(a1->Count() == 4, "unexpected count");
          MOZ_ASSERT(a2->Count() == 4, "unexpected count");
          AddTransformTranslate(aCoeff1, a1->Item(1), aCoeff2, a2->Item(1),
                                arr->Item(1));
          AddTransformTranslate(aCoeff1, a1->Item(2), aCoeff2, a2->Item(2),
                                arr->Item(2));
          AddTransformTranslate(aCoeff1, a1->Item(3), aCoeff2, a2->Item(3),
                                arr->Item(3));
          break;
      }
      case eCSSKeyword_scale3d: {
          MOZ_ASSERT(a1->Count() == 4, "unexpected count");
          MOZ_ASSERT(a2->Count() == 4, "unexpected count");

          AddTransformScale(aCoeff1, a1->Item(1), aCoeff2, a2->Item(1),
                            arr->Item(1));
          AddTransformScale(aCoeff1, a1->Item(2), aCoeff2, a2->Item(2),
                            arr->Item(2));
          AddTransformScale(aCoeff1, a1->Item(3), aCoeff2, a2->Item(3),
                            arr->Item(3));

          break;
      }
      // It would probably be nicer to animate skew in tangent space
      // rather than angle space.  However, it's easy to specify
      // skews with infinite tangents, and behavior changes pretty
      // drastically when crossing such skews (since the direction of
      // animation flips), so interop is probably more important here.
      case eCSSKeyword_skew: {
        MOZ_ASSERT(a1->Count() == 2 || a1->Count() == 3,
                   "unexpected count");
        MOZ_ASSERT(a2->Count() == 2 || a2->Count() == 3,
                   "unexpected count");

        nsCSSValue zero(0.0f, eCSSUnit_Radian);
        // Add Y component of skew.
        AddCSSValueAngle(aCoeff1,
                         a1->Count() == 3 ? a1->Item(2) : zero,
                         aCoeff2,
                         a2->Count() == 3 ? a2->Item(2) : zero,
                         arr->Item(2));

        // Add X component of skew (which can be merged with case below
        // in non-DEBUG).
        AddCSSValueAngle(aCoeff1, a1->Item(1), aCoeff2, a2->Item(1),
                         arr->Item(1));

        break;
      }
      case eCSSKeyword_skewx:
      case eCSSKeyword_skewy:
      case eCSSKeyword_rotate:
      case eCSSKeyword_rotatex:
      case eCSSKeyword_rotatey:
      case eCSSKeyword_rotatez: {
        MOZ_ASSERT(a1->Count() == 2, "unexpected count");
        MOZ_ASSERT(a2->Count() == 2, "unexpected count");

        AddCSSValueAngle(aCoeff1, a1->Item(1), aCoeff2, a2->Item(1),
                         arr->Item(1));

        break;
      }
      case eCSSKeyword_rotate3d: {
        Point3D vector1(a1->Item(1).GetFloatValue(),
                        a1->Item(2).GetFloatValue(),
                        a1->Item(3).GetFloatValue());
        vector1.Normalize();
        Point3D vector2(a2->Item(1).GetFloatValue(),
                        a2->Item(2).GetFloatValue(),
                        a2->Item(3).GetFloatValue());
        vector2.Normalize();

        // Handle rotate3d with matched (normalized) vectors,
        // otherwise fallthrough to the next switch statement
        // and do matrix decomposition.
        if (vector1 == vector2) {
          // We skipped appending a transform function above for rotate3d,
          // so do it now.
          arr = StyleAnimationValue::AppendTransformFunction(tfunc, resultTail);
          arr->Item(1).SetFloatValue(vector1.x, eCSSUnit_Number);
          arr->Item(2).SetFloatValue(vector1.y, eCSSUnit_Number);
          arr->Item(3).SetFloatValue(vector1.z, eCSSUnit_Number);

          AddCSSValueAngle(aCoeff1, a1->Item(4), aCoeff2, a2->Item(4),
                           arr->Item(4));
          break;
        }
        // FALL THROUGH
      }
      case eCSSKeyword_matrix:
      case eCSSKeyword_matrix3d:
      case eCSSKeyword_interpolatematrix:
      case eCSSKeyword_perspective: {
        // FIXME: If the matrix contains only numbers then we could decompose
        // here.

        // Construct temporary lists with only this item in them.
        nsCSSValueList tempList1, tempList2;
        tempList1.mValue = aList1->mValue;
        tempList2.mValue = aList2->mValue;

        if (aList1 == aList2) {
          *resultTail =
            AddDifferentTransformLists(aCoeff1, &tempList1, aCoeff2, &tempList1);
        } else {
          *resultTail =
            AddDifferentTransformLists(aCoeff1, &tempList1, aCoeff2, &tempList2);
        }

        // Now advance resultTail to point to the new tail slot.
        while (*resultTail) {
          resultTail = &(*resultTail)->mNext;
        }

        break;
      }
      default:
        MOZ_ASSERT(false, "unknown transform function");
    }

    aList1 = aList1->mNext;
    aList2 = aList2->mNext;
  } while (aList1);
  MOZ_ASSERT(!aList2, "list length mismatch");
  MOZ_ASSERT(!*resultTail,
             "resultTail isn't pointing to the tail");

  return result.forget();
}

static void
AddPositions(double aCoeff1, const nsCSSValue& aPos1,
             double aCoeff2, const nsCSSValue& aPos2,
             nsCSSValue& aResultPos)
{
  const nsCSSValue::Array* posArray1 = aPos1.GetArrayValue();
  const nsCSSValue::Array* posArray2 = aPos2.GetArrayValue();
  nsCSSValue::Array* resultPosArray = nsCSSValue::Array::Create(4);
  aResultPos.SetArrayValue(resultPosArray, eCSSUnit_Array);

  /* Only iterate over elements 1 and 3. The <position> is
   * 'uncomputed' to only those elements.
   */
  for (size_t i = 1; i < 4; i += 2) {
    const nsCSSValue& v1 = posArray1->Item(i);
    const nsCSSValue& v2 = posArray2->Item(i);
    nsCSSValue& vr = resultPosArray->Item(i);
    AddCSSValueCanonicalCalc(aCoeff1, v1,
                             aCoeff2, v2, vr);
  }
}

bool
StyleAnimationValue::AddWeighted(nsCSSProperty aProperty,
                                 double aCoeff1,
                                 const StyleAnimationValue& aValue1,
                                 double aCoeff2,
                                 const StyleAnimationValue& aValue2,
                                 StyleAnimationValue& aResultValue)
{
  Unit commonUnit =
    GetCommonUnit(aProperty, aValue1.GetUnit(), aValue2.GetUnit());
  // Maybe need a followup method to convert the inputs into the common
  // unit-type, if they don't already match it. (Or would it make sense to do
  // that in GetCommonUnit? in which case maybe ConvertToCommonUnit would be
  // better.)

  switch (commonUnit) {
    case eUnit_Null:
    case eUnit_Auto:
    case eUnit_None:
    case eUnit_Normal:
    case eUnit_UnparsedString:
      return false;

    case eUnit_Enumerated:
      switch (aProperty) {
        case eCSSProperty_font_stretch: {
          // Animate just like eUnit_Integer.
          int32_t result = floor(aCoeff1 * double(aValue1.GetIntValue()) +
                                 aCoeff2 * double(aValue2.GetIntValue()));
          if (result < NS_STYLE_FONT_STRETCH_ULTRA_CONDENSED) {
            result = NS_STYLE_FONT_STRETCH_ULTRA_CONDENSED;
          } else if (result > NS_STYLE_FONT_STRETCH_ULTRA_EXPANDED) {
            result = NS_STYLE_FONT_STRETCH_ULTRA_EXPANDED;
          }
          aResultValue.SetIntValue(result, eUnit_Enumerated);
          return true;
        }
        default:
          return false;
      }
    case eUnit_Visibility: {
      int32_t enum1 = aValue1.GetIntValue();
      int32_t enum2 = aValue2.GetIntValue();
      if (enum1 == enum2) {
        aResultValue.SetIntValue(enum1, eUnit_Visibility);
        return true;
      }
      if ((enum1 == NS_STYLE_VISIBILITY_VISIBLE) ==
          (enum2 == NS_STYLE_VISIBILITY_VISIBLE)) {
        return false;
      }
      int32_t val1 = enum1 == NS_STYLE_VISIBILITY_VISIBLE;
      int32_t val2 = enum2 == NS_STYLE_VISIBILITY_VISIBLE;
      double interp = aCoeff1 * val1 + aCoeff2 * val2;
      int32_t result = interp > 0.0 ? NS_STYLE_VISIBILITY_VISIBLE
                                    : (val1 ? enum2 : enum1);
      aResultValue.SetIntValue(result, eUnit_Visibility);
      return true;
    }
    case eUnit_Integer: {
      // http://dev.w3.org/csswg/css3-transitions/#animation-of-property-types-
      // says we should use floor
      int32_t result = floor(aCoeff1 * double(aValue1.GetIntValue()) +
                             aCoeff2 * double(aValue2.GetIntValue()));
      if (aProperty == eCSSProperty_font_weight) {
        if (result < 100) {
          result = 100;
        } else if (result > 900) {
          result = 900;
        }
        result -= result % 100;
      } else {
        result = RestrictValue(aProperty, result);
      }
      aResultValue.SetIntValue(result, eUnit_Integer);
      return true;
    }
    case eUnit_Coord: {
      aResultValue.SetCoordValue(RestrictValue(aProperty, NSToCoordRound(
        aCoeff1 * aValue1.GetCoordValue() +
        aCoeff2 * aValue2.GetCoordValue())));
      return true;
    }
    case eUnit_Percent: {
      aResultValue.SetPercentValue(RestrictValue(aProperty,
        aCoeff1 * aValue1.GetPercentValue() +
        aCoeff2 * aValue2.GetPercentValue()));
      return true;
    }
    case eUnit_Float: {
      aResultValue.SetFloatValue(RestrictValue(aProperty,
        aCoeff1 * aValue1.GetFloatValue() +
        aCoeff2 * aValue2.GetFloatValue()));
      return true;
    }
    case eUnit_Color: {
      nscolor color1 = aValue1.GetColorValue();
      nscolor color2 = aValue2.GetColorValue();
      // FIXME (spec): The CSS transitions spec doesn't say whether
      // colors are premultiplied, but things work better when they are,
      // so use premultiplication.  Spec issue is still open per
      // http://lists.w3.org/Archives/Public/www-style/2009Jul/0050.html

      // To save some math, scale the alpha down to a 0-1 scale, but
      // leave the color components on a 0-255 scale.
      double A1 = NS_GET_A(color1) * (1.0 / 255.0);
      double R1 = NS_GET_R(color1) * A1;
      double G1 = NS_GET_G(color1) * A1;
      double B1 = NS_GET_B(color1) * A1;
      double A2 = NS_GET_A(color2) * (1.0 / 255.0);
      double R2 = NS_GET_R(color2) * A2;
      double G2 = NS_GET_G(color2) * A2;
      double B2 = NS_GET_B(color2) * A2;
      double Aresf = (A1 * aCoeff1 + A2 * aCoeff2);
      nscolor resultColor;
      if (Aresf <= 0.0) {
        resultColor = NS_RGBA(0, 0, 0, 0);
      } else {
        if (Aresf > 1.0) {
          Aresf = 1.0;
        }
        double factor = 1.0 / Aresf;
        uint8_t Ares = NSToIntRound(Aresf * 255.0);
        uint8_t Rres = ClampColor((R1 * aCoeff1 + R2 * aCoeff2) * factor);
        uint8_t Gres = ClampColor((G1 * aCoeff1 + G2 * aCoeff2) * factor);
        uint8_t Bres = ClampColor((B1 * aCoeff1 + B2 * aCoeff2) * factor);
        resultColor = NS_RGBA(Rres, Gres, Bres, Ares);
      }
      aResultValue.SetColorValue(resultColor);
      return true;
    }
    case eUnit_Calc: {
      PixelCalcValue v1 = ExtractCalcValue(aValue1);
      PixelCalcValue v2 = ExtractCalcValue(aValue2);
      double len = aCoeff1 * v1.mLength + aCoeff2 * v2.mLength;
      double pct = aCoeff1 * v1.mPercent + aCoeff2 * v2.mPercent;
      bool hasPct = (aCoeff1 != 0.0 && v1.mHasPercent) ||
                      (aCoeff2 != 0.0 && v2.mHasPercent);
      nsCSSValue *val = new nsCSSValue();
      nsCSSValue::Array *arr = nsCSSValue::Array::Create(1);
      val->SetArrayValue(arr, eCSSUnit_Calc);
      if (hasPct) {
        nsCSSValue::Array *arr2 = nsCSSValue::Array::Create(2);
        arr2->Item(0).SetFloatValue(len, eCSSUnit_Pixel);
        arr2->Item(1).SetPercentValue(pct);
        arr->Item(0).SetArrayValue(arr2, eCSSUnit_Calc_Plus);
      } else {
        arr->Item(0).SetFloatValue(len, eCSSUnit_Pixel);
      }
      aResultValue.SetAndAdoptCSSValueValue(val, eUnit_Calc);
      return true;
    }
    case eUnit_ObjectPosition: {
      const nsCSSValue* position1 = aValue1.GetCSSValueValue();
      const nsCSSValue* position2 = aValue2.GetCSSValueValue();

      nsAutoPtr<nsCSSValue> result(new nsCSSValue);
      AddPositions(aCoeff1, *position1,
                   aCoeff2, *position2, *result);

      aResultValue.SetAndAdoptCSSValueValue(result.forget(),
                                            eUnit_ObjectPosition);
      return true;
    }
    case eUnit_CSSValuePair: {
      const nsCSSValuePair *pair1 = aValue1.GetCSSValuePairValue();
      const nsCSSValuePair *pair2 = aValue2.GetCSSValuePairValue();
      nsCSSUnit unit[2];
      unit[0] = GetCommonUnit(aProperty, pair1->mXValue.GetUnit(),
                              pair2->mXValue.GetUnit());
      unit[1] = GetCommonUnit(aProperty, pair1->mYValue.GetUnit(),
                              pair2->mYValue.GetUnit());
      if (unit[0] == eCSSUnit_Null || unit[1] == eCSSUnit_Null ||
          unit[0] == eCSSUnit_URL || unit[0] == eCSSUnit_Enumerated) {
        return false;
      }

      nsAutoPtr<nsCSSValuePair> result(new nsCSSValuePair);
      static nsCSSValue nsCSSValuePair::* const pairValues[2] = {
        &nsCSSValuePair::mXValue, &nsCSSValuePair::mYValue
      };
      uint32_t restrictions = nsCSSProps::ValueRestrictions(aProperty);
      for (uint32_t i = 0; i < 2; ++i) {
        nsCSSValue nsCSSValuePair::*member = pairValues[i];
        if (!AddCSSValuePixelPercentCalc(restrictions, unit[i],
                                         aCoeff1, pair1->*member,
                                         aCoeff2, pair2->*member,
                                         result->*member) ) {
          MOZ_ASSERT(false, "unexpected unit");
          return false;
        }
      }

      aResultValue.SetAndAdoptCSSValuePairValue(result.forget(),
                                                eUnit_CSSValuePair);
      return true;
    }
    case eUnit_CSSValueTriplet: {
      nsCSSValueTriplet triplet1(*aValue1.GetCSSValueTripletValue());
      nsCSSValueTriplet triplet2(*aValue2.GetCSSValueTripletValue());

      nsCSSUnit unit[3];
      unit[0] = GetCommonUnit(aProperty, triplet1.mXValue.GetUnit(),
                              triplet2.mXValue.GetUnit());
      unit[1] = GetCommonUnit(aProperty, triplet1.mYValue.GetUnit(),
                               triplet2.mYValue.GetUnit());
      unit[2] = GetCommonUnit(aProperty, triplet1.mZValue.GetUnit(),
                              triplet2.mZValue.GetUnit());
      if (unit[0] == eCSSUnit_Null || unit[1] == eCSSUnit_Null ||
          unit[2] == eCSSUnit_Null) {
        return false;
      }

      nsAutoPtr<nsCSSValueTriplet> result(new nsCSSValueTriplet);
      static nsCSSValue nsCSSValueTriplet::* const tripletValues[3] = {
        &nsCSSValueTriplet::mXValue, &nsCSSValueTriplet::mYValue, &nsCSSValueTriplet::mZValue
      };
      uint32_t restrictions = nsCSSProps::ValueRestrictions(aProperty);
      for (uint32_t i = 0; i < 3; ++i) {
        nsCSSValue nsCSSValueTriplet::*member = tripletValues[i];
        if (!AddCSSValuePixelPercentCalc(restrictions, unit[i],
                                         aCoeff1, &triplet1->*member,
                                         aCoeff2, &triplet2->*member,
                                         result->*member) ) {
          MOZ_ASSERT(false, "unexpected unit");
          return false;
        }
      }

      aResultValue.SetAndAdoptCSSValueTripletValue(result.forget(),
                                                   eUnit_CSSValueTriplet);
      return true;
    }
    case eUnit_CSSRect: {
      MOZ_ASSERT(nsCSSProps::ValueRestrictions(aProperty) == 0,
                 "must add code for handling value restrictions");
      const nsCSSRect *rect1 = aValue1.GetCSSRectValue();
      const nsCSSRect *rect2 = aValue2.GetCSSRectValue();
      if (rect1->mTop.GetUnit() != rect2->mTop.GetUnit() ||
          rect1->mRight.GetUnit() != rect2->mRight.GetUnit() ||
          rect1->mBottom.GetUnit() != rect2->mBottom.GetUnit() ||
          rect1->mLeft.GetUnit() != rect2->mLeft.GetUnit()) {
        // At least until we have calc()
        return false;
      }

      nsAutoPtr<nsCSSRect> result(new nsCSSRect);
      for (uint32_t i = 0; i < ArrayLength(nsCSSRect::sides); ++i) {
        nsCSSValue nsCSSRect::*member = nsCSSRect::sides[i];
        MOZ_ASSERT((rect1->*member).GetUnit() == (rect2->*member).GetUnit(),
                   "should have returned above");
        switch ((rect1->*member).GetUnit()) {
          case eCSSUnit_Pixel:
            AddCSSValuePixel(aCoeff1, rect1->*member, aCoeff2, rect2->*member,
                             result->*member);
            break;
          case eCSSUnit_Auto:
            if (float(aCoeff1 + aCoeff2) != 1.0f) {
              // Interpolating between two auto values makes sense;
              // adding in other ratios does not.
              return false;
            }
            (result->*member).SetAutoValue();
            break;
          default:
            MOZ_ASSERT(false, "unexpected unit");
            return false;
        }
      }

      aResultValue.SetAndAdoptCSSRectValue(result.forget(), eUnit_CSSRect);
      return true;
    }
    case eUnit_Dasharray: {
      const nsCSSValueList *list1 = aValue1.GetCSSValueListValue();
      const nsCSSValueList *list2 = aValue2.GetCSSValueListValue();

      uint32_t len1 = 0, len2 = 0;
      for (const nsCSSValueList *v = list1; v; v = v->mNext) {
        ++len1;
      }
      for (const nsCSSValueList *v = list2; v; v = v->mNext) {
        ++len2;
      }
      MOZ_ASSERT(len1 > 0 && len2 > 0, "unexpected length");
      if (list1->mValue.GetUnit() == eCSSUnit_None ||
          list2->mValue.GetUnit() == eCSSUnit_None) {
        // One of our values is "none".  Can't do addition with that.
        MOZ_ASSERT(
          (list1->mValue.GetUnit() != eCSSUnit_None || len1 == 1) &&
          (list2->mValue.GetUnit() != eCSSUnit_None || len2 == 1),
          "multi-value valuelist with 'none' as first element");
        return false;
      }

      nsAutoPtr<nsCSSValueList> result;
      nsCSSValueList **resultTail = getter_Transfers(result);
      for (uint32_t i = 0, i_end = EuclidLCM<uint32_t>(len1, len2); i != i_end; ++i) {
        const nsCSSValue &v1 = list1->mValue;
        const nsCSSValue &v2 = list2->mValue;
        MOZ_ASSERT(v1.GetUnit() == eCSSUnit_Number ||
                   v1.GetUnit() == eCSSUnit_Percent, "unexpected");
        MOZ_ASSERT(v2.GetUnit() == eCSSUnit_Number ||
                   v2.GetUnit() == eCSSUnit_Percent, "unexpected");
        if (v1.GetUnit() != v2.GetUnit()) {
          // Can't animate between lengths and percentages (until calc()).
          return false;
        }

        nsCSSValueList *item = new nsCSSValueList;
        *resultTail = item;
        resultTail = &item->mNext;

        if (v1.GetUnit() == eCSSUnit_Number) {
          AddCSSValueNumber(aCoeff1, v1, aCoeff2, v2, item->mValue,
                            CSS_PROPERTY_VALUE_NONNEGATIVE);
        } else {
          AddCSSValuePercent(aCoeff1, v1, aCoeff2, v2, item->mValue,
                             CSS_PROPERTY_VALUE_NONNEGATIVE);
        }

        list1 = list1->mNext;
        if (!list1) {
          list1 = aValue1.GetCSSValueListValue();
        }
        list2 = list2->mNext;
        if (!list2) {
          list2 = aValue2.GetCSSValueListValue();
        }
      }

      aResultValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                eUnit_Dasharray);
      return true;
    }
    case eUnit_Shadow: {
      // This is implemented according to:
      // http://dev.w3.org/csswg/css3-transitions/#animation-of-property-types-
      // and the third item in the summary of:
      // http://lists.w3.org/Archives/Public/www-style/2009Jul/0050.html
      const nsCSSValueList *shadow1 = aValue1.GetCSSValueListValue();
      const nsCSSValueList *shadow2 = aValue2.GetCSSValueListValue();
      nsAutoPtr<nsCSSValueList> result;
      nsCSSValueList **resultTail = getter_Transfers(result);
      while (shadow1 && shadow2) {
        if (!AddShadowItems(aCoeff1, shadow1->mValue,
                            aCoeff2, shadow2->mValue,
                            resultTail)) {
          return false;
        }
        shadow1 = shadow1->mNext;
        shadow2 = shadow2->mNext;
      }
      if (shadow1 || shadow2) {
        const nsCSSValueList *longShadow;
        double longCoeff;
        if (shadow1) {
          longShadow = shadow1;
          longCoeff = aCoeff1;
        } else {
          longShadow = shadow2;
          longCoeff = aCoeff2;
        }

        while (longShadow) {
          // Passing coefficients that add to less than 1 produces the
          // desired result of interpolating "0 0 0 transparent" with
          // the current shadow.
          if (!AddShadowItems(longCoeff, longShadow->mValue,
                              0.0, longShadow->mValue,
                              resultTail)) {
            return false;
          }

          longShadow = longShadow->mNext;
        }
      }
      aResultValue.SetAndAdoptCSSValueListValue(result.forget(), eUnit_Shadow);
      return true;
    }

    case eUnit_Filter: {
      const nsCSSValueList *list1 = aValue1.GetCSSValueListValue();
      const nsCSSValueList *list2 = aValue2.GetCSSValueListValue();

      nsAutoPtr<nsCSSValueList> result;
      nsCSSValueList **resultTail = getter_Transfers(result);
      while (list1 || list2) {
        MOZ_ASSERT(!*resultTail,
          "resultTail isn't pointing to the tail (may leak)");
        if ((list1 && list1->mValue.GetUnit() != eCSSUnit_Function) ||
            (list2 && list2->mValue.GetUnit() != eCSSUnit_Function)) {
          // If we don't have filter-functions, we must have filter-URLs, which
          // we can't add or interpolate.
          return false;
        }

        if (!AddFilterFunction(aCoeff1, list1, aCoeff2, list2, resultTail)) {
          // filter function mismatch
          return false;
        }

        // move to next list items
        if (list1) {
          list1 = list1->mNext;
        }
        if (list2) {
          list2 = list2->mNext;
        }
      }
      MOZ_ASSERT(!*resultTail,
                 "resultTail isn't pointing to the tail (may leak)");

      aResultValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                eUnit_Filter);
      return true;
    }

    case eUnit_Transform: {
      const nsCSSValueList* list1 = aValue1.GetCSSValueSharedListValue()->mHead;
      const nsCSSValueList* list2 = aValue2.GetCSSValueSharedListValue()->mHead;

      MOZ_ASSERT(list1);
      MOZ_ASSERT(list2);

      // We want to avoid the matrix decomposition when we can, since
      // avoiding it can produce better results both for compound
      // transforms and for skew and skewY (see below).  We can do this
      // in two cases:
      //   (1) if one of the transforms is 'none'
      //   (2) if the lists have the same length and the transform
      //       functions match
      nsAutoPtr<nsCSSValueList> result;
      if (list1->mValue.GetUnit() == eCSSUnit_None) {
        if (list2->mValue.GetUnit() == eCSSUnit_None) {
          result = new nsCSSValueList;
          if (result) {
            result->mValue.SetNoneValue();
          }
        } else {
          result = AddTransformLists(0, list2, aCoeff2, list2);
        }
      } else {
        if (list2->mValue.GetUnit() == eCSSUnit_None) {
          result = AddTransformLists(0, list1, aCoeff1, list1);
        } else {
          bool match = true;

          {
            const nsCSSValueList *item1 = list1, *item2 = list2;
            do {
              nsCSSKeyword func1 = nsStyleTransformMatrix::TransformFunctionOf(
                                     item1->mValue.GetArrayValue());
              nsCSSKeyword func2 = nsStyleTransformMatrix::TransformFunctionOf(
                                     item2->mValue.GetArrayValue());

              if (!TransformFunctionsMatch(func1, func2)) {
                break;
              }

              item1 = item1->mNext;
              item2 = item2->mNext;
            } while (item1 && item2);
            if (item1 || item2) {
              // Either |break| above or length mismatch.
              match = false;
            }
          }

          if (match) {
            result = AddTransformLists(aCoeff1, list1, aCoeff2, list2);
          } else {
            result = AddDifferentTransformLists(aCoeff1, list1, aCoeff2, list2);
          }
        }
      }

      aResultValue.SetTransformValue(new nsCSSValueSharedList(result.forget()));
      return true;
    }
    case eUnit_BackgroundPosition: {
      const nsCSSValueList *position1 = aValue1.GetCSSValueListValue();
      const nsCSSValueList *position2 = aValue2.GetCSSValueListValue();
      nsAutoPtr<nsCSSValueList> result;
      nsCSSValueList **resultTail = getter_Transfers(result);
      while (position1 && position2) {
        nsCSSValueList *item = new nsCSSValueList;
        *resultTail = item;
        resultTail = &item->mNext;

        AddPositions(aCoeff1, position1->mValue,
                     aCoeff2, position2->mValue, item->mValue);

        position1 = position1->mNext;
        position2 = position2->mNext;
      }

      // Check for different lengths
      if (position1 || position2) {
        return false;
      }

      aResultValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                eUnit_BackgroundPosition);
      return true;
    }
    case eUnit_CSSValuePairList: {
      const nsCSSValuePairList *list1 = aValue1.GetCSSValuePairListValue();
      const nsCSSValuePairList *list2 = aValue2.GetCSSValuePairListValue();
      nsAutoPtr<nsCSSValuePairList> result;
      nsCSSValuePairList **resultTail = getter_Transfers(result);
      do {
        nsCSSValuePairList *item = new nsCSSValuePairList;
        *resultTail = item;
        resultTail = &item->mNext;

        static nsCSSValue nsCSSValuePairList::* const pairListValues[] = {
          &nsCSSValuePairList::mXValue,
          &nsCSSValuePairList::mYValue,
        };
        uint32_t restrictions = nsCSSProps::ValueRestrictions(aProperty);
        for (uint32_t i = 0; i < ArrayLength(pairListValues); ++i) {
          const nsCSSValue &v1 = list1->*(pairListValues[i]);
          const nsCSSValue &v2 = list2->*(pairListValues[i]);
          nsCSSValue &vr = item->*(pairListValues[i]);
          nsCSSUnit unit =
            GetCommonUnit(aProperty, v1.GetUnit(), v2.GetUnit());
          if (unit == eCSSUnit_Null) {
            return false;
          }
          if (!AddCSSValuePixelPercentCalc(restrictions, unit, aCoeff1, v1,
                                           aCoeff2, v2, vr) ) {
            if (v1 != v2) {
              return false;
            }
            vr = v1;
          }
        }
        list1 = list1->mNext;
        list2 = list2->mNext;
      } while (list1 && list2);
      if (list1 || list2) {
        // We can't interpolate lists of different lengths.
        return false;
      }

      aResultValue.SetAndAdoptCSSValuePairListValue(result.forget());
      return true;
    }
  }

  MOZ_ASSERT(false, "Can't interpolate using the given common unit");
  return false;
}

already_AddRefed<css::StyleRule>
BuildStyleRule(nsCSSProperty aProperty,
               dom::Element* aTargetElement,
               const nsAString& aSpecifiedValue,
               bool aUseSVGMode)
{
  // Set up an empty CSS Declaration
  nsAutoPtr<css::Declaration> declaration(new css::Declaration());
  declaration->InitializeEmpty();

  bool changed; // ignored, but needed as outparam for ParseProperty
  nsIDocument* doc = aTargetElement->OwnerDoc();
  nsCOMPtr<nsIURI> baseURI = aTargetElement->GetBaseURI();
  nsCSSParser parser(doc->CSSLoader());

  nsCSSProperty propertyToCheck = nsCSSProps::IsShorthand(aProperty) ?
    nsCSSProps::SubpropertyEntryFor(aProperty)[0] : aProperty;

  // Get a parser, parse the property, and check for CSS parsing errors.
  // If this fails, we bail out and delete the declaration.
  parser.ParseProperty(aProperty, aSpecifiedValue, doc->GetDocumentURI(),
                       baseURI, aTargetElement->NodePrincipal(), declaration,
                       &changed, false, aUseSVGMode);

  // check whether property parsed without CSS parsing errors
  if (!declaration->HasNonImportantValueFor(propertyToCheck)) {
    NS_WARNING("failure in BuildStyleRule");
    return nullptr;
  }

  nsRefPtr<css::StyleRule> rule = new css::StyleRule(nullptr,
                                                     declaration.forget(),
                                                     0, 0);
  return rule.forget();
}

inline
already_AddRefed<nsStyleContext>
LookupStyleContext(dom::Element* aElement)
{
  nsIDocument* doc = aElement->GetCurrentDoc();
  nsIPresShell* shell = doc->GetShell();
  if (!shell) {
    return nullptr;
  }
  return nsComputedDOMStyle::GetStyleContextForElement(aElement, nullptr, shell);
}

bool
StyleAnimationValue::ComputeValue(nsCSSProperty aProperty,
                                  dom::Element* aTargetElement,
                                  const nsAString& aSpecifiedValue,
                                  bool aUseSVGMode,
                                  StyleAnimationValue& aComputedValue,
                                  bool* aIsContextSensitive)
{
  MOZ_ASSERT(aTargetElement, "null target element");
  MOZ_ASSERT(aTargetElement->GetCurrentDoc(),
             "we should only be able to actively animate nodes that "
             "are in a document");

  // Parse specified value into a temporary css::StyleRule
  nsRefPtr<css::StyleRule> styleRule =
    BuildStyleRule(aProperty, aTargetElement, aSpecifiedValue, aUseSVGMode);
  if (!styleRule) {
    return false;
  }

  if (nsCSSProps::IsShorthand(aProperty) ||
      nsCSSProps::kAnimTypeTable[aProperty] == eStyleAnimType_None) {
    // Just capture the specified value
    aComputedValue.SetUnparsedStringValue(nsString(aSpecifiedValue));
    if (aIsContextSensitive) {
      // Since we're just returning the string as-is, aComputedValue isn't going
      // to change depending on the context
      *aIsContextSensitive = false;
    }
    return true;
  }

  // Look up style context for our target element
  nsRefPtr<nsStyleContext> styleContext = LookupStyleContext(aTargetElement);
  if (!styleContext) {
    return false;
  }
  nsStyleSet* styleSet = styleContext->PresContext()->StyleSet();

  nsRefPtr<nsStyleContext> tmpStyleContext;
  if (aIsContextSensitive) {
    nsCOMArray<nsIStyleRule> ruleArray;
    ruleArray.AppendObject(styleSet->InitialStyleRule());
    ruleArray.AppendObject(styleRule);
    styleRule->RuleMatched();
    tmpStyleContext =
      styleSet->ResolveStyleByAddingRules(styleContext, ruleArray);
    if (!tmpStyleContext) {
      return false;
    }

    // Force walk of rule tree
    nsStyleStructID sid = nsCSSProps::kSIDTable[aProperty];
    tmpStyleContext->StyleData(sid);

    // If the rule node will have cached style data if the value is not
    // context-sensitive. So if there's nothing cached, it's not context
    // sensitive.
    *aIsContextSensitive =
      !tmpStyleContext->RuleNode()->NodeHasCachedData(sid);
  }

  // If we're not concerned whether the property is context sensitive then just
  // add the rule to a new temporary style context alongside the target
  // element's style context.
  // Also, if we previously discovered that this property IS context-sensitive
  // then we need to throw the temporary style context out since the property's
  // value may have been biased by the 'initial' values supplied.
  if (!aIsContextSensitive || *aIsContextSensitive) {
    nsCOMArray<nsIStyleRule> ruleArray;
    ruleArray.AppendObject(styleRule);
    styleRule->RuleMatched();
    tmpStyleContext =
      styleSet->ResolveStyleByAddingRules(styleContext, ruleArray);
    if (!tmpStyleContext) {
      return false;
    }
  }

  // Extract computed value of our property from the temporary style rule
  return ExtractComputedValue(aProperty, tmpStyleContext, aComputedValue);
}

bool
StyleAnimationValue::UncomputeValue(nsCSSProperty aProperty,
                                    const StyleAnimationValue& aComputedValue,
                                    nsCSSValue& aSpecifiedValue)
{
  Unit unit = aComputedValue.GetUnit();
  switch (unit) {
    case eUnit_Normal:
      aSpecifiedValue.SetNormalValue();
      break;
    case eUnit_Auto:
      aSpecifiedValue.SetAutoValue();
      break;
    case eUnit_None:
      aSpecifiedValue.SetNoneValue();
      break;
    case eUnit_Enumerated:
    case eUnit_Visibility:
      aSpecifiedValue.
        SetIntValue(aComputedValue.GetIntValue(), eCSSUnit_Enumerated);
      break;
    case eUnit_Integer:
      aSpecifiedValue.
        SetIntValue(aComputedValue.GetIntValue(), eCSSUnit_Integer);
      break;
    case eUnit_Coord:
      nscoordToCSSValue(aComputedValue.GetCoordValue(), aSpecifiedValue);
      break;
    case eUnit_Percent:
      aSpecifiedValue.SetPercentValue(aComputedValue.GetPercentValue());
      break;
    case eUnit_Float:
      aSpecifiedValue.
        SetFloatValue(aComputedValue.GetFloatValue(), eCSSUnit_Number);
      break;
    case eUnit_Color:
      // colors can be alone, or part of a paint server
      aSpecifiedValue.SetColorValue(aComputedValue.GetColorValue());
      break;
    case eUnit_Calc:
    case eUnit_ObjectPosition: {
      nsCSSValue* val = aComputedValue.GetCSSValueValue();
      // Sanity-check that the underlying unit in the nsCSSValue is what we
      // expect for our StyleAnimationValue::Unit:
      MOZ_ASSERT((unit == eUnit_Calc && val->GetUnit() == eCSSUnit_Calc) ||
                 (unit == eUnit_ObjectPosition &&
                  val->GetUnit() == eCSSUnit_Array),
                 "unexpected unit");
      aSpecifiedValue = *val;
      break;
    }
    case eUnit_CSSValuePair: {
      // Rule node processing expects pair values to be collapsed to a
      // single value if both halves would be equal, for most but not
      // all properties.  At present, all animatable properties that
      // use pairs do expect collapsing.
      const nsCSSValuePair* pair = aComputedValue.GetCSSValuePairValue();
      if (pair->mXValue == pair->mYValue) {
        aSpecifiedValue = pair->mXValue;
      } else {
        aSpecifiedValue.SetPairValue(pair);
      }
    } break;
    case eUnit_CSSValueTriplet: {
      // Rule node processing expects triplet values to be collapsed to a
      // single value if both halves would be equal, for most but not
      // all properties.  At present, all animatable properties that
      // use pairs do expect collapsing.
      const nsCSSValueTriplet* triplet = aComputedValue.GetCSSValueTripletValue();
      if (triplet->mXValue == triplet->mYValue && triplet->mYValue == triplet->mZValue) {
        aSpecifiedValue = triplet->mXValue;
      } else {
        aSpecifiedValue.SetTripletValue(triplet);
      }
    } break;
    case eUnit_CSSRect: {
      nsCSSRect& rect = aSpecifiedValue.SetRectValue();
      rect = *aComputedValue.GetCSSRectValue();
    } break;
    case eUnit_Dasharray:
    case eUnit_Shadow:
    case eUnit_Filter:
    case eUnit_BackgroundPosition:
      aSpecifiedValue.
        SetDependentListValue(aComputedValue.GetCSSValueListValue());
      break;
    case eUnit_Transform:
      aSpecifiedValue.
        SetSharedListValue(aComputedValue.GetCSSValueSharedListValue());
      break;
    case eUnit_CSSValuePairList:
      aSpecifiedValue.
        SetDependentPairListValue(aComputedValue.GetCSSValuePairListValue());
      break;
    default:
      return false;
  }
  return true;
}

bool
StyleAnimationValue::UncomputeValue(nsCSSProperty aProperty,
                                    const StyleAnimationValue& aComputedValue,
                                    nsAString& aSpecifiedValue)
{
  aSpecifiedValue.Truncate(); // Clear outparam, if it's not already empty

  if (aComputedValue.GetUnit() == eUnit_UnparsedString) {
    aComputedValue.GetStringValue(aSpecifiedValue);
    return true;
  }
  nsCSSValue val;
  if (!StyleAnimationValue::UncomputeValue(aProperty, aComputedValue, val)) {
    return false;
  }

  val.AppendToString(aProperty, aSpecifiedValue, nsCSSValue::eNormalized);
  return true;
}

inline const void*
StyleDataAtOffset(const void* aStyleStruct, ptrdiff_t aOffset)
{
  return reinterpret_cast<const char*>(aStyleStruct) + aOffset;
}

inline void*
StyleDataAtOffset(void* aStyleStruct, ptrdiff_t aOffset)
{
  return reinterpret_cast<char*>(aStyleStruct) + aOffset;
}

static void
ExtractBorderColor(nsStyleContext* aStyleContext, const void* aStyleBorder,
                   mozilla::css::Side aSide,
                   StyleAnimationValue& aComputedValue)
{
  nscolor color;
  bool foreground;
  static_cast<const nsStyleBorder*>(aStyleBorder)->
    GetBorderColor(aSide, color, foreground);
  if (foreground) {
    // FIXME: should add test for this
    color = aStyleContext->StyleColor()->mColor;
  }
  aComputedValue.SetColorValue(color);
}

static bool
StyleCoordToValue(const nsStyleCoord& aCoord, StyleAnimationValue& aValue)
{
  switch (aCoord.GetUnit()) {
    case eStyleUnit_Normal:
      aValue.SetNormalValue();
      break;
    case eStyleUnit_Auto:
      aValue.SetAutoValue();
      break;
    case eStyleUnit_None:
      aValue.SetNoneValue();
      break;
    case eStyleUnit_Percent:
      aValue.SetPercentValue(aCoord.GetPercentValue());
      break;
    case eStyleUnit_Factor:
      aValue.SetFloatValue(aCoord.GetFactorValue());
      break;
    case eStyleUnit_Coord:
      aValue.SetCoordValue(aCoord.GetCoordValue());
      break;
    case eStyleUnit_Enumerated:
      aValue.SetIntValue(aCoord.GetIntValue(),
                         StyleAnimationValue::eUnit_Enumerated);
      break;
    case eStyleUnit_Integer:
      aValue.SetIntValue(aCoord.GetIntValue(),
                         StyleAnimationValue::eUnit_Integer);
      break;
    case eStyleUnit_Calc: {
      nsAutoPtr<nsCSSValue> val(new nsCSSValue);
      SetCalcValue(aCoord.GetCalcValue(), *val);
      aValue.SetAndAdoptCSSValueValue(val.forget(),
                                      StyleAnimationValue::eUnit_Calc);
      break;
    }
    default:
      return false;
  }
  return true;
}

static bool
StyleCoordToCSSValue(const nsStyleCoord& aCoord, nsCSSValue& aCSSValue)
{
  switch (aCoord.GetUnit()) {
    case eStyleUnit_Coord:
      nscoordToCSSValue(aCoord.GetCoordValue(), aCSSValue);
      break;
    case eStyleUnit_Factor:
      aCSSValue.SetFloatValue(aCoord.GetFactorValue(), eCSSUnit_Number);
      break;
    case eStyleUnit_Percent:
      aCSSValue.SetPercentValue(aCoord.GetPercentValue());
      break;
    case eStyleUnit_Calc:
      SetCalcValue(aCoord.GetCalcValue(), aCSSValue);
      break;
    case eStyleUnit_Degree:
      aCSSValue.SetFloatValue(aCoord.GetAngleValue(), eCSSUnit_Degree);
      break;
    case eStyleUnit_Grad:
      aCSSValue.SetFloatValue(aCoord.GetAngleValue(), eCSSUnit_Grad);
      break;
    case eStyleUnit_Radian:
      aCSSValue.SetFloatValue(aCoord.GetAngleValue(), eCSSUnit_Radian);
      break;
    case eStyleUnit_Turn:
      aCSSValue.SetFloatValue(aCoord.GetAngleValue(), eCSSUnit_Turn);
      break;
    default:
      MOZ_ASSERT(false, "unexpected unit");
      return false;
  }
  return true;
}

static void
SetPositionValue(const nsStyleBackground::Position& aPos, nsCSSValue& aCSSValue)
{
  nsRefPtr<nsCSSValue::Array> posArray = nsCSSValue::Array::Create(4);
  aCSSValue.SetArrayValue(posArray.get(), eCSSUnit_Array);

  // NOTE: Array entries #0 and #2 here are intentionally left untouched, with
  // eCSSUnit_Null.  The purpose of these entries in our specified-style
  // <position> representation is to store edge names.  But for values
  // extracted from computed style (which is what we're dealing with here),
  // we'll just have a normalized "x,y" position, with no edge names needed.
  nsCSSValue& xValue = posArray->Item(1);
  nsCSSValue& yValue = posArray->Item(3);

  SetCalcValue(&aPos.mXPosition, xValue);
  SetCalcValue(&aPos.mYPosition, yValue);
}

/*
 * Assign |aOutput = aInput|, except with any non-pixel lengths
 * replaced with the equivalent in pixels, and any non-canonical calc()
 * expressions replaced with canonical ones.
 */
static void
SubstitutePixelValues(nsStyleContext* aStyleContext,
                      const nsCSSValue& aInput, nsCSSValue& aOutput)
{
  if (aInput.IsCalcUnit()) {
    bool canStoreInRuleTree = true;
    nsRuleNode::ComputedCalc c =
      nsRuleNode::SpecifiedCalcToComputedCalc(aInput, aStyleContext,
                                              aStyleContext->PresContext(),
                                              canStoreInRuleTree);
    nsStyleCoord::CalcValue c2;
    c2.mLength = c.mLength;
    c2.mPercent = c.mPercent;
    c2.mHasPercent = true; // doesn't matter for transform translate
    SetCalcValue(&c2, aOutput);
  } else if (aInput.UnitHasArrayValue()) {
    const nsCSSValue::Array *inputArray = aInput.GetArrayValue();
    nsRefPtr<nsCSSValue::Array> outputArray =
      nsCSSValue::Array::Create(inputArray->Count());
    for (size_t i = 0, i_end = inputArray->Count(); i < i_end; ++i) {
      SubstitutePixelValues(aStyleContext,
                            inputArray->Item(i), outputArray->Item(i));
    }
    aOutput.SetArrayValue(outputArray, aInput.GetUnit());
  } else if (aInput.IsLengthUnit() &&
             aInput.GetUnit() != eCSSUnit_Pixel) {
    bool canStoreInRuleTree = true;
    nscoord len = nsRuleNode::CalcLength(aInput, aStyleContext,
                                         aStyleContext->PresContext(),
                                         canStoreInRuleTree);
    aOutput.SetFloatValue(nsPresContext::AppUnitsToFloatCSSPixels(len),
                          eCSSUnit_Pixel);
  } else {
    aOutput = aInput;
  }
}

bool
StyleAnimationValue::ExtractComputedValue(nsCSSProperty aProperty,
                                          nsStyleContext* aStyleContext,
                                          StyleAnimationValue& aComputedValue)
{
  MOZ_ASSERT(0 <= aProperty && aProperty < eCSSProperty_COUNT_no_shorthands,
             "bad property");
  const void* styleStruct =
    aStyleContext->StyleData(nsCSSProps::kSIDTable[aProperty]);
  ptrdiff_t ssOffset = nsCSSProps::kStyleStructOffsetTable[aProperty];
  nsStyleAnimType animType = nsCSSProps::kAnimTypeTable[aProperty];
  MOZ_ASSERT(0 <= ssOffset || animType == eStyleAnimType_Custom,
             "must be dealing with animatable property");
  switch (animType) {
    case eStyleAnimType_Custom:
      switch (aProperty) {
        // For border-width, ignore the border-image business (which
        // only exists until we update our implementation to the current
        // spec) and use GetComputedBorder

        #define BORDER_WIDTH_CASE(prop_, side_)                               \
        case prop_:                                                           \
          aComputedValue.SetCoordValue(                                       \
            static_cast<const nsStyleBorder*>(styleStruct)->                  \
              GetComputedBorder().side_);                                     \
          break;
        BORDER_WIDTH_CASE(eCSSProperty_border_bottom_width, bottom)
        BORDER_WIDTH_CASE(eCSSProperty_border_left_width, left)
        BORDER_WIDTH_CASE(eCSSProperty_border_right_width, right)
        BORDER_WIDTH_CASE(eCSSProperty_border_top_width, top)
        #undef BORDER_WIDTH_CASE

        case eCSSProperty__moz_column_rule_width:
          aComputedValue.SetCoordValue(
            static_cast<const nsStyleColumn*>(styleStruct)->
              GetComputedColumnRuleWidth());
          break;

        case eCSSProperty_border_bottom_color:
          ExtractBorderColor(aStyleContext, styleStruct, NS_SIDE_BOTTOM,
                             aComputedValue);
          break;
        case eCSSProperty_border_left_color:
          ExtractBorderColor(aStyleContext, styleStruct, NS_SIDE_LEFT,
                             aComputedValue);
          break;
        case eCSSProperty_border_right_color:
          ExtractBorderColor(aStyleContext, styleStruct, NS_SIDE_RIGHT,
                             aComputedValue);
          break;
        case eCSSProperty_border_top_color:
          ExtractBorderColor(aStyleContext, styleStruct, NS_SIDE_TOP,
                             aComputedValue);
          break;

        case eCSSProperty_outline_color: {
          const nsStyleOutline *styleOutline =
            static_cast<const nsStyleOutline*>(styleStruct);
          nscolor color;
          if (!styleOutline->GetOutlineColor(color))
            color = aStyleContext->StyleColor()->mColor;
          aComputedValue.SetColorValue(color);
          break;
        }

        case eCSSProperty__moz_column_rule_color: {
          const nsStyleColumn *styleColumn =
            static_cast<const nsStyleColumn*>(styleStruct);
          nscolor color;
          if (styleColumn->mColumnRuleColorIsForeground) {
            color = aStyleContext->StyleColor()->mColor;
          } else {
            color = styleColumn->mColumnRuleColor;
          }
          aComputedValue.SetColorValue(color);
          break;
        }

        case eCSSProperty__moz_column_count: {
          const nsStyleColumn *styleColumn =
            static_cast<const nsStyleColumn*>(styleStruct);
          if (styleColumn->mColumnCount == NS_STYLE_COLUMN_COUNT_AUTO) {
            aComputedValue.SetAutoValue();
          } else {
            aComputedValue.SetIntValue(styleColumn->mColumnCount,
                                       eUnit_Integer);
          }
          break;
        }

        case eCSSProperty_order: {
          const nsStylePosition *stylePosition =
            static_cast<const nsStylePosition*>(styleStruct);
          aComputedValue.SetIntValue(stylePosition->mOrder,
                                     eUnit_Integer);
          break;
        }

        case eCSSProperty_text_decoration_color: {
          const nsStyleTextReset *styleTextReset =
            static_cast<const nsStyleTextReset*>(styleStruct);
          nscolor color;
          bool isForeground;
          styleTextReset->GetDecorationColor(color, isForeground);
          if (isForeground) {
            color = aStyleContext->StyleColor()->mColor;
          }
          aComputedValue.SetColorValue(color);
          break;
        }

        case eCSSProperty_text_decoration_style: {
          uint8_t decorationStyle =
            static_cast<const nsStyleTextReset*>(styleStruct)->
              GetDecorationStyle();
          aComputedValue.SetIntValue(decorationStyle, eUnit_Enumerated);
          break;
        }

        case eCSSProperty_border_spacing: {
          const nsStyleTableBorder *styleTableBorder =
            static_cast<const nsStyleTableBorder*>(styleStruct);
          nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
          nscoordToCSSValue(styleTableBorder->mBorderSpacingCol, pair->mXValue);
          nscoordToCSSValue(styleTableBorder->mBorderSpacingRow, pair->mYValue);
          aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                      eUnit_CSSValuePair);
          break;
        }

        case eCSSProperty_transform_origin: {
          const nsStyleDisplay *styleDisplay =
            static_cast<const nsStyleDisplay*>(styleStruct);
          nsAutoPtr<nsCSSValueTriplet> triplet(new nsCSSValueTriplet);
          if (!StyleCoordToCSSValue(styleDisplay->mTransformOrigin[0],
                                    triplet->mXValue) ||
              !StyleCoordToCSSValue(styleDisplay->mTransformOrigin[1],
                                    triplet->mYValue) ||
              !StyleCoordToCSSValue(styleDisplay->mTransformOrigin[2],
                                    triplet->mZValue)) {
            return false;
          }
          aComputedValue.SetAndAdoptCSSValueTripletValue(triplet.forget(),
                                                         eUnit_CSSValueTriplet);
          break;
        }

        case eCSSProperty_perspective_origin: {
          const nsStyleDisplay *styleDisplay =
            static_cast<const nsStyleDisplay*>(styleStruct);
          nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
          if (!StyleCoordToCSSValue(styleDisplay->mPerspectiveOrigin[0],
                                    pair->mXValue) ||
              !StyleCoordToCSSValue(styleDisplay->mPerspectiveOrigin[1],
                                    pair->mYValue)) {
            return false;
          }
          aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                      eUnit_CSSValuePair);
          break;
        }

        case eCSSProperty_stroke_dasharray: {
          const nsStyleSVG *svg = static_cast<const nsStyleSVG*>(styleStruct);
          MOZ_ASSERT((svg->mStrokeDasharray != nullptr) ==
                     (svg->mStrokeDasharrayLength != 0),
                     "pointer/length mismatch");
          nsAutoPtr<nsCSSValueList> result;
          if (svg->mStrokeDasharray) {
            MOZ_ASSERT(svg->mStrokeDasharrayLength > 0,
                       "non-null list should have positive length");
            nsCSSValueList **resultTail = getter_Transfers(result);
            for (uint32_t i = 0, i_end = svg->mStrokeDasharrayLength;
                 i != i_end; ++i) {
              nsCSSValueList *item = new nsCSSValueList;
              *resultTail = item;
              resultTail = &item->mNext;

              const nsStyleCoord &coord = svg->mStrokeDasharray[i];
              nsCSSValue &value = item->mValue;
              switch (coord.GetUnit()) {
                case eStyleUnit_Coord:
                  // Number means the same thing as length; we want to
                  // animate them the same way.  Normalize both to number
                  // since it has more accuracy (float vs nscoord).
                  value.SetFloatValue(nsPresContext::
                    AppUnitsToFloatCSSPixels(coord.GetCoordValue()),
                    eCSSUnit_Number);
                  break;
                case eStyleUnit_Factor:
                  value.SetFloatValue(coord.GetFactorValue(),
                                      eCSSUnit_Number);
                  break;
                case eStyleUnit_Percent:
                  value.SetPercentValue(coord.GetPercentValue());
                  break;
                default:
                  MOZ_ASSERT(false, "unexpected unit");
                  return false;
              }
            }
          } else {
            result = new nsCSSValueList;
            result->mValue.SetNoneValue();
          }
          aComputedValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                      eUnit_Dasharray);
          break;
        }

        case eCSSProperty_font_stretch: {
          int16_t stretch =
            static_cast<const nsStyleFont*>(styleStruct)->mFont.stretch;
          static_assert(NS_STYLE_FONT_STRETCH_ULTRA_CONDENSED == -4 &&
                        NS_STYLE_FONT_STRETCH_ULTRA_EXPANDED == 4,
                        "font stretch constants not as expected");
          if (stretch < NS_STYLE_FONT_STRETCH_ULTRA_CONDENSED ||
              stretch > NS_STYLE_FONT_STRETCH_ULTRA_EXPANDED) {
            return false;
          }
          aComputedValue.SetIntValue(stretch, eUnit_Enumerated);
          return true;
        }

        case eCSSProperty_font_weight: {
          uint16_t weight =
            static_cast<const nsStyleFont*>(styleStruct)->mFont.weight;
          if (weight % 100 != 0) {
            return false;
          }
          aComputedValue.SetIntValue(weight, eUnit_Integer);
          return true;
        }

        case eCSSProperty_image_region: {
          const nsStyleList *list =
            static_cast<const nsStyleList*>(styleStruct);
          const nsRect &srect = list->mImageRegion;
          if (srect.IsEmpty()) {
            aComputedValue.SetAutoValue();
            break;
          }

          nsCSSRect *vrect = new nsCSSRect;
          nscoordToCSSValue(srect.x, vrect->mLeft);
          nscoordToCSSValue(srect.y, vrect->mTop);
          nscoordToCSSValue(srect.XMost(), vrect->mRight);
          nscoordToCSSValue(srect.YMost(), vrect->mBottom);
          aComputedValue.SetAndAdoptCSSRectValue(vrect, eUnit_CSSRect);
          break;
        }

        case eCSSProperty_clip: {
          const nsStyleDisplay *display =
            static_cast<const nsStyleDisplay*>(styleStruct);
          if (!(display->mClipFlags & NS_STYLE_CLIP_RECT)) {
            aComputedValue.SetAutoValue();
          } else {
            nsCSSRect *vrect = new nsCSSRect;
            const nsRect &srect = display->mClip;
            if (display->mClipFlags & NS_STYLE_CLIP_TOP_AUTO) {
              vrect->mTop.SetAutoValue();
            } else {
              nscoordToCSSValue(srect.y, vrect->mTop);
            }
            if (display->mClipFlags & NS_STYLE_CLIP_RIGHT_AUTO) {
              vrect->mRight.SetAutoValue();
            } else {
              nscoordToCSSValue(srect.XMost(), vrect->mRight);
            }
            if (display->mClipFlags & NS_STYLE_CLIP_BOTTOM_AUTO) {
              vrect->mBottom.SetAutoValue();
            } else {
              nscoordToCSSValue(srect.YMost(), vrect->mBottom);
            }
            if (display->mClipFlags & NS_STYLE_CLIP_LEFT_AUTO) {
              vrect->mLeft.SetAutoValue();
            } else {
              nscoordToCSSValue(srect.x, vrect->mLeft);
            }
            aComputedValue.SetAndAdoptCSSRectValue(vrect, eUnit_CSSRect);
          }
          break;
        }

        case eCSSProperty_object_position: {
          const nsStylePosition* stylePos =
            static_cast<const nsStylePosition*>(styleStruct);

          nsAutoPtr<nsCSSValue> val(new nsCSSValue);
          SetPositionValue(stylePos->mObjectPosition, *val);

          aComputedValue.SetAndAdoptCSSValueValue(val.forget(),
                                                  eUnit_ObjectPosition);
          break;
        }

        case eCSSProperty_background_position: {
          const nsStyleBackground *bg =
            static_cast<const nsStyleBackground*>(styleStruct);
          nsAutoPtr<nsCSSValueList> result;
          nsCSSValueList **resultTail = getter_Transfers(result);
          MOZ_ASSERT(bg->mPositionCount > 0, "unexpected count");
          for (uint32_t i = 0, i_end = bg->mPositionCount; i != i_end; ++i) {
            nsCSSValueList *item = new nsCSSValueList;
            *resultTail = item;
            resultTail = &item->mNext;
            SetPositionValue(bg->mLayers[i].mPosition, item->mValue);
          }

          aComputedValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                      eUnit_BackgroundPosition);
          break;
        }

        case eCSSProperty_background_size: {
          const nsStyleBackground *bg =
            static_cast<const nsStyleBackground*>(styleStruct);
          nsAutoPtr<nsCSSValuePairList> result;
          nsCSSValuePairList **resultTail = getter_Transfers(result);
          MOZ_ASSERT(bg->mSizeCount > 0, "unexpected count");
          for (uint32_t i = 0, i_end = bg->mSizeCount; i != i_end; ++i) {
            nsCSSValuePairList *item = new nsCSSValuePairList;
            *resultTail = item;
            resultTail = &item->mNext;

            const nsStyleBackground::Size &size = bg->mLayers[i].mSize;
            switch (size.mWidthType) {
              case nsStyleBackground::Size::eContain:
              case nsStyleBackground::Size::eCover:
                item->mXValue.SetIntValue(size.mWidthType,
                                          eCSSUnit_Enumerated);
                break;
              case nsStyleBackground::Size::eAuto:
                item->mXValue.SetAutoValue();
                break;
              case nsStyleBackground::Size::eLengthPercentage:
                // XXXbz is there a good reason we can't just
                // SetCalcValue(&size.mWidth, item->mXValue) here?
                if (!size.mWidth.mHasPercent &&
                    // negative values must have come from calc()
                    size.mWidth.mLength >= 0) {
                  MOZ_ASSERT(size.mWidth.mPercent == 0.0f,
                             "Shouldn't have mPercent");
                  nscoordToCSSValue(size.mWidth.mLength, item->mXValue);
                } else if (size.mWidth.mLength == 0 &&
                           // negative values must have come from calc()
                           size.mWidth.mPercent >= 0.0f) {
                  item->mXValue.SetPercentValue(size.mWidth.mPercent);
                } else {
                  SetCalcValue(&size.mWidth, item->mXValue);
                }
                break;
            }

            switch (size.mHeightType) {
              case nsStyleBackground::Size::eContain:
              case nsStyleBackground::Size::eCover:
                // leave it null
                break;
              case nsStyleBackground::Size::eAuto:
                item->mYValue.SetAutoValue();
                break;
              case nsStyleBackground::Size::eLengthPercentage:
                // XXXbz is there a good reason we can't just
                // SetCalcValue(&size.mHeight, item->mYValue) here?
                if (!size.mHeight.mHasPercent &&
                    // negative values must have come from calc()
                    size.mHeight.mLength >= 0) {
                  MOZ_ASSERT(size.mHeight.mPercent == 0.0f,
                             "Shouldn't have mPercent");
                  nscoordToCSSValue(size.mHeight.mLength, item->mYValue);
                } else if (size.mHeight.mLength == 0 &&
                           // negative values must have come from calc()
                           size.mHeight.mPercent >= 0.0f) {
                  item->mYValue.SetPercentValue(size.mHeight.mPercent);
                } else {
                  SetCalcValue(&size.mHeight, item->mYValue);
                }
                break;
            }
          }

          aComputedValue.SetAndAdoptCSSValuePairListValue(result.forget());
          break;
        }

        case eCSSProperty_filter: {
          const nsStyleSVGReset *svgReset =
            static_cast<const nsStyleSVGReset*>(styleStruct);
          const nsTArray<nsStyleFilter>& filters = svgReset->mFilters;
          nsAutoPtr<nsCSSValueList> result;
          nsCSSValueList **resultTail = getter_Transfers(result);
          for (uint32_t i = 0; i < filters.Length(); ++i) {
            nsCSSValueList *item = new nsCSSValueList;
            *resultTail = item;
            resultTail = &item->mNext;
            const nsStyleFilter& filter = filters[i];
            int32_t type = filter.GetType();
            if (type == NS_STYLE_FILTER_URL) {
              nsIDocument* doc = aStyleContext->PresContext()->Document();
              nsRefPtr<nsStringBuffer> uriAsStringBuffer =
                GetURIAsUtf16StringBuffer(filter.GetURL());
              nsRefPtr<mozilla::css::URLValue> url =
                new mozilla::css::URLValue(filter.GetURL(),
                                           uriAsStringBuffer,
                                           doc->GetDocumentURI(),
                                           doc->NodePrincipal());
              item->mValue.SetURLValue(url);
            } else {
              nsCSSKeyword functionName =
                nsCSSProps::ValueToKeywordEnum(type,
                  nsCSSProps::kFilterFunctionKTable);
              nsCSSValue::Array* filterArray =
                item->mValue.InitFunction(functionName, 1);
              if (type >= NS_STYLE_FILTER_BLUR && type <= NS_STYLE_FILTER_HUE_ROTATE) {
                if (!StyleCoordToCSSValue(
                      filter.GetFilterParameter(),
                      filterArray->Item(1))) {
                  return false;
                }
              } else if (type == NS_STYLE_FILTER_DROP_SHADOW) {
                nsCSSValueList* shadowResult = filterArray->Item(1).SetListValue();
                nsAutoPtr<nsCSSValueList> tmpShadowValue;
                nsCSSValueList **tmpShadowResultTail = getter_Transfers(tmpShadowValue);
                nsCSSShadowArray* shadowArray = filter.GetDropShadow();
                MOZ_ASSERT(shadowArray->Length() == 1,
                           "expected exactly one shadow");
                AppendCSSShadowValue(shadowArray->ShadowAt(0), tmpShadowResultTail);
                *shadowResult = *tmpShadowValue;
              } else {
                // We checked all possible nsStyleFilter types but
                // NS_STYLE_FILTER_NULL before. We should never enter this path.
                NS_NOTREACHED("no other filter functions defined");
                return false;
              }
            }
          }

          aComputedValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                      eUnit_Filter);
          break;
        }

        case eCSSProperty_transform: {
          const nsStyleDisplay *display =
            static_cast<const nsStyleDisplay*>(styleStruct);
          nsAutoPtr<nsCSSValueList> result;
          if (display->mSpecifiedTransform) {
            // Clone, and convert all lengths (not percents) to pixels.
            nsCSSValueList **resultTail = getter_Transfers(result);
            for (const nsCSSValueList *l = display->mSpecifiedTransform->mHead;
                 l; l = l->mNext) {
              nsCSSValueList *clone = new nsCSSValueList;
              *resultTail = clone;
              resultTail = &clone->mNext;

              SubstitutePixelValues(aStyleContext, l->mValue, clone->mValue);
            }
          } else {
            result = new nsCSSValueList();
            result->mValue.SetNoneValue();
          }

          aComputedValue.SetTransformValue(
              new nsCSSValueSharedList(result.forget()));
          break;
        }

        default:
          MOZ_ASSERT(false, "missing property implementation");
          return false;
      };
      return true;
    case eStyleAnimType_Coord: {
      const nsStyleCoord& coord = *static_cast<const nsStyleCoord*>(
        StyleDataAtOffset(styleStruct, ssOffset));
      if (nsCSSProps::PropHasFlags(aProperty, CSS_PROPERTY_NUMBERS_ARE_PIXELS) &&
          coord.GetUnit() == eStyleUnit_Coord) {
        // For SVG properties where number means the same thing as length,
        // we want to animate them the same way.  Normalize both to number
        // since it has more accuracy (float vs nscoord).
        aComputedValue.SetFloatValue(nsPresContext::
          AppUnitsToFloatCSSPixels(coord.GetCoordValue()));
        return true;
      }
      return StyleCoordToValue(coord, aComputedValue);
    }
    case eStyleAnimType_Sides_Top:
    case eStyleAnimType_Sides_Right:
    case eStyleAnimType_Sides_Bottom:
    case eStyleAnimType_Sides_Left: {
      static_assert(
       NS_SIDE_TOP    == eStyleAnimType_Sides_Top   -eStyleAnimType_Sides_Top &&
       NS_SIDE_RIGHT  == eStyleAnimType_Sides_Right -eStyleAnimType_Sides_Top &&
       NS_SIDE_BOTTOM == eStyleAnimType_Sides_Bottom-eStyleAnimType_Sides_Top &&
       NS_SIDE_LEFT   == eStyleAnimType_Sides_Left  -eStyleAnimType_Sides_Top,
       "box side constants out of sync with animation side constants");

      const nsStyleCoord &coord = static_cast<const nsStyleSides*>(
        StyleDataAtOffset(styleStruct, ssOffset))->
          Get(mozilla::css::Side(animType - eStyleAnimType_Sides_Top));
      return StyleCoordToValue(coord, aComputedValue);
    }
    case eStyleAnimType_Corner_TopLeft:
    case eStyleAnimType_Corner_TopRight:
    case eStyleAnimType_Corner_BottomRight:
    case eStyleAnimType_Corner_BottomLeft: {
      static_assert(
       NS_CORNER_TOP_LEFT     == eStyleAnimType_Corner_TopLeft -
                                 eStyleAnimType_Corner_TopLeft        &&
       NS_CORNER_TOP_RIGHT    == eStyleAnimType_Corner_TopRight -
                                 eStyleAnimType_Corner_TopLeft        &&
       NS_CORNER_BOTTOM_RIGHT == eStyleAnimType_Corner_BottomRight -
                                 eStyleAnimType_Corner_TopLeft        &&
       NS_CORNER_BOTTOM_LEFT  == eStyleAnimType_Corner_BottomLeft -
                                 eStyleAnimType_Corner_TopLeft,
       "box corner constants out of sync with animation corner constants");

      const nsStyleCorners *corners = static_cast<const nsStyleCorners*>(
        StyleDataAtOffset(styleStruct, ssOffset));
      uint8_t fullCorner = animType - eStyleAnimType_Corner_TopLeft;
      const nsStyleCoord &horiz =
        corners->Get(NS_FULL_TO_HALF_CORNER(fullCorner, false));
      const nsStyleCoord &vert =
        corners->Get(NS_FULL_TO_HALF_CORNER(fullCorner, true));
      nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
      if (!StyleCoordToCSSValue(horiz, pair->mXValue) ||
          !StyleCoordToCSSValue(vert, pair->mYValue)) {
        return false;
      }
      aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                  eUnit_CSSValuePair);
      return true;
    }
    case eStyleAnimType_nscoord:
      aComputedValue.SetCoordValue(*static_cast<const nscoord*>(
        StyleDataAtOffset(styleStruct, ssOffset)));
      return true;
    case eStyleAnimType_EnumU8:
      aComputedValue.SetIntValue(*static_cast<const uint8_t*>(
        StyleDataAtOffset(styleStruct, ssOffset)), eUnit_Enumerated);
      return true;
    case eStyleAnimType_float:
      aComputedValue.SetFloatValue(*static_cast<const float*>(
        StyleDataAtOffset(styleStruct, ssOffset)));
      if (aProperty == eCSSProperty_font_size_adjust &&
          aComputedValue.GetFloatValue() == -1.0f) {
        // In nsStyleFont, we set mFont.sizeAdjust to -1.0 to represent
        // font-size-adjust: none.  Here, we have to treat this as a keyword
        // instead of a float value, to make sure we don't end up doing
        // interpolation with it.
        aComputedValue.SetNoneValue();
      }
      return true;
    case eStyleAnimType_Color:
      aComputedValue.SetColorValue(*static_cast<const nscolor*>(
        StyleDataAtOffset(styleStruct, ssOffset)));
      return true;
    case eStyleAnimType_PaintServer: {
      const nsStyleSVGPaint &paint = *static_cast<const nsStyleSVGPaint*>(
        StyleDataAtOffset(styleStruct, ssOffset));
      if (paint.mType == eStyleSVGPaintType_Color) {
        aComputedValue.SetColorValue(paint.mPaint.mColor);
        return true;
      }
      if (paint.mType == eStyleSVGPaintType_Server) {
        if (!paint.mPaint.mPaintServer) {
          NS_WARNING("Null paint server");
          return false;
        }
        nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
        nsRefPtr<nsStringBuffer> uriAsStringBuffer =
          GetURIAsUtf16StringBuffer(paint.mPaint.mPaintServer);
        NS_ENSURE_TRUE(!!uriAsStringBuffer, false);
        nsIDocument* doc = aStyleContext->PresContext()->Document();
        nsRefPtr<mozilla::css::URLValue> url =
          new mozilla::css::URLValue(paint.mPaint.mPaintServer,
                                     uriAsStringBuffer,
                                     doc->GetDocumentURI(),
                                     doc->NodePrincipal());
        pair->mXValue.SetURLValue(url);
        pair->mYValue.SetColorValue(paint.mFallbackColor);
        aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                    eUnit_CSSValuePair);
        return true;
      }
      if (paint.mType == eStyleSVGPaintType_ContextFill ||
          paint.mType == eStyleSVGPaintType_ContextStroke) {
        nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
        pair->mXValue.SetIntValue(paint.mType == eStyleSVGPaintType_ContextFill ?
                                  NS_COLOR_CONTEXT_FILL : NS_COLOR_CONTEXT_STROKE,
                                  eCSSUnit_Enumerated);
        pair->mYValue.SetColorValue(paint.mFallbackColor);
        aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                    eUnit_CSSValuePair);
        return true;
      }
      MOZ_ASSERT(paint.mType == eStyleSVGPaintType_None,
                 "Unexpected SVG paint type");
      aComputedValue.SetNoneValue();
      return true;
    }
    case eStyleAnimType_Shadow: {
      const nsCSSShadowArray *shadowArray =
        *static_cast<const nsRefPtr<nsCSSShadowArray>*>(
          StyleDataAtOffset(styleStruct, ssOffset));
      if (!shadowArray) {
        aComputedValue.SetAndAdoptCSSValueListValue(nullptr, eUnit_Shadow);
        return true;
      }
      nsAutoPtr<nsCSSValueList> result;
      nsCSSValueList **resultTail = getter_Transfers(result);
      for (uint32_t i = 0, i_end = shadowArray->Length(); i < i_end; ++i) {
        AppendCSSShadowValue(shadowArray->ShadowAt(i), resultTail);
      }
      aComputedValue.SetAndAdoptCSSValueListValue(result.forget(),
                                                  eUnit_Shadow);
      return true;
    }
    case eStyleAnimType_None:
      NS_NOTREACHED("shouldn't use on non-animatable properties");
  }
  return false;
}

StyleAnimationValue::StyleAnimationValue(int32_t aInt, Unit aUnit,
                                         IntegerConstructorType)
{
  NS_ASSERTION(IsIntUnit(aUnit), "unit must be of integer type");
  mUnit = aUnit;
  mValue.mInt = aInt;
}

StyleAnimationValue::StyleAnimationValue(nscoord aLength, CoordConstructorType)
{
  mUnit = eUnit_Coord;
  mValue.mCoord = aLength;
}

StyleAnimationValue::StyleAnimationValue(float aPercent,
                                         PercentConstructorType)
{
  mUnit = eUnit_Percent;
  mValue.mFloat = aPercent;
  MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
}

StyleAnimationValue::StyleAnimationValue(float aFloat, FloatConstructorType)
{
  mUnit = eUnit_Float;
  mValue.mFloat = aFloat;
  MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
}

StyleAnimationValue::StyleAnimationValue(nscolor aColor, ColorConstructorType)
{
  mUnit = eUnit_Color;
  mValue.mColor = aColor;
}

StyleAnimationValue&
StyleAnimationValue::operator=(const StyleAnimationValue& aOther)
{
  FreeValue();

  mUnit = aOther.mUnit;
  switch (mUnit) {
    case eUnit_Null:
    case eUnit_Normal:
    case eUnit_Auto:
    case eUnit_None:
      break;
    case eUnit_Enumerated:
    case eUnit_Visibility:
    case eUnit_Integer:
      mValue.mInt = aOther.mValue.mInt;
      break;
    case eUnit_Coord:
      mValue.mCoord = aOther.mValue.mCoord;
      break;
    case eUnit_Percent:
    case eUnit_Float:
      mValue.mFloat = aOther.mValue.mFloat;
      MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
      break;
    case eUnit_Color:
      mValue.mColor = aOther.mValue.mColor;
      break;
    case eUnit_Calc:
    case eUnit_ObjectPosition:
      MOZ_ASSERT(IsCSSValueUnit(mUnit),
                 "This clause is for handling nsCSSValue-backed units");
      MOZ_ASSERT(aOther.mValue.mCSSValue, "values may not be null");
      mValue.mCSSValue = new nsCSSValue(*aOther.mValue.mCSSValue);
      break;
    case eUnit_CSSValuePair:
      MOZ_ASSERT(aOther.mValue.mCSSValuePair,
                 "value pairs may not be null");
      mValue.mCSSValuePair = new nsCSSValuePair(*aOther.mValue.mCSSValuePair);
      break;
    case eUnit_CSSValueTriplet:
      MOZ_ASSERT(aOther.mValue.mCSSValueTriplet,
                 "value triplets may not be null");
      mValue.mCSSValueTriplet = new nsCSSValueTriplet(*aOther.mValue.mCSSValueTriplet);
      break;
    case eUnit_CSSRect:
      MOZ_ASSERT(aOther.mValue.mCSSRect, "rects may not be null");
      mValue.mCSSRect = new nsCSSRect(*aOther.mValue.mCSSRect);
      break;
    case eUnit_Dasharray:
    case eUnit_Shadow:
    case eUnit_Filter:
    case eUnit_BackgroundPosition:
      MOZ_ASSERT(mUnit == eUnit_Shadow || mUnit == eUnit_Filter ||
                 aOther.mValue.mCSSValueList,
                 "value lists other than shadows and filters may not be null");
      if (aOther.mValue.mCSSValueList) {
        mValue.mCSSValueList = aOther.mValue.mCSSValueList->Clone();
      } else {
        mValue.mCSSValueList = nullptr;
      }
      break;
    case eUnit_Transform:
      mValue.mCSSValueSharedList = aOther.mValue.mCSSValueSharedList;
      mValue.mCSSValueSharedList->AddRef();
      break;
    case eUnit_CSSValuePairList:
      MOZ_ASSERT(aOther.mValue.mCSSValuePairList,
                 "value pair lists may not be null");
      mValue.mCSSValuePairList = aOther.mValue.mCSSValuePairList->Clone();
      break;
    case eUnit_UnparsedString:
      MOZ_ASSERT(aOther.mValue.mString, "expecting non-null string");
      mValue.mString = aOther.mValue.mString;
      mValue.mString->AddRef();
      break;
  }

  return *this;
}

void
StyleAnimationValue::SetNormalValue()
{
  FreeValue();
  mUnit = eUnit_Normal;
}

void
StyleAnimationValue::SetAutoValue()
{
  FreeValue();
  mUnit = eUnit_Auto;
}

void
StyleAnimationValue::SetNoneValue()
{
  FreeValue();
  mUnit = eUnit_None;
}

void
StyleAnimationValue::SetIntValue(int32_t aInt, Unit aUnit)
{
  NS_ASSERTION(IsIntUnit(aUnit), "unit must be of integer type");
  FreeValue();
  mUnit = aUnit;
  mValue.mInt = aInt;
}

void
StyleAnimationValue::SetCoordValue(nscoord aLength)
{
  FreeValue();
  mUnit = eUnit_Coord;
  mValue.mCoord = aLength;
}

void
StyleAnimationValue::SetPercentValue(float aPercent)
{
  FreeValue();
  mUnit = eUnit_Percent;
  mValue.mFloat = aPercent;
  MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
}

void
StyleAnimationValue::SetFloatValue(float aFloat)
{
  FreeValue();
  mUnit = eUnit_Float;
  mValue.mFloat = aFloat;
  MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
}

void
StyleAnimationValue::SetColorValue(nscolor aColor)
{
  FreeValue();
  mUnit = eUnit_Color;
  mValue.mColor = aColor;
}

void
StyleAnimationValue::SetUnparsedStringValue(const nsString& aString)
{
  FreeValue();
  mUnit = eUnit_UnparsedString;
  mValue.mString = nsCSSValue::BufferFromString(aString).take();
}

void
StyleAnimationValue::SetAndAdoptCSSValueValue(nsCSSValue *aValue,
                                              Unit aUnit)
{
  FreeValue();
  MOZ_ASSERT(IsCSSValueUnit(aUnit), "bad unit");
  MOZ_ASSERT(aValue != nullptr, "values may not be null");
  mUnit = aUnit;
  mValue.mCSSValue = aValue; // take ownership
}

void
StyleAnimationValue::SetAndAdoptCSSValuePairValue(nsCSSValuePair *aValuePair,
                                                  Unit aUnit)
{
  FreeValue();
  MOZ_ASSERT(IsCSSValuePairUnit(aUnit), "bad unit");
  MOZ_ASSERT(aValuePair != nullptr, "value pairs may not be null");
  mUnit = aUnit;
  mValue.mCSSValuePair = aValuePair; // take ownership
}

void
StyleAnimationValue::SetAndAdoptCSSValueTripletValue(
                       nsCSSValueTriplet *aValueTriplet, Unit aUnit)
{
    FreeValue();
    MOZ_ASSERT(IsCSSValueTripletUnit(aUnit), "bad unit");
    MOZ_ASSERT(aValueTriplet != nullptr, "value pairs may not be null");
    mUnit = aUnit;
    mValue.mCSSValueTriplet = aValueTriplet; // take ownership
}

void
StyleAnimationValue::SetAndAdoptCSSRectValue(nsCSSRect *aRect, Unit aUnit)
{
  FreeValue();
  MOZ_ASSERT(IsCSSRectUnit(aUnit), "bad unit");
  MOZ_ASSERT(aRect != nullptr, "value pairs may not be null");
  mUnit = aUnit;
  mValue.mCSSRect = aRect; // take ownership
}

void
StyleAnimationValue::SetAndAdoptCSSValueListValue(nsCSSValueList *aValueList,
                                                  Unit aUnit)
{
  FreeValue();
  MOZ_ASSERT(IsCSSValueListUnit(aUnit), "bad unit");
  MOZ_ASSERT(aUnit == eUnit_Shadow || aUnit == eUnit_Filter ||
             aValueList != nullptr,
             "value lists other than shadows and filters may not be null");
  mUnit = aUnit;
  mValue.mCSSValueList = aValueList; // take ownership
}

void
StyleAnimationValue::SetTransformValue(nsCSSValueSharedList* aList)
{
  FreeValue();
  mUnit = eUnit_Transform;
  mValue.mCSSValueSharedList = aList;
  mValue.mCSSValueSharedList->AddRef();
}

void
StyleAnimationValue::SetAndAdoptCSSValuePairListValue(
                       nsCSSValuePairList *aValuePairList)
{
  FreeValue();
  MOZ_ASSERT(aValuePairList, "may not be null");
  mUnit = eUnit_CSSValuePairList;
  mValue.mCSSValuePairList = aValuePairList; // take ownership
}

void
StyleAnimationValue::FreeValue()
{
  if (IsCSSValueUnit(mUnit)) {
    delete mValue.mCSSValue;
  } else if (IsCSSValueListUnit(mUnit)) {
    delete mValue.mCSSValueList;
  } else if (IsCSSValueSharedListValue(mUnit)) {
    mValue.mCSSValueSharedList->Release();
  } else if (IsCSSValuePairUnit(mUnit)) {
    delete mValue.mCSSValuePair;
  } else if (IsCSSValueTripletUnit(mUnit)) {
    delete mValue.mCSSValueTriplet;
  } else if (IsCSSRectUnit(mUnit)) {
    delete mValue.mCSSRect;
  } else if (IsCSSValuePairListUnit(mUnit)) {
    delete mValue.mCSSValuePairList;
  } else if (IsStringUnit(mUnit)) {
    MOZ_ASSERT(mValue.mString, "expecting non-null string");
    mValue.mString->Release();
  }
}

bool
StyleAnimationValue::operator==(const StyleAnimationValue& aOther) const
{
  if (mUnit != aOther.mUnit) {
    return false;
  }

  switch (mUnit) {
    case eUnit_Null:
    case eUnit_Normal:
    case eUnit_Auto:
    case eUnit_None:
      return true;
    case eUnit_Enumerated:
    case eUnit_Visibility:
    case eUnit_Integer:
      return mValue.mInt == aOther.mValue.mInt;
    case eUnit_Coord:
      return mValue.mCoord == aOther.mValue.mCoord;
    case eUnit_Percent:
    case eUnit_Float:
      return mValue.mFloat == aOther.mValue.mFloat;
    case eUnit_Color:
      return mValue.mColor == aOther.mValue.mColor;
    case eUnit_Calc:
    case eUnit_ObjectPosition:
      MOZ_ASSERT(IsCSSValueUnit(mUnit),
                 "This clause is for handling nsCSSValue-backed units");
      return *mValue.mCSSValue == *aOther.mValue.mCSSValue;
    case eUnit_CSSValuePair:
      return *mValue.mCSSValuePair == *aOther.mValue.mCSSValuePair;
    case eUnit_CSSValueTriplet:
      return *mValue.mCSSValueTriplet == *aOther.mValue.mCSSValueTriplet;
    case eUnit_CSSRect:
      return *mValue.mCSSRect == *aOther.mValue.mCSSRect;
    case eUnit_Dasharray:
    case eUnit_Shadow:
    case eUnit_Filter:
    case eUnit_BackgroundPosition:
      return nsCSSValueList::Equal(mValue.mCSSValueList,
                                   aOther.mValue.mCSSValueList);
    case eUnit_Transform:
      return *mValue.mCSSValueSharedList == *aOther.mValue.mCSSValueSharedList;
    case eUnit_CSSValuePairList:
      return nsCSSValuePairList::Equal(mValue.mCSSValuePairList,
                                       aOther.mValue.mCSSValuePairList);
    case eUnit_UnparsedString:
      return (NS_strcmp(GetStringBufferValue(),
                        aOther.GetStringBufferValue()) == 0);
  }

  NS_NOTREACHED("incomplete case");
  return false;
}