gecko/layout/style/nsTransitionManager.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is nsTransitionManager.
 *
 * The Initial Developer of the Original Code is the Mozilla Foundation.
 * Portions created by the Initial Developer are Copyright (C) 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   L. David Baron <dbaron@dbaron.org>, Mozilla Corporation (original author)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

/* Code to start and animate CSS transitions. */

#include "nsTransitionManager.h"
#include "nsIContent.h"
#include "nsStyleContext.h"
#include "nsCSSProps.h"
#include "mozilla/TimeStamp.h"
#include "nsRefreshDriver.h"
#include "nsRuleProcessorData.h"
#include "nsIStyleRule.h"
#include "nsRuleWalker.h"
#include "nsRuleData.h"
#include "nsSMILKeySpline.h"
#include "gfxColor.h"
#include "nsCSSPropertySet.h"
#include "nsStyleAnimation.h"
#include "nsEventDispatcher.h"
#include "nsGUIEvent.h"
#include "mozilla/dom/Element.h"

using mozilla::TimeStamp;
using mozilla::TimeDuration;

namespace dom = mozilla::dom;

/*****************************************************************************
 * Per-Element data                                                          *
 *****************************************************************************/

struct ElementPropertyTransition
{
  nsCSSProperty mProperty;
  nsStyleAnimation::Value mStartValue, mEndValue;
  TimeStamp mStartTime; // actual start plus transition delay

  // data from the relevant nsTransition
  TimeDuration mDuration;
  nsSMILKeySpline mTimingFunction;

  // This is the start value to be used for a check for whether a
  // transition is being reversed.  Normally the same as mStartValue,
  // except when this transition started as the reversal of another
  // in-progress transition.  Needed so we can handle two reverses in a
  // row.
  nsStyleAnimation::Value mStartForReversingTest;
  // Likewise, the portion (in value space) of the "full" reversed
  // transition that we're actually covering.  For example, if a :hover
  // effect has a transition that moves the element 10px to the right
  // (by changing 'left' from 0px to 10px), and the mouse moves in to
  // the element (starting the transition) but then moves out after the
  // transition has advanced 4px, the second transition (from 10px/4px
  // to 0px) will have mReversePortion of 0.4.  (If the mouse then moves
  // in again when the transition is back to 2px, the mReversePortion
  // for the third transition (from 0px/2px to 10px) will be 0.8.
  double mReversePortion;

  // Compute the portion of the *value* space that we should be through
  // at the given time.  (The input to the transition timing function
  // has time units, the output has value units.)
  double ValuePortionFor(TimeStamp aRefreshTime) const;

  PRBool IsRemovedSentinel() const
  {
    return mStartTime.IsNull();
  }

  void SetRemovedSentinel()
  {
    // assign the null time stamp
    mStartTime = TimeStamp();
  }
};

double
ElementPropertyTransition::ValuePortionFor(TimeStamp aRefreshTime) const
{
  // Set |timePortion| to the portion of the way we are through the time
  // input to the transition's timing function (always within the range
  // 0-1).
  double duration = mDuration.ToSeconds();
  NS_ABORT_IF_FALSE(duration >= 0.0, "negative duration forbidden");
  double timePortion;
  if (duration == 0.0) {
    // When duration is zero, we can still have a transition when delay
    // is nonzero.  mStartTime already incorporates delay.
    if (aRefreshTime >= mStartTime) {
      timePortion = 1.0;
    } else {
      timePortion = 0.0;
    }
  } else {
    timePortion = (aRefreshTime - mStartTime).ToSeconds() / duration;
    if (timePortion < 0.0)
      timePortion = 0.0; // use start value during transition-delay
    if (timePortion > 1.0)
      timePortion = 1.0; // we might be behind on flushing
  }

  return mTimingFunction.GetSplineValue(timePortion);
}

/**
 * A style rule that maps property-nsStyleAnimation::Value pairs.
 */
class AnimValuesStyleRule : public nsIStyleRule
{
public:
  // nsISupports implementation
  NS_DECL_ISUPPORTS

  // nsIStyleRule implementation
  virtual void MapRuleInfoInto(nsRuleData* aRuleData);
#ifdef DEBUG
  virtual void List(FILE* out = stdout, PRInt32 aIndent = 0) const;
#endif

  void AddValue(nsCSSProperty aProperty, nsStyleAnimation::Value &aStartValue)
  {
    PropertyValuePair v = { aProperty, aStartValue };
    mPropertyValuePairs.AppendElement(v);
  }

  // Caller must fill in returned value, when non-null.
  nsStyleAnimation::Value* AddEmptyValue(nsCSSProperty aProperty)
  {
    PropertyValuePair *p = mPropertyValuePairs.AppendElement();
    if (!p) {
      return nsnull;
    }
    p->mProperty = aProperty;
    return &p->mValue;
  }

  struct PropertyValuePair {
    nsCSSProperty mProperty;
    nsStyleAnimation::Value mValue;
  };

private:
  nsTArray<PropertyValuePair> mPropertyValuePairs;
};

struct ElementTransitions : public PRCList
{
  ElementTransitions(dom::Element *aElement, nsIAtom *aElementProperty,
                     nsTransitionManager *aTransitionManager)
    : mElement(aElement)
    , mElementProperty(aElementProperty)
    , mTransitionManager(aTransitionManager)
  {
    PR_INIT_CLIST(this);
  }
  ~ElementTransitions()
  {
    PR_REMOVE_LINK(this);
    mTransitionManager->TransitionsRemoved();
  }

  void Destroy()
  {
    // This will call our destructor.
    mElement->DeleteProperty(mElementProperty);
  }

  void EnsureStyleRuleFor(TimeStamp aRefreshTime);


  // Either zero or one for each CSS property:
  nsTArray<ElementPropertyTransition> mPropertyTransitions;

  // This style rule overrides style data with the currently
  // transitioning value for an element that is executing a transition.
  // It only matches when styling with animation.  When we style without
  // animation, we need to not use it so that we can detect any new
  // changes; if necessary we restyle immediately afterwards with
  // animation.
  nsRefPtr<AnimValuesStyleRule> mStyleRule;
  // The refresh time associated with mStyleRule.
  TimeStamp mStyleRuleRefreshTime;

  dom::Element *mElement;

  // the atom we use in mElement's prop table (must be a static atom,
  // i.e., in an atom list)
  nsIAtom *mElementProperty;

  nsTransitionManager *mTransitionManager;
};

static void
ElementTransitionsPropertyDtor(void           *aObject,
                               nsIAtom        *aPropertyName,
                               void           *aPropertyValue,
                               void           *aData)
{
  ElementTransitions *et = static_cast<ElementTransitions*>(aPropertyValue);
  delete et;
}

void
ElementTransitions::EnsureStyleRuleFor(TimeStamp aRefreshTime)
{
  if (!mStyleRule || mStyleRuleRefreshTime != aRefreshTime) {
    mStyleRule = new AnimValuesStyleRule();
    mStyleRuleRefreshTime = aRefreshTime;

    for (PRUint32 i = 0, i_end = mPropertyTransitions.Length(); i < i_end; ++i)
    {
      ElementPropertyTransition &pt = mPropertyTransitions[i];
      if (pt.IsRemovedSentinel()) {
        continue;
      }

      nsStyleAnimation::Value *val = mStyleRule->AddEmptyValue(pt.mProperty);
      if (!val) {
        continue;
      }

      double valuePortion = pt.ValuePortionFor(aRefreshTime);
#ifdef DEBUG
      PRBool ok =
#endif
        nsStyleAnimation::Interpolate(pt.mProperty,
                                      pt.mStartValue, pt.mEndValue,
                                      valuePortion, *val);
      NS_ABORT_IF_FALSE(ok, "could not interpolate values");
    }
  }
}

NS_IMPL_ISUPPORTS1(AnimValuesStyleRule, nsIStyleRule)

/* virtual */ void
AnimValuesStyleRule::MapRuleInfoInto(nsRuleData* aRuleData)
{
  nsStyleContext *contextParent = aRuleData->mStyleContext->GetParent();
  if (contextParent && contextParent->HasPseudoElementData()) {
    // Don't apply transitions to things inside of pseudo-elements.
    // FIXME (Bug 522599): Add tests for this.
    return;
  }

  for (PRUint32 i = 0, i_end = mPropertyValuePairs.Length(); i < i_end; ++i) {
    PropertyValuePair &cv = mPropertyValuePairs[i];
    if (aRuleData->mSIDs & nsCachedStyleData::GetBitForSID(
                             nsCSSProps::kSIDTable[cv.mProperty]))
    {
      nsCSSValue *prop = aRuleData->ValueFor(cv.mProperty);
      if (prop->GetUnit() == eCSSUnit_Null) {
#ifdef DEBUG
        PRBool ok =
#endif
          nsStyleAnimation::UncomputeValue(cv.mProperty,
                                           aRuleData->mPresContext,
                                           cv.mValue, *prop);
        NS_ABORT_IF_FALSE(ok, "could not store computed value");
      }
    }
  }
}

#ifdef DEBUG
/* virtual */ void
AnimValuesStyleRule::List(FILE* out, PRInt32 aIndent) const
{
  // WRITE ME?
}
#endif

/*****************************************************************************
 * nsTransitionManager                                                       *
 *****************************************************************************/

nsTransitionManager::nsTransitionManager(nsPresContext *aPresContext)
  : mPresContext(aPresContext)
{
  PR_INIT_CLIST(&mElementTransitions);
}

nsTransitionManager::~nsTransitionManager()
{
  NS_ABORT_IF_FALSE(!mPresContext, "Disconnect should have been called");
}

void
nsTransitionManager::Disconnect()
{
  // Content nodes might outlive the transition manager.
  RemoveAllTransitions();

  mPresContext = nsnull;
}

void
nsTransitionManager::RemoveAllTransitions()
{
  while (!PR_CLIST_IS_EMPTY(&mElementTransitions)) {
    ElementTransitions *head = static_cast<ElementTransitions*>(
                                 PR_LIST_HEAD(&mElementTransitions));
    head->Destroy();
  }
}

static PRBool
TransExtractComputedValue(nsCSSProperty aProperty,
                          nsStyleContext* aStyleContext,
                          nsStyleAnimation::Value& aComputedValue)
{
  PRBool result =
    nsStyleAnimation::ExtractComputedValue(aProperty, aStyleContext,
                                           aComputedValue);
  if (aProperty == eCSSProperty_visibility) {
    NS_ABORT_IF_FALSE(aComputedValue.GetUnit() ==
                        nsStyleAnimation::eUnit_Enumerated,
                      "unexpected unit");
    aComputedValue.SetIntValue(aComputedValue.GetIntValue(),
                               nsStyleAnimation::eUnit_Visibility);
  }
  return result;
}

already_AddRefed<nsIStyleRule>
nsTransitionManager::StyleContextChanged(dom::Element *aElement,
                                         nsStyleContext *aOldStyleContext,
                                         nsStyleContext *aNewStyleContext)
{
  NS_PRECONDITION(aOldStyleContext->GetPseudo() ==
                      aNewStyleContext->GetPseudo(),
                  "pseudo type mismatch");
  // If we were called from ReparentStyleContext, this assertion would
  // actually fire.  If we need to be called from there, we can probably
  // just remove it; the condition probably isn't critical, although
  // it's worth thinking about some more.
  NS_PRECONDITION(aOldStyleContext->HasPseudoElementData() ==
                      aNewStyleContext->HasPseudoElementData(),
                  "pseudo type mismatch");

  // NOTE: Things in this function (and ConsiderStartingTransition)
  // should never call PeekStyleData because we don't preserve gotten
  // structs across reframes.

  // Return sooner (before the startedAny check below) for the most
  // common case: no transitions specified or running.
  const nsStyleDisplay *disp = aNewStyleContext->GetStyleDisplay();
  nsCSSPseudoElements::Type pseudoType = aNewStyleContext->GetPseudoType();
  if (pseudoType != nsCSSPseudoElements::ePseudo_NotPseudoElement) {
    if (pseudoType != nsCSSPseudoElements::ePseudo_before &&
        pseudoType != nsCSSPseudoElements::ePseudo_after) {
      return nsnull;
    }

    NS_ASSERTION((pseudoType == nsCSSPseudoElements::ePseudo_before &&
                  aElement->Tag() == nsGkAtoms::mozgeneratedcontentbefore) ||
                 (pseudoType == nsCSSPseudoElements::ePseudo_after &&
                  aElement->Tag() == nsGkAtoms::mozgeneratedcontentafter),
                 "Unexpected aElement coming through");

    // Else the element we want to use from now on is the element the
    // :before or :after is attached to.
    aElement = aElement->GetParent()->AsElement();
  }

  ElementTransitions *et =
      GetElementTransitions(aElement, pseudoType, PR_FALSE);
  if (!et &&
      disp->mTransitionPropertyCount == 1 &&
      disp->mTransitions[0].GetDelay() == 0.0f &&
      disp->mTransitions[0].GetDuration() == 0.0f) {
    return nsnull;
  }      


  if (aNewStyleContext->PresContext()->IsProcessingAnimationStyleChange()) {
    return nsnull;
  }
  
  if (aNewStyleContext->GetParent() &&
      aNewStyleContext->GetParent()->HasPseudoElementData()) {
    // Ignore transitions on things that inherit properties from
    // pseudo-elements.
    // FIXME (Bug 522599): Add tests for this.
    return nsnull;
  }

  // Per http://lists.w3.org/Archives/Public/www-style/2009Aug/0109.html
  // I'll consider only the transitions from the number of items in
  // 'transition-property' on down, and later ones will override earlier
  // ones (tracked using |whichStarted|).
  PRBool startedAny = PR_FALSE;
  nsCSSPropertySet whichStarted;
  for (PRUint32 i = disp->mTransitionPropertyCount; i-- != 0; ) {
    const nsTransition& t = disp->mTransitions[i];
    // Check delay and duration first, since they default to zero, and
    // when they're both zero, we can ignore the transition.
    if (t.GetDelay() != 0.0f || t.GetDuration() != 0.0f) {
      // We might have something to transition.  See if any of the
      // properties in question changed and are animatable.
      // FIXME: Would be good to find a way to share code between this
      // interpretation of transition-property and the one below.
      nsCSSProperty property = t.GetProperty();
      if (property == eCSSPropertyExtra_no_properties ||
          property == eCSSProperty_UNKNOWN) {
        // Nothing to do, but need to exclude this from cases below.
      } else if (property == eCSSPropertyExtra_all_properties) {
        for (nsCSSProperty p = nsCSSProperty(0); 
             p < eCSSProperty_COUNT_no_shorthands;
             p = nsCSSProperty(p + 1)) {
          ConsiderStartingTransition(p, t, aElement, et,
                                     aOldStyleContext, aNewStyleContext,
                                     &startedAny, &whichStarted);
        }
      } else if (nsCSSProps::IsShorthand(property)) {
        CSSPROPS_FOR_SHORTHAND_SUBPROPERTIES(subprop, property) {
          ConsiderStartingTransition(*subprop, t, aElement, et,
                                     aOldStyleContext, aNewStyleContext,
                                     &startedAny, &whichStarted);
        }
      } else {
        ConsiderStartingTransition(property, t, aElement, et,
                                   aOldStyleContext, aNewStyleContext,
                                   &startedAny, &whichStarted);
      }
    }
  }

  // Stop any transitions for properties that are no longer in
  // 'transition-property'.
  // Also stop any transitions for properties that just changed (and are
  // still in the set of properties to transition), but we didn't just
  // start the transition because delay and duration are both zero.
  if (et) {
    PRBool checkProperties =
      disp->mTransitions[0].GetProperty() != eCSSPropertyExtra_all_properties;
    nsCSSPropertySet allTransitionProperties;
    if (checkProperties) {
      for (PRUint32 i = disp->mTransitionPropertyCount; i-- != 0; ) {
        const nsTransition& t = disp->mTransitions[i];
        // FIXME: Would be good to find a way to share code between this
        // interpretation of transition-property and the one above.
        nsCSSProperty property = t.GetProperty();
        if (property == eCSSPropertyExtra_no_properties ||
            property == eCSSProperty_UNKNOWN) {
          // Nothing to do, but need to exclude this from cases below.
        } else if (property == eCSSPropertyExtra_all_properties) {
          for (nsCSSProperty p = nsCSSProperty(0); 
               p < eCSSProperty_COUNT_no_shorthands;
               p = nsCSSProperty(p + 1)) {
            allTransitionProperties.AddProperty(p);
          }
        } else if (nsCSSProps::IsShorthand(property)) {
          CSSPROPS_FOR_SHORTHAND_SUBPROPERTIES(subprop, property) {
            allTransitionProperties.AddProperty(*subprop);
          }
        } else {
          allTransitionProperties.AddProperty(property);
        }
      }
    }

    nsTArray<ElementPropertyTransition> &pts = et->mPropertyTransitions;
    PRUint32 i = pts.Length();
    NS_ABORT_IF_FALSE(i != 0, "empty transitions list?");
    nsStyleAnimation::Value currentValue;
    do {
      --i;
      ElementPropertyTransition &pt = pts[i];
          // properties no longer in 'transition-property'
      if ((checkProperties &&
           !allTransitionProperties.HasProperty(pt.mProperty)) ||
          // properties whose computed values changed but delay and
          // duration are both zero
          !TransExtractComputedValue(pt.mProperty, aNewStyleContext,
                                     currentValue) ||
          currentValue != pt.mEndValue) {
        // stop the transition
        pts.RemoveElementAt(i);
      }
    } while (i != 0);

    if (pts.IsEmpty()) {
      et->Destroy();
      et = nsnull;
    }
  }

  if (!startedAny) {
    return nsnull;
  }

  NS_ABORT_IF_FALSE(et, "must have element transitions if we started "
                        "any transitions");

  // In the CSS working group discussion (2009 Jul 15 telecon,
  // http://www.w3.org/mid/4A5E1470.4030904@inkedblade.net ) of
  // http://lists.w3.org/Archives/Public/www-style/2009Jun/0121.html ,
  // the working group decided that a transition property on an
  // element should not cause any transitions if the property change
  // is itself inheriting a value that is transitioning on an
  // ancestor.  So, to get the correct behavior, we continue the
  // restyle that caused this transition using a "covering" rule that
  // covers up any changes on which we started transitions, so that
  // descendants don't start their own transitions.  (In the case of
  // negative transition delay, this covering rule produces different
  // results than applying the transition rule immediately would).
  // Our caller is responsible for restyling again using this covering
  // rule.

  nsRefPtr<AnimValuesStyleRule> coverRule = new AnimValuesStyleRule;
  if (!coverRule) {
    NS_WARNING("out of memory");
    return nsnull;
  }
  
  nsTArray<ElementPropertyTransition> &pts = et->mPropertyTransitions;
  for (PRUint32 i = 0, i_end = pts.Length(); i < i_end; ++i) {
    ElementPropertyTransition &pt = pts[i];
    if (whichStarted.HasProperty(pt.mProperty)) {
      coverRule->AddValue(pt.mProperty, pt.mStartValue);
    }
  }

  return coverRule.forget();
}

void
nsTransitionManager::ConsiderStartingTransition(nsCSSProperty aProperty,
                       const nsTransition& aTransition,
                       dom::Element *aElement,
                       ElementTransitions *&aElementTransitions,
                       nsStyleContext *aOldStyleContext,
                       nsStyleContext *aNewStyleContext,
                       PRBool *aStartedAny,
                       nsCSSPropertySet *aWhichStarted)
{
  // IsShorthand itself will assert if aProperty is not a property.
  NS_ABORT_IF_FALSE(!nsCSSProps::IsShorthand(aProperty),
                    "property out of range");

  if (aWhichStarted->HasProperty(aProperty)) {
    // A later item in transition-property already started a
    // transition for this property, so we ignore this one.
    // See comment above and
    // http://lists.w3.org/Archives/Public/www-style/2009Aug/0109.html .
    return;
  }

  if (nsCSSProps::kAnimTypeTable[aProperty] == eStyleAnimType_None) {
    return;
  }

  ElementPropertyTransition pt;
  nsStyleAnimation::Value dummyValue;
  PRBool haveValues =
    TransExtractComputedValue(aProperty, aOldStyleContext, pt.mStartValue) &&
    TransExtractComputedValue(aProperty, aNewStyleContext, pt.mEndValue);
  PRBool shouldAnimate =
    haveValues &&
    pt.mStartValue != pt.mEndValue &&
    // Check that we can interpolate between these values
    // (If this is ever a performance problem, we could add a
    // CanInterpolate method, but it seems fine for now.)
    nsStyleAnimation::Interpolate(aProperty, pt.mStartValue, pt.mEndValue,
                                  0.5, dummyValue);

  PRUint32 currentIndex = nsTArray<ElementPropertyTransition>::NoIndex;
  if (aElementTransitions) {
    nsTArray<ElementPropertyTransition> &pts =
      aElementTransitions->mPropertyTransitions;
    for (PRUint32 i = 0, i_end = pts.Length(); i < i_end; ++i) {
      if (pts[i].mProperty == aProperty) {
        currentIndex = i;
        break;
      }
    }
  }

  nsPresContext *presContext = aNewStyleContext->PresContext();

  if (!shouldAnimate) {
    nsTArray<ElementPropertyTransition> &pts =
      aElementTransitions->mPropertyTransitions;
    if (currentIndex != nsTArray<ElementPropertyTransition>::NoIndex &&
        (!haveValues || pts[currentIndex].mEndValue != pt.mEndValue)) {
      // We're in the middle of a transition, but just got a
      // non-transition style change changing to exactly the
      // current in-progress value.   (This is quite easy to cause
      // using 'transition-delay'.)
      //
      // We also check that this current in-progress value is different
      // from the end value; we don't want to cancel a transition that
      // is almost done (and whose current value rounds to its end
      // value) just because we got an unrelated style change.
      pts.RemoveElementAt(currentIndex);
      if (pts.IsEmpty()) {
        aElementTransitions->Destroy();
        // |aElementTransitions| is now a dangling pointer!
        aElementTransitions = nsnull;
      }
      // WalkTransitionRule already called RestyleForAnimation.
    }
    return;
  }

  TimeStamp mostRecentRefresh =
    presContext->RefreshDriver()->MostRecentRefresh();

  const nsTimingFunction &tf = aTransition.GetTimingFunction();
  float delay = aTransition.GetDelay();
  float duration = aTransition.GetDuration();
  if (duration < 0.0) {
    // The spec says a negative duration is treated as zero.
    duration = 0.0;
  }
  pt.mStartForReversingTest = pt.mStartValue;
  pt.mReversePortion = 1.0;

  // We need to check two things if we have a currently running
  // transition for this property.
  if (currentIndex != nsTArray<ElementPropertyTransition>::NoIndex) {
    const ElementPropertyTransition &oldPT =
      aElementTransitions->mPropertyTransitions[currentIndex];

    if (oldPT.mEndValue == pt.mEndValue) {
      // If we got a style change that changed the value to the endpoint
      // of the currently running transition, we don't want to interrupt
      // its timing function.
      // WalkTransitionRule already called RestyleForAnimation.
      return;
    }

    // If the new transition reverses the old one, we'll need to handle
    // the timing differently.
    if (!oldPT.IsRemovedSentinel() &&
        oldPT.mStartForReversingTest == pt.mEndValue) {
      // Compute the appropriate negative transition-delay such that right
      // now we'd end up at the current position.
      double valuePortion =
        oldPT.ValuePortionFor(mostRecentRefresh) * oldPT.mReversePortion +
        (1.0 - oldPT.mReversePortion); 
      // A timing function with negative y1 (or y2!) might make
      // valuePortion negative.  In this case, we still want to apply our
      // reversing logic based on relative distances, not make duration
      // negative.
      if (valuePortion < 0.0)
        valuePortion = -valuePortion;
      // A timing function with y2 (or y1!) greater than one might
      // advance past its terminal value.  It's probably a good idea to
      // clamp valuePortion to be at most one to preserve the invariant
      // that a transition will complete within at most its specified
      // time.
      if (valuePortion > 1.0)
        valuePortion = 1.0;

      // Negative delays are essentially part of the transition
      // function, so reduce them along with the duration, but don't
      // reduce positive delays.
      if (delay < 0.0f)
        delay *= valuePortion;
      duration *= valuePortion;

      pt.mStartForReversingTest = oldPT.mEndValue;
      pt.mReversePortion = valuePortion;
    }
  }

  pt.mProperty = aProperty;
  pt.mStartTime = mostRecentRefresh + TimeDuration::FromMilliseconds(delay);
  pt.mDuration = TimeDuration::FromMilliseconds(duration);
  pt.mTimingFunction.Init(tf.mX1, tf.mY1, tf.mX2, tf.mY2);

  if (!aElementTransitions) {
    aElementTransitions =
      GetElementTransitions(aElement, aNewStyleContext->GetPseudoType(),
                            PR_TRUE);
    if (!aElementTransitions) {
      NS_WARNING("allocating ElementTransitions failed");
      return;
    }
  }
  
  nsTArray<ElementPropertyTransition> &pts =
    aElementTransitions->mPropertyTransitions;
#ifdef DEBUG
  for (PRUint32 i = 0, i_end = pts.Length(); i < i_end; ++i) {
    NS_ABORT_IF_FALSE(i == currentIndex ||
                      pts[i].mProperty != aProperty,
                      "duplicate transitions for property");
  }
#endif
  if (currentIndex != nsTArray<ElementPropertyTransition>::NoIndex) {
    pts[currentIndex] = pt;
  } else {
    if (!pts.AppendElement(pt)) {
      NS_WARNING("out of memory");
      return;
    }
  }

  nsRestyleHint hint =
    aNewStyleContext->GetPseudoType() ==
      nsCSSPseudoElements::ePseudo_NotPseudoElement ?
    eRestyle_Self : eRestyle_Subtree;
  presContext->PresShell()->RestyleForAnimation(aElement, hint);

  *aStartedAny = PR_TRUE;
  aWhichStarted->AddProperty(aProperty);
}

ElementTransitions*
nsTransitionManager::GetElementTransitions(dom::Element *aElement,
                                           nsCSSPseudoElements::Type aPseudoType,
                                           PRBool aCreateIfNeeded)
{
  if (!aCreateIfNeeded && PR_CLIST_IS_EMPTY(&mElementTransitions)) {
    // Early return for the most common case.
    return nsnull;
  }

  nsIAtom *propName;
  if (aPseudoType == nsCSSPseudoElements::ePseudo_NotPseudoElement) {
    propName = nsGkAtoms::transitionsProperty;
  } else if (aPseudoType == nsCSSPseudoElements::ePseudo_before) {
    propName = nsGkAtoms::transitionsOfBeforeProperty;
  } else if (aPseudoType == nsCSSPseudoElements::ePseudo_after) {
    propName = nsGkAtoms::transitionsOfAfterProperty;
  } else {
    NS_ASSERTION(!aCreateIfNeeded,
                 "should never try to create transitions for pseudo "
                 "other than :before or :after");
    return nsnull;
  }
  ElementTransitions *et = static_cast<ElementTransitions*>(
                             aElement->GetProperty(propName));
  if (!et && aCreateIfNeeded) {
    // FIXME: Consider arena-allocating?
    et = new ElementTransitions(aElement, propName, this);
    if (!et) {
      NS_WARNING("out of memory");
      return nsnull;
    }
    nsresult rv = aElement->SetProperty(propName, et,
                                        ElementTransitionsPropertyDtor, nsnull);
    if (NS_FAILED(rv)) {
      NS_WARNING("SetProperty failed");
      delete et;
      return nsnull;
    }

    AddElementTransitions(et);
  }

  return et;
}

void
nsTransitionManager::AddElementTransitions(ElementTransitions* aElementTransitions)
{
  if (PR_CLIST_IS_EMPTY(&mElementTransitions)) {
    // We need to observe the refresh driver.
    nsRefreshDriver *rd = mPresContext->RefreshDriver();
    rd->AddRefreshObserver(this, Flush_Style);
  }

  PR_INSERT_BEFORE(aElementTransitions, &mElementTransitions);
}

/*
 * nsISupports implementation
 */

NS_IMPL_ISUPPORTS1(nsTransitionManager, nsIStyleRuleProcessor)

/*
 * nsIStyleRuleProcessor implementation
 */

void
nsTransitionManager::WalkTransitionRule(RuleProcessorData* aData,
                                        nsCSSPseudoElements::Type aPseudoType)
{
  ElementTransitions *et =
    GetElementTransitions(aData->mElement, aPseudoType, PR_FALSE);
  if (!et) {
    return;
  }

  if (aData->mPresContext->IsProcessingRestyles() &&
      !aData->mPresContext->IsProcessingAnimationStyleChange()) {
    // If we're processing a normal style change rather than one from
    // animation, don't add the transition rule.  This allows us to
    // compute the new style value rather than having the transition
    // override it, so that we can start transitioning differently.

    // We need to immediately restyle with animation
    // after doing this.
    if (et) {
      nsRestyleHint hint =
        aPseudoType == nsCSSPseudoElements::ePseudo_NotPseudoElement ?
        eRestyle_Self : eRestyle_Subtree;
      mPresContext->PresShell()->RestyleForAnimation(aData->mElement, hint);
    }
    return;
  }

  et->EnsureStyleRuleFor(
    aData->mPresContext->RefreshDriver()->MostRecentRefresh());

  aData->mRuleWalker->Forward(et->mStyleRule);
}

/* virtual */ void
nsTransitionManager::RulesMatching(ElementRuleProcessorData* aData)
{
  NS_ABORT_IF_FALSE(aData->mPresContext == mPresContext,
                    "pres context mismatch");
  WalkTransitionRule(aData,
                     nsCSSPseudoElements::ePseudo_NotPseudoElement);
}

/* virtual */ void
nsTransitionManager::RulesMatching(PseudoElementRuleProcessorData* aData)
{
  NS_ABORT_IF_FALSE(aData->mPresContext == mPresContext,
                    "pres context mismatch");

  // Note:  If we're the only thing keeping a pseudo-element frame alive
  // (per ProbePseudoStyleContext), we still want to keep it alive, so
  // this is ok.
  WalkTransitionRule(aData, aData->mPseudoType);
}

/* virtual */ void
nsTransitionManager::RulesMatching(AnonBoxRuleProcessorData* aData)
{
}

#ifdef MOZ_XUL
/* virtual */ void
nsTransitionManager::RulesMatching(XULTreeRuleProcessorData* aData)
{
}
#endif

nsRestyleHint
nsTransitionManager::HasStateDependentStyle(StateRuleProcessorData* aData)
{
  return nsRestyleHint(0);
}

PRBool
nsTransitionManager::HasDocumentStateDependentStyle(StateRuleProcessorData* aData)
{
  return PR_FALSE;
}

nsRestyleHint
nsTransitionManager::HasAttributeDependentStyle(AttributeRuleProcessorData* aData)
{
  return nsRestyleHint(0);
}

/* virtual */ PRBool
nsTransitionManager::MediumFeaturesChanged(nsPresContext* aPresContext)
{
  return PR_FALSE;
}

struct TransitionEventInfo {
  nsCOMPtr<nsIContent> mElement;
  nsTransitionEvent mEvent;

  TransitionEventInfo(nsIContent *aElement, nsCSSProperty aProperty,
                      TimeDuration aDuration)
    : mElement(aElement),
      mEvent(PR_TRUE, NS_TRANSITION_END,
             NS_ConvertUTF8toUTF16(nsCSSProps::GetStringValue(aProperty)),
             aDuration.ToSeconds())
  {
  }

  // nsTransitionEvent doesn't support copy-construction, so we need
  // to ourselves in order to work with nsTArray
  TransitionEventInfo(const TransitionEventInfo &aOther)
    : mElement(aOther.mElement),
      mEvent(PR_TRUE, NS_TRANSITION_END,
             aOther.mEvent.propertyName, aOther.mEvent.elapsedTime)
  {
  }
};

/* virtual */ void
nsTransitionManager::WillRefresh(mozilla::TimeStamp aTime)
{
  NS_ABORT_IF_FALSE(mPresContext,
                    "refresh driver should not notify additional observers "
                    "after pres context has been destroyed");
  if (!mPresContext->GetPresShell()) {
    // Someone might be keeping mPresContext alive past the point
    // where it has been torn down; don't bother doing anything in
    // this case.  But do get rid of all our transitions so we stop
    // triggering refreshes.
    RemoveAllTransitions();
    return;
  }

  nsTArray<TransitionEventInfo> events;

  // Trim transitions that have completed, and post restyle events for
  // frames that are still transitioning.
  {
    PRCList *next = PR_LIST_HEAD(&mElementTransitions);
    while (next != &mElementTransitions) {
      ElementTransitions *et = static_cast<ElementTransitions*>(next);
      next = PR_NEXT_LINK(next);

      NS_ABORT_IF_FALSE(et->mElement->GetCurrentDoc() ==
                          mPresContext->Document(),
                        "nsGenericElement::UnbindFromTree should have "
                        "destroyed the element transitions object");

      PRUint32 i = et->mPropertyTransitions.Length();
      NS_ABORT_IF_FALSE(i != 0, "empty transitions list?");
      do {
        --i;
        ElementPropertyTransition &pt = et->mPropertyTransitions[i];
        if (pt.IsRemovedSentinel()) {
          // Actually remove transitions one cycle after their
          // completion.  See comment below.
          et->mPropertyTransitions.RemoveElementAt(i);
        } else if (pt.mStartTime + pt.mDuration <= aTime) {
          // This transition has completed.

          // Fire transitionend events only for transitions on elements
          // and not those on pseudo-elements, since we can't target an
          // event at pseudo-elements.
          if (et->mElementProperty == nsGkAtoms::transitionsProperty) {
            nsCSSProperty prop = pt.mProperty;
            if (nsCSSProps::PropHasFlags(prop, CSS_PROPERTY_REPORT_OTHER_NAME))
            {
              prop = nsCSSProps::OtherNameFor(prop);
            }
            events.AppendElement(
              TransitionEventInfo(et->mElement, prop, pt.mDuration));
          }

          // Leave this transition in the list for one more refresh
          // cycle, since we haven't yet processed its style change, and
          // if we also have (already, or will have from processing
          // transitionend events or other refresh driver notifications)
          // a non-animation style change that would affect it, we need
          // to know not to start a new transition for the transition
          // from the almost-completed value to the final value.
          pt.SetRemovedSentinel();
        }
      } while (i != 0);

      // We need to restyle even if the transition rule no longer
      // applies (in which case we just made it not apply).
      NS_ASSERTION(et->mElementProperty == nsGkAtoms::transitionsProperty ||
                   et->mElementProperty == nsGkAtoms::transitionsOfBeforeProperty ||
                   et->mElementProperty == nsGkAtoms::transitionsOfAfterProperty,
                   "Unexpected element property; might restyle too much");
      nsRestyleHint hint = et->mElementProperty == nsGkAtoms::transitionsProperty ?
        eRestyle_Self : eRestyle_Subtree;
      mPresContext->PresShell()->RestyleForAnimation(et->mElement, hint);

      if (et->mPropertyTransitions.IsEmpty()) {
        et->Destroy();
        // |et| is now a dangling pointer!
        et = nsnull;
      }
    }
  }

  // We might have removed transitions above.
  TransitionsRemoved();

  for (PRUint32 i = 0, i_end = events.Length(); i < i_end; ++i) {
    TransitionEventInfo &info = events[i];
    nsEventDispatcher::Dispatch(info.mElement, mPresContext, &info.mEvent);

    if (!mPresContext) {
      break;
    }
  }
}

void
nsTransitionManager::TransitionsRemoved()
{
  // If we have no transitions left, remove ourselves from the refresh
  // driver.
  if (PR_CLIST_IS_EMPTY(&mElementTransitions)) {
    mPresContext->RefreshDriver()->RemoveRefreshObserver(this, Flush_Style);
  }
}