The Tor Browser: layout/generic/nsFlexContainerFrame.cpp@b8a032363ba2 (annotated)

layout/generic/nsFlexContainerFrame.cpp@b8a032363ba2 (annotated)

layout/generic/nsFlexContainerFrame.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=2 et sw=2 tw=80: */
 /* This Source Code is subject to the terms of the Mozilla Public License
  * version 2.0 (the "License"). You can obtain a copy of the License at
  * http://mozilla.org/MPL/2.0/. */
 /* rendering object for CSS "display: flex" */
 #include "nsFlexContainerFrame.h"
 #include "nsContentUtils.h"
 #include "nsCSSAnonBoxes.h"
 #include "nsDisplayList.h"
 #include "nsIFrameInlines.h"
 #include "nsLayoutUtils.h"
 #include "nsPlaceholderFrame.h"
 #include "nsPresContext.h"
 #include "nsStyleContext.h"
 #include "prlog.h"
 #include <algorithm>
 #include "mozilla/LinkedList.h"
 using namespace mozilla;
 using namespace mozilla::css;
 using namespace mozilla::layout;
 // Convenience typedefs for helper classes that we forward-declare in .h file
 // (so that nsFlexContainerFrame methods can use them as parameters):
 typedef nsFlexContainerFrame::FlexItem FlexItem;
 typedef nsFlexContainerFrame::FlexLine FlexLine;
 typedef nsFlexContainerFrame::FlexboxAxisTracker FlexboxAxisTracker;
 typedef nsFlexContainerFrame::StrutInfo StrutInfo;
 #ifdef PR_LOGGING
 static PRLogModuleInfo*
 GetFlexContainerLog()
 {
   static PRLogModuleInfo *sLog;
   if (!sLog)
     sLog = PR_NewLogModule("nsFlexContainerFrame");
   return sLog;
 }
 #endif /* PR_LOGGING */
 // XXXdholbert Some of this helper-stuff should be separated out into a general
 // "LogicalAxisUtils.h" helper.  Should that be a class, or a namespace (under
 // what super-namespace?), or what?
 // Helper enums
 // ============
 // Represents a physical orientation for an axis.
 // The directional suffix indicates the direction in which the axis *grows*.
 // So e.g. eAxis_LR means a horizontal left-to-right axis, whereas eAxis_BT
 // means a vertical bottom-to-top axis.
 // NOTE: The order here is important -- these values are used as indices into
 // the static array 'kAxisOrientationToSidesMap', defined below.
 enum AxisOrientationType {
   eAxis_LR,
   eAxis_RL,
   eAxis_TB,
   eAxis_BT,
   eNumAxisOrientationTypes // For sizing arrays that use these values as indices
 };
 // Represents one or the other extreme of an axis (e.g. for the main axis, the
 // main-start vs. main-end edge.
 // NOTE: The order here is important -- these values are used as indices into
 // the sub-arrays in 'kAxisOrientationToSidesMap', defined below.
 enum AxisEdgeType {
   eAxisEdge_Start,
   eAxisEdge_End,
   eNumAxisEdges // For sizing arrays that use these values as indices
 };
 // This array maps each axis orientation to a pair of corresponding
 // [start, end] physical mozilla::css::Side values.
 static const Side
 kAxisOrientationToSidesMap[eNumAxisOrientationTypes][eNumAxisEdges] = {
   { eSideLeft,   eSideRight  },  // eAxis_LR
   { eSideRight,  eSideLeft   },  // eAxis_RL
   { eSideTop,    eSideBottom },  // eAxis_TB
   { eSideBottom, eSideTop }      // eAxis_BT
 };
 // Helper structs / classes / methods
 // ==================================
 // Indicates whether advancing along the given axis is equivalent to
 // increasing our X or Y position (as opposed to decreasing it).
 static inline bool
 AxisGrowsInPositiveDirection(AxisOrientationType aAxis)
 {
   return eAxis_LR == aAxis || eAxis_TB == aAxis;
 }
 // Indicates whether the given axis is horizontal.
 static inline bool
 IsAxisHorizontal(AxisOrientationType aAxis)
 {
   return eAxis_LR == aAxis || eAxis_RL == aAxis;
 }
 // Given an AxisOrientationType, returns the "reverse" AxisOrientationType
 // (in the same dimension, but the opposite direction)
 static inline AxisOrientationType
 GetReverseAxis(AxisOrientationType aAxis)
 {
   AxisOrientationType reversedAxis;
   if (aAxis % 2 == 0) {
     // even enum value. Add 1 to reverse.
     reversedAxis = AxisOrientationType(aAxis + 1);
   } else {
     // odd enum value. Subtract 1 to reverse.
     reversedAxis = AxisOrientationType(aAxis - 1);
   }
   // Check that we're still in the enum's valid range
   MOZ_ASSERT(reversedAxis >= eAxis_LR &&
              reversedAxis <= eAxis_BT);
   return reversedAxis;
 }
 // Returns aFrame's computed value for 'height' or 'width' -- whichever is in
 // the same dimension as aAxis.
 static inline const nsStyleCoord&
 GetSizePropertyForAxis(const nsIFrame* aFrame, AxisOrientationType aAxis)
 {
   const nsStylePosition* stylePos = aFrame->StylePosition();
   return IsAxisHorizontal(aAxis) ?
     stylePos->mWidth :
     stylePos->mHeight;
 }
 /**
  * Converts a logical position in a given axis into a position in the
  * corresponding physical (x or y) axis. If the logical axis already maps
  * directly onto one of our physical axes (i.e. LTR or TTB), then the logical
  * and physical positions are equal; otherwise, we subtract the logical
  * position from the container-size in that axis, to flip the polarity.
  * (so e.g. a logical position of 2px in a RTL 20px-wide container
  * would correspond to a physical position of 18px.)
  */
 static nscoord
 PhysicalPosFromLogicalPos(nscoord aLogicalPosn,
                           nscoord aLogicalContainerSize,
                           AxisOrientationType aAxis) {
   if (AxisGrowsInPositiveDirection(aAxis)) {
     return aLogicalPosn;
   }
   return aLogicalContainerSize - aLogicalPosn;
 }
 static nscoord
 MarginComponentForSide(const nsMargin& aMargin, Side aSide)
 {
   switch (aSide) {
     case eSideLeft:
       return aMargin.left;
     case eSideRight:
       return aMargin.right;
     case eSideTop:
       return aMargin.top;
     case eSideBottom:
       return aMargin.bottom;
   }
   NS_NOTREACHED("unexpected Side enum");
   return aMargin.left; // have to return something
                        // (but something's busted if we got here)
 }
 static nscoord&
 MarginComponentForSide(nsMargin& aMargin, Side aSide)
 {
   switch (aSide) {
     case eSideLeft:
       return aMargin.left;
     case eSideRight:
       return aMargin.right;
     case eSideTop:
       return aMargin.top;
     case eSideBottom:
       return aMargin.bottom;
   }
   NS_NOTREACHED("unexpected Side enum");
   return aMargin.left; // have to return something
                        // (but something's busted if we got here)
 }
 // Helper-macro to let us pick one of two expressions to evaluate
 // (a width expression vs. a height expression), to get a main-axis or
 // cross-axis component.
 // For code that has e.g. a nsSize object, FlexboxAxisTracker::GetMainComponent
 // and GetCrossComponent are cleaner; but in cases where we simply have
 // two separate expressions for width and height (which may be expensive to
 // evaluate), these macros will ensure that only the expression for the correct
 // axis gets evaluated.
 #define GET_MAIN_COMPONENT(axisTracker_, width_, height_)  \
   IsAxisHorizontal((axisTracker_).GetMainAxis()) ? (width_) : (height_)
 #define GET_CROSS_COMPONENT(axisTracker_, width_, height_)  \
   IsAxisHorizontal((axisTracker_).GetCrossAxis()) ? (width_) : (height_)
 // Encapsulates our flex container's main & cross axes.
 class MOZ_STACK_CLASS nsFlexContainerFrame::FlexboxAxisTracker {
 public:
   FlexboxAxisTracker(nsFlexContainerFrame* aFlexContainerFrame);
   // Accessors:
   AxisOrientationType GetMainAxis() const  { return mMainAxis;  }
   AxisOrientationType GetCrossAxis() const { return mCrossAxis; }
   nscoord GetMainComponent(const nsSize& aSize) const {
     return GET_MAIN_COMPONENT(*this, aSize.width, aSize.height);
   }
   int32_t GetMainComponent(const nsIntSize& aIntSize) const {
     return GET_MAIN_COMPONENT(*this, aIntSize.width, aIntSize.height);
   }
   nscoord GetCrossComponent(const nsSize& aSize) const {
     return GET_CROSS_COMPONENT(*this, aSize.width, aSize.height);
   }
   int32_t GetCrossComponent(const nsIntSize& aIntSize) const {
     return GET_CROSS_COMPONENT(*this, aIntSize.width, aIntSize.height);
   }
   nscoord GetMarginSizeInMainAxis(const nsMargin& aMargin) const {
     return IsAxisHorizontal(mMainAxis) ?
       aMargin.LeftRight() :
       aMargin.TopBottom();
   }
   nscoord GetMarginSizeInCrossAxis(const nsMargin& aMargin) const {
     return IsAxisHorizontal(mCrossAxis) ?
       aMargin.LeftRight() :
       aMargin.TopBottom();
   }
   /**
    * Converts a logical point into a "physical" x,y point.
    *
    * In the simplest case where the main-axis is left-to-right and the
    * cross-axis is top-to-bottom, this just returns
    * nsPoint(aMainPosn, aCrossPosn).
    *
    *  @arg aMainPosn  The main-axis position -- i.e an offset from the
    *                  main-start edge of the container's content box.
    *  @arg aCrossPosn The cross-axis position -- i.e an offset from the
    *                  cross-start edge of the container's content box.
    *  @return A nsPoint representing the same position (in coordinates
    *          relative to the container's content box).
    */
   nsPoint PhysicalPointFromLogicalPoint(nscoord aMainPosn,
                                         nscoord aCrossPosn,
                                         nscoord aContainerMainSize,
                                         nscoord aContainerCrossSize) const {
     nscoord physicalPosnInMainAxis =
       PhysicalPosFromLogicalPos(aMainPosn, aContainerMainSize, mMainAxis);
     nscoord physicalPosnInCrossAxis =
       PhysicalPosFromLogicalPos(aCrossPosn, aContainerCrossSize, mCrossAxis);
     return IsAxisHorizontal(mMainAxis) ?
       nsPoint(physicalPosnInMainAxis, physicalPosnInCrossAxis) :
       nsPoint(physicalPosnInCrossAxis, physicalPosnInMainAxis);
   }
   nsSize PhysicalSizeFromLogicalSizes(nscoord aMainSize,
                                       nscoord aCrossSize) const {
     return IsAxisHorizontal(mMainAxis) ?
       nsSize(aMainSize, aCrossSize) :
       nsSize(aCrossSize, aMainSize);
   }
   // Are my axes reversed with respect to what the author asked for?
   // (We may reverse the axes in the FlexboxAxisTracker constructor and set
   // this flag, to avoid reflowing our children in bottom-to-top order.)
   bool AreAxesInternallyReversed() const
   {
     return mAreAxesInternallyReversed;
   }
 private:
   AxisOrientationType mMainAxis;
   AxisOrientationType mCrossAxis;
   bool mAreAxesInternallyReversed;
 };
 /**
  * Represents a flex item.
  * Includes the various pieces of input that the Flexbox Layout Algorithm uses
  * to resolve a flexible width.
  */
 class nsFlexContainerFrame::FlexItem : public LinkedListElement<FlexItem>
 {
 public:
   // Normal constructor:
   FlexItem(nsIFrame* aChildFrame,
            float aFlexGrow, float aFlexShrink, nscoord aMainBaseSize,
            nscoord aMainMinSize, nscoord aMainMaxSize,
            nscoord aCrossMinSize, nscoord aCrossMaxSize,
            nsMargin aMargin, nsMargin aBorderPadding,
            const FlexboxAxisTracker& aAxisTracker);
   // Simplified constructor, to be used only for generating "struts":
   FlexItem(nsIFrame* aChildFrame, nscoord aCrossSize);
   // Accessors
   nsIFrame* Frame() const          { return mFrame; }
   nscoord GetFlexBaseSize() const  { return mFlexBaseSize; }
   nscoord GetMainMinSize() const   { return mMainMinSize; }
   nscoord GetMainMaxSize() const   { return mMainMaxSize; }
   // Note: These return the main-axis position and size of our *content box*.
   nscoord GetMainSize() const      { return mMainSize; }
   nscoord GetMainPosition() const  { return mMainPosn; }
   nscoord GetCrossMinSize() const  { return mCrossMinSize; }
   nscoord GetCrossMaxSize() const  { return mCrossMaxSize; }
   // Note: These return the cross-axis position and size of our *content box*.
   nscoord GetCrossSize() const     { return mCrossSize;  }
   nscoord GetCrossPosition() const { return mCrossPosn; }
   // Convenience methods to compute the main & cross size of our *margin-box*.
   // The caller is responsible for telling us the right axis, so that we can
   // pull out the appropriate components of our margin/border/padding structs.
   nscoord GetOuterMainSize(AxisOrientationType aMainAxis) const
   {
     return mMainSize + GetMarginBorderPaddingSizeInAxis(aMainAxis);
   }
   nscoord GetOuterCrossSize(AxisOrientationType aCrossAxis) const
   {
     return mCrossSize + GetMarginBorderPaddingSizeInAxis(aCrossAxis);
   }
   // Returns the distance between this FlexItem's baseline and the cross-start
   // edge of its margin-box. Used in baseline alignment.
   // (This function needs to be told what cross axis is & which edge we're
   // measuring the baseline from, so that it can look up the appropriate
   // components from mMargin.)
   nscoord GetBaselineOffsetFromOuterCrossEdge(AxisOrientationType aCrossAxis,
                                               AxisEdgeType aEdge) const;
   float GetShareOfFlexWeightSoFar() const { return mShareOfFlexWeightSoFar; }
   bool IsFrozen() const            { return mIsFrozen; }
   bool HadMinViolation() const     { return mHadMinViolation; }
   bool HadMaxViolation() const     { return mHadMaxViolation; }
   // Indicates whether this item received a preliminary "measuring" reflow
   // before its actual reflow.
   bool HadMeasuringReflow() const  { return mHadMeasuringReflow; }
   // Indicates whether this item's cross-size has been stretched (from having
   // "align-self: stretch" with an auto cross-size and no auto margins in the
   // cross axis).
   bool IsStretched() const         { return mIsStretched; }
   // Indicates whether this item is a "strut" left behind by an element with
   // visibility:collapse.
   bool IsStrut() const             { return mIsStrut; }
   uint8_t GetAlignSelf() const     { return mAlignSelf; }
   // Returns the flex weight that we should use in the "resolving flexible
   // lengths" algorithm.  If we're using flex grow, we just return that;
   // otherwise, we use the "scaled flex shrink weight" (scaled by our flex
   // base size, so that when both large and small items are shrinking,
   // the large items shrink more).
   float GetFlexWeightToUse(bool aIsUsingFlexGrow)
   {
     if (IsFrozen()) {
       return 0.0f;
     }
     if (aIsUsingFlexGrow) {
       return mFlexGrow;
     }
     // We're using flex-shrink --> return mFlexShrink * mFlexBaseSize
     if (mFlexBaseSize == 0) {
       // Special-case for mFlexBaseSize == 0 -- we have no room to shrink, so
       // regardless of mFlexShrink, we should just return 0.
       // (This is really a special-case for when mFlexShrink is infinity, to
       // avoid performing mFlexShrink * mFlexBaseSize = inf * 0 = undefined.)
       return 0.0f;
     }
     return mFlexShrink * mFlexBaseSize;
   }
   // Getters for margin:
   // ===================
   const nsMargin& GetMargin() const { return mMargin; }
   // Returns the margin component for a given mozilla::css::Side
   nscoord GetMarginComponentForSide(Side aSide) const
   { return MarginComponentForSide(mMargin, aSide); }
   // Returns the total space occupied by this item's margins in the given axis
   nscoord GetMarginSizeInAxis(AxisOrientationType aAxis) const
   {
     Side startSide = kAxisOrientationToSidesMap[aAxis][eAxisEdge_Start];
     Side endSide = kAxisOrientationToSidesMap[aAxis][eAxisEdge_End];
     return GetMarginComponentForSide(startSide) +
       GetMarginComponentForSide(endSide);
   }
   // Getters for border/padding
   // ==========================
   const nsMargin& GetBorderPadding() const { return mBorderPadding; }
   // Returns the border+padding component for a given mozilla::css::Side
   nscoord GetBorderPaddingComponentForSide(Side aSide) const
   { return MarginComponentForSide(mBorderPadding, aSide); }
   // Returns the total space occupied by this item's borders and padding in
   // the given axis
   nscoord GetBorderPaddingSizeInAxis(AxisOrientationType aAxis) const
   {
     Side startSide = kAxisOrientationToSidesMap[aAxis][eAxisEdge_Start];
     Side endSide = kAxisOrientationToSidesMap[aAxis][eAxisEdge_End];
     return GetBorderPaddingComponentForSide(startSide) +
       GetBorderPaddingComponentForSide(endSide);
   }
   // Getter for combined margin/border/padding
   // =========================================
   // Returns the total space occupied by this item's margins, borders and
   // padding in the given axis
   nscoord GetMarginBorderPaddingSizeInAxis(AxisOrientationType aAxis) const
   {
     return GetMarginSizeInAxis(aAxis) + GetBorderPaddingSizeInAxis(aAxis);
   }
   // Setters
   // =======
   // This sets our flex base size, and then updates the main size to the
   // base size clamped to our main-axis [min,max] constraints.
   void SetFlexBaseSizeAndMainSize(nscoord aNewFlexBaseSize)
   {
     MOZ_ASSERT(!mIsFrozen || mFlexBaseSize == NS_INTRINSICSIZE,
                "flex base size shouldn't change after we're frozen "
                "(unless we're just resolving an intrinsic size)");
     mFlexBaseSize = aNewFlexBaseSize;
     // Before we've resolved flexible lengths, we keep mMainSize set to
     // the 'hypothetical main size', which is the flex base size, clamped
     // to the [min,max] range:
     mMainSize = NS_CSS_MINMAX(mFlexBaseSize, mMainMinSize, mMainMaxSize);
   }
   // Setters used while we're resolving flexible lengths
   // ---------------------------------------------------
   // Sets the main-size of our flex item's content-box.
   void SetMainSize(nscoord aNewMainSize)
   {
     MOZ_ASSERT(!mIsFrozen, "main size shouldn't change after we're frozen");
     mMainSize = aNewMainSize;
   }
   void SetShareOfFlexWeightSoFar(float aNewShare)
   {
     MOZ_ASSERT(!mIsFrozen || aNewShare == 0.0f,
                "shouldn't be giving this item any share of the weight "
                "after it's frozen");
     mShareOfFlexWeightSoFar = aNewShare;
   }
   void Freeze() { mIsFrozen = true; }
   void SetHadMinViolation()
   {
     MOZ_ASSERT(!mIsFrozen,
                "shouldn't be changing main size & having violations "
                "after we're frozen");
     mHadMinViolation = true;
   }
   void SetHadMaxViolation()
   {
     MOZ_ASSERT(!mIsFrozen,
                "shouldn't be changing main size & having violations "
                "after we're frozen");
     mHadMaxViolation = true;
   }
   void ClearViolationFlags()
   { mHadMinViolation = mHadMaxViolation = false; }
   // Setters for values that are determined after we've resolved our main size
   // -------------------------------------------------------------------------
   // Sets the main-axis position of our flex item's content-box.
   // (This is the distance between the main-start edge of the flex container
   // and the main-start edge of the flex item's content-box.)
   void SetMainPosition(nscoord aPosn) {
     MOZ_ASSERT(mIsFrozen, "main size should be resolved before this");
     mMainPosn  = aPosn;
   }
   // Sets the cross-size of our flex item's content-box.
   void SetCrossSize(nscoord aCrossSize) {
     MOZ_ASSERT(!mIsStretched,
                "Cross size shouldn't be modified after it's been stretched");
     mCrossSize = aCrossSize;
   }
   // Sets the cross-axis position of our flex item's content-box.
   // (This is the distance between the cross-start edge of the flex container
   // and the cross-start edge of the flex item.)
   void SetCrossPosition(nscoord aPosn) {
     MOZ_ASSERT(mIsFrozen, "main size should be resolved before this");
     mCrossPosn = aPosn;
   }
   void SetAscent(nscoord aAscent) {
     mAscent = aAscent;
   }
   void SetHadMeasuringReflow() {
     mHadMeasuringReflow = true;
   }
   void SetIsStretched() {
     MOZ_ASSERT(mIsFrozen, "main size should be resolved before this");
     mIsStretched = true;
   }
   // Setter for margin components (for resolving "auto" margins)
   void SetMarginComponentForSide(Side aSide, nscoord aLength)
   {
     MOZ_ASSERT(mIsFrozen, "main size should be resolved before this");
     MarginComponentForSide(mMargin, aSide) = aLength;
   }
   void ResolveStretchedCrossSize(nscoord aLineCrossSize,
                                  const FlexboxAxisTracker& aAxisTracker);
   uint32_t GetNumAutoMarginsInAxis(AxisOrientationType aAxis) const;
 protected:
   // Our frame:
   nsIFrame* const mFrame;
   // Values that we already know in constructor: (and are hence mostly 'const')
   const float mFlexGrow;
   const float mFlexShrink;
   const nsMargin mBorderPadding;
   nsMargin mMargin; // non-const because we need to resolve auto margins
   nscoord mFlexBaseSize;
   const nscoord mMainMinSize;
   const nscoord mMainMaxSize;
   const nscoord mCrossMinSize;
   const nscoord mCrossMaxSize;
   // Values that we compute after constructor:
   nscoord mMainSize;
   nscoord mMainPosn;
   nscoord mCrossSize;
   nscoord mCrossPosn;
   nscoord mAscent;
   // Temporary state, while we're resolving flexible widths (for our main size)
   // XXXdholbert To save space, we could use a union to make these variables
   // overlay the same memory as some other member vars that aren't touched
   // until after main-size has been resolved. In particular, these could share
   // memory with mMainPosn through mAscent, and mIsStretched.
   float mShareOfFlexWeightSoFar;
   bool mIsFrozen;
   bool mHadMinViolation;
   bool mHadMaxViolation;
   // Misc:
   bool mHadMeasuringReflow; // Did this item get a preliminary reflow,
                             // to measure its desired height?
   bool mIsStretched; // See IsStretched() documentation
   bool mIsStrut;     // Is this item a "strut" left behind by an element
                      // with visibility:collapse?
   uint8_t mAlignSelf; // My "align-self" computed value (with "auto"
                       // swapped out for parent"s "align-items" value,
                       // in our constructor).
 };
 /**
  * Represents a single flex line in a flex container.
  * Manages a linked list of the FlexItems that are in the line.
  */
 class nsFlexContainerFrame::FlexLine : public LinkedListElement<FlexLine>
 {
 public:
   FlexLine()
   : mNumItems(0),
     mTotalInnerHypotheticalMainSize(0),
     mTotalOuterHypotheticalMainSize(0),
     mLineCrossSize(0),
     mBaselineOffset(nscoord_MIN)
   {}
   // Returns the sum of our FlexItems' outer hypothetical main sizes.
   // ("outer" = margin-box, and "hypothetical" = before flexing)
   nscoord GetTotalOuterHypotheticalMainSize() const {
     return mTotalOuterHypotheticalMainSize;
   }
   // Accessors for our FlexItems & information about them:
   FlexItem* GetFirstItem()
   {
     MOZ_ASSERT(mItems.isEmpty() == (mNumItems == 0),
                "mNumItems bookkeeping is off");
     return mItems.getFirst();
   }
   const FlexItem* GetFirstItem() const
   {
     MOZ_ASSERT(mItems.isEmpty() == (mNumItems == 0),
                "mNumItems bookkeeping is off");
     return mItems.getFirst();
   }
   bool IsEmpty() const
   {
     MOZ_ASSERT(mItems.isEmpty() == (mNumItems == 0),
                "mNumItems bookkeeping is off");
     return mItems.isEmpty();
   }
   uint32_t NumItems() const
   {
     MOZ_ASSERT(mItems.isEmpty() == (mNumItems == 0),
                "mNumItems bookkeeping is off");
     return mNumItems;
   }
   // Adds the given FlexItem to our list of items (at the front or back
   // depending on aShouldInsertAtFront), and adds its hypothetical
   // outer & inner main sizes to our totals. Use this method instead of
   // directly modifying the item list, so that our bookkeeping remains correct.
   void AddItem(FlexItem* aItem,
                bool aShouldInsertAtFront,
                nscoord aItemInnerHypotheticalMainSize,
                nscoord aItemOuterHypotheticalMainSize)
   {
     if (aShouldInsertAtFront) {
       mItems.insertFront(aItem);
     } else {
       mItems.insertBack(aItem);
     }
     mNumItems++;
     mTotalInnerHypotheticalMainSize += aItemInnerHypotheticalMainSize;
     mTotalOuterHypotheticalMainSize += aItemOuterHypotheticalMainSize;
   }
   // Computes the cross-size and baseline position of this FlexLine, based on
   // its FlexItems.
   void ComputeCrossSizeAndBaseline(const FlexboxAxisTracker& aAxisTracker);
   // Returns the cross-size of this line.
   nscoord GetLineCrossSize() const { return mLineCrossSize; }
   // Setter for line cross-size -- needed for cases where the flex container
   // imposes a cross-size on the line. (e.g. for single-line flexbox, or for
   // multi-line flexbox with 'align-content: stretch')
   void SetLineCrossSize(nscoord aLineCrossSize) {
     mLineCrossSize = aLineCrossSize;
   }
   /**
    * Returns the offset within this line where any baseline-aligned FlexItems
    * should place their baseline. Usually, this represents a distance from the
    * line's cross-start edge, but if we're internally reversing the axes (see
    * AreAxesInternallyReversed()), this instead represents the distance from
    * its cross-end edge.
    *
    * If there are no baseline-aligned FlexItems, returns nscoord_MIN.
    */
   nscoord GetBaselineOffset() const {
     return mBaselineOffset;
   }
   // Runs the "Resolving Flexible Lengths" algorithm from section 9.7 of the
   // CSS flexbox spec to distribute aFlexContainerMainSize among our flex items.
   void ResolveFlexibleLengths(nscoord aFlexContainerMainSize);
   void PositionItemsInMainAxis(uint8_t aJustifyContent,
                                nscoord aContentBoxMainSize,
                                const FlexboxAxisTracker& aAxisTracker);
   void PositionItemsInCrossAxis(nscoord aLineStartPosition,
                                 const FlexboxAxisTracker& aAxisTracker);
   friend class AutoFlexLineListClearer; // (needs access to mItems)
 private:
   // Helper for ResolveFlexibleLengths():
   void FreezeOrRestoreEachFlexibleSize(const nscoord aTotalViolation,
                                        bool aIsFinalIteration);
   LinkedList<FlexItem> mItems; // Linked list of this line's flex items.
   uint32_t mNumItems; // Number of FlexItems in this line (in |mItems|).
                       // (Shouldn't change after GenerateFlexLines finishes
                       // with this line -- at least, not until we add support
                       // for splitting lines across continuations. Then we can
                       // update this count carefully.)
   nscoord mTotalInnerHypotheticalMainSize;
   nscoord mTotalOuterHypotheticalMainSize;
   nscoord mLineCrossSize;
   nscoord mBaselineOffset;
 };
 // Information about a strut left behind by a FlexItem that's been collapsed
 // using "visibility:collapse".
 struct nsFlexContainerFrame::StrutInfo {
   StrutInfo(uint32_t aItemIdx, nscoord aStrutCrossSize)
     : mItemIdx(aItemIdx),
       mStrutCrossSize(aStrutCrossSize)
   {
   }
   uint32_t mItemIdx;      // Index in the child list.
   nscoord mStrutCrossSize; // The cross-size of this strut.
 };
 static void
 BuildStrutInfoFromCollapsedItems(const FlexLine* aFirstLine,
                                  nsTArray<StrutInfo>& aStruts)
 {
   MOZ_ASSERT(aFirstLine, "null first line pointer");
   MOZ_ASSERT(aStruts.IsEmpty(),
              "We should only build up StrutInfo once per reflow, so "
              "aStruts should be empty when this is called");
   uint32_t itemIdxInContainer = 0;
   for (const FlexLine* line = aFirstLine; line; line = line->getNext()) {
     for (const FlexItem* item = line->GetFirstItem(); item;
          item = item->getNext()) {
       if (NS_STYLE_VISIBILITY_COLLAPSE ==
           item->Frame()->StyleVisibility()->mVisible) {
         // Note the cross size of the line as the item's strut size.
         aStruts.AppendElement(StrutInfo(itemIdxInContainer,
                                         line->GetLineCrossSize()));
       }
       itemIdxInContainer++;
     }
   }
 }
 // Helper-function to find the first non-anonymous-box descendent of aFrame.
 static nsIFrame*
 GetFirstNonAnonBoxDescendant(nsIFrame* aFrame)
 {
   while (aFrame) {
     nsIAtom* pseudoTag = aFrame->StyleContext()->GetPseudo();
     // If aFrame isn't an anonymous container, then it'll do.
     if (!pseudoTag ||                                 // No pseudotag.
         !nsCSSAnonBoxes::IsAnonBox(pseudoTag) ||      // Pseudotag isn't anon.
         pseudoTag == nsCSSAnonBoxes::mozNonElement) { // Text, not a container.
       break;
     }
     // Otherwise, descend to its first child and repeat.
     // SPECIAL CASE: if we're dealing with an anonymous table, then it might
     // be wrapping something non-anonymous in its caption or col-group lists
     // (instead of its principal child list), so we have to look there.
     // (Note: For anonymous tables that have a non-anon cell *and* a non-anon
     // column, we'll always return the column. This is fine; we're really just
     // looking for a handle to *anything* with a meaningful content node inside
     // the table, for use in DOM comparisons to things outside of the table.)
     if (MOZ_UNLIKELY(aFrame->GetType() == nsGkAtoms::tableOuterFrame)) {
       nsIFrame* captionDescendant =
         GetFirstNonAnonBoxDescendant(aFrame->GetFirstChild(kCaptionList));
       if (captionDescendant) {
         return captionDescendant;
       }
     } else if (MOZ_UNLIKELY(aFrame->GetType() == nsGkAtoms::tableFrame)) {
       nsIFrame* colgroupDescendant =
         GetFirstNonAnonBoxDescendant(aFrame->GetFirstChild(kColGroupList));
       if (colgroupDescendant) {
         return colgroupDescendant;
       }
     }
     // USUAL CASE: Descend to the first child in principal list.
     aFrame = aFrame->GetFirstPrincipalChild();
   }
   return aFrame;
 }
 /**
  * Sorting helper-function that compares two frames' "order" property-values,
  * and if they're equal, compares the DOM positions of their corresponding
  * content nodes. Returns true if aFrame1 is "less than or equal to" aFrame2
  * according to this comparison.
  *
  * Note: This can't be a static function, because we need to pass it as a
  * template argument. (Only functions with external linkage can be passed as
  * template arguments.)
  *
  * @return true if the computed "order" property of aFrame1 is less than that
  *         of aFrame2, or if the computed "order" values are equal and aFrame1's
  *         corresponding DOM node is earlier than aFrame2's in the DOM tree.
  *         Otherwise, returns false.
  */
 bool
 IsOrderLEQWithDOMFallback(nsIFrame* aFrame1,
                           nsIFrame* aFrame2)
 {
   MOZ_ASSERT(aFrame1->IsFlexItem() && aFrame2->IsFlexItem(),
              "this method only intended for comparing flex items");
   if (aFrame1 == aFrame2) {
     // Anything is trivially LEQ itself, so we return "true" here... but it's
     // probably bad if we end up actually needing this, so let's assert.
     NS_ERROR("Why are we checking if a frame is LEQ itself?");
     return true;
   }
   // If we've got a placeholder frame, use its out-of-flow frame's 'order' val.
   {
     nsIFrame* aRealFrame1 = nsPlaceholderFrame::GetRealFrameFor(aFrame1);
     nsIFrame* aRealFrame2 = nsPlaceholderFrame::GetRealFrameFor(aFrame2);
     int32_t order1 = aRealFrame1->StylePosition()->mOrder;
     int32_t order2 = aRealFrame2->StylePosition()->mOrder;
     if (order1 != order2) {
       return order1 < order2;
     }
   }
   // The "order" values are equal, so we need to fall back on DOM comparison.
   // For that, we need to dig through any anonymous box wrapper frames to find
   // the actual frame that corresponds to our child content.
   aFrame1 = GetFirstNonAnonBoxDescendant(aFrame1);
   aFrame2 = GetFirstNonAnonBoxDescendant(aFrame2);
   MOZ_ASSERT(aFrame1 && aFrame2,
              "why do we have an anonymous box without any "
              "non-anonymous descendants?");
   // Special case:
   // If either frame is for generated content from ::before or ::after, then
   // we can't use nsContentUtils::PositionIsBefore(), since that method won't
   // recognize generated content as being an actual sibling of other nodes.
   // We know where ::before and ::after nodes *effectively* insert in the DOM
   // tree, though (at the beginning & end), so we can just special-case them.
   nsIAtom* pseudo1 = aFrame1->StyleContext()->GetPseudo();
   nsIAtom* pseudo2 = aFrame2->StyleContext()->GetPseudo();
   if (pseudo1 == nsCSSPseudoElements::before ||
       pseudo2 == nsCSSPseudoElements::after) {
     // frame1 is ::before and/or frame2 is ::after => frame1 is LEQ frame2.
     return true;
   }
   if (pseudo1 == nsCSSPseudoElements::after ||
       pseudo2 == nsCSSPseudoElements::before) {
     // frame1 is ::after and/or frame2 is ::before => frame1 is not LEQ frame2.
     return false;
   }
   // Usual case: Compare DOM position.
   nsIContent* content1 = aFrame1->GetContent();
   nsIContent* content2 = aFrame2->GetContent();
   MOZ_ASSERT(content1 != content2,
              "Two different flex items are using the same nsIContent node for "
              "comparison, so we may be sorting them in an arbitrary order");
   return nsContentUtils::PositionIsBefore(content1, content2);
 }
 /**
  * Sorting helper-function that compares two frames' "order" property-values.
  * Returns true if aFrame1 is "less than or equal to" aFrame2 according to this
  * comparison.
  *
  * Note: This can't be a static function, because we need to pass it as a
  * template argument. (Only functions with external linkage can be passed as
  * template arguments.)
  *
  * @return true if the computed "order" property of aFrame1 is less than or
  *         equal to that of aFrame2.  Otherwise, returns false.
  */
 bool
 IsOrderLEQ(nsIFrame* aFrame1,
            nsIFrame* aFrame2)
 {
   MOZ_ASSERT(aFrame1->IsFlexItem() && aFrame2->IsFlexItem(),
              "this method only intended for comparing flex items");
   // If we've got a placeholder frame, use its out-of-flow frame's 'order' val.
   nsIFrame* aRealFrame1 = nsPlaceholderFrame::GetRealFrameFor(aFrame1);
   nsIFrame* aRealFrame2 = nsPlaceholderFrame::GetRealFrameFor(aFrame2);
   int32_t order1 = aRealFrame1->StylePosition()->mOrder;
   int32_t order2 = aRealFrame2->StylePosition()->mOrder;
   return order1 <= order2;
 }
 bool
 nsFlexContainerFrame::IsHorizontal()
 {
   const FlexboxAxisTracker axisTracker(this);
   return IsAxisHorizontal(axisTracker.GetMainAxis());
 }
 FlexItem*
 nsFlexContainerFrame::GenerateFlexItemForChild(
   nsPresContext* aPresContext,
   nsIFrame*      aChildFrame,
   const nsHTMLReflowState& aParentReflowState,
   const FlexboxAxisTracker& aAxisTracker)
 {
   // Create temporary reflow state just for sizing -- to get hypothetical
   // main-size and the computed values of min / max main-size property.
   // (This reflow state will _not_ be used for reflow.)
   nsHTMLReflowState childRS(aPresContext, aParentReflowState, aChildFrame,
                             nsSize(aParentReflowState.ComputedWidth(),
                                    aParentReflowState.ComputedHeight()));
   // FLEX GROW & SHRINK WEIGHTS
   // --------------------------
   const nsStylePosition* stylePos = aChildFrame->StylePosition();
   float flexGrow   = stylePos->mFlexGrow;
   float flexShrink = stylePos->mFlexShrink;
   // MAIN SIZES (flex base size, min/max size)
   // -----------------------------------------
   nscoord flexBaseSize = GET_MAIN_COMPONENT(aAxisTracker,
                                             childRS.ComputedWidth(),
                                             childRS.ComputedHeight());
   nscoord mainMinSize = GET_MAIN_COMPONENT(aAxisTracker,
                                            childRS.ComputedMinWidth(),
                                            childRS.ComputedMinHeight());
   nscoord mainMaxSize = GET_MAIN_COMPONENT(aAxisTracker,
                                            childRS.ComputedMaxWidth(),
                                            childRS.ComputedMaxHeight());
   // This is enforced by the nsHTMLReflowState where these values come from:
   MOZ_ASSERT(mainMinSize <= mainMaxSize, "min size is larger than max size");
   // CROSS MIN/MAX SIZE
   // ------------------
   nscoord crossMinSize = GET_CROSS_COMPONENT(aAxisTracker,
                                              childRS.ComputedMinWidth(),
                                              childRS.ComputedMinHeight());
   nscoord crossMaxSize = GET_CROSS_COMPONENT(aAxisTracker,
                                              childRS.ComputedMaxWidth(),
                                              childRS.ComputedMaxHeight());
   // SPECIAL-CASE FOR WIDGET-IMPOSED SIZES
   // Check if we're a themed widget, in which case we might have a minimum
   // main & cross size imposed by our widget (which we can't go below), or
   // (more severe) our widget might have only a single valid size.
   bool isFixedSizeWidget = false;
   const nsStyleDisplay* disp = aChildFrame->StyleDisplay();
   if (aChildFrame->IsThemed(disp)) {
     nsIntSize widgetMinSize(0, 0);
     bool canOverride = true;
     aPresContext->GetTheme()->
       GetMinimumWidgetSize(childRS.rendContext, aChildFrame,
                            disp->mAppearance,
                            &widgetMinSize, &canOverride);
     nscoord widgetMainMinSize =
       aPresContext->DevPixelsToAppUnits(
         aAxisTracker.GetMainComponent(widgetMinSize));
     nscoord widgetCrossMinSize =
       aPresContext->DevPixelsToAppUnits(
         aAxisTracker.GetCrossComponent(widgetMinSize));
     // GMWS() returns border-box. We need content-box, so subtract
     // borderPadding (but don't let that push our min sizes below 0).
     nsMargin& bp = childRS.ComputedPhysicalBorderPadding();
     widgetMainMinSize = std::max(widgetMainMinSize -
                                  aAxisTracker.GetMarginSizeInMainAxis(bp), 0);
     widgetCrossMinSize = std::max(widgetCrossMinSize -
                                   aAxisTracker.GetMarginSizeInCrossAxis(bp), 0);
     if (!canOverride) {
       // Fixed-size widget: freeze our main-size at the widget's mandated size.
       // (Set min and max main-sizes to that size, too, to keep us from
       // clamping to any other size later on.)
       flexBaseSize = mainMinSize = mainMaxSize = widgetMainMinSize;
       crossMinSize = crossMaxSize = widgetCrossMinSize;
       isFixedSizeWidget = true;
     } else {
       // Variable-size widget: ensure our min/max sizes are at least as large
       // as the widget's mandated minimum size, so we don't flex below that.
       mainMinSize = std::max(mainMinSize, widgetMainMinSize);
       mainMaxSize = std::max(mainMaxSize, widgetMainMinSize);
       crossMinSize = std::max(crossMinSize, widgetCrossMinSize);
       crossMaxSize = std::max(crossMaxSize, widgetCrossMinSize);
     }
   }
   // Construct the flex item!
   FlexItem* item = new FlexItem(aChildFrame,
                                 flexGrow, flexShrink, flexBaseSize,
                                 mainMinSize, mainMaxSize,
                                 crossMinSize, crossMaxSize,
                                 childRS.ComputedPhysicalMargin(),
                                 childRS.ComputedPhysicalBorderPadding(),
                                 aAxisTracker);
   // If we're inflexible, we can just freeze to our hypothetical main-size
   // up-front. Similarly, if we're a fixed-size widget, we only have one
   // valid size, so we freeze to keep ourselves from flexing.
   if (isFixedSizeWidget || (flexGrow == 0.0f && flexShrink == 0.0f)) {
     item->Freeze();
   }
   return item;
 }
 nsresult
 nsFlexContainerFrame::
   ResolveFlexItemMaxContentSizing(nsPresContext* aPresContext,
                                   FlexItem& aFlexItem,
                                   const nsHTMLReflowState& aParentReflowState,
                                   const FlexboxAxisTracker& aAxisTracker)
 {
   if (IsAxisHorizontal(aAxisTracker.GetMainAxis())) {
     // Nothing to do -- this function is only for measuring flex items
     // in a vertical flex container.
     return NS_OK;
   }
   if (NS_AUTOHEIGHT != aFlexItem.GetFlexBaseSize()) {
     // Nothing to do; this function's only relevant for flex items
     // with a base size of "auto" (or equivalent).
     // XXXdholbert If & when we handle "min-height: min-content" for flex items,
     // we'll want to resolve that in this function, too.
     return NS_OK;
   }
   // If we get here, we're vertical and our main size ended up being
   // unconstrained. We need to use our "max-content" height, which is what we
   // get from reflowing into our available width.
   // Note: This has to come *after* we construct the FlexItem, since we
   // invoke at least one convenience method (ResolveStretchedCrossSize) which
   // requires a FlexItem.
   // Give the item a special reflow with "mIsFlexContainerMeasuringHeight"
   // set.  This tells it to behave as if it had "height: auto", regardless
   // of what the "height" property is actually set to.
   nsHTMLReflowState
     childRSForMeasuringHeight(aPresContext, aParentReflowState,
                               aFlexItem.Frame(),
                               nsSize(aParentReflowState.ComputedWidth(),
                                      NS_UNCONSTRAINEDSIZE),
                               -1, -1, nsHTMLReflowState::CALLER_WILL_INIT);
   childRSForMeasuringHeight.mFlags.mIsFlexContainerMeasuringHeight = true;
   childRSForMeasuringHeight.Init(aPresContext);
   aFlexItem.ResolveStretchedCrossSize(aParentReflowState.ComputedWidth(),
                                       aAxisTracker);
   if (aFlexItem.IsStretched()) {
     childRSForMeasuringHeight.SetComputedWidth(aFlexItem.GetCrossSize());
     childRSForMeasuringHeight.mFlags.mHResize = true;
   }
   // If this item is flexible (vertically), then we assume that the
   // computed-height we're reflowing with now could be different
   // from the one we'll use for this flex item's "actual" reflow later on.
   // In that case, we need to be sure the flex item treats this as a
   // vertical resize, even though none of its ancestors are necessarily
   // being vertically resized.
   // (Note: We don't have to do this for width, because InitResizeFlags
   // will always turn on mHResize on when it sees that the computed width
   // is different from current width, and that's all we need.)
   if (!aFlexItem.IsFrozen()) {  // Are we flexible?
     childRSForMeasuringHeight.mFlags.mVResize = true;
   }
   nsHTMLReflowMetrics childDesiredSize(childRSForMeasuringHeight);
   nsReflowStatus childReflowStatus;
   const uint32_t flags = NS_FRAME_NO_MOVE_FRAME;
   nsresult rv = ReflowChild(aFlexItem.Frame(), aPresContext,
                             childDesiredSize, childRSForMeasuringHeight,
 , 0, flags, childReflowStatus);
   NS_ENSURE_SUCCESS(rv, rv);
   MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
              "We gave flex item unconstrained available height, so it "
              "should be complete");
   rv = FinishReflowChild(aFlexItem.Frame(), aPresContext,
                          childDesiredSize, &childRSForMeasuringHeight,
 , 0, flags);
   NS_ENSURE_SUCCESS(rv, rv);
   // Subtract border/padding in vertical axis, to get _just_
   // the effective computed value of the "height" property.
   nscoord childDesiredHeight = childDesiredSize.Height() -
     childRSForMeasuringHeight.ComputedPhysicalBorderPadding().TopBottom();
   childDesiredHeight = std::max(0, childDesiredHeight);
   aFlexItem.SetFlexBaseSizeAndMainSize(childDesiredHeight);
   aFlexItem.SetHadMeasuringReflow();
   return NS_OK;
 }
 FlexItem::FlexItem(nsIFrame* aChildFrame,
                    float aFlexGrow, float aFlexShrink, nscoord aFlexBaseSize,
                    nscoord aMainMinSize,  nscoord aMainMaxSize,
                    nscoord aCrossMinSize, nscoord aCrossMaxSize,
                    nsMargin aMargin, nsMargin aBorderPadding,
                    const FlexboxAxisTracker& aAxisTracker)
   : mFrame(aChildFrame),
     mFlexGrow(aFlexGrow),
     mFlexShrink(aFlexShrink),
     mBorderPadding(aBorderPadding),
     mMargin(aMargin),
     mMainMinSize(aMainMinSize),
     mMainMaxSize(aMainMaxSize),
     mCrossMinSize(aCrossMinSize),
     mCrossMaxSize(aCrossMaxSize),
     mMainPosn(0),
     mCrossSize(0),
     mCrossPosn(0),
     mAscent(0),
     mShareOfFlexWeightSoFar(0.0f),
     mIsFrozen(false),
     mHadMinViolation(false),
     mHadMaxViolation(false),
     mHadMeasuringReflow(false),
     mIsStretched(false),
     mIsStrut(false),
     mAlignSelf(aChildFrame->StylePosition()->mAlignSelf)
 {
   MOZ_ASSERT(mFrame, "expecting a non-null child frame");
   MOZ_ASSERT(mFrame->GetType() != nsGkAtoms::placeholderFrame,
              "placeholder frames should not be treated as flex items");
   MOZ_ASSERT(!(mFrame->GetStateBits() & NS_FRAME_OUT_OF_FLOW),
              "out-of-flow frames should not be treated as flex items");
   SetFlexBaseSizeAndMainSize(aFlexBaseSize);
   // Assert that any "auto" margin components are set to 0.
   // (We'll resolve them later; until then, we want to treat them as 0-sized.)
 #ifdef DEBUG
   {
     const nsStyleSides& styleMargin = mFrame->StyleMargin()->mMargin;
     NS_FOR_CSS_SIDES(side) {
       if (styleMargin.GetUnit(side) == eStyleUnit_Auto) {
         MOZ_ASSERT(GetMarginComponentForSide(side) == 0,
                    "Someone else tried to resolve our auto margin");
       }
     }
   }
 #endif // DEBUG
   // Resolve "align-self: auto" to parent's "align-items" value.
   if (mAlignSelf == NS_STYLE_ALIGN_SELF_AUTO) {
     mAlignSelf =
       mFrame->StyleContext()->GetParent()->StylePosition()->mAlignItems;
   }
   // If the flex item's inline axis is the same as the cross axis, then
   // 'align-self:baseline' is identical to 'flex-start'. If that's the case, we
   // just directly convert our align-self value here, so that we don't have to
   // handle this with special cases elsewhere.
   // Moreover: for the time being (until we support writing-modes),
   // all inline axes are horizontal -- so we can just check if the cross axis
   // is horizontal.
   // FIXME: Once we support writing-mode (vertical text), this IsAxisHorizontal
   // check won't be sufficient anymore -- we'll actually need to compare our
   // inline axis vs. the cross axis.
   if (mAlignSelf == NS_STYLE_ALIGN_ITEMS_BASELINE &&
       IsAxisHorizontal(aAxisTracker.GetCrossAxis())) {
     mAlignSelf = NS_STYLE_ALIGN_ITEMS_FLEX_START;
   }
 }
 // Simplified constructor for creating a special "strut" FlexItem, for a child
 // with visibility:collapse. The strut has 0 main-size, and it only exists to
 // impose a minimum cross size on whichever FlexLine it ends up in.
 FlexItem::FlexItem(nsIFrame* aChildFrame, nscoord aCrossSize)
   : mFrame(aChildFrame),
     mFlexGrow(0.0f),
     mFlexShrink(0.0f),
     // mBorderPadding uses default constructor,
     // mMargin uses default constructor,
     mFlexBaseSize(0),
     mMainMinSize(0),
     mMainMaxSize(0),
     mCrossMinSize(0),
     mCrossMaxSize(0),
     mMainSize(0),
     mMainPosn(0),
     mCrossSize(aCrossSize),
     mCrossPosn(0),
     mAscent(0),
     mShareOfFlexWeightSoFar(0.0f),
     mIsFrozen(true),
     mHadMinViolation(false),
     mHadMaxViolation(false),
     mHadMeasuringReflow(false),
     mIsStretched(false),
     mIsStrut(true), // (this is the constructor for making struts, after all)
     mAlignSelf(NS_STYLE_ALIGN_ITEMS_FLEX_START)
 {
   MOZ_ASSERT(mFrame, "expecting a non-null child frame");
   MOZ_ASSERT(NS_STYLE_VISIBILITY_COLLAPSE ==
              mFrame->StyleVisibility()->mVisible,
              "Should only make struts for children with 'visibility:collapse'");
   MOZ_ASSERT(mFrame->GetType() != nsGkAtoms::placeholderFrame,
              "placeholder frames should not be treated as flex items");
   MOZ_ASSERT(!(mFrame->GetStateBits() & NS_FRAME_OUT_OF_FLOW),
              "out-of-flow frames should not be treated as flex items");
 }
 nscoord
 FlexItem::GetBaselineOffsetFromOuterCrossEdge(AxisOrientationType aCrossAxis,
                                               AxisEdgeType aEdge) const
 {
   // NOTE: Currently, 'mAscent' (taken from reflow) is an inherently vertical
   // measurement -- it's the distance from the border-top edge of this FlexItem
   // to its baseline. So, we can really only do baseline alignment when the
   // cross axis is vertical. (The FlexItem constructor enforces this when
   // resolving the item's "mAlignSelf" value).
   MOZ_ASSERT(!IsAxisHorizontal(aCrossAxis),
              "Only expecting to be doing baseline computations when the "
              "cross axis is vertical");
   Side sideToMeasureFrom = kAxisOrientationToSidesMap[aCrossAxis][aEdge];
   nscoord marginTopToBaseline = mAscent + mMargin.top;
   if (sideToMeasureFrom == eSideTop) {
     // Measuring from top (normal case): the distance from the margin-box top
     // edge to the baseline is just ascent + margin-top.
     return marginTopToBaseline;
   }
   MOZ_ASSERT(sideToMeasureFrom == eSideBottom,
              "We already checked that we're dealing with a vertical axis, and "
              "we're not using the top side, so that only leaves the bottom...");
   // Measuring from bottom: The distance from the margin-box bottom edge to the
   // baseline is just the margin-box cross size (i.e. outer cross size), minus
   // the already-computed distance from margin-top to baseline.
   return GetOuterCrossSize(aCrossAxis) - marginTopToBaseline;
 }
 uint32_t
 FlexItem::GetNumAutoMarginsInAxis(AxisOrientationType aAxis) const
 {
   uint32_t numAutoMargins = 0;
   const nsStyleSides& styleMargin = mFrame->StyleMargin()->mMargin;
   for (uint32_t i = 0; i < eNumAxisEdges; i++) {
     Side side = kAxisOrientationToSidesMap[aAxis][i];
     if (styleMargin.GetUnit(side) == eStyleUnit_Auto) {
       numAutoMargins++;
     }
   }
   // Mostly for clarity:
   MOZ_ASSERT(numAutoMargins <= 2,
              "We're just looking at one item along one dimension, so we "
              "should only have examined 2 margins");
   return numAutoMargins;
 }
 // Keeps track of our position along a particular axis (where a '0' position
 // corresponds to the 'start' edge of that axis).
 // This class shouldn't be instantiated directly -- rather, it should only be
 // instantiated via its subclasses defined below.
 class MOZ_STACK_CLASS PositionTracker {
 public:
   // Accessor for the current value of the position that we're tracking.
   inline nscoord GetPosition() const { return mPosition; }
   inline AxisOrientationType GetAxis() const { return mAxis; }
   // Advances our position across the start edge of the given margin, in the
   // axis we're tracking.
   void EnterMargin(const nsMargin& aMargin)
   {
     Side side = kAxisOrientationToSidesMap[mAxis][eAxisEdge_Start];
     mPosition += MarginComponentForSide(aMargin, side);
   }
   // Advances our position across the end edge of the given margin, in the axis
   // we're tracking.
   void ExitMargin(const nsMargin& aMargin)
   {
     Side side = kAxisOrientationToSidesMap[mAxis][eAxisEdge_End];
     mPosition += MarginComponentForSide(aMargin, side);
   }
   // Advances our current position from the start side of a child frame's
   // border-box to the frame's upper or left edge (depending on our axis).
   // (Note that this is a no-op if our axis grows in positive direction.)
   void EnterChildFrame(nscoord aChildFrameSize)
   {
     if (!AxisGrowsInPositiveDirection(mAxis))
       mPosition += aChildFrameSize;
   }
   // Advances our current position from a frame's upper or left border-box edge
   // (whichever is in the axis we're tracking) to the 'end' side of the frame
   // in the axis that we're tracking. (Note that this is a no-op if our axis
   // grows in the negative direction.)
   void ExitChildFrame(nscoord aChildFrameSize)
   {
     if (AxisGrowsInPositiveDirection(mAxis))
       mPosition += aChildFrameSize;
   }
 protected:
   // Protected constructor, to be sure we're only instantiated via a subclass.
   PositionTracker(AxisOrientationType aAxis)
     : mPosition(0),
       mAxis(aAxis)
   {}
 private:
   // Private copy-constructor, since we don't want any instances of our
   // subclasses to be accidentally copied.
   PositionTracker(const PositionTracker& aOther)
     : mPosition(aOther.mPosition),
       mAxis(aOther.mAxis)
   {}
 protected:
   // Member data:
   nscoord mPosition;               // The position we're tracking
   const AxisOrientationType mAxis; // The axis along which we're moving
 };
 // Tracks our position in the main axis, when we're laying out flex items.
 // The "0" position represents the main-start edge of the flex container's
 // content-box.
 class MOZ_STACK_CLASS MainAxisPositionTracker : public PositionTracker {
 public:
   MainAxisPositionTracker(const FlexboxAxisTracker& aAxisTracker,
                           const FlexLine* aLine,
                           uint8_t aJustifyContent,
                           nscoord aContentBoxMainSize);
   ~MainAxisPositionTracker() {
     MOZ_ASSERT(mNumPackingSpacesRemaining == 0,
                "miscounted the number of packing spaces");
     MOZ_ASSERT(mNumAutoMarginsInMainAxis == 0,
                "miscounted the number of auto margins");
   }
   // Advances past the packing space (if any) between two flex items
   void TraversePackingSpace();
   // If aItem has any 'auto' margins in the main axis, this method updates the
   // corresponding values in its margin.
   void ResolveAutoMarginsInMainAxis(FlexItem& aItem);
 private:
   nscoord  mPackingSpaceRemaining;
   uint32_t mNumAutoMarginsInMainAxis;
   uint32_t mNumPackingSpacesRemaining;
   uint8_t  mJustifyContent;
 };
 // Utility class for managing our position along the cross axis along
 // the whole flex container (at a higher level than a single line).
 // The "0" position represents the cross-start edge of the flex container's
 // content-box.
 class MOZ_STACK_CLASS CrossAxisPositionTracker : public PositionTracker {
 public:
   CrossAxisPositionTracker(FlexLine* aFirstLine,
                            uint8_t aAlignContent,
                            nscoord aContentBoxCrossSize,
                            bool aIsCrossSizeDefinite,
                            const FlexboxAxisTracker& aAxisTracker);
   // Advances past the packing space (if any) between two flex lines
   void TraversePackingSpace();
   // Advances past the given FlexLine
   void TraverseLine(FlexLine& aLine) { mPosition += aLine.GetLineCrossSize(); }
 private:
   // Redeclare the frame-related methods from PositionTracker as private with
   // MOZ_DELETE, to be sure (at compile time) that no client code can invoke
   // them. (Unlike the other PositionTracker derived classes, this class here
   // deals with FlexLines, not with individual FlexItems or frames.)
   void EnterMargin(const nsMargin& aMargin) MOZ_DELETE;
   void ExitMargin(const nsMargin& aMargin) MOZ_DELETE;
   void EnterChildFrame(nscoord aChildFrameSize) MOZ_DELETE;
   void ExitChildFrame(nscoord aChildFrameSize) MOZ_DELETE;
   nscoord  mPackingSpaceRemaining;
   uint32_t mNumPackingSpacesRemaining;
   uint8_t  mAlignContent;
 };
 // Utility class for managing our position along the cross axis, *within* a
 // single flex line.
 class MOZ_STACK_CLASS SingleLineCrossAxisPositionTracker : public PositionTracker {
 public:
   SingleLineCrossAxisPositionTracker(const FlexboxAxisTracker& aAxisTracker);
   void ResolveAutoMarginsInCrossAxis(const FlexLine& aLine,
                                      FlexItem& aItem);
   void EnterAlignPackingSpace(const FlexLine& aLine,
                               const FlexItem& aItem,
                               const FlexboxAxisTracker& aAxisTracker);
   // Resets our position to the cross-start edge of this line.
   inline void ResetPosition() { mPosition = 0; }
 };
 //----------------------------------------------------------------------
 // Frame class boilerplate
 // =======================
 NS_QUERYFRAME_HEAD(nsFlexContainerFrame)
   NS_QUERYFRAME_ENTRY(nsFlexContainerFrame)
 NS_QUERYFRAME_TAIL_INHERITING(nsFlexContainerFrameSuper)
 NS_IMPL_FRAMEARENA_HELPERS(nsFlexContainerFrame)
 nsIFrame*
 NS_NewFlexContainerFrame(nsIPresShell* aPresShell,
                          nsStyleContext* aContext)
 {
   return new (aPresShell) nsFlexContainerFrame(aContext);
 }
 //----------------------------------------------------------------------
 // nsFlexContainerFrame Method Implementations
 // ===========================================
 /* virtual */
 nsFlexContainerFrame::~nsFlexContainerFrame()
 {
 }
 template<bool IsLessThanOrEqual(nsIFrame*, nsIFrame*)>
 /* static */ bool
 nsFlexContainerFrame::SortChildrenIfNeeded()
 {
   if (nsIFrame::IsFrameListSorted<IsLessThanOrEqual>(mFrames)) {
     return false;
   }
   nsIFrame::SortFrameList<IsLessThanOrEqual>(mFrames);
   return true;
 }
 /* virtual */
 nsIAtom*
 nsFlexContainerFrame::GetType() const
 {
   return nsGkAtoms::flexContainerFrame;
 }
 #ifdef DEBUG_FRAME_DUMP
 nsresult
 nsFlexContainerFrame::GetFrameName(nsAString& aResult) const
 {
   return MakeFrameName(NS_LITERAL_STRING("FlexContainer"), aResult);
 }
 #endif
 // Helper for BuildDisplayList, to implement this special-case for flex items
 // from the spec:
 //    Flex items paint exactly the same as block-level elements in the
 //    normal flow, except that 'z-index' values other than 'auto' create
 //    a stacking context even if 'position' is 'static'.
 // http://www.w3.org/TR/2012/CR-css3-flexbox-20120918/#painting
 uint32_t
 GetDisplayFlagsForFlexItem(nsIFrame* aFrame)
 {
   MOZ_ASSERT(aFrame->IsFlexItem(), "Should only be called on flex items");
   const nsStylePosition* pos = aFrame->StylePosition();
   if (pos->mZIndex.GetUnit() == eStyleUnit_Integer) {
     return nsIFrame::DISPLAY_CHILD_FORCE_STACKING_CONTEXT;
   }
   return nsIFrame::DISPLAY_CHILD_FORCE_PSEUDO_STACKING_CONTEXT;
 }
 void
 nsFlexContainerFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                        const nsRect&           aDirtyRect,
                                        const nsDisplayListSet& aLists)
 {
   NS_ASSERTION(
     nsIFrame::IsFrameListSorted<IsOrderLEQWithDOMFallback>(mFrames),
     "Child frames aren't sorted correctly");
   DisplayBorderBackgroundOutline(aBuilder, aLists);
   // Our children are all block-level, so their borders/backgrounds all go on
   // the BlockBorderBackgrounds list.
   nsDisplayListSet childLists(aLists, aLists.BlockBorderBackgrounds());
   for (nsFrameList::Enumerator e(mFrames); !e.AtEnd(); e.Next()) {
     BuildDisplayListForChild(aBuilder, e.get(), aDirtyRect, childLists,
                              GetDisplayFlagsForFlexItem(e.get()));
   }
 }
 #ifdef DEBUG
 // helper for the debugging method below
 bool
 FrameWantsToBeInAnonymousFlexItem(nsIFrame* aFrame)
 {
   // Note: This needs to match the logic in
   // nsCSSFrameConstructor::FrameConstructionItem::NeedsAnonFlexItem()
   return (aFrame->IsFrameOfType(nsIFrame::eLineParticipant) ||
           nsGkAtoms::placeholderFrame == aFrame->GetType());
 }
 // Debugging method, to let us assert that our anonymous flex items are
 // set up correctly -- in particular, we assert:
 //  (1) we don't have any inline non-replaced children
 //  (2) we don't have any consecutive anonymous flex items
 //  (3) we don't have any empty anonymous flex items
 //
 // XXXdholbert This matches what nsCSSFrameConstructor currently does, and what
 // the spec used to say.  However, the spec has now changed regarding what
 // types of content get wrapped in an anonymous flexbox item.  The patch that
 // implements those changes (in nsCSSFrameConstructor) will need to change
 // this method as well.
 void
 nsFlexContainerFrame::SanityCheckAnonymousFlexItems() const
 {
   bool prevChildWasAnonFlexItem = false;
   for (nsIFrame* child = mFrames.FirstChild(); child;
        child = child->GetNextSibling()) {
     MOZ_ASSERT(!FrameWantsToBeInAnonymousFlexItem(child),
                "frame wants to be inside an anonymous flex item, "
                "but it isn't");
     if (child->StyleContext()->GetPseudo() ==
         nsCSSAnonBoxes::anonymousFlexItem) {
       MOZ_ASSERT(!prevChildWasAnonFlexItem ||
                  HasAnyStateBits(NS_STATE_FLEX_CHILDREN_REORDERED),
                  "two anon flex items in a row (shouldn't happen, unless our "
                  "children have been reordered with the 'order' property)");
       nsIFrame* firstWrappedChild = child->GetFirstPrincipalChild();
       MOZ_ASSERT(firstWrappedChild,
                  "anonymous flex item is empty (shouldn't happen)");
       prevChildWasAnonFlexItem = true;
     } else {
       prevChildWasAnonFlexItem = false;
     }
   }
 }
 #endif // DEBUG
 // Based on the sign of aTotalViolation, this function freezes a subset of our
 // flexible sizes, and restores the remaining ones to their initial pref sizes.
 void
 FlexLine::FreezeOrRestoreEachFlexibleSize(const nscoord aTotalViolation,
                                           bool aIsFinalIteration)
 {
   enum FreezeType {
     eFreezeEverything,
     eFreezeMinViolations,
     eFreezeMaxViolations
   };
   FreezeType freezeType;
   if (aTotalViolation == 0) {
     freezeType = eFreezeEverything;
   } else if (aTotalViolation > 0) {
     freezeType = eFreezeMinViolations;
   } else { // aTotalViolation < 0
     freezeType = eFreezeMaxViolations;
   }
   for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
     MOZ_ASSERT(!item->HadMinViolation() || !item->HadMaxViolation(),
                "Can have either min or max violation, but not both");
     if (!item->IsFrozen()) {
       if (eFreezeEverything == freezeType ||
           (eFreezeMinViolations == freezeType && item->HadMinViolation()) ||
           (eFreezeMaxViolations == freezeType && item->HadMaxViolation())) {
         MOZ_ASSERT(item->GetMainSize() >= item->GetMainMinSize(),
                    "Freezing item at a size below its minimum");
         MOZ_ASSERT(item->GetMainSize() <= item->GetMainMaxSize(),
                    "Freezing item at a size above its maximum");
         item->Freeze();
       } else if (MOZ_UNLIKELY(aIsFinalIteration)) {
         // XXXdholbert If & when bug 765861 is fixed, we should upgrade this
         // assertion to be fatal except in documents with enormous lengths.
         NS_ERROR("Final iteration still has unfrozen items, this shouldn't"
                  " happen unless there was nscoord under/overflow.");
         item->Freeze();
       } // else, we'll reset this item's main size to its flex base size on the
         // next iteration of this algorithm.
       // Clear this item's violation(s), now that we've dealt with them
       item->ClearViolationFlags();
     }
   }
 }
 void
 FlexLine::ResolveFlexibleLengths(nscoord aFlexContainerMainSize)
 {
   PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG, ("ResolveFlexibleLengths\n"));
   if (IsEmpty()) {
     return;
   }
   // Subtract space occupied by our items' margins/borders/padding, so we can
   // just be dealing with the space available for our flex items' content
   // boxes.
   nscoord spaceReservedForMarginBorderPadding =
     mTotalOuterHypotheticalMainSize - mTotalInnerHypotheticalMainSize;
   nscoord spaceAvailableForFlexItemsContentBoxes =
     aFlexContainerMainSize - spaceReservedForMarginBorderPadding;
   // Determine whether we're going to be growing or shrinking items.
   const bool isUsingFlexGrow =
     (mTotalOuterHypotheticalMainSize < aFlexContainerMainSize);
   // NOTE: I claim that this chunk of the algorithm (the looping part) needs to
   // run the loop at MOST mNumItems times.  This claim should hold up
   // because we'll freeze at least one item on each loop iteration, and once
   // we've run out of items to freeze, there's nothing left to do.  However,
   // in most cases, we'll break out of this loop long before we hit that many
   // iterations.
   for (uint32_t iterationCounter = 0;
        iterationCounter < mNumItems; iterationCounter++) {
     // Set every not-yet-frozen item's used main size to its
     // flex base size, and subtract all the used main sizes from our
     // total amount of space to determine the 'available free space'
     // (positive or negative) to be distributed among our flexible items.
     nscoord availableFreeSpace = spaceAvailableForFlexItemsContentBoxes;
     for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
       if (!item->IsFrozen()) {
         item->SetMainSize(item->GetFlexBaseSize());
       }
       availableFreeSpace -= item->GetMainSize();
     }
     PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
            (" available free space = %d\n", availableFreeSpace));
     // If sign of free space matches the type of flexing that we're doing, give
     // each flexible item a portion of availableFreeSpace.
     if ((availableFreeSpace > 0 && isUsingFlexGrow) ||
         (availableFreeSpace < 0 && !isUsingFlexGrow)) {
       // STRATEGY: On each item, we compute & store its "share" of the total
       // flex weight that we've seen so far:
       //   curFlexWeight / runningFlexWeightSum
       //
       // Then, when we go to actually distribute the space (in the next loop),
       // we can simply walk backwards through the elements and give each item
       // its "share" multiplied by the remaining available space.
       //
       // SPECIAL CASE: If the sum of the flex weights is larger than the
       // maximum representable float (overflowing to infinity), then we can't
       // sensibly divide out proportional shares anymore. In that case, we
       // simply treat the flex item(s) with the largest flex weights as if
       // their weights were infinite (dwarfing all the others), and we
       // distribute all of the available space among them.
       float runningFlexWeightSum = 0.0f;
       float largestFlexWeight = 0.0f;
       uint32_t numItemsWithLargestFlexWeight = 0;
       for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
         float curFlexWeight = item->GetFlexWeightToUse(isUsingFlexGrow);
         MOZ_ASSERT(curFlexWeight >= 0.0f, "weights are non-negative");
         runningFlexWeightSum += curFlexWeight;
         if (NS_finite(runningFlexWeightSum)) {
           if (curFlexWeight == 0.0f) {
             item->SetShareOfFlexWeightSoFar(0.0f);
           } else {
             item->SetShareOfFlexWeightSoFar(curFlexWeight /
                                             runningFlexWeightSum);
           }
         } // else, the sum of weights overflows to infinity, in which
           // case we don't bother with "SetShareOfFlexWeightSoFar" since
           // we know we won't use it. (instead, we'll just give every
           // item with the largest flex weight an equal share of space.)
         // Update our largest-flex-weight tracking vars
         if (curFlexWeight > largestFlexWeight) {
           largestFlexWeight = curFlexWeight;
           numItemsWithLargestFlexWeight = 1;
         } else if (curFlexWeight == largestFlexWeight) {
           numItemsWithLargestFlexWeight++;
         }
       }
       if (runningFlexWeightSum != 0.0f) { // no distribution if no flexibility
         PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
                (" Distributing available space:"));
         // NOTE: It's important that we traverse our items in *reverse* order
         // here, for correct width distribution according to the items'
         // "ShareOfFlexWeightSoFar" progressively-calculated values.
         for (FlexItem* item = mItems.getLast(); item;
              item = item->getPrevious()) {
           if (!item->IsFrozen()) {
             // To avoid rounding issues, we compute the change in size for this
             // item, and then subtract it from the remaining available space.
             nscoord sizeDelta = 0;
             if (NS_finite(runningFlexWeightSum)) {
               float myShareOfRemainingSpace =
                 item->GetShareOfFlexWeightSoFar();
               MOZ_ASSERT(myShareOfRemainingSpace >= 0.0f &&
                          myShareOfRemainingSpace <= 1.0f,
                          "my share should be nonnegative fractional amount");
               if (myShareOfRemainingSpace == 1.0f) {
                 // (We special-case 1.0f to avoid float error from converting
                 // availableFreeSpace from integer*1.0f --> float --> integer)
                 sizeDelta = availableFreeSpace;
               } else if (myShareOfRemainingSpace > 0.0f) {
                 sizeDelta = NSToCoordRound(availableFreeSpace *
                                            myShareOfRemainingSpace);
               }
             } else if (item->GetFlexWeightToUse(isUsingFlexGrow) ==
                        largestFlexWeight) {
               // Total flexibility is infinite, so we're just distributing
               // the available space equally among the items that are tied for
               // having the largest weight (and this is one of those items).
               sizeDelta =
                 NSToCoordRound(availableFreeSpace /
                                float(numItemsWithLargestFlexWeight));
               numItemsWithLargestFlexWeight--;
             }
             availableFreeSpace -= sizeDelta;
             item->SetMainSize(item->GetMainSize() + sizeDelta);
             PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
                    ("  child %p receives %d, for a total of %d\n",
                     item, sizeDelta, item->GetMainSize()));
           }
         }
       }
     }
     // Fix min/max violations:
     nscoord totalViolation = 0; // keeps track of adjustments for min/max
     PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
            (" Checking for violations:"));
     for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
       if (!item->IsFrozen()) {
         if (item->GetMainSize() < item->GetMainMinSize()) {
           // min violation
           totalViolation += item->GetMainMinSize() - item->GetMainSize();
           item->SetMainSize(item->GetMainMinSize());
           item->SetHadMinViolation();
         } else if (item->GetMainSize() > item->GetMainMaxSize()) {
           // max violation
           totalViolation += item->GetMainMaxSize() - item->GetMainSize();
           item->SetMainSize(item->GetMainMaxSize());
           item->SetHadMaxViolation();
         }
       }
     }
     FreezeOrRestoreEachFlexibleSize(totalViolation,
                                     iterationCounter + 1 == mNumItems);
     PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
            (" Total violation: %d\n", totalViolation));
     if (totalViolation == 0) {
       break;
     }
   }
   // Post-condition: all lengths should've been frozen.
 #ifdef DEBUG
   for (const FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
     MOZ_ASSERT(item->IsFrozen(),
                "All flexible lengths should've been resolved");
   }
 #endif // DEBUG
 }
 MainAxisPositionTracker::
   MainAxisPositionTracker(const FlexboxAxisTracker& aAxisTracker,
                           const FlexLine* aLine,
                           uint8_t aJustifyContent,
                           nscoord aContentBoxMainSize)
   : PositionTracker(aAxisTracker.GetMainAxis()),
     mPackingSpaceRemaining(aContentBoxMainSize), // we chip away at this below
     mNumAutoMarginsInMainAxis(0),
     mNumPackingSpacesRemaining(0),
     mJustifyContent(aJustifyContent)
 {
   // mPackingSpaceRemaining is initialized to the container's main size.  Now
   // we'll subtract out the main sizes of our flex items, so that it ends up
   // with the *actual* amount of packing space.
   for (const FlexItem* item = aLine->GetFirstItem(); item;
        item = item->getNext()) {
     mPackingSpaceRemaining -= item->GetOuterMainSize(mAxis);
     mNumAutoMarginsInMainAxis += item->GetNumAutoMarginsInAxis(mAxis);
   }
   if (mPackingSpaceRemaining <= 0) {
     // No available packing space to use for resolving auto margins.
     mNumAutoMarginsInMainAxis = 0;
   }
   // If packing space is negative, 'space-between' behaves like 'flex-start',
   // and 'space-around' behaves like 'center'. In those cases, it's simplest to
   // just pretend we have a different 'justify-content' value and share code.
   if (mPackingSpaceRemaining < 0) {
     if (mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_SPACE_BETWEEN) {
       mJustifyContent = NS_STYLE_JUSTIFY_CONTENT_FLEX_START;
     } else if (mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_SPACE_AROUND) {
       mJustifyContent = NS_STYLE_JUSTIFY_CONTENT_CENTER;
     }
   }
   // If our main axis is (internally) reversed, swap the justify-content
   // "flex-start" and "flex-end" behaviors:
   if (aAxisTracker.AreAxesInternallyReversed()) {
     if (mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_FLEX_START) {
       mJustifyContent = NS_STYLE_JUSTIFY_CONTENT_FLEX_END;
     } else if (mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_FLEX_END) {
       mJustifyContent = NS_STYLE_JUSTIFY_CONTENT_FLEX_START;
     }
   }
   // Figure out how much space we'll set aside for auto margins or
   // packing spaces, and advance past any leading packing-space.
   if (mNumAutoMarginsInMainAxis == 0 &&
       mPackingSpaceRemaining != 0 &&
       !aLine->IsEmpty()) {
     switch (mJustifyContent) {
       case NS_STYLE_JUSTIFY_CONTENT_FLEX_START:
         // All packing space should go at the end --> nothing to do here.
         break;
       case NS_STYLE_JUSTIFY_CONTENT_FLEX_END:
         // All packing space goes at the beginning
         mPosition += mPackingSpaceRemaining;
         break;
       case NS_STYLE_JUSTIFY_CONTENT_CENTER:
         // Half the packing space goes at the beginning
         mPosition += mPackingSpaceRemaining / 2;
         break;
       case NS_STYLE_JUSTIFY_CONTENT_SPACE_BETWEEN:
         MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                    "negative packing space should make us use 'flex-start' "
                    "instead of 'space-between'");
         // 1 packing space between each flex item, no packing space at ends.
         mNumPackingSpacesRemaining = aLine->NumItems() - 1;
         break;
       case NS_STYLE_JUSTIFY_CONTENT_SPACE_AROUND:
         MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                    "negative packing space should make us use 'center' "
                    "instead of 'space-around'");
         // 1 packing space between each flex item, plus half a packing space
         // at beginning & end.  So our number of full packing-spaces is equal
         // to the number of flex items.
         mNumPackingSpacesRemaining = aLine->NumItems();
         if (mNumPackingSpacesRemaining > 0) {
           // The edges (start/end) share one full packing space
           nscoord totalEdgePackingSpace =
             mPackingSpaceRemaining / mNumPackingSpacesRemaining;
           // ...and we'll use half of that right now, at the start
           mPosition += totalEdgePackingSpace / 2;
           // ...but we need to subtract all of it right away, so that we won't
           // hand out any of it to intermediate packing spaces.
           mPackingSpaceRemaining -= totalEdgePackingSpace;
           mNumPackingSpacesRemaining--;
         }
         break;
       default:
         MOZ_CRASH("Unexpected justify-content value");
     }
   }
   MOZ_ASSERT(mNumPackingSpacesRemaining == 0 ||
              mNumAutoMarginsInMainAxis == 0,
              "extra space should either go to packing space or to "
              "auto margins, but not to both");
 }
 void
 MainAxisPositionTracker::ResolveAutoMarginsInMainAxis(FlexItem& aItem)
 {
   if (mNumAutoMarginsInMainAxis) {
     const nsStyleSides& styleMargin = aItem.Frame()->StyleMargin()->mMargin;
     for (uint32_t i = 0; i < eNumAxisEdges; i++) {
       Side side = kAxisOrientationToSidesMap[mAxis][i];
       if (styleMargin.GetUnit(side) == eStyleUnit_Auto) {
         // NOTE: This integer math will skew the distribution of remainder
         // app-units towards the end, which is fine.
         nscoord curAutoMarginSize =
           mPackingSpaceRemaining / mNumAutoMarginsInMainAxis;
         MOZ_ASSERT(aItem.GetMarginComponentForSide(side) == 0,
                    "Expecting auto margins to have value '0' before we "
                    "resolve them");
         aItem.SetMarginComponentForSide(side, curAutoMarginSize);
         mNumAutoMarginsInMainAxis--;
         mPackingSpaceRemaining -= curAutoMarginSize;
       }
     }
   }
 }
 void
 MainAxisPositionTracker::TraversePackingSpace()
 {
   if (mNumPackingSpacesRemaining) {
     MOZ_ASSERT(mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_SPACE_BETWEEN ||
                mJustifyContent == NS_STYLE_JUSTIFY_CONTENT_SPACE_AROUND,
                "mNumPackingSpacesRemaining only applies for "
                "space-between/space-around");
     MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                "ran out of packing space earlier than we expected");
     // NOTE: This integer math will skew the distribution of remainder
     // app-units towards the end, which is fine.
     nscoord curPackingSpace =
       mPackingSpaceRemaining / mNumPackingSpacesRemaining;
     mPosition += curPackingSpace;
     mNumPackingSpacesRemaining--;
     mPackingSpaceRemaining -= curPackingSpace;
   }
 }
 CrossAxisPositionTracker::
   CrossAxisPositionTracker(FlexLine* aFirstLine,
                            uint8_t aAlignContent,
                            nscoord aContentBoxCrossSize,
                            bool aIsCrossSizeDefinite,
                            const FlexboxAxisTracker& aAxisTracker)
   : PositionTracker(aAxisTracker.GetCrossAxis()),
     mPackingSpaceRemaining(0),
     mNumPackingSpacesRemaining(0),
     mAlignContent(aAlignContent)
 {
   MOZ_ASSERT(aFirstLine, "null first line pointer");
   if (aIsCrossSizeDefinite && !aFirstLine->getNext()) {
     // "If the flex container has only a single line (even if it's a
     // multi-line flex container) and has a definite cross size, the cross
     // size of the flex line is the flex container's inner cross size."
     // SOURCE: http://dev.w3.org/csswg/css-flexbox/#algo-line-break
     // NOTE: This means (by definition) that there's no packing space, which
     // means we don't need to be concerned with "align-conent" at all and we
     // can return early. This is handy, because this is the usual case (for
     // single-line flexbox).
     aFirstLine->SetLineCrossSize(aContentBoxCrossSize);
     return;
   }
   // NOTE: The rest of this function should essentially match
   // MainAxisPositionTracker's constructor, though with FlexLines instead of
   // FlexItems, and with the additional value "stretch" (and of course with
   // cross sizes instead of main sizes.)
   // Figure out how much packing space we have (container's cross size minus
   // all the lines' cross sizes).  Also, share this loop to count how many
   // lines we have. (We need that count in some cases below.)
   mPackingSpaceRemaining = aContentBoxCrossSize;
   uint32_t numLines = 0;
   for (FlexLine* line = aFirstLine; line; line = line->getNext()) {
     mPackingSpaceRemaining -= line->GetLineCrossSize();
     numLines++;
   }
   // If packing space is negative, 'space-between' and 'stretch' behave like
   // 'flex-start', and 'space-around' behaves like 'center'. In those cases,
   // it's simplest to just pretend we have a different 'align-content' value
   // and share code.
   if (mPackingSpaceRemaining < 0) {
     if (mAlignContent == NS_STYLE_ALIGN_CONTENT_SPACE_BETWEEN ||
         mAlignContent == NS_STYLE_ALIGN_CONTENT_STRETCH) {
       mAlignContent = NS_STYLE_ALIGN_CONTENT_FLEX_START;
     } else if (mAlignContent == NS_STYLE_ALIGN_CONTENT_SPACE_AROUND) {
       mAlignContent = NS_STYLE_ALIGN_CONTENT_CENTER;
     }
   }
   // If our cross axis is (internally) reversed, swap the align-content
   // "flex-start" and "flex-end" behaviors:
   if (aAxisTracker.AreAxesInternallyReversed()) {
     if (mAlignContent == NS_STYLE_ALIGN_CONTENT_FLEX_START) {
       mAlignContent = NS_STYLE_ALIGN_CONTENT_FLEX_END;
     } else if (mAlignContent == NS_STYLE_ALIGN_CONTENT_FLEX_END) {
       mAlignContent = NS_STYLE_ALIGN_CONTENT_FLEX_START;
     }
   }
   // Figure out how much space we'll set aside for packing spaces, and advance
   // past any leading packing-space.
   if (mPackingSpaceRemaining != 0) {
     switch (mAlignContent) {
       case NS_STYLE_ALIGN_CONTENT_FLEX_START:
         // All packing space should go at the end --> nothing to do here.
         break;
       case NS_STYLE_ALIGN_CONTENT_FLEX_END:
         // All packing space goes at the beginning
         mPosition += mPackingSpaceRemaining;
         break;
       case NS_STYLE_ALIGN_CONTENT_CENTER:
         // Half the packing space goes at the beginning
         mPosition += mPackingSpaceRemaining / 2;
         break;
       case NS_STYLE_ALIGN_CONTENT_SPACE_BETWEEN:
         MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                    "negative packing space should make us use 'flex-start' "
                    "instead of 'space-between'");
         // 1 packing space between each flex line, no packing space at ends.
         mNumPackingSpacesRemaining = numLines - 1;
         break;
       case NS_STYLE_ALIGN_CONTENT_SPACE_AROUND: {
         MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                    "negative packing space should make us use 'center' "
                    "instead of 'space-around'");
         // 1 packing space between each flex line, plus half a packing space
         // at beginning & end.  So our number of full packing-spaces is equal
         // to the number of flex lines.
         mNumPackingSpacesRemaining = numLines;
         // The edges (start/end) share one full packing space
         nscoord totalEdgePackingSpace =
           mPackingSpaceRemaining / mNumPackingSpacesRemaining;
         // ...and we'll use half of that right now, at the start
         mPosition += totalEdgePackingSpace / 2;
         // ...but we need to subtract all of it right away, so that we won't
         // hand out any of it to intermediate packing spaces.
         mPackingSpaceRemaining -= totalEdgePackingSpace;
         mNumPackingSpacesRemaining--;
         break;
       }
       case NS_STYLE_ALIGN_CONTENT_STRETCH: {
         // Split space equally between the lines:
         MOZ_ASSERT(mPackingSpaceRemaining > 0,
                    "negative packing space should make us use 'flex-start' "
                    "instead of 'stretch' (and we shouldn't bother with this "
                    "code if we have 0 packing space)");
         uint32_t numLinesLeft = numLines;
         for (FlexLine* line = aFirstLine; line; line = line->getNext()) {
           // Our share is the amount of space remaining, divided by the number
           // of lines remainig.
           MOZ_ASSERT(numLinesLeft > 0, "miscalculated num lines");
           nscoord shareOfExtraSpace = mPackingSpaceRemaining / numLinesLeft;
           nscoord newSize = line->GetLineCrossSize() + shareOfExtraSpace;
           line->SetLineCrossSize(newSize);
           mPackingSpaceRemaining -= shareOfExtraSpace;
           numLinesLeft--;
         }
         MOZ_ASSERT(numLinesLeft == 0, "miscalculated num lines");
         break;
       }
       default:
         MOZ_CRASH("Unexpected align-content value");
     }
   }
 }
 void
 CrossAxisPositionTracker::TraversePackingSpace()
 {
   if (mNumPackingSpacesRemaining) {
     MOZ_ASSERT(mAlignContent == NS_STYLE_ALIGN_CONTENT_SPACE_BETWEEN ||
                mAlignContent == NS_STYLE_ALIGN_CONTENT_SPACE_AROUND,
                "mNumPackingSpacesRemaining only applies for "
                "space-between/space-around");
     MOZ_ASSERT(mPackingSpaceRemaining >= 0,
                "ran out of packing space earlier than we expected");
     // NOTE: This integer math will skew the distribution of remainder
     // app-units towards the end, which is fine.
     nscoord curPackingSpace =
       mPackingSpaceRemaining / mNumPackingSpacesRemaining;
     mPosition += curPackingSpace;
     mNumPackingSpacesRemaining--;
     mPackingSpaceRemaining -= curPackingSpace;
   }
 }
 SingleLineCrossAxisPositionTracker::
   SingleLineCrossAxisPositionTracker(const FlexboxAxisTracker& aAxisTracker)
   : PositionTracker(aAxisTracker.GetCrossAxis())
 {
 }
 void
 FlexLine::ComputeCrossSizeAndBaseline(const FlexboxAxisTracker& aAxisTracker)
 {
   nscoord crossStartToFurthestBaseline = nscoord_MIN;
   nscoord crossEndToFurthestBaseline = nscoord_MIN;
   nscoord largestOuterCrossSize = 0;
   for (const FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
     nscoord curOuterCrossSize =
       item->GetOuterCrossSize(aAxisTracker.GetCrossAxis());
     if (item->GetAlignSelf() == NS_STYLE_ALIGN_ITEMS_BASELINE &&
         item->GetNumAutoMarginsInAxis(aAxisTracker.GetCrossAxis()) == 0) {
       // FIXME: Once we support "writing-mode", we'll have to do baseline
       // alignment in vertical flex containers here (w/ horizontal cross-axes).
       // Find distance from our item's cross-start and cross-end margin-box
       // edges to its baseline.
       //
       // Here's a diagram of a flex-item that we might be doing this on.
       // "mmm" is the margin-box, "bbb" is the border-box. The bottom of
       // the text "BASE" is the baseline.
       //
       // ---(cross-start)---
       //                ___              ___            ___
       //   mmmmmmmmmmmm  |                |margin-start  |
       //   m          m  |               _|_   ___       |
       //   m bbbbbbbb m  |curOuterCrossSize     |        |crossStartToBaseline
       //   m b      b m  |                      |ascent  |
       //   m b BASE b m  |                     _|_      _|_
       //   m b      b m  |                               |
       //   m bbbbbbbb m  |                               |crossEndToBaseline
       //   m          m  |                               |
       //   mmmmmmmmmmmm _|_                             _|_
       //
       // ---(cross-end)---
       //
       // We already have the curOuterCrossSize, margin-start, and the ascent.
       // * We can get crossStartToBaseline by adding margin-start + ascent.
       // * If we subtract that from the curOuterCrossSize, we get
       //   crossEndToBaseline.
       nscoord crossStartToBaseline =
         item->GetBaselineOffsetFromOuterCrossEdge(aAxisTracker.GetCrossAxis(),
                                                   eAxisEdge_Start);
       nscoord crossEndToBaseline = curOuterCrossSize - crossStartToBaseline;
       // Now, update our "largest" values for these (across all the flex items
       // in this flex line), so we can use them in computing the line's cross
       // size below:
       crossStartToFurthestBaseline = std::max(crossStartToFurthestBaseline,
                                               crossStartToBaseline);
       crossEndToFurthestBaseline = std::max(crossEndToFurthestBaseline,
                                             crossEndToBaseline);
     } else {
       largestOuterCrossSize = std::max(largestOuterCrossSize, curOuterCrossSize);
     }
   }
   // The line's baseline offset is the distance from the line's edge (start or
   // end, depending on whether we've flipped the axes) to the furthest
   // item-baseline. The item(s) with that baseline will be exactly aligned with
   // the line's edge.
   mBaselineOffset = aAxisTracker.AreAxesInternallyReversed() ?
     crossEndToFurthestBaseline : crossStartToFurthestBaseline;
   // The line's cross-size is the larger of:
   //  (a) [largest cross-start-to-baseline + largest baseline-to-cross-end] of
   //      all baseline-aligned items with no cross-axis auto margins...
   // and
   //  (b) largest cross-size of all other children.
   mLineCrossSize = std::max(crossStartToFurthestBaseline +
                             crossEndToFurthestBaseline,
                             largestOuterCrossSize);
 }
 void
 FlexItem::ResolveStretchedCrossSize(nscoord aLineCrossSize,
                                     const FlexboxAxisTracker& aAxisTracker)
 {
   AxisOrientationType crossAxis = aAxisTracker.GetCrossAxis();
   // We stretch IFF we are align-self:stretch, have no auto margins in
   // cross axis, and have cross-axis size property == "auto". If any of those
   // conditions don't hold up, we won't stretch.
   if (mAlignSelf != NS_STYLE_ALIGN_ITEMS_STRETCH ||
       GetNumAutoMarginsInAxis(crossAxis) != 0 ||
       eStyleUnit_Auto != GetSizePropertyForAxis(mFrame, crossAxis).GetUnit()) {
     return;
   }
   // If we've already been stretched, we can bail out early, too.
   // No need to redo the calculation.
   if (mIsStretched) {
     return;
   }
   // Reserve space for margins & border & padding, and then use whatever
   // remains as our item's cross-size (clamped to its min/max range).
   nscoord stretchedSize = aLineCrossSize -
     GetMarginBorderPaddingSizeInAxis(crossAxis);
   stretchedSize = NS_CSS_MINMAX(stretchedSize, mCrossMinSize, mCrossMaxSize);
   // Update the cross-size & make a note that it's stretched, so we know to
   // override the reflow state's computed cross-size in our final reflow.
   SetCrossSize(stretchedSize);
   mIsStretched = true;
 }
 void
 SingleLineCrossAxisPositionTracker::
   ResolveAutoMarginsInCrossAxis(const FlexLine& aLine,
                                 FlexItem& aItem)
 {
   // Subtract the space that our item is already occupying, to see how much
   // space (if any) is available for its auto margins.
   nscoord spaceForAutoMargins = aLine.GetLineCrossSize() -
     aItem.GetOuterCrossSize(mAxis);
   if (spaceForAutoMargins <= 0) {
     return; // No available space  --> nothing to do
   }
   uint32_t numAutoMargins = aItem.GetNumAutoMarginsInAxis(mAxis);
   if (numAutoMargins == 0) {
     return; // No auto margins --> nothing to do.
   }
   // OK, we have at least one auto margin and we have some available space.
   // Give each auto margin a share of the space.
   const nsStyleSides& styleMargin = aItem.Frame()->StyleMargin()->mMargin;
   for (uint32_t i = 0; i < eNumAxisEdges; i++) {
     Side side = kAxisOrientationToSidesMap[mAxis][i];
     if (styleMargin.GetUnit(side) == eStyleUnit_Auto) {
       MOZ_ASSERT(aItem.GetMarginComponentForSide(side) == 0,
                  "Expecting auto margins to have value '0' before we "
                  "update them");
       // NOTE: integer divison is fine here; numAutoMargins is either 1 or 2.
       // If it's 2 & spaceForAutoMargins is odd, 1st margin gets smaller half.
       nscoord curAutoMarginSize = spaceForAutoMargins / numAutoMargins;
       aItem.SetMarginComponentForSide(side, curAutoMarginSize);
       numAutoMargins--;
       spaceForAutoMargins -= curAutoMarginSize;
     }
   }
 }
 void
 SingleLineCrossAxisPositionTracker::
   EnterAlignPackingSpace(const FlexLine& aLine,
                          const FlexItem& aItem,
                          const FlexboxAxisTracker& aAxisTracker)
 {
   // We don't do align-self alignment on items that have auto margins
   // in the cross axis.
   if (aItem.GetNumAutoMarginsInAxis(mAxis)) {
     return;
   }
   uint8_t alignSelf = aItem.GetAlignSelf();
   // NOTE: 'stretch' behaves like 'flex-start' once we've stretched any
   // auto-sized items (which we've already done).
   if (alignSelf == NS_STYLE_ALIGN_ITEMS_STRETCH) {
     alignSelf = NS_STYLE_ALIGN_ITEMS_FLEX_START;
   }
   // If our cross axis is (internally) reversed, swap the align-self
   // "flex-start" and "flex-end" behaviors:
   if (aAxisTracker.AreAxesInternallyReversed()) {
     if (alignSelf == NS_STYLE_ALIGN_ITEMS_FLEX_START) {
       alignSelf = NS_STYLE_ALIGN_ITEMS_FLEX_END;
     } else if (alignSelf == NS_STYLE_ALIGN_ITEMS_FLEX_END) {
       alignSelf = NS_STYLE_ALIGN_ITEMS_FLEX_START;
     }
   }
   switch (alignSelf) {
     case NS_STYLE_ALIGN_ITEMS_FLEX_START:
       // No space to skip over -- we're done.
       break;
     case NS_STYLE_ALIGN_ITEMS_FLEX_END:
       mPosition += aLine.GetLineCrossSize() - aItem.GetOuterCrossSize(mAxis);
       break;
     case NS_STYLE_ALIGN_ITEMS_CENTER:
       // Note: If cross-size is odd, the "after" space will get the extra unit.
       mPosition +=
         (aLine.GetLineCrossSize() - aItem.GetOuterCrossSize(mAxis)) / 2;
       break;
     case NS_STYLE_ALIGN_ITEMS_BASELINE: {
       // Normally, baseline-aligned items are collectively aligned with the
       // line's cross-start edge; however, if our cross axis is (internally)
       // reversed, we instead align them with the cross-end edge.
       nscoord itemBaselineOffset =
         aItem.GetBaselineOffsetFromOuterCrossEdge(mAxis,
           aAxisTracker.AreAxesInternallyReversed() ?
           eAxisEdge_End : eAxisEdge_Start);
       nscoord lineBaselineOffset = aLine.GetBaselineOffset();
       NS_ASSERTION(lineBaselineOffset >= itemBaselineOffset,
                    "failed at finding largest baseline offset");
       // How much do we need to adjust our position (from the line edge),
       // to get the item's baseline to hit the line's baseline offset:
       nscoord baselineDiff = lineBaselineOffset - itemBaselineOffset;
       if (aAxisTracker.AreAxesInternallyReversed()) {
         // Advance to align item w/ line's flex-end edge (as in FLEX_END case):
         mPosition += aLine.GetLineCrossSize() - aItem.GetOuterCrossSize(mAxis);
         // ...and step *back* by the baseline adjustment:
         mPosition -= baselineDiff;
       } else {
         // mPosition is already at line's flex-start edge.
         // From there, we step *forward* by the baseline adjustment:
         mPosition += baselineDiff;
       }
       break;
     }
     default:
       NS_NOTREACHED("Unexpected align-self value");
       break;
   }
 }
 FlexboxAxisTracker::FlexboxAxisTracker(
   nsFlexContainerFrame* aFlexContainerFrame)
   : mAreAxesInternallyReversed(false)
 {
   const nsStylePosition* pos = aFlexContainerFrame->StylePosition();
   uint32_t flexDirection = pos->mFlexDirection;
   uint32_t cssDirection =
     aFlexContainerFrame->StyleVisibility()->mDirection;
   MOZ_ASSERT(cssDirection == NS_STYLE_DIRECTION_LTR ||
              cssDirection == NS_STYLE_DIRECTION_RTL,
              "Unexpected computed value for 'direction' property");
   // (Not asserting for flexDirection here; it's checked by the switch below.)
   // These are defined according to writing-modes' definitions of
   // start/end (for the inline dimension) and before/after (for the block
   // dimension), here:
   //   http://www.w3.org/TR/css3-writing-modes/#logical-directions
   // (NOTE: I'm intentionally not calling this "inlineAxis"/"blockAxis", since
   // those terms have explicit definition in the writing-modes spec, which are
   // the opposite of how I'd be using them here.)
   // XXXdholbert Once we support the 'writing-mode' property, use its value
   // here to further customize inlineDimension & blockDimension.
   // Inline dimension ("start-to-end"):
   AxisOrientationType inlineDimension =
     cssDirection == NS_STYLE_DIRECTION_RTL ? eAxis_RL : eAxis_LR;
   // Block dimension ("before-to-after"):
   AxisOrientationType blockDimension = eAxis_TB;
   // Determine main axis:
   switch (flexDirection) {
     case NS_STYLE_FLEX_DIRECTION_ROW:
       mMainAxis = inlineDimension;
       break;
     case NS_STYLE_FLEX_DIRECTION_ROW_REVERSE:
       mMainAxis = GetReverseAxis(inlineDimension);
       break;
     case NS_STYLE_FLEX_DIRECTION_COLUMN:
       mMainAxis = blockDimension;
       break;
     case NS_STYLE_FLEX_DIRECTION_COLUMN_REVERSE:
       mMainAxis = GetReverseAxis(blockDimension);
       break;
     default:
       MOZ_CRASH("Unexpected computed value for 'flex-flow' property");
   }
   // Determine cross axis:
   // (This is set up so that a bogus |flexDirection| value will
   // give us blockDimension.
   if (flexDirection == NS_STYLE_FLEX_DIRECTION_COLUMN ||
       flexDirection == NS_STYLE_FLEX_DIRECTION_COLUMN_REVERSE) {
     mCrossAxis = inlineDimension;
   } else {
     mCrossAxis = blockDimension;
   }
   // "flex-wrap: wrap-reverse" reverses our cross axis.
   if (pos->mFlexWrap == NS_STYLE_FLEX_WRAP_WRAP_REVERSE) {
     mCrossAxis = GetReverseAxis(mCrossAxis);
   }
   // Master switch to enable/disable bug 983427's code for reversing our axes
   // and reversing some logic, to avoid reflowing children in bottom-to-top
   // order. (This switch can be removed eventually, but for now, it allows
   // this special-case code path to be compared against the normal code path.)
   static bool sPreventBottomToTopChildOrdering = true;
   if (sPreventBottomToTopChildOrdering) {
     // If either axis is bottom-to-top, we flip both axes (and set a flag
     // so that we can flip some logic to make the reversal transparent).
     if (eAxis_BT == mMainAxis || eAxis_BT == mCrossAxis) {
       mMainAxis = GetReverseAxis(mMainAxis);
       mCrossAxis = GetReverseAxis(mCrossAxis);
       mAreAxesInternallyReversed = true;
     }
   }
   MOZ_ASSERT(IsAxisHorizontal(mMainAxis) != IsAxisHorizontal(mCrossAxis),
              "main & cross axes should be in different dimensions");
 }
 // Allocates a new FlexLine, adds it to the given LinkedList (at the front or
 // back depending on aShouldInsertAtFront), and returns a pointer to it.
 static FlexLine*
 AddNewFlexLineToList(LinkedList<FlexLine>& aLines,
                      bool aShouldInsertAtFront)
 {
   FlexLine* newLine = new FlexLine();
   if (aShouldInsertAtFront) {
     aLines.insertFront(newLine);
   } else {
     aLines.insertBack(newLine);
   }
   return newLine;
 }
 nsresult
 nsFlexContainerFrame::GenerateFlexLines(
   nsPresContext* aPresContext,
   const nsHTMLReflowState& aReflowState,
   nscoord aContentBoxMainSize,
   nscoord aAvailableHeightForContent,
   const nsTArray<StrutInfo>& aStruts,
   const FlexboxAxisTracker& aAxisTracker,
   LinkedList<FlexLine>& aLines)
 {
   MOZ_ASSERT(aLines.isEmpty(), "Expecting outparam to start out empty");
   const bool isSingleLine =
     NS_STYLE_FLEX_WRAP_NOWRAP == aReflowState.mStylePosition->mFlexWrap;
   // If we're transparently reversing axes, then we'll need to link up our
   // FlexItems and FlexLines in the reverse order, so that the rest of flex
   // layout (with flipped axes) will still produce the correct result.
   // Here, we declare a convenience bool that we'll pass when adding a new
   // FlexLine or FlexItem, to make us insert it at the beginning of its list
   // (so the list ends up reversed).
   const bool shouldInsertAtFront = aAxisTracker.AreAxesInternallyReversed();
   // We have at least one FlexLine. Even an empty flex container has a single
   // (empty) flex line.
   FlexLine* curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
   nscoord wrapThreshold;
   if (isSingleLine) {
     // Not wrapping. Set threshold to sentinel value that tells us not to wrap.
     wrapThreshold = NS_UNCONSTRAINEDSIZE;
   } else {
     // Wrapping! Set wrap threshold to flex container's content-box main-size.
     wrapThreshold = aContentBoxMainSize;
     // If the flex container doesn't have a definite content-box main-size
     // (e.g. if we're 'height:auto'), make sure we at least wrap when we hit
     // its max main-size.
     if (wrapThreshold == NS_UNCONSTRAINEDSIZE) {
       const nscoord flexContainerMaxMainSize =
         GET_MAIN_COMPONENT(aAxisTracker,
                            aReflowState.ComputedMaxWidth(),
                            aReflowState.ComputedMaxHeight());
       wrapThreshold = flexContainerMaxMainSize;
     }
     // Also: if we're vertical and paginating, we may need to wrap sooner
     // (before we run off the end of the page)
     if (!IsAxisHorizontal(aAxisTracker.GetMainAxis()) &&
         aAvailableHeightForContent != NS_UNCONSTRAINEDSIZE) {
       wrapThreshold = std::min(wrapThreshold, aAvailableHeightForContent);
     }
   }
   // Tracks the index of the next strut, in aStruts (and when this hits
   // aStruts.Length(), that means there are no more struts):
   uint32_t nextStrutIdx = 0;
   // Overall index of the current flex item in the flex container. (This gets
   // checked against entries in aStruts.)
   uint32_t itemIdxInContainer = 0;
   for (nsFrameList::Enumerator e(mFrames); !e.AtEnd(); e.Next()) {
     nsIFrame* childFrame = e.get();
     // Honor "page-break-before", if we're multi-line and this line isn't empty:
     if (!isSingleLine && !curLine->IsEmpty() &&
         childFrame->StyleDisplay()->mBreakBefore) {
       curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
     }
     nsAutoPtr<FlexItem> item;
     if (nextStrutIdx < aStruts.Length() &&
         aStruts[nextStrutIdx].mItemIdx == itemIdxInContainer) {
       // Use the simplified "strut" FlexItem constructor:
       item = new FlexItem(childFrame, aStruts[nextStrutIdx].mStrutCrossSize);
       nextStrutIdx++;
     } else {
       item = GenerateFlexItemForChild(aPresContext, childFrame,
                                       aReflowState, aAxisTracker);
       nsresult rv = ResolveFlexItemMaxContentSizing(aPresContext, *item,
                                                     aReflowState, aAxisTracker);
       NS_ENSURE_SUCCESS(rv,rv);
     }
     nscoord itemInnerHypotheticalMainSize = item->GetMainSize();
     nscoord itemOuterHypotheticalMainSize =
       item->GetOuterMainSize(aAxisTracker.GetMainAxis());
     // Check if we need to wrap |item| to a new line
     // (i.e. check if its outer hypothetical main size pushes our line over
     // the threshold)
     if (wrapThreshold != NS_UNCONSTRAINEDSIZE &&
         !curLine->IsEmpty() && // No need to wrap at start of a line.
         wrapThreshold < (curLine->GetTotalOuterHypotheticalMainSize() +
                          itemOuterHypotheticalMainSize)) {
       curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
     }
     // Add item to current flex line (and update the line's bookkeeping about
     // how large its items collectively are).
     curLine->AddItem(item.forget(), shouldInsertAtFront,
                      itemInnerHypotheticalMainSize,
                      itemOuterHypotheticalMainSize);
     // Honor "page-break-after", if we're multi-line and have more children:
     if (!isSingleLine && childFrame->GetNextSibling() &&
         childFrame->StyleDisplay()->mBreakAfter) {
       curLine = AddNewFlexLineToList(aLines, shouldInsertAtFront);
     }
     itemIdxInContainer++;
   }
   return NS_OK;
 }
 // Retrieves the content-box main-size of our flex container from the
 // reflow state (specifically, the main-size of *this continuation* of the
 // flex container).
 nscoord
 nsFlexContainerFrame::GetMainSizeFromReflowState(
   const nsHTMLReflowState& aReflowState,
   const FlexboxAxisTracker& aAxisTracker)
 {
   if (IsAxisHorizontal(aAxisTracker.GetMainAxis())) {
     // Horizontal case is easy -- our main size is our computed width
     // (which is already resolved).
     return aReflowState.ComputedWidth();
   }
   return GetEffectiveComputedHeight(aReflowState);
 }
 // Returns the largest outer hypothetical main-size of any line in |aLines|.
 // (i.e. the hypothetical main-size of the largest line)
 static nscoord
 GetLargestLineMainSize(const FlexLine* aFirstLine)
 {
   nscoord largestLineOuterSize = 0;
   for (const FlexLine* line = aFirstLine; line; line = line->getNext()) {
     largestLineOuterSize = std::max(largestLineOuterSize,
                                     line->GetTotalOuterHypotheticalMainSize());
   }
   return largestLineOuterSize;
 }
 // Returns the content-box main-size of our flex container, based on the
 // available height (if appropriate) and the main-sizes of the flex items.
 static nscoord
 ClampFlexContainerMainSize(const nsHTMLReflowState& aReflowState,
                            const FlexboxAxisTracker& aAxisTracker,
                            nscoord aUnclampedMainSize,
                            nscoord aAvailableHeightForContent,
                            const FlexLine* aFirstLine,
                            nsReflowStatus& aStatus)
 {
   MOZ_ASSERT(aFirstLine, "null first line pointer");
   if (IsAxisHorizontal(aAxisTracker.GetMainAxis())) {
     // Horizontal case is easy -- our main size should already be resolved
     // before we get a call to Reflow. We don't have to worry about doing
     // page-breaking or shrinkwrapping in the horizontal axis.
     return aUnclampedMainSize;
   }
   if (aUnclampedMainSize != NS_INTRINSICSIZE) {
     // Vertical case, with fixed height:
     if (aAvailableHeightForContent == NS_UNCONSTRAINEDSIZE ||
         aUnclampedMainSize < aAvailableHeightForContent) {
       // Not in a fragmenting context, OR no need to fragment because we have
       // more available height than we need. Either way, just use our fixed
       // height.  (Note that the reflow state has already done the appropriate
       // min/max-height clamping.)
       return aUnclampedMainSize;
     }
     // Fragmenting *and* our fixed height is too tall for available height:
     // Mark incomplete so we get a next-in-flow, and take up all of the
     // available height (or the amount of height required by our children, if
     // that's larger; but of course not more than our own computed height).
     // XXXdholbert For now, we don't support pushing children to our next
     // continuation or splitting children, so "amount of height required by
     // our children" is just the main-size (height) of our longest flex line.
     NS_FRAME_SET_INCOMPLETE(aStatus);
     nscoord largestLineOuterSize = GetLargestLineMainSize(aFirstLine);
     if (largestLineOuterSize <= aAvailableHeightForContent) {
       return aAvailableHeightForContent;
     }
     return std::min(aUnclampedMainSize, largestLineOuterSize);
   }
   // Vertical case, with auto-height:
   // Resolve auto-height to the largest FlexLine-length, clamped to our
   // computed min/max main-size properties (min-height & max-height).
   // XXXdholbert Handle constrained-aAvailableHeightForContent case here.
   nscoord largestLineOuterSize = GetLargestLineMainSize(aFirstLine);
   return NS_CSS_MINMAX(largestLineOuterSize,
                        aReflowState.ComputedMinHeight(),
                        aReflowState.ComputedMaxHeight());
 }
 nscoord
 nsFlexContainerFrame::ComputeCrossSize(const nsHTMLReflowState& aReflowState,
                                        const FlexboxAxisTracker& aAxisTracker,
                                        nscoord aSumLineCrossSizes,
                                        nscoord aAvailableHeightForContent,
                                        bool* aIsDefinite,
                                        nsReflowStatus& aStatus)
 {
   MOZ_ASSERT(aIsDefinite, "outparam pointer must be non-null");
   if (IsAxisHorizontal(aAxisTracker.GetCrossAxis())) {
     // Cross axis is horizontal: our cross size is our computed width
     // (which is already resolved).
     *aIsDefinite = true;
     return aReflowState.ComputedWidth();
   }
   nscoord effectiveComputedHeight = GetEffectiveComputedHeight(aReflowState);
   if (effectiveComputedHeight != NS_INTRINSICSIZE) {
     // Cross-axis is vertical, and we have a fixed height:
     *aIsDefinite = true;
     if (aAvailableHeightForContent == NS_UNCONSTRAINEDSIZE ||
         effectiveComputedHeight < aAvailableHeightForContent) {
       // Not in a fragmenting context, OR no need to fragment because we have
       // more available height than we need. Either way, just use our fixed
       // height.  (Note that the reflow state has already done the appropriate
       // min/max-height clamping.)
       return effectiveComputedHeight;
     }
     // Fragmenting *and* our fixed height is too tall for available height:
     // Mark incomplete so we get a next-in-flow, and take up all of the
     // available height (or the amount of height required by our children, if
     // that's larger; but of course not more than our own computed height).
     // XXXdholbert For now, we don't support pushing children to our next
     // continuation or splitting children, so "amount of height required by
     // our children" is just our line-height.
     NS_FRAME_SET_INCOMPLETE(aStatus);
     if (aSumLineCrossSizes <= aAvailableHeightForContent) {
       return aAvailableHeightForContent;
     }
     return std::min(effectiveComputedHeight, aSumLineCrossSizes);
   }
   // Cross axis is vertical and we have auto-height: shrink-wrap our line(s),
   // subject to our min-size / max-size constraints in that (vertical) axis.
   // XXXdholbert Handle constrained-aAvailableHeightForContent case here.
   *aIsDefinite = false;
   return NS_CSS_MINMAX(aSumLineCrossSizes,
                        aReflowState.ComputedMinHeight(),
                        aReflowState.ComputedMaxHeight());
 }
 void
 FlexLine::PositionItemsInMainAxis(uint8_t aJustifyContent,
                                   nscoord aContentBoxMainSize,
                                   const FlexboxAxisTracker& aAxisTracker)
 {
   MainAxisPositionTracker mainAxisPosnTracker(aAxisTracker, this,
                                               aJustifyContent,
                                               aContentBoxMainSize);
   for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
     nscoord itemMainBorderBoxSize =
       item->GetMainSize() +
       item->GetBorderPaddingSizeInAxis(mainAxisPosnTracker.GetAxis());
     // Resolve any main-axis 'auto' margins on aChild to an actual value.
     mainAxisPosnTracker.ResolveAutoMarginsInMainAxis(*item);
     // Advance our position tracker to child's upper-left content-box corner,
     // and use that as its position in the main axis.
     mainAxisPosnTracker.EnterMargin(item->GetMargin());
     mainAxisPosnTracker.EnterChildFrame(itemMainBorderBoxSize);
     item->SetMainPosition(mainAxisPosnTracker.GetPosition());
     mainAxisPosnTracker.ExitChildFrame(itemMainBorderBoxSize);
     mainAxisPosnTracker.ExitMargin(item->GetMargin());
     mainAxisPosnTracker.TraversePackingSpace();
   }
 }
 // Helper method to take care of children who ASK_FOR_BASELINE, when
 // we need their baseline.
 static void
 ResolveReflowedChildAscent(nsIFrame* aFrame,
                            nsHTMLReflowMetrics& aChildDesiredSize)
 {
   if (aChildDesiredSize.TopAscent() == nsHTMLReflowMetrics::ASK_FOR_BASELINE) {
     // Use GetFirstLineBaseline(), or just GetBaseline() if that fails.
     nscoord ascent;
     if (nsLayoutUtils::GetFirstLineBaseline(aFrame, &ascent)) {
       aChildDesiredSize.SetTopAscent(ascent);
     } else {
       aChildDesiredSize.SetTopAscent(aFrame->GetBaseline());
     }
   }
 }
 /**
  * Given the flex container's "logical ascent" (i.e. distance from the
  * flex container's content-box cross-start edge to its baseline), returns
  * its actual physical ascent value (the distance from the *border-box* top
  * edge to its baseline).
  */
 static nscoord
 ComputePhysicalAscentFromLogicalAscent(nscoord aLogicalAscent,
                                        nscoord aContentBoxCrossSize,
                                        const nsHTMLReflowState& aReflowState,
                                        const FlexboxAxisTracker& aAxisTracker)
 {
   return aReflowState.ComputedPhysicalBorderPadding().top +
     PhysicalPosFromLogicalPos(aLogicalAscent, aContentBoxCrossSize,
                               aAxisTracker.GetCrossAxis());
 }
 nsresult
 nsFlexContainerFrame::SizeItemInCrossAxis(
   nsPresContext* aPresContext,
   const FlexboxAxisTracker& aAxisTracker,
   nsHTMLReflowState& aChildReflowState,
   FlexItem& aItem)
 {
   // In vertical flexbox (with horizontal cross-axis), we can just trust the
   // reflow state's computed-width as our cross-size. We also don't need to
   // record the baseline because we'll have converted any "align-self:baseline"
   // items to be "align-self:flex-start" in the FlexItem constructor.
   // FIXME: Once we support writing-mode (vertical text), we will be able to
   // have baseline-aligned items in a vertical flexbox, and we'll need to
   // record baseline information here.
   if (IsAxisHorizontal(aAxisTracker.GetCrossAxis())) {
     MOZ_ASSERT(aItem.GetAlignSelf() != NS_STYLE_ALIGN_ITEMS_BASELINE,
                "In vert flex container, we depend on FlexItem constructor to "
                "convert 'align-self: baseline' to 'align-self: flex-start'");
     aItem.SetCrossSize(aChildReflowState.ComputedWidth());
     return NS_OK;
   }
   MOZ_ASSERT(!aItem.HadMeasuringReflow(),
              "We shouldn't need more than one measuring reflow");
   if (aItem.GetAlignSelf() == NS_STYLE_ALIGN_ITEMS_STRETCH) {
     // This item's got "align-self: stretch", so we probably imposed a
     // stretched computed height on it during its previous reflow. We're
     // not imposing that height for *this* measuring reflow, so we need to
     // tell it to treat this reflow as a vertical resize (regardless of
     // whether any of its ancestors are being resized).
     aChildReflowState.mFlags.mVResize = true;
   }
   nsHTMLReflowMetrics childDesiredSize(aChildReflowState);
   nsReflowStatus childReflowStatus;
   const uint32_t flags = NS_FRAME_NO_MOVE_FRAME;
   nsresult rv = ReflowChild(aItem.Frame(), aPresContext,
                             childDesiredSize, aChildReflowState,
 , 0, flags, childReflowStatus);
   aItem.SetHadMeasuringReflow();
   NS_ENSURE_SUCCESS(rv, rv);
   // XXXdholbert Once we do pagination / splitting, we'll need to actually
   // handle incomplete childReflowStatuses. But for now, we give our kids
   // unconstrained available height, which means they should always complete.
   MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
              "We gave flex item unconstrained available height, so it "
              "should be complete");
   // Tell the child we're done with its initial reflow.
   // (Necessary for e.g. GetBaseline() to work below w/out asserting)
   rv = FinishReflowChild(aItem.Frame(), aPresContext,
                          childDesiredSize, &aChildReflowState, 0, 0, flags);
   NS_ENSURE_SUCCESS(rv, rv);
   // Save the sizing info that we learned from this reflow
   // -----------------------------------------------------
   // Tentatively store the child's desired content-box cross-size.
   // Note that childDesiredSize is the border-box size, so we have to
   // subtract border & padding to get the content-box size.
   // (Note that at this point in the code, we know our cross axis is vertical,
   // so we don't bother with making aAxisTracker pick the cross-axis component
   // for us.)
   nscoord crossAxisBorderPadding = aItem.GetBorderPadding().TopBottom();
   if (childDesiredSize.Height() < crossAxisBorderPadding) {
     // Child's requested size isn't large enough for its border/padding!
     // This is OK for the trivial nsFrame::Reflow() impl, but other frame
     // classes should know better. So, if we get here, the child had better be
     // an instance of nsFrame (i.e. it should return null from GetType()).
     // XXXdholbert Once we've fixed bug 765861, we should upgrade this to an
     // assertion that trivially passes if bug 765861's flag has been flipped.
     NS_WARN_IF_FALSE(!aItem.Frame()->GetType(),
                      "Child should at least request space for border/padding");
     aItem.SetCrossSize(0);
   } else {
     // (normal case)
     aItem.SetCrossSize(childDesiredSize.Height() - crossAxisBorderPadding);
   }
   // If we need to do baseline-alignment, store the child's ascent.
   if (aItem.GetAlignSelf() == NS_STYLE_ALIGN_ITEMS_BASELINE) {
     ResolveReflowedChildAscent(aItem.Frame(), childDesiredSize);
     aItem.SetAscent(childDesiredSize.TopAscent());
   }
   return NS_OK;
 }
 void
 FlexLine::PositionItemsInCrossAxis(nscoord aLineStartPosition,
                                    const FlexboxAxisTracker& aAxisTracker)
 {
   SingleLineCrossAxisPositionTracker lineCrossAxisPosnTracker(aAxisTracker);
   for (FlexItem* item = mItems.getFirst(); item; item = item->getNext()) {
     // First, stretch the item's cross size (if appropriate), and resolve any
     // auto margins in this axis.
     item->ResolveStretchedCrossSize(mLineCrossSize, aAxisTracker);
     lineCrossAxisPosnTracker.ResolveAutoMarginsInCrossAxis(*this, *item);
     // Compute the cross-axis position of this item
     nscoord itemCrossBorderBoxSize =
       item->GetCrossSize() +
       item->GetBorderPaddingSizeInAxis(aAxisTracker.GetCrossAxis());
     lineCrossAxisPosnTracker.EnterAlignPackingSpace(*this, *item, aAxisTracker);
     lineCrossAxisPosnTracker.EnterMargin(item->GetMargin());
     lineCrossAxisPosnTracker.EnterChildFrame(itemCrossBorderBoxSize);
     item->SetCrossPosition(aLineStartPosition +
                            lineCrossAxisPosnTracker.GetPosition());
     // Back out to cross-axis edge of the line.
     lineCrossAxisPosnTracker.ResetPosition();
   }
 }
 nsresult
 nsFlexContainerFrame::Reflow(nsPresContext*           aPresContext,
                              nsHTMLReflowMetrics&     aDesiredSize,
                              const nsHTMLReflowState& aReflowState,
                              nsReflowStatus&          aStatus)
 {
   DO_GLOBAL_REFLOW_COUNT("nsFlexContainerFrame");
   DISPLAY_REFLOW(aPresContext, this, aReflowState, aDesiredSize, aStatus);
   PR_LOG(GetFlexContainerLog(), PR_LOG_DEBUG,
          ("Reflow() for nsFlexContainerFrame %p\n", this));
   if (IsFrameTreeTooDeep(aReflowState, aDesiredSize, aStatus)) {
     return NS_OK;
   }
   // We (and our children) can only depend on our ancestor's height if we have
   // a percent-height, or if we're positioned and we have "top" and "bottom"
   // set and have height:auto.  (There are actually other cases, too -- e.g. if
   // our parent is itself a vertical flex container and we're flexible -- but
   // we'll let our ancestors handle those sorts of cases.)
   const nsStylePosition* stylePos = StylePosition();
   if (stylePos->mHeight.HasPercent() ||
       (StyleDisplay()->IsAbsolutelyPositionedStyle() &&
        eStyleUnit_Auto == stylePos->mHeight.GetUnit() &&
        eStyleUnit_Auto != stylePos->mOffset.GetTopUnit() &&
        eStyleUnit_Auto != stylePos->mOffset.GetBottomUnit())) {
     AddStateBits(NS_FRAME_CONTAINS_RELATIVE_HEIGHT);
   }
 #ifdef DEBUG
   SanityCheckAnonymousFlexItems();
 #endif // DEBUG
   // If we've never reordered our children, then we can trust that they're
   // already in DOM-order, and we only need to consider their "order" property
   // when checking them for sortedness & sorting them.
   //
   // After we actually sort them, though, we can't trust that they're in DOM
   // order anymore.  So, from that point on, our sort & sorted-order-checking
   // operations need to use a fancier LEQ function that also takes DOM order
   // into account, so that we can honor the spec's requirement that frames w/
   // equal "order" values are laid out in DOM order.
   if (!HasAnyStateBits(NS_STATE_FLEX_CHILDREN_REORDERED)) {
     if (SortChildrenIfNeeded<IsOrderLEQ>()) {
       AddStateBits(NS_STATE_FLEX_CHILDREN_REORDERED);
     }
   } else {
     SortChildrenIfNeeded<IsOrderLEQWithDOMFallback>();
   }
   const FlexboxAxisTracker axisTracker(this);
   // If we're being fragmented into a constrained height, subtract off
   // borderpadding-top from it, to get the available height for our
   // content box. (Don't subtract if we're skipping top border/padding,
   // though.)
   nscoord availableHeightForContent = aReflowState.AvailableHeight();
   if (availableHeightForContent != NS_UNCONSTRAINEDSIZE &&
       !(GetSkipSides() & (1 << NS_SIDE_TOP))) {
     availableHeightForContent -= aReflowState.ComputedPhysicalBorderPadding().top;
     // (Don't let that push availableHeightForContent below zero, though):
     availableHeightForContent = std::max(availableHeightForContent, 0);
   }
   nscoord contentBoxMainSize = GetMainSizeFromReflowState(aReflowState,
                                                           axisTracker);
   nsAutoTArray<StrutInfo, 1> struts;
   nsresult rv = DoFlexLayout(aPresContext, aDesiredSize, aReflowState, aStatus,
                              contentBoxMainSize, availableHeightForContent,
                              struts, axisTracker);
   if (NS_SUCCEEDED(rv) && !struts.IsEmpty()) {
     // We're restarting flex layout, with new knowledge of collapsed items.
     rv = DoFlexLayout(aPresContext, aDesiredSize, aReflowState, aStatus,
                       contentBoxMainSize, availableHeightForContent,
                       struts, axisTracker);
   }
   return rv;
 }
 // RAII class to clean up a list of FlexLines.
 // Specifically, this removes each line from the list, deletes all the
 // FlexItems in its list, and deletes the FlexLine.
 class MOZ_STACK_CLASS AutoFlexLineListClearer
 {
 public:
   AutoFlexLineListClearer(LinkedList<FlexLine>& aLines
                           MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
   : mLines(aLines)
   {
     MOZ_GUARD_OBJECT_NOTIFIER_INIT;
   }
   ~AutoFlexLineListClearer()
   {
     while (FlexLine* line = mLines.popFirst()) {
       while (FlexItem* item = line->mItems.popFirst()) {
         delete item;
       }
       delete line;
     }
   }
 private:
   LinkedList<FlexLine>& mLines;
   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
 };
 nsresult
 nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
                                    nsHTMLReflowMetrics&     aDesiredSize,
                                    const nsHTMLReflowState& aReflowState,
                                    nsReflowStatus&          aStatus,
                                    nscoord aContentBoxMainSize,
                                    nscoord aAvailableHeightForContent,
                                    nsTArray<StrutInfo>& aStruts,
                                    const FlexboxAxisTracker& aAxisTracker)
 {
   aStatus = NS_FRAME_COMPLETE;
   LinkedList<FlexLine> lines;
   AutoFlexLineListClearer cleanupLines(lines);
   nsresult rv = GenerateFlexLines(aPresContext, aReflowState,
                                   aContentBoxMainSize,
                                   aAvailableHeightForContent,
                                   aStruts, aAxisTracker, lines);
   NS_ENSURE_SUCCESS(rv, rv);
   aContentBoxMainSize =
     ClampFlexContainerMainSize(aReflowState, aAxisTracker,
                                aContentBoxMainSize, aAvailableHeightForContent,
                                lines.getFirst(), aStatus);
   for (FlexLine* line = lines.getFirst(); line; line = line->getNext()) {
     line->ResolveFlexibleLengths(aContentBoxMainSize);
   }
   // Cross Size Determination - Flexbox spec section 9.4
   // ===================================================
   // Calculate the hypothetical cross size of each item:
   nscoord sumLineCrossSizes = 0;
   for (FlexLine* line = lines.getFirst(); line; line = line->getNext()) {
     for (FlexItem* item = line->GetFirstItem(); item; item = item->getNext()) {
       // (If the item's already been stretched, or it's a strut, then it
       // already knows its cross size.  Don't bother trying to recalculate it.)
       if (!item->IsStretched() && !item->IsStrut()) {
         nsHTMLReflowState childReflowState(aPresContext, aReflowState,
                                            item->Frame(),
                                            nsSize(aReflowState.ComputedWidth(),
                                                   NS_UNCONSTRAINEDSIZE));
         // Override computed main-size
         if (IsAxisHorizontal(aAxisTracker.GetMainAxis())) {
           childReflowState.SetComputedWidth(item->GetMainSize());
         } else {
           childReflowState.SetComputedHeight(item->GetMainSize());
         }
         nsresult rv = SizeItemInCrossAxis(aPresContext, aAxisTracker,
                                           childReflowState, *item);
         NS_ENSURE_SUCCESS(rv, rv);
       }
     }
     // Now that we've finished with this line's items, size the line itself:
     line->ComputeCrossSizeAndBaseline(aAxisTracker);
     sumLineCrossSizes += line->GetLineCrossSize();
   }
   bool isCrossSizeDefinite;
   const nscoord contentBoxCrossSize =
     ComputeCrossSize(aReflowState, aAxisTracker, sumLineCrossSizes,
                      aAvailableHeightForContent, &isCrossSizeDefinite, aStatus);
   // Set up state for cross-axis alignment, at a high level (outside the
   // scope of a particular flex line)
   CrossAxisPositionTracker
     crossAxisPosnTracker(lines.getFirst(),
                          aReflowState.mStylePosition->mAlignContent,
                          contentBoxCrossSize, isCrossSizeDefinite,
                          aAxisTracker);
   // Now that we know the cross size of each line (including
   // "align-content:stretch" adjustments, from the CrossAxisPositionTracker
   // constructor), we can create struts for any flex items with
   // "visibility: collapse" (and restart flex layout).
   if (aStruts.IsEmpty()) { // (Don't make struts if we already did)
     BuildStrutInfoFromCollapsedItems(lines.getFirst(), aStruts);
     if (!aStruts.IsEmpty()) {
       // Restart flex layout, using our struts.
       return NS_OK;
     }
   }
   // If the container should derive its baseline from the first FlexLine,
   // do that here (while crossAxisPosnTracker is conveniently pointing
   // at the cross-start edge of that line, which the line's baseline offset is
   // measured from):
   nscoord flexContainerAscent;
   if (!aAxisTracker.AreAxesInternallyReversed()) {
     nscoord firstLineBaselineOffset = lines.getFirst()->GetBaselineOffset();
     if (firstLineBaselineOffset == nscoord_MIN) {
       // No baseline-aligned items in line. Use sentinel value to prompt us to
       // get baseline from the first FlexItem after we've reflowed it.
       flexContainerAscent = nscoord_MIN;
     } else  {
       flexContainerAscent =
         ComputePhysicalAscentFromLogicalAscent(
           crossAxisPosnTracker.GetPosition() + firstLineBaselineOffset,
           contentBoxCrossSize, aReflowState, aAxisTracker);
     }
   }
   for (FlexLine* line = lines.getFirst(); line; line = line->getNext()) {
     // Main-Axis Alignment - Flexbox spec section 9.5
     // ==============================================
     line->PositionItemsInMainAxis(aReflowState.mStylePosition->mJustifyContent,
                                   aContentBoxMainSize,
                                   aAxisTracker);
     // Cross-Axis Alignment - Flexbox spec section 9.6
     // ===============================================
     line->PositionItemsInCrossAxis(crossAxisPosnTracker.GetPosition(),
                                    aAxisTracker);
     crossAxisPosnTracker.TraverseLine(*line);
     crossAxisPosnTracker.TraversePackingSpace();
   }
   // If the container should derive its baseline from the last FlexLine,
   // do that here (while crossAxisPosnTracker is conveniently pointing
   // at the cross-end edge of that line, which the line's baseline offset is
   // measured from):
   if (aAxisTracker.AreAxesInternallyReversed()) {
     nscoord lastLineBaselineOffset = lines.getLast()->GetBaselineOffset();
     if (lastLineBaselineOffset == nscoord_MIN) {
       // No baseline-aligned items in line. Use sentinel value to prompt us to
       // get baseline from the last FlexItem after we've reflowed it.
       flexContainerAscent = nscoord_MIN;
     } else {
       flexContainerAscent =
         ComputePhysicalAscentFromLogicalAscent(
           crossAxisPosnTracker.GetPosition() - lastLineBaselineOffset,
           contentBoxCrossSize, aReflowState, aAxisTracker);
     }
   }
   // Before giving each child a final reflow, calculate the origin of the
   // flex container's content box (with respect to its border-box), so that
   // we can compute our flex item's final positions.
   nsMargin containerBorderPadding(aReflowState.ComputedPhysicalBorderPadding());
   ApplySkipSides(containerBorderPadding, &aReflowState);
   const nsPoint containerContentBoxOrigin(containerBorderPadding.left,
                                           containerBorderPadding.top);
   // FINAL REFLOW: Give each child frame another chance to reflow, now that
   // we know its final size and position.
   for (const FlexLine* line = lines.getFirst(); line; line = line->getNext()) {
     for (const FlexItem* item = line->GetFirstItem(); item;
          item = item->getNext()) {
       nsPoint physicalPosn = aAxisTracker.PhysicalPointFromLogicalPoint(
                                item->GetMainPosition(),
                                item->GetCrossPosition(),
                                aContentBoxMainSize,
                                contentBoxCrossSize);
       // Adjust physicalPosn to be relative to the container's border-box
       // (i.e. its frame rect), instead of the container's content-box:
       physicalPosn += containerContentBoxOrigin;
       nsHTMLReflowState childReflowState(aPresContext, aReflowState,
                                          item->Frame(),
                                          nsSize(aReflowState.ComputedWidth(),
                                                 NS_UNCONSTRAINEDSIZE));
       // Keep track of whether we've overriden the child's computed height
       // and/or width, so we can set its resize flags accordingly.
       bool didOverrideComputedWidth = false;
       bool didOverrideComputedHeight = false;
       // Override computed main-size
       if (IsAxisHorizontal(aAxisTracker.GetMainAxis())) {
         childReflowState.SetComputedWidth(item->GetMainSize());
         didOverrideComputedWidth = true;
       } else {
         childReflowState.SetComputedHeight(item->GetMainSize());
         didOverrideComputedHeight = true;
       }
       // Override reflow state's computed cross-size, for stretched items.
       if (item->IsStretched()) {
         MOZ_ASSERT(item->GetAlignSelf() == NS_STYLE_ALIGN_ITEMS_STRETCH,
                    "stretched item w/o 'align-self: stretch'?");
         if (IsAxisHorizontal(aAxisTracker.GetCrossAxis())) {
           childReflowState.SetComputedWidth(item->GetCrossSize());
           didOverrideComputedWidth = true;
         } else {
           // If this item's height is stretched, it's a relative height.
           item->Frame()->AddStateBits(NS_FRAME_CONTAINS_RELATIVE_HEIGHT);
           childReflowState.SetComputedHeight(item->GetCrossSize());
           didOverrideComputedHeight = true;
         }
       }
       // XXXdholbert Might need to actually set the correct margins in the
       // reflow state at some point, so that they can be saved on the frame for
       // UsedMarginProperty().  Maybe doesn't matter though...?
       // If we're overriding the computed width or height, *and* we had an
       // earlier "measuring" reflow, then this upcoming reflow needs to be
       // treated as a resize.
       if (item->HadMeasuringReflow()) {
         if (didOverrideComputedWidth) {
           // (This is somewhat redundant, since the reflow state already
           // sets mHResize whenever our computed width has changed since the
           // previous reflow. Still, it's nice for symmetry, and it may become
           // necessary once we support orthogonal flows.)
           childReflowState.mFlags.mHResize = true;
         }
         if (didOverrideComputedHeight) {
           childReflowState.mFlags.mVResize = true;
         }
       }
       // NOTE: Be very careful about doing anything else with childReflowState
       // after this point, because some of its methods (e.g. SetComputedWidth)
       // internally call InitResizeFlags and stomp on mVResize & mHResize.
       nsHTMLReflowMetrics childDesiredSize(childReflowState);
       nsReflowStatus childReflowStatus;
       nsresult rv = ReflowChild(item->Frame(), aPresContext,
                                 childDesiredSize, childReflowState,
                                 physicalPosn.x, physicalPosn.y,
 , childReflowStatus);
       NS_ENSURE_SUCCESS(rv, rv);
       // XXXdholbert Once we do pagination / splitting, we'll need to actually
       // handle incomplete childReflowStatuses. But for now, we give our kids
       // unconstrained available height, which means they should always
       // complete.
       MOZ_ASSERT(NS_FRAME_IS_COMPLETE(childReflowStatus),
                  "We gave flex item unconstrained available height, so it "
                  "should be complete");
       childReflowState.ApplyRelativePositioning(&physicalPosn);
       rv = FinishReflowChild(item->Frame(), aPresContext,
                              childDesiredSize, &childReflowState,
                              physicalPosn.x, physicalPosn.y, 0);
       NS_ENSURE_SUCCESS(rv, rv);
       // If this is our first child and we haven't established a baseline for
       // the container yet (i.e. if we don't have 'align-self: baseline' on any
       // children), then use this child's baseline as the container's baseline.
       if (item->Frame() == mFrames.FirstChild() &&
           flexContainerAscent == nscoord_MIN) {
         ResolveReflowedChildAscent(item->Frame(), childDesiredSize);
         // (We use GetNormalPosition() instead of physicalPosn because we don't
         // want relative positioning on the child to affect the baseline that we
         // read from it).
         flexContainerAscent = item->Frame()->GetNormalPosition().y +
           childDesiredSize.TopAscent();
       }
     }
   }
   nsSize desiredContentBoxSize =
     aAxisTracker.PhysicalSizeFromLogicalSizes(aContentBoxMainSize,
                                               contentBoxCrossSize);
   aDesiredSize.Width() = desiredContentBoxSize.width +
     containerBorderPadding.LeftRight();
   // Does *NOT* include bottom border/padding yet (we add that a bit lower down)
   aDesiredSize.Height() = desiredContentBoxSize.height +
     containerBorderPadding.top;
   if (flexContainerAscent == nscoord_MIN) {
     // Still don't have our baseline set -- this happens if we have no
     // children (or if our children are huge enough that they have nscoord_MIN
     // as their baseline... in which case, we'll use the wrong baseline, but no
     // big deal)
     NS_WARN_IF_FALSE(lines.getFirst()->IsEmpty(),
                      "Have flex items but didn't get an ascent - that's odd "
                      "(or there are just gigantic sizes involved)");
     // Per spec, just use the bottom of content-box.
     flexContainerAscent = aDesiredSize.Height();
   }
   aDesiredSize.SetTopAscent(flexContainerAscent);
   // Now: If we're complete, add bottom border/padding to desired height
   // (unless that pushes us over available height, in which case we become
   // incomplete (unless we already weren't asking for any height, in which case
   // we stay complete to avoid looping forever)).
   // NOTE: If we're auto-height, we allow our bottom border/padding to push us
   // over the available height without requesting a continuation, for
   // consistency with the behavior of "display:block" elements.
   if (NS_FRAME_IS_COMPLETE(aStatus)) {
     // NOTE: We can't use containerBorderPadding.bottom for this, because if
     // we're auto-height, ApplySkipSides will have zeroed it (because it
     // assumed we might get a continuation). We have the correct value in
     // aReflowState.ComputedPhyiscalBorderPadding().bottom, though, so we use that.
     nscoord desiredHeightWithBottomBP =
       aDesiredSize.Height() + aReflowState.ComputedPhysicalBorderPadding().bottom;
     if (aReflowState.AvailableHeight() == NS_UNCONSTRAINEDSIZE ||
         aDesiredSize.Height() == 0 ||
         desiredHeightWithBottomBP <= aReflowState.AvailableHeight() ||
         aReflowState.ComputedHeight() == NS_INTRINSICSIZE) {
       // Update desired height to include bottom border/padding
       aDesiredSize.Height() = desiredHeightWithBottomBP;
     } else {
       // We couldn't fit bottom border/padding, so we'll need a continuation.
       NS_FRAME_SET_INCOMPLETE(aStatus);
     }
   }
   // Overflow area = union(my overflow area, kids' overflow areas)
   aDesiredSize.SetOverflowAreasToDesiredBounds();
   for (nsFrameList::Enumerator e(mFrames); !e.AtEnd(); e.Next()) {
     ConsiderChildOverflow(aDesiredSize.mOverflowAreas, e.get());
   }
   FinishReflowWithAbsoluteFrames(aPresContext, aDesiredSize,
                                  aReflowState, aStatus);
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize)
   return NS_OK;
 }
 /* virtual */ nscoord
 nsFlexContainerFrame::GetMinWidth(nsRenderingContext* aRenderingContext)
 {
   nscoord minWidth = 0;
   DISPLAY_MIN_WIDTH(this, minWidth);
   FlexboxAxisTracker axisTracker(this);
   for (nsFrameList::Enumerator e(mFrames); !e.AtEnd(); e.Next()) {
     nscoord childMinWidth =
       nsLayoutUtils::IntrinsicForContainer(aRenderingContext, e.get(),
                                            nsLayoutUtils::MIN_WIDTH);
     // For a horizontal single-line flex container, the intrinsic min width is
     // the sum of its items' min widths.
     // For a vertical flex container, or for a multi-line horizontal flex
     // container, the intrinsic min width is the max of its items' min widths.
     if (IsAxisHorizontal(axisTracker.GetMainAxis()) &&
         NS_STYLE_FLEX_WRAP_NOWRAP == StylePosition()->mFlexWrap) {
       minWidth += childMinWidth;
     } else {
       minWidth = std::max(minWidth, childMinWidth);
     }
   }
   return minWidth;
 }
 /* virtual */ nscoord
 nsFlexContainerFrame::GetPrefWidth(nsRenderingContext* aRenderingContext)
 {
   nscoord prefWidth = 0;
   DISPLAY_PREF_WIDTH(this, prefWidth);
   // XXXdholbert Optimization: We could cache our intrinsic widths like
   // nsBlockFrame does (and return it early from this function if it's set).
   // Whenever anything happens that might change it, set it to
   // NS_INTRINSIC_WIDTH_UNKNOWN (like nsBlockFrame::MarkIntrinsicWidthsDirty
   // does)
   FlexboxAxisTracker axisTracker(this);
   for (nsFrameList::Enumerator e(mFrames); !e.AtEnd(); e.Next()) {
     nscoord childPrefWidth =
       nsLayoutUtils::IntrinsicForContainer(aRenderingContext, e.get(),
                                            nsLayoutUtils::PREF_WIDTH);
     if (IsAxisHorizontal(axisTracker.GetMainAxis())) {
       prefWidth += childPrefWidth;
     } else {
       prefWidth = std::max(prefWidth, childPrefWidth);
     }
   }
   return prefWidth;
 }

The Tor Browser / annotate

layout/generic/nsFlexContainerFrame.cpp@b8a032363ba2 (annotated)

layout/generic/nsFlexContainerFrame.cpp