Bug 783470 part 3: Use the strut metadata we've saved to actually build special "strut" FlexItems on our second pass through reflow. r=mats

layout/generic/nsFlexContainerFrame.cpp

@@ -279,6 +279,7 @@ private:
 // to resolve a flexible width.
 class FlexItem {
 public:
+  // Normal constructor:
   FlexItem(nsIFrame* aChildFrame,
            float aFlexGrow, float aFlexShrink, nscoord aMainBaseSize,
            nscoord aMainMinSize, nscoord aMainMaxSize,
@@ -286,6 +287,9 @@ public:
            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; }
@@ -327,6 +331,10 @@ public:
   // 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
@@ -544,6 +552,8 @@ protected:
   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).
@@ -1036,6 +1046,7 @@ FlexItem::FlexItem(nsIFrame* aChildFrame,
     mHadMaxViolation(false),
     mHadMeasuringReflow(false),
     mIsStretched(false),
+    mIsStrut(false),
     mAlignSelf(aChildFrame->StylePosition()->mAlignSelf)
 {
   MOZ_ASSERT(aChildFrame, "expecting a non-null child frame");
@@ -1078,6 +1089,39 @@ FlexItem::FlexItem(nsIFrame* aChildFrame,
   }
 }
 
+// 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(NS_STYLE_VISIBILITY_COLLAPSE ==
+             mFrame->StyleVisibility()->mVisible,
+             "Should only make struts for children with 'visibility:collapse'");
+}
+
 nscoord
 FlexItem::GetBaselineOffsetFromOuterCrossStart(
   AxisOrientationType aCrossAxis) const
@@ -2216,6 +2260,7 @@ nsFlexContainerFrame::GenerateFlexLines(
   const nsHTMLReflowState& aReflowState,
   nscoord aContentBoxMainSize,
   nscoord aAvailableHeightForContent,
+  const nsTArray<StrutInfo>& aStruts,
   const FlexboxAxisTracker& aAxisTracker,
   nsTArray<FlexLine>& aLines)
 {
@@ -2260,6 +2305,14 @@ nsFlexContainerFrame::GenerateFlexLines(
     }
   }
 
+  // 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();
 
@@ -2269,13 +2322,24 @@ nsFlexContainerFrame::GenerateFlexLines(
       curLine = aLines.AppendElement();
     }
 
-    FlexItem* item = curLine->mItems.AppendElement(
-                       GenerateFlexItemForChild(aPresContext, childFrame,
-                                                aReflowState, aAxisTracker));
+    FlexItem* item;
+    if (nextStrutIdx < aStruts.Length() &&
+        aStruts[nextStrutIdx].mItemIdx == itemIdxInContainer) {
+
+      // Use the simplified "strut" FlexItem constructor:
+      item = curLine->mItems.AppendElement(
+               FlexItem(childFrame, aStruts[nextStrutIdx].mStrutCrossSize));
+      nextStrutIdx++;
+    } else {
+      item = curLine->mItems.AppendElement(
+               GenerateFlexItemForChild(aPresContext, childFrame,
+                                        aReflowState, aAxisTracker));
+
+      nsresult rv = ResolveFlexItemMaxContentSizing(aPresContext, *item,
+                                                    aReflowState, aAxisTracker);
+      NS_ENSURE_SUCCESS(rv,rv);
+    }
 
-    nsresult rv = ResolveFlexItemMaxContentSizing(aPresContext, *item,
-                                                  aReflowState, aAxisTracker);
-    NS_ENSURE_SUCCESS(rv,rv);
     nscoord itemInnerHypotheticalMainSize = item->GetMainSize();
     nscoord itemOuterHypotheticalMainSize = item->GetMainSize() +
       item->GetMarginBorderPaddingSizeInAxis(aAxisTracker.GetMainAxis());
@@ -2313,6 +2377,7 @@ nsFlexContainerFrame::GenerateFlexLines(
         childFrame->StyleDisplay()->mBreakAfter) {
       curLine = aLines.AppendElement();
     }
+    itemIdxInContainer++;
   }
 
   return NS_OK;
@@ -2732,7 +2797,7 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
   nsresult rv = GenerateFlexLines(aPresContext, aReflowState,
                                   aContentBoxMainSize,
                                   aAvailableHeightForContent,
-                                  aAxisTracker, lines);
+                                  aStruts, aAxisTracker, lines);
   NS_ENSURE_SUCCESS(rv, rv);
 
   aContentBoxMainSize =
@@ -2752,9 +2817,9 @@ nsFlexContainerFrame::DoFlexLayout(nsPresContext*           aPresContext,
     for (uint32_t i = 0; i < line.mItems.Length(); ++i) {
       FlexItem& curItem = line.mItems[i];
 
-      // (If the item's already been stretched, then it already knows its
-      // cross size.  Don't bother trying to recalculate it.)
-      if (!curItem.IsStretched()) {
+      // (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 (!curItem.IsStretched() && !curItem.IsStrut()) {
         nsHTMLReflowState childReflowState(aPresContext, aReflowState,
                                            curItem.Frame(),
                                            nsSize(aReflowState.ComputedWidth(),

layout/generic/nsFlexContainerFrame.h

@@ -124,6 +124,7 @@ protected:
                              const nsHTMLReflowState& aReflowState,
                              nscoord aContentBoxMainSize,
                              nscoord aAvailableHeightForContent,
+                             const nsTArray<StrutInfo>& aStruts,
                              const FlexboxAxisTracker& aAxisTracker,
                              nsTArray<FlexLine>& aLines);