Bug 386801 - nsAbsoluteContainingBlock doesn't need to store a child list name; this shaves four bytes off nsViewportFrame, nsBlockFrame, and nsPositionedInlineFrame. r+sr+a=dbaron

layout/generic/nsAbsoluteContainingBlock.h

@@ -52,24 +52,36 @@ class nsIFrame;
 class nsPresContext;
 
 /**
- * This class contains the logic for being an absolute containing block.
+ * This class contains the logic for being an absolute containing block.  This
+ * class is used within viewport frames (for frames representing content with
+ * fixed position) and blocks (for frames representing absolutely positioned
+ * content), since each set of frames is absolutely positioned with respect to
+ * its parent.
  *
  * There is no principal child list, just a named child list which contains
- * the absolutely positioned frames
+ * the absolutely positioned frames.
  *
  * All functions include as the first argument the frame that is delegating
- * the request
+ * the request.
  *
- * @see nsGkAtoms::absoluteList
+ * @see nsGkAtoms::absoluteList and nsGkAtoms::fixedList
  */
 class nsAbsoluteContainingBlock
 {
 public:
-  nsAbsoluteContainingBlock() { }          // useful for debugging
+  nsAbsoluteContainingBlock(nsIAtom* aChildListName)
+#ifdef DEBUG
+    : mChildListName(aChildListName)
+#endif
+  {
+    NS_ASSERTION(mChildListName == nsGkAtoms::absoluteList ||
+                 mChildListName == nsGkAtoms::fixedList,
+                 "should either represent position:fixed or absolute content");
+  }
 
-  virtual ~nsAbsoluteContainingBlock() { } // useful for debugging
-
-  virtual nsIAtom* GetChildListName() const { return nsGkAtoms::absoluteList; }
+#ifdef DEBUG
+  nsIAtom* GetChildListName() const { return mChildListName; }
+#endif
 
   nsresult FirstChild(const nsIFrame* aDelegatingFrame,
                       nsIAtom*        aListName,
@@ -135,6 +147,8 @@ protected:
   nsFrameList mAbsoluteFrames;  // additional named child list
 
 #ifdef DEBUG
+   nsIAtom* const mChildListName; // nsGkAtoms::fixedList or nsGkAtoms::absoluteList
+
   // helper routine for debug printout
   void PrettyUC(nscoord aSize,
                 char*   aBuf);

layout/generic/nsBlockFrame.cpp

@@ -517,7 +517,7 @@ nsBlockFrame::GetBaseline() const
 nsIFrame*
 nsBlockFrame::GetFirstChild(nsIAtom* aListName) const
 {
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     nsIFrame* result = nsnull;
     mAbsoluteContainer.FirstChild(this, aListName, &result);
     return result;
@@ -561,7 +561,7 @@ nsBlockFrame::GetAdditionalChildListName(PRInt32 aIndex) const
   case NS_BLOCK_FRAME_OVERFLOW_OOF_LIST_INDEX:
     return nsGkAtoms::overflowOutOfFlowList;
   case NS_BLOCK_FRAME_ABSOLUTE_LIST_INDEX:
-    return mAbsoluteContainer.GetChildListName();
+    return nsGkAtoms::absoluteList;
   default:
     return nsnull;
   }
@@ -4639,7 +4639,7 @@ nsBlockFrame::AppendFrames(nsIAtom*  aListName,
     return NS_OK;
   }
   if (aListName) {
-    if (mAbsoluteContainer.GetChildListName() == aListName) {
+    if (nsGkAtoms::absoluteList == aListName) {
       return mAbsoluteContainer.AppendFrames(this, aListName, aFrameList);
     }
     else if (nsGkAtoms::floatList == aListName) {
@@ -4688,7 +4688,7 @@ nsBlockFrame::InsertFrames(nsIAtom*  aListName,
                "inserting after sibling frame with different parent");
 
   if (aListName) {
-    if (mAbsoluteContainer.GetChildListName() == aListName) {
+    if (nsGkAtoms::absoluteList == aListName) {
       return mAbsoluteContainer.InsertFrames(this, aListName, aPrevFrame,
                                              aFrameList);
     }
@@ -4981,7 +4981,7 @@ nsBlockFrame::RemoveFrame(nsIAtom*  aListName,
       MarkSameSpaceManagerLinesDirty(this);
     }
   }
-  else if (mAbsoluteContainer.GetChildListName() == aListName) {
+  else if (nsGkAtoms::absoluteList == aListName) {
     return mAbsoluteContainer.RemoveFrame(this, aListName, aOldFrame);
   }
   else if (nsGkAtoms::floatList == aListName) {
@@ -5024,7 +5024,7 @@ nsBlockFrame::DoRemoveOutOfFlowFrame(nsIFrame* aFrame)
   // Remove aFrame from the appropriate list.
   if (display->IsAbsolutelyPositioned()) {
     block->mAbsoluteContainer.RemoveFrame(block,
-                                          block->mAbsoluteContainer.GetChildListName(),
+                                          nsGkAtoms::absoluteList,
                                           aFrame);
     aFrame->Destroy();
   }
@@ -6096,7 +6096,7 @@ nsBlockFrame::SetInitialChildList(nsIAtom*        aListName,
 {
   nsresult rv = NS_OK;
 
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     mAbsoluteContainer.SetInitialChildList(this, aListName, aChildList);
   }
   else if (nsGkAtoms::floatList == aListName) {

layout/generic/nsBlockFrame.h

@@ -289,6 +289,7 @@ protected:
     : nsHTMLContainerFrame(aContext)
     , mMinWidth(NS_INTRINSIC_WIDTH_UNKNOWN)
     , mPrefWidth(NS_INTRINSIC_WIDTH_UNKNOWN)
+    , mAbsoluteContainer(nsGkAtoms::absoluteList)
   {
 #ifdef DEBUG
   InitDebugFlags();

layout/generic/nsInlineFrame.cpp

@@ -993,7 +993,7 @@ nsPositionedInlineFrame::SetInitialChildList(nsIAtom*        aListName,
 {
   nsresult  rv;
 
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     rv = mAbsoluteContainer.SetInitialChildList(this, aListName, aChildList);
   } else {
     rv = nsInlineFrame::SetInitialChildList(aListName, aChildList);
@@ -1008,7 +1008,7 @@ nsPositionedInlineFrame::AppendFrames(nsIAtom*        aListName,
 {
   nsresult  rv;
   
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     rv = mAbsoluteContainer.AppendFrames(this, aListName, aFrameList);
   } else {
     rv = nsInlineFrame::AppendFrames(aListName, aFrameList);
@@ -1024,7 +1024,7 @@ nsPositionedInlineFrame::InsertFrames(nsIAtom*        aListName,
 {
   nsresult  rv;
 
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     rv = mAbsoluteContainer.InsertFrames(this, aListName, aPrevFrame,
                                          aFrameList);
   } else {
@@ -1040,7 +1040,7 @@ nsPositionedInlineFrame::RemoveFrame(nsIAtom*        aListName,
 {
   nsresult  rv;
 
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     rv = mAbsoluteContainer.RemoveFrame(this, aListName, aOldFrame);
   } else {
     rv = nsInlineFrame::RemoveFrame(aListName, aOldFrame);
@@ -1062,7 +1062,7 @@ nsIAtom*
 nsPositionedInlineFrame::GetAdditionalChildListName(PRInt32 aIndex) const
 {
   if (0 == aIndex) {
-    return mAbsoluteContainer.GetChildListName();
+    return nsGkAtoms::absoluteList;
   }
   return nsnull;
 }
@@ -1070,7 +1070,7 @@ nsPositionedInlineFrame::GetAdditionalChildListName(PRInt32 aIndex) const
 nsIFrame*
 nsPositionedInlineFrame::GetFirstChild(nsIAtom* aListName) const
 {
-  if (mAbsoluteContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::absoluteList == aListName) {
     nsIFrame* result = nsnull;
     mAbsoluteContainer.FirstChild(this, aListName, &result);
     return result;

layout/generic/nsInlineFrame.h

@@ -245,7 +245,10 @@ protected:
 class nsPositionedInlineFrame : public nsInlineFrame
 {
 public:
-  nsPositionedInlineFrame(nsStyleContext* aContext) : nsInlineFrame(aContext) {}
+  nsPositionedInlineFrame(nsStyleContext* aContext)
+    : nsInlineFrame(aContext)
+    , mAbsoluteContainer(nsGkAtoms::absoluteList)
+  {}
 
   virtual ~nsPositionedInlineFrame() { } // useful for debugging
 

layout/generic/nsViewportFrame.cpp

@@ -78,7 +78,7 @@ ViewportFrame::SetInitialChildList(nsIAtom*        aListName,
 #ifdef NS_DEBUG
   nsFrame::VerifyDirtyBitSet(aChildList);
 #endif
-  if (mFixedContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::fixedList == aListName) {
     rv = mFixedContainer.SetInitialChildList(this, aListName, aChildList);
   } 
   else {
@@ -115,7 +115,7 @@ ViewportFrame::AppendFrames(nsIAtom*        aListName,
 {
   nsresult rv = NS_OK;
 
-  if (mFixedContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::fixedList == aListName) {
     rv = mFixedContainer.AppendFrames(this, aListName, aFrameList);
   }
   else {
@@ -134,7 +134,7 @@ ViewportFrame::InsertFrames(nsIAtom*        aListName,
 {
   nsresult rv = NS_OK;
 
-  if (mFixedContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::fixedList == aListName) {
     rv = mFixedContainer.InsertFrames(this, aListName, aPrevFrame, aFrameList);
   }
   else {
@@ -152,7 +152,7 @@ ViewportFrame::RemoveFrame(nsIAtom*        aListName,
 {
   nsresult rv = NS_OK;
 
-  if (mFixedContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::fixedList == aListName) {
     rv = mFixedContainer.RemoveFrame(this, aListName, aOldFrame);
   }
   else {
@@ -170,7 +170,7 @@ ViewportFrame::GetAdditionalChildListName(PRInt32 aIndex) const
   NS_PRECONDITION(aIndex >= 0, "illegal index");
 
   if (0 == aIndex) {
-    return mFixedContainer.GetChildListName();
+    return nsGkAtoms::fixedList;
   }
 
   return nsnull;
@@ -179,7 +179,7 @@ ViewportFrame::GetAdditionalChildListName(PRInt32 aIndex) const
 nsIFrame*
 ViewportFrame::GetFirstChild(nsIAtom* aListName) const
 {
-  if (mFixedContainer.GetChildListName() == aListName) {
+  if (nsGkAtoms::fixedList == aListName) {
     nsIFrame* result = nsnull;
     mFixedContainer.FirstChild(this, aListName, &result);
     return result;

layout/generic/nsViewportFrame.h

@@ -49,15 +49,6 @@
 #include "nsIPresShell.h"
 #include "nsAbsoluteContainingBlock.h"
 
-class nsFixedContainingBlock : public nsAbsoluteContainingBlock {
-public:
-  nsFixedContainingBlock() { }          // useful for debugging
-
-  virtual ~nsFixedContainingBlock() { } // useful for debugging
-
-  virtual nsIAtom* GetChildListName() const { return nsGkAtoms::fixedList; }
-};
-
 /**
   * ViewportFrame is the parent of a single child - the doc root frame or a scroll frame 
   * containing the doc root frame. ViewportFrame stores this child in its primary child 
@@ -68,7 +59,10 @@ class ViewportFrame : public nsContainerFrame {
 public:
   typedef nsContainerFrame Super;
 
-  ViewportFrame(nsStyleContext* aContext) : nsContainerFrame(aContext) {}
+  ViewportFrame(nsStyleContext* aContext)
+    : nsContainerFrame(aContext)
+    , mFixedContainer(nsGkAtoms::fixedList)
+  {}
   virtual ~ViewportFrame() { } // useful for debugging
 
   virtual void Destroy();
@@ -126,7 +120,9 @@ protected:
   nsPoint AdjustReflowStateForScrollbars(nsHTMLReflowState* aReflowState) const;
 
 protected:
-  nsFixedContainingBlock mFixedContainer;
+  // position: fixed content is really content which is absolutely positioned with
+  // respect to the viewport.
+  nsAbsoluteContainingBlock mFixedContainer;
 };