Issue #146 - Part 3: Create nsDisplayTableFixedPosition to avoid display

list collisions when processing the background image of a table.

layout/base/nsDisplayList.cpp

@@ -80,6 +80,8 @@
 #include "nsPluginFrame.h"
 #include "DisplayItemScrollClip.h"
 #include "nsSVGMaskFrame.h"
+#include "nsTableCellFrame.h"
+#include "nsTableColFrame.h"
 
 // GetCurrentTime is defined in winbase.h as zero argument macro forwarding to
 // GetTickCount().
@@ -2632,7 +2634,8 @@ nsDisplayBackgroundImage::AppendBackgroundItemsToTop(nsDisplayListBuilder* aBuil
                                                      nsDisplayList* aList,
                                                      bool aAllowWillPaintBorderOptimization,
                                                      nsStyleContext* aStyleContext,
-                                                     const nsRect& aBackgroundOriginRect)
+                                                     const nsRect& aBackgroundOriginRect,
+                                                     nsIFrame* aSecondaryReferenceFrame)
 {
   nsStyleContext* bgSC = aStyleContext;
   const nsStyleBackground* bg = nullptr;
@@ -2752,8 +2755,17 @@ nsDisplayBackgroundImage::AppendBackgroundItemsToTop(nsDisplayListBuilder* aBuil
       new (aBuilder) nsDisplayBackgroundImage(aBuilder, aFrame, i, bgOriginRect, bg);
 
     if (bgItem->ShouldFixToViewport(aBuilder)) {
-      thisItemList.AppendNewToTop(
+      if (aSecondaryReferenceFrame) {
-        nsDisplayFixedPosition::CreateForFixedBackground(aBuilder, aFrame, bgItem, i));
+        thisItemList.AppendNewToTop(
+          nsDisplayTableFixedPosition::CreateForFixedBackground(aBuilder,
+                                                                aSecondaryReferenceFrame,
+                                                                bgItem,
+                                                                i,
+                                                                aFrame));
+      } else {
+        thisItemList.AppendNewToTop(
+          nsDisplayFixedPosition::CreateForFixedBackground(aBuilder, aFrame, bgItem, i));
+      }
     } else {
       thisItemList.AppendNewToTop(bgItem);
     }
@@ -5277,6 +5289,51 @@ bool nsDisplayFixedPosition::TryMerge(nsDisplayItem* aItem) {
   return true;
 }
 
+TableType
+GetTableTypeFromFrame(nsIFrame* aFrame)
+{
+  nsIAtom* type = aFrame->GetType();
+  if (type == nsGkAtoms::tableFrame) {
+    return TableType::TABLE;
+  } else if (type == nsGkAtoms::tableColFrame) {
+    return TableType::TABLE_COL;
+  } else if (type == nsGkAtoms::tableColGroupFrame) {
+    return TableType::TABLE_COL_GROUP;
+  } else if (type == nsGkAtoms::tableRowFrame) {
+    return TableType::TABLE_ROW;
+  } else if (type == nsGkAtoms::tableRowGroupFrame) {
+    return TableType::TABLE_ROW_GROUP;
+  } else if (type == nsGkAtoms::tableCellFrame) {
+    return TableType::TABLE_CELL;
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Invalid frame.");
+    return TableType::TABLE;
+  }
+}
+
+nsDisplayTableFixedPosition::nsDisplayTableFixedPosition(nsDisplayListBuilder* aBuilder,
+                                                         nsIFrame* aFrame,
+                                                         nsDisplayList* aList,
+                                                         uint32_t aIndex,
+                                                         nsIFrame* aAncestorFrame)
+  : nsDisplayFixedPosition(aBuilder, aFrame, aList, aIndex)
+  , mTableType(GetTableTypeFromFrame(aAncestorFrame))
+{
+}
+
+/* static */ nsDisplayTableFixedPosition*
+nsDisplayTableFixedPosition::CreateForFixedBackground(nsDisplayListBuilder* aBuilder,
+                                                      nsIFrame* aFrame,
+                                                      nsDisplayBackgroundImage* aImage,
+                                                      uint32_t aIndex,
+                                                      nsIFrame* aAncestorFrame)
+{
+  nsDisplayList temp;
+  temp.AppendToTop(aImage);
+
+  return new (aBuilder) nsDisplayTableFixedPosition(aBuilder, aFrame, &temp, aIndex + 1, aAncestorFrame);
+}
+
 nsDisplayStickyPosition::nsDisplayStickyPosition(nsDisplayListBuilder* aBuilder,
                                                  nsIFrame* aFrame,
                                                  nsDisplayList* aList)

layout/base/nsDisplayList.h

@@ -2738,7 +2738,8 @@ public:
                                          nsDisplayList* aList,
                                          bool aAllowWillPaintBorderOptimization = true,
                                          nsStyleContext* aStyleContext = nullptr,
-                                         const nsRect& aBackgroundOriginRect = nsRect());
+                                         const nsRect& aBackgroundOriginRect = nsRect(),
+                                         nsIFrame* aSecondaryReferenceFrame = nullptr);
 
   virtual LayerState GetLayerState(nsDisplayListBuilder* aBuilder,
                                    LayerManager* aManager,
@@ -2838,6 +2839,25 @@ protected:
   bool mShouldTreatAsFixed;
 };
 
+enum class TableType : uint8_t {
+  TABLE,
+  TABLE_COL,
+  TABLE_COL_GROUP,
+  TABLE_ROW,
+  TABLE_ROW_GROUP,
+  TABLE_CELL,
+
+  TABLE_TYPE_MAX
+};
+
+enum class TableTypeBits : uint8_t {
+  COUNT = 3
+};
+
+static_assert(
+  static_cast<uint8_t>(TableType::TABLE_TYPE_MAX) < (1 << (static_cast<uint8_t>(TableTypeBits::COUNT) + 1)),
+  "TableType cannot fit with TableTypeBits::COUNT");
+TableType GetTableTypeFromFrame(nsIFrame* aFrame);
 
 /**
  * A display item to paint the native theme background for a frame.
@@ -3736,7 +3756,7 @@ public:
     return mAnimatedGeometryRootForScrollMetadata;
   }
 
-private:
+protected:
   // For background-attachment:fixed
   nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
                          nsDisplayList* aList, uint32_t aIndex);
@@ -3747,6 +3767,27 @@ private:
   bool mIsFixedBackground;
 };
 
+class nsDisplayTableFixedPosition : public nsDisplayFixedPosition
+{
+public:
+  static nsDisplayTableFixedPosition* CreateForFixedBackground(nsDisplayListBuilder* aBuilder,
+                                                               nsIFrame* aFrame,
+                                                               nsDisplayBackgroundImage* aImage,
+                                                               uint32_t aIndex,
+                                                               nsIFrame* aAncestorFrame);
+
+  virtual uint32_t GetPerFrameKey() override {
+    return (mIndex << (nsDisplayItem::TYPE_BITS + static_cast<uint8_t>(TableTypeBits::COUNT))) |
+           (static_cast<uint8_t>(mTableType) << nsDisplayItem::TYPE_BITS) |
+           nsDisplayItem::GetPerFrameKey();
+  }
+protected:
+  nsDisplayTableFixedPosition(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              nsDisplayList* aList, uint32_t aIndex, nsIFrame* aAncestorFrame);
+
+  TableType mTableType;
+};
+
 /**
  * This creates an empty scrollable layer. It has no child layers.
  * It is used to record the existence of a scrollable frame in the layer

layout/tables/nsTableFrame.cpp

@@ -1194,13 +1194,14 @@ PaintRowBackground(nsTableRowFrame* aRow,
                    const nsDisplayListSet& aLists,
                    const nsPoint& aOffset = nsPoint())
 {
-  // Compute background rect by iterating all cell frame.
+  // Compute background rect by iterating over all cell frames.
   for (nsTableCellFrame* cell = aRow->GetFirstCell(); cell; cell = cell->GetNextCell()) {
     auto cellRect = cell->GetRectRelativeToSelf() + cell->GetNormalPosition() + aOffset;
     nsDisplayBackgroundImage::AppendBackgroundItemsToTop(aBuilder, aFrame, cellRect,
                                                          aLists.BorderBackground(),
                                                          true, nullptr,
-                                                         aFrame->GetRectRelativeToSelf());
+                                                         aFrame->GetRectRelativeToSelf(),
+                                                         cell);
   }
 }
 
@@ -1232,7 +1233,8 @@ PaintRowGroupBackgroundByColIdx(nsTableRowGroupFrame* aRowGroup,
         nsDisplayBackgroundImage::AppendBackgroundItemsToTop(aBuilder, aFrame, cellRect,
                                                              aLists.BorderBackground(),
                                                              true, nullptr,
-                                                             aFrame->GetRectRelativeToSelf());
+                                                             aFrame->GetRectRelativeToSelf(),
+                                                             cell);
       }
     }
   }