From 6d504711a01e9be34725f9add22cc7aa311cb14f Mon Sep 17 00:00:00 2001
From: wolfbeast <mcwerewolf@wolfbeast.com>
Date: Mon, 16 Mar 2020 09:30:31 +0100
Subject: Issue #1355 - Make addition of cell border display items depend on
 whether they should be drawn.

This reduces the size of display lists for tables by only adding display
list items that are actually going to be visibly drawn, which will help
overall performance of table drawing.
---
 layout/tables/nsTableFrame.cpp | 83 ++++++++++++++++++++++++++++++++++++++++--
 layout/tables/nsTableFrame.h   | 33 +++++++++++++++++
 2 files changed, 112 insertions(+), 4 deletions(-)

diff --git a/layout/tables/nsTableFrame.cpp b/layout/tables/nsTableFrame.cpp
index 4257c9c57..e5a48139a 100644
--- a/layout/tables/nsTableFrame.cpp
+++ b/layout/tables/nsTableFrame.cpp
@@ -1268,6 +1268,74 @@ PaintRowGroupBackgroundByColIdx(nsTableRowGroupFrame* aRowGroup,
   }
 }
 
+static inline bool FrameHasBorder(nsIFrame* f)
+{
+  if (!f->StyleVisibility()->IsVisible()) {
+    return false;
+  }
+
+  if (f->StyleBorder()->HasBorder()) {
+    return true;
+  }
+
+  return false;
+}
+
+void nsTableFrame::CalcHasBCBorders()
+{
+  if (!IsBorderCollapse()) {
+    SetHasBCBorders(false);
+    return;
+  }
+
+  if (FrameHasBorder(this)) {
+    SetHasBCBorders(true);
+    return;
+  }
+
+  // Check col and col group has borders.
+  for (nsIFrame* f : this->GetChildList(kColGroupList)) {
+    if (FrameHasBorder(f)) {
+      SetHasBCBorders(true);
+      return;
+    }
+
+    nsTableColGroupFrame *colGroup = static_cast<nsTableColGroupFrame*>(f);
+    for (nsTableColFrame* col = colGroup->GetFirstColumn(); col; col = col->GetNextCol()) {
+      if (FrameHasBorder(col)) {
+        SetHasBCBorders(true);
+        return;
+      }
+    }
+  }
+
+  // check row group, row and cell has borders.
+  RowGroupArray rowGroups;
+  OrderRowGroups(rowGroups);
+  for (nsTableRowGroupFrame* rowGroup : rowGroups) {
+    if (FrameHasBorder(rowGroup)) {
+      SetHasBCBorders(true);
+      return;
+    }
+
+    for (nsTableRowFrame* row = rowGroup->GetFirstRow(); row; row = row->GetNextRow()) {
+      if (FrameHasBorder(row)) {
+        SetHasBCBorders(true);
+        return;
+      }
+
+      for (nsTableCellFrame* cell = row->GetFirstCell(); cell; cell = cell->GetNextCell()) {
+        if (FrameHasBorder(cell)) {
+          SetHasBCBorders(true);
+          return;
+        }
+      }
+    }
+  }
+
+  SetHasBCBorders(false);
+}
+
 /* static */ void
 nsTableFrame::DisplayGenericTablePart(nsDisplayListBuilder* aBuilder,
                                       nsFrame* aFrame,
@@ -1375,11 +1443,16 @@ nsTableFrame::DisplayGenericTablePart(nsDisplayListBuilder* aBuilder,
       nsTableFrame* table = static_cast<nsTableFrame*>(aFrame);
       // In the collapsed border model, overlay all collapsed borders.
       if (table->IsBorderCollapse()) {
-        aLists.BorderBackground()->AppendNewToTop(
-          new (aBuilder) nsDisplayTableBorderCollapse(aBuilder, table));
+        if (table->HasBCBorders()) {
+          aLists.BorderBackground()->AppendNewToTop(
+            new (aBuilder) nsDisplayTableBorderCollapse(aBuilder, table));
+        }
       } else {
-        aLists.BorderBackground()->AppendNewToTop(
-          new (aBuilder) nsDisplayBorder(aBuilder, table));
+        const nsStyleBorder* borderStyle = aFrame->StyleBorder();
+        if (borderStyle->HasBorder()) {
+          aLists.BorderBackground()->AppendNewToTop(
+            new (aBuilder) nsDisplayBorder(aBuilder, table));
+        }
       }
     }
   }
@@ -4101,6 +4174,7 @@ nsTableFrame::AddBCDamageArea(const TableArea& aValue)
 #endif
 
   SetNeedToCalcBCBorders(true);
+  SetNeedToCalcHasBCBorders(true);
   // Get the property
   BCPropertyData* value = GetOrCreateBCProperty();
   if (value) {
@@ -4141,6 +4215,7 @@ nsTableFrame::SetFullBCDamageArea()
   NS_ASSERTION(IsBorderCollapse(), "invalid SetFullBCDamageArea call");
 
   SetNeedToCalcBCBorders(true);
+  SetNeedToCalcHasBCBorders(true);
 
   BCPropertyData* value = GetOrCreateBCProperty();
   if (value) {
diff --git a/layout/tables/nsTableFrame.h b/layout/tables/nsTableFrame.h
index a6b786402..d739faa72 100644
--- a/layout/tables/nsTableFrame.h
+++ b/layout/tables/nsTableFrame.h
@@ -761,6 +761,13 @@ public:
   bool NeedToCollapse() const;
   void SetNeedToCollapse(bool aValue);
 
+  bool NeedToCalcHasBCBorders() const;
+  void SetNeedToCalcHasBCBorders(bool aValue);
+
+  void CalcHasBCBorders();
+  bool HasBCBorders();
+  void SetHasBCBorders(bool aValue);
+
   /** The GeometryDirty bit is similar to the NS_FRAME_IS_DIRTY frame
     * state bit, which implies that all descendants are dirty.  The
     * GeometryDirty still implies that all the parts of the table are
@@ -870,6 +877,8 @@ protected:
     uint32_t mIStartContBCBorder:8;
     uint32_t mNeedToCollapse:1;        // rows, cols that have visibility:collapse need to be collapsed
     uint32_t mResizedColumns:1;        // have we resized columns since last reflow?
+    uint32_t mNeedToCalcHasBCBorders:1;
+    uint32_t mHasBCBorders:1;
   } mBits;
 
   nsTableCellMap*         mCellMap;            // maintains the relationships between rows, cols, and cells
@@ -965,6 +974,30 @@ inline void nsTableFrame::SetNeedToCalcBCBorders(bool aValue)
   mBits.mNeedToCalcBCBorders = (unsigned)aValue;
 }
 
+inline bool nsTableFrame::NeedToCalcHasBCBorders() const
+{
+  return (bool)mBits.mNeedToCalcHasBCBorders;
+}
+
+inline void nsTableFrame::SetNeedToCalcHasBCBorders(bool aValue)
+{
+  mBits.mNeedToCalcHasBCBorders = (unsigned)aValue;
+}
+
+inline bool nsTableFrame::HasBCBorders()
+{
+  if (NeedToCalcHasBCBorders()) {
+    CalcHasBCBorders();
+    SetNeedToCalcHasBCBorders(false);
+  }
+  return (bool)mBits.mHasBCBorders;
+}
+
+inline void nsTableFrame::SetHasBCBorders(bool aValue)
+{
+  mBits.mHasBCBorders = (unsigned)aValue;
+}
+
 inline nscoord
 nsTableFrame::GetContinuousIStartBCBorderWidth() const
 {
-- 
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