Bug 530686. Only create an nsDisplayTableBorderBackground when it's going to have something to paint, since having one can disable some scrolling optimizations. r=dbaron

layout/base/tests/scrolling_helper.html

@@ -121,6 +121,13 @@ iframe {
   <div style="height:300px; background:-moz-linear-gradient(top, red, black);"></div>
 </div>
 
+<div id="testTableNoBackground" class="testcase">
+  <table style="position:fixed; width:200px; height:200px;">
+    <tr><td></td></tr>
+  </table>
+  <div style="height:300px; background:-moz-linear-gradient(top, red, black);"></div>
+</div>
+
 <script>
 var testcases = document.querySelectorAll("div.testcase");
 var tests = [];
@@ -295,6 +302,13 @@ function testHiddenTable(blitRegion, paintRegion) {
      "Should repaint area that was scrolled into view: " + paintRegion.toString());
 }
 
+function testTableNoBackground(blitRegion, paintRegion) {
+  ok(blitRegion.equalsRegion(new Region([[0,0,200,180]])),
+     "Should blit everything that was already visible: " + blitRegion.toString());
+  ok(paintRegion.equalsRegion(new Region([[0,180,200,200]])),
+     "Should repaint area that was scrolled into view: " + paintRegion.toString());
+}
+
 function clientRectToRect(cr)
 {
   return [cr.left, cr.top, cr.right, cr.bottom];

layout/generic/nsFrame.cpp

@@ -927,15 +927,6 @@ nsIFrame::DisplayCaret(nsDisplayListBuilder* aBuilder,
       new (aBuilder) nsDisplayCaret(this, aBuilder->GetCaret()));
 }
 
-PRBool
-nsFrame::HasBorder() const
-{
-  // Border images contribute to the background of the content area
-  // even if there's no border proper.
-  return (GetUsedBorder() != nsMargin(0,0,0,0) ||
-          GetStyleBorder()->IsBorderImageLoaded());
-}
-
 nsresult
 nsFrame::DisplayBackgroundUnconditional(nsDisplayListBuilder*   aBuilder,
                                         const nsDisplayListSet& aLists,

layout/generic/nsFrame.h

@@ -540,11 +540,6 @@ protected:
   nsFrame(nsStyleContext* aContext);
   virtual ~nsFrame();
 
-  /**
-   * @return PR_FALSE if this frame definitely has no borders at all
-   */                 
-  PRBool HasBorder() const;
-
   /**
    * To be called by |BuildDisplayLists| of this class or derived classes to add
    * a translucent overlay if this frame's content is selected.

layout/generic/nsIFrame.h

@@ -725,6 +725,17 @@ public:
   // -moz-appearance and is not chrome
   nsCSSShadowArray* GetEffectiveBoxShadows();
 
+  /**
+   * @return PR_FALSE if this frame definitely has no borders at all
+   */                 
+  PRBool HasBorder() const
+  {
+    // Border images contribute to the background of the content area
+    // even if there's no border proper.
+    return (GetUsedBorder() != nsMargin(0,0,0,0) ||
+            GetStyleBorder()->IsBorderImageLoaded());
+  }
+
   /**
    * Accessor functions for geometric parent
    */

layout/tables/nsTableCellFrame.cpp

@@ -448,8 +448,9 @@ nsTableCellFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     PRBool isRoot = aBuilder->IsAtRootOfPseudoStackingContext();
     if (!isRoot) {
       nsDisplayTableItem* currentItem = aBuilder->GetCurrentTableItem();
-      NS_ASSERTION(currentItem, "No current table item???");
-      currentItem->UpdateForFrameBackground(this);
+      if (currentItem) {
+        currentItem->UpdateForFrameBackground(this);
+      }
     }
 
     // display outset box-shadows if we need to.

layout/tables/nsTableFrame.cpp

@@ -1269,9 +1269,12 @@ nsTableFrame::DisplayGenericTablePart(nsDisplayListBuilder* aBuilder,
 
   if (aFrame->IsVisibleForPainting(aBuilder)) {
     nsDisplayTableItem* currentItem = aBuilder->GetCurrentTableItem();
-    NS_ASSERTION(currentItem, "No current table item!");
-    currentItem->UpdateForFrameBackground(aFrame);
-  
+    // currentItem may be null, when none of the table parts have a
+    // background or border
+    if (currentItem) {
+      currentItem->UpdateForFrameBackground(aFrame);
+    }
+
     // Paint the outset box-shadows for the table frames
     PRBool hasBoxShadow = aFrame->GetStyleBorder()->mBoxShadow != nsnull;
     if (hasBoxShadow) {
@@ -1326,19 +1329,26 @@ IsFrameAllowedInTable(nsIAtom* aType)
 #endif
 
 static PRBool
-AnyTablePartVisible(nsIFrame* aFrame)
+AnyTablePartHasBorderOrBackground(nsIFrame* aFrame)
 {
   NS_ASSERTION(IsFrameAllowedInTable(aFrame->GetType()), "unexpected frame type");
-  if (aFrame->GetStyleVisibility()->IsVisible())
+
+  if (aFrame->GetStyleVisibility()->IsVisible() &&
+      (!aFrame->GetStyleBackground()->IsTransparent() ||
+       aFrame->GetStyleDisplay()->mAppearance ||
+       aFrame->HasBorder()))
     return PR_TRUE;
+
   nsTableCellFrame *cellFrame = do_QueryFrame(aFrame);
   if (cellFrame)
     return PR_FALSE;
+
   nsFrameList children = aFrame->GetChildList(nsnull);
   for (nsIFrame* f = children.FirstChild(); f; f = f->GetNextSibling()) {
-    if (AnyTablePartVisible(f))
+    if (AnyTablePartHasBorderOrBackground(f))
       return PR_TRUE;
   }
+
   return PR_FALSE;
 }
 
@@ -1369,7 +1379,7 @@ nsTableFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   // This background is created if any of the table parts are visible.
   // Specific visibility decisions are delegated to the table background
   // painter, which handles borders and backgrounds for the table.
-  if (AnyTablePartVisible(this)) {
+  if (AnyTablePartHasBorderOrBackground(this)) {
     item = new (aBuilder) nsDisplayTableBorderBackground(this);
     nsresult rv = aLists.BorderBackground()->AppendNewToTop(item);
     NS_ENSURE_SUCCESS(rv, rv);