Bug 564991. Part 44: Move IsFixedAndCoveringViewport implementation to nsDisplayBackground so it can work on any frame, not just the canvas background. r=tnikkel

layout/base/nsDisplayList.cpp

@@ -57,6 +57,7 @@
 #include "nsSVGIntegrationUtils.h"
 #endif
 #include "nsLayoutUtils.h"
+#include "nsIScrollableFrame.h"
 
 #include "imgIContainer.h"
 #include "nsIInterfaceRequestorUtils.h"
@@ -709,6 +710,10 @@ nsDisplayBackground::IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuild
   NS_ASSERTION(aBuilder->IsMovingFrame(mFrame),
               "IsVaryingRelativeToMovingFrame called on non-moving frame!");
 
+  // theme background overrides any other background and is never fixed
+  if (mIsThemed)
+    return PR_FALSE;
+
   nsPresContext* presContext = mFrame->PresContext();
   nsStyleContext *bgSC;
   PRBool hasBG =
@@ -729,6 +734,46 @@ nsDisplayBackground::IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuild
   return movingFrame->PresContext() == presContext;
 }
 
+PRBool
+nsDisplayBackground::IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder)
+{
+  if (mIsThemed)
+    return PR_FALSE;
+
+  nsPresContext* presContext = mFrame->PresContext();
+  nsStyleContext* bgSC;
+  PRBool hasBG =
+    nsCSSRendering::FindBackground(presContext, mFrame, &bgSC);
+  if (!hasBG)
+    return PR_FALSE;
+
+  const nsStyleBackground* bg = bgSC->GetStyleBackground();
+  if (!bg->HasFixedBackground())
+    return PR_FALSE;
+
+  NS_FOR_VISIBLE_BACKGROUND_LAYERS_BACK_TO_FRONT(i, bg) {
+    const nsStyleBackground::Layer& layer = bg->mLayers[i];
+    if (layer.mAttachment != NS_STYLE_BG_ATTACHMENT_FIXED &&
+        !layer.mImage.IsEmpty()) {
+      return PR_FALSE;
+    }
+    if (layer.mClip != NS_STYLE_BG_CLIP_BORDER)
+      return PR_FALSE;
+  }
+
+  if (nsLayoutUtils::HasNonZeroCorner(mFrame->GetStyleBorder()->mBorderRadius))
+    return PR_FALSE;
+
+  nsRect bounds = GetBounds(aBuilder);
+  nsIFrame* rootScrollFrame = presContext->PresShell()->GetRootScrollFrame();
+  if (!rootScrollFrame)
+    return PR_FALSE;
+  nsIScrollableFrame* scrollable = do_QueryFrame(rootScrollFrame);
+  nsRect scrollport = scrollable->GetScrollPortRect() +
+    aBuilder->ToReferenceFrame(rootScrollFrame);
+  return bounds.Contains(scrollport);
+}
+
 void
 nsDisplayBackground::Paint(nsDisplayListBuilder* aBuilder,
                            nsIRenderingContext* aCtx) {

layout/base/nsDisplayList.h

@@ -542,6 +542,8 @@ public:
   /**
    * @return PR_FALSE if the painting performed by the item is invariant
    * when frame aFrame is moved relative to aBuilder->GetRootMovingFrame().
+   * In other words, if you render the item at locations P and P', the rendering
+   * only differs by the translation.
    * This can only be called when aBuilder->IsMovingFrame(mFrame) is true.
    * It return PR_TRUE for all wrapped lists.
    */
@@ -549,8 +551,8 @@ public:
   { return PR_FALSE; }
   /**
    * @return PR_TRUE if the contents of this item are rendered fixed relative
-   * to the nearest viewport *and* they cover the viewport. Only return true
-   * if the contents actually vary when scrolling in the viewport.
+   * to the nearest viewport *and* they cover the viewport's scrollport.
+   * Only return true if the contents actually vary when scrolling in the viewport.
    */
   virtual PRBool IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder)
   { return PR_FALSE; }
@@ -1311,6 +1313,7 @@ public:
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor);
+  virtual PRBool IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder);
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   NS_DISPLAY_DECL_NAME("Background", TYPE_BACKGROUND)

layout/generic/nsCanvasFrame.cpp

@@ -249,37 +249,6 @@ nsRect nsCanvasFrame::CanvasArea() const
   return result;
 }
 
-PRBool
-nsDisplayCanvasBackground::IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder)
-{
-  if (mIsThemed)
-    return PR_FALSE;
-
-  nsPresContext* presContext = mFrame->PresContext();
-  nsStyleContext* bgSC;
-  PRBool hasBG =
-    nsCSSRendering::FindBackground(presContext, mFrame, &bgSC);
-  NS_ASSERTION(hasBG, "This item should have been pruned if it has no real background");
-  if (!hasBG)
-    return PR_FALSE;
-
-  const nsStyleBackground* bg = bgSC->GetStyleBackground();
-  if (!bg->HasFixedBackground())
-    return PR_FALSE;
-
-  NS_FOR_VISIBLE_BACKGROUND_LAYERS_BACK_TO_FRONT(i, bg) {
-    const nsStyleBackground::Layer& layer = bg->mLayers[i];
-    if (layer.mAttachment != NS_STYLE_BG_ATTACHMENT_FIXED &&
-        !layer.mImage.IsEmpty()) {
-      return PR_FALSE;
-    }
-  }
-
-  // The canvas background always covers the (scrolled) area of the
-  // viewport
-  return PR_TRUE;
-}
-
 void
 nsDisplayCanvasBackground::Paint(nsDisplayListBuilder* aBuilder,
                                  nsIRenderingContext* aCtx)

layout/generic/nsCanvasFrame.h

@@ -184,7 +184,6 @@ public:
     return NS_GET_A(mExtraBackgroundColor) == 255 ||
            nsDisplayBackground::IsOpaque(aBuilder);
   }
-  virtual PRBool IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor)
   {
     nscolor background;