Bug 564991. Part 26: Put background-attachment:fixed backgrounds that propagated to the canvas in their own layer. r=mats,sr=dbaron

layout/base/FrameLayerBuilder.cpp

@@ -877,6 +877,18 @@ ContainerState::ProcessDisplayItems(const nsDisplayList& aList,
                                                 &offsetToActiveScrolledRoot);
       NS_ASSERTION(offsetToActiveScrolledRoot == f->GetOffsetTo(activeScrolledRoot),
                    "Wrong offset");
+      if (item->IsFixedAndCoveringViewport(mBuilder)) {
+        // Make its active scrolled root be the active scrolled root of
+        // the enclosing viewport, since it shouldn't be scrolled by scrolled
+        // frames in its document. InvalidateFixedBackgroundFramesFromList in
+        // nsGfxScrollFrame will not repaint this item when scrolling occurs.
+        nsIFrame* viewportFrame =
+          nsLayoutUtils::GetClosestFrameOfType(f, nsGkAtoms::viewportFrame);
+        NS_ASSERTION(viewportFrame, "no viewport???");
+        activeScrolledRoot =
+          nsLayoutUtils::GetActiveScrolledRootFor(viewportFrame, mBuilder->ReferenceFrame(),
+                                                  &offsetToActiveScrolledRoot);
+      }
 
       nscolor uniformColor;
       PRBool isUniform = item->IsUniform(mBuilder, &uniformColor);

layout/base/nsDisplayList.cpp

@@ -631,13 +631,26 @@ static PRBool RoundedRectContainsRect(const nsRect& aRoundedRect,
   return PR_FALSE;
 }
 
+PRBool
+nsDisplayBackground::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                       nsRegion* aVisibleRegion,
+                                       nsRegion* aVisibleRegionBeforeMove)
+{
+  // Return false if the background was propagated away from this
+  // frame. We don't want this display item to show up and confuse
+  // anything.
+  nsStyleContext* bgSC;
+  return mIsThemed ||
+    nsCSSRendering::FindBackground(mFrame->PresContext(), mFrame, &bgSC);
+}
+
 PRBool
 nsDisplayBackground::IsOpaque(nsDisplayListBuilder* aBuilder) {
   // theme background overrides any other background
   if (mIsThemed)
     return mThemeTransparency == nsITheme::eOpaque;
 
-  nsStyleContext *bgSC;
+  nsStyleContext* bgSC;
   if (!nsCSSRendering::FindBackground(mFrame->PresContext(), mFrame, &bgSC))
     return PR_FALSE;
   const nsStyleBackground* bg = bgSC->GetStyleBackground();
@@ -694,7 +707,7 @@ nsDisplayBackground::IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuild
   nsPresContext* presContext = mFrame->PresContext();
   nsStyleContext *bgSC;
   PRBool hasBG =
-    nsCSSRendering::FindBackground(mFrame->PresContext(), mFrame, &bgSC);
+    nsCSSRendering::FindBackground(presContext, mFrame, &bgSC);
   if (!hasBG)
     return PR_FALSE;
   const nsStyleBackground* bg = bgSC->GetStyleBackground();

layout/base/nsDisplayList.h

@@ -547,6 +547,13 @@ public:
    */
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder)
   { 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.
+   */
+  virtual PRBool IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder)
+  { return PR_FALSE; }
 
   /**
    * @return LAYER_NONE if BuildLayer will return null. In this case
@@ -1290,13 +1297,16 @@ public:
   {
     aOutFrames->AppendElement(mFrame);
   }
+  virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                   nsRegion* aVisibleRegion,
+                                   nsRegion* aVisibleRegionBeforeMove);
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor);
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   NS_DISPLAY_DECL_NAME("Background", TYPE_BACKGROUND)
-private:
+protected:
   /* Used to cache mFrame->IsThemed() since it isn't a cheap call */
   PRPackedBool mIsThemed;
   nsITheme::Transparency mThemeTransparency;

layout/generic/nsCanvasFrame.cpp

@@ -249,6 +249,37 @@ 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

@@ -171,11 +171,20 @@ public:
     mExtraBackgroundColor = NS_RGBA(0,0,0,0);
   }
 
+  virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                   nsRegion* aVisibleRegion,
+                                   nsRegion* aVisibleRegionBeforeMove)
+  {
+    return NS_GET_A(mExtraBackgroundColor) > 0 ||
+           nsDisplayBackground::ComputeVisibility(aBuilder, aVisibleRegion,
+                                                  aVisibleRegionBeforeMove);
+  }
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder)
   {
     return NS_GET_A(mExtraBackgroundColor) == 255 ||
            nsDisplayBackground::IsOpaque(aBuilder);
   }
+  virtual PRBool IsFixedAndCoveringViewport(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor)
   {
     nscolor background;

layout/generic/nsGfxScrollFrame.cpp

@@ -1555,9 +1555,13 @@ InvalidateFixedBackgroundFramesFromList(nsDisplayListBuilder* aBuilder,
     if (sublist) {
       InvalidateFixedBackgroundFramesFromList(aBuilder, *sublist);
     } else if (item->IsVaryingRelativeToMovingFrame(aBuilder)) {
-      nsIFrame* f = item->GetUnderlyingFrame();
+      if (item->IsFixedAndCoveringViewport(aBuilder)) {
-      NS_ASSERTION(f, "No underlying frame for varying item?");
+        // FrameLayerBuilder takes care of scrolling these
-      f->Invalidate(item->GetVisibleRect() - aBuilder->ToReferenceFrame(f));
+      } else {
+        nsIFrame* f = item->GetUnderlyingFrame();
+        NS_ASSERTION(f, "No underlying frame for varying item?");
+        f->Invalidate(item->GetVisibleRect() - aBuilder->ToReferenceFrame(f));
+      }
     }
   }
 }