Bug 820131 - Compute a more accurate bounds for nsDisplayBoxShadowOuter. r=roc

layout/base/nsDisplayList.cpp

@@ -2384,7 +2384,13 @@ nsDisplayBoxShadowOuter::Paint(nsDisplayListBuilder* aBuilder,
 nsRect
 nsDisplayBoxShadowOuter::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
   *aSnap = false;
-  return mFrame->GetVisualOverflowRectRelativeToSelf() + ToReferenceFrame();
+  return mBounds;
+}
+
+nsRect
+nsDisplayBoxShadowOuter::GetBoundsInternal() {
+  return nsLayoutUtils::GetBoxShadowRectForFrame(mFrame, mFrame->GetSize()) +
+         ToReferenceFrame();
 }
 
 bool

layout/base/nsDisplayList.h

@@ -1970,6 +1970,7 @@ public:
   nsDisplayBoxShadowOuter(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
     : nsDisplayItem(aBuilder, aFrame) {
     MOZ_COUNT_CTOR(nsDisplayBoxShadowOuter);
+    mBounds = GetBoundsInternal();
   }
 #ifdef NS_BUILD_REFCNT_LOGGING
   virtual ~nsDisplayBoxShadowOuter() {
@@ -1999,8 +2000,11 @@ public:
     }
   }
 
+  nsRect GetBoundsInternal();
+
 private:
   nsRegion mVisibleRegion;
+  nsRect mBounds;
 };
 
 /**

layout/base/nsLayoutUtils.cpp

@@ -5216,3 +5216,32 @@ nsLayoutUtils::FontSizeInflationEnabled(nsPresContext *aPresContext)
 
   return true;
 }
+
+/* static */ nsRect
+nsLayoutUtils::GetBoxShadowRectForFrame(nsIFrame* aFrame, 
+                                        const nsSize& aFrameSize)
+{
+  nsCSSShadowArray* boxShadows = aFrame->GetStyleBorder()->mBoxShadow;
+  if (!boxShadows) {
+    return nsRect();
+  }
+  
+  nsRect shadows;
+  int32_t A2D = aFrame->PresContext()->AppUnitsPerDevPixel();
+  for (uint32_t i = 0; i < boxShadows->Length(); ++i) {
+    nsRect tmpRect(nsPoint(0, 0), aFrameSize);
+    nsCSSShadowItem* shadow = boxShadows->ShadowAt(i);
+
+    // inset shadows are never painted outside the frame
+    if (shadow->mInset)
+      continue;
+
+    tmpRect.MoveBy(nsPoint(shadow->mXOffset, shadow->mYOffset));
+    tmpRect.Inflate(shadow->mSpread);
+    tmpRect.Inflate(
+      nsContextBoxBlur::GetBlurRadiusMargin(shadow->mRadius, A2D));
+    shadows.UnionRect(shadows, tmpRect);
+  }
+  return shadows;
+}
+

layout/base/nsLayoutUtils.h

@@ -1766,6 +1766,14 @@ public:
   static bool PointIsCloserToRect(PointType aPoint, const RectType& aRect,
                                   CoordType& aClosestXDistance,
                                   CoordType& aClosestYDistance);
+  /**
+   * Computes the box shadow rect for the frame, or returns an empty rect if
+   * there are no shadows.
+   *
+   * @param aFrame Frame to compute shadows for.
+   * @param aFrameSize Size of aFrame (in case it hasn't been set yet).
+   */
+  static nsRect GetBoxShadowRectForFrame(nsIFrame* aFrame, const nsSize& aFrameSize);
 
 #ifdef DEBUG
   /**

layout/generic/nsFrame.cpp

@@ -5110,27 +5110,7 @@ ComputeOutlineAndEffectsRect(nsIFrame* aFrame,
   }
 
   // box-shadow
-  nsCSSShadowArray* boxShadows = aFrame->GetStyleBorder()->mBoxShadow;
-  if (boxShadows) {
-    nsRect shadows;
-    int32_t A2D = aFrame->PresContext()->AppUnitsPerDevPixel();
-    for (uint32_t i = 0; i < boxShadows->Length(); ++i) {
-      nsRect tmpRect(nsPoint(0, 0), aNewSize);
-      nsCSSShadowItem* shadow = boxShadows->ShadowAt(i);
-
-      // inset shadows are never painted outside the frame
-      if (shadow->mInset)
-        continue;
-
-      tmpRect.MoveBy(nsPoint(shadow->mXOffset, shadow->mYOffset));
-      tmpRect.Inflate(shadow->mSpread, shadow->mSpread);
-      tmpRect.Inflate(
-        nsContextBoxBlur::GetBlurRadiusMargin(shadow->mRadius, A2D));
-
-      shadows.UnionRect(shadows, tmpRect);
-    }
-    r.UnionRect(r, shadows);
-  }
+  r.UnionRect(r, nsLayoutUtils::GetBoxShadowRectForFrame(aFrame, aNewSize));
 
   const nsStyleOutline* outline = aFrame->GetStyleOutline();
   uint8_t outlineStyle = outline->GetOutlineStyle();