Don't always fully repaint on viewport resize

Source/core/rendering/style/FillLayer.cpp

Index: Source/core/rendering/style/FillLayer.cpp
diff --git a/Source/core/rendering/style/FillLayer.cpp b/Source/core/rendering/style/FillLayer.cpp
index 907a80d5b52cf5884b11f9d920229f42dc620e42..176f648709e9ac0fe5892be37267c396e997dd43 100644
--- a/Source/core/rendering/style/FillLayer.cpp
+++ b/Source/core/rendering/style/FillLayer.cpp
@@ -355,6 +355,50 @@ bool FillLayer::imagesAreLoaded() const
     return true;
 }
 
+bool FillLayer::needsFullRepaintOnContainerWidthChange() const
+{
+    if (m_image) {
+        if (m_repeatX != RepeatFill && m_repeatX != NoRepeatFill)
+            return true;
+        if (m_xPosition.isPercent() && !m_xPosition.isZero())
+            return true;
+        if (m_backgroundXOrigin != LeftEdge)
+            return true;
+        if (m_sizeType != SizeLength && m_sizeType != SizeNone)
+            return true;
+        if (m_sizeType == SizeLength) {
+            if (m_sizeLength.width().isPercent() && !m_sizeLength.width().isZero())
+                return true;
+            if (m_sizeLength.width().isAuto() && m_sizeLength.height().isPercent() && !m_sizeLength.height().isZero())
+                return true;
+        }
+    }
+
+    return m_next && m_next->needsFullRepaintOnContainerWidthChange();
+}
+
+bool FillLayer::needsFullRepaintOnContainerHeightChange() const
+{
+    if (m_image) {

[Xianzhu, 2014/05/20 21:15:20]

Does this still look scaring?

The other two choices are:

1. Don't add these functions. RenderView fully repaints when there is any
background-image;

2. Simplify the function by returning true when the background-image's settings
are not by default, i.e.

   if (m_repeatY != RepeatFill
       || !m_yPosition().isZero()
       || m_backgroundYOrigin != TopEdge
       || m_sizeType != SizeNone)
       return true;

wdyt?

+        if (m_repeatY != RepeatFill && m_repeatY != NoRepeatFill)
+            return true;
+        if (m_yPosition.isPercent() && !m_yPosition.isZero())
+            return true;
+        if (m_backgroundYOrigin != TopEdge)
+            return true;
+        if (m_sizeType != SizeLength && m_sizeType != SizeNone)
+            return true;
+        if (m_sizeType == SizeLength) {
+            if (m_sizeLength.height().isPercent() && !m_sizeLength.height().isZero())
+                return true;
+            if (m_sizeLength.height().isAuto() && m_sizeLength.width().isPercent() && !m_sizeLength.width().isZero())
+                return true;
+        }
+    }
+
+    return m_next && m_next->needsFullRepaintOnContainerHeightChange();
+}
+
 bool FillLayer::hasOpaqueImage(const RenderObject* renderer) const
 {
     if (!m_image)