Don't invalidate paint on background image change if it's obscured

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 6afb5f4d8739a566deca49491e37c711d15a3459..f260e4094fbd28f352e3bab0bd9ca71ea921bf11 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1484,7 +1484,8 @@ void LayoutBox::imageChanged(WrappedImagePtr image, const IntRect*)
     if ((style()->borderImage().image() && style()->borderImage().image()->data() == image)
         || (style()->maskBoxImage().image() && style()->maskBoxImage().image()->data() == image)) {
         setShouldDoFullPaintInvalidation();
-        return;
+    } else if (!invalidatePaintOfImageLayers(image, style()->backgroundLayers())) {
+        invalidatePaintOfImageLayers(image, style()->maskLayers());
     }
 
     ShapeValue* shapeOutsideValue = style()->shapeOutside();

[chrishtr, 2016/08/09 16:05:17]

I guess you're fixing a bug also that this code didn't use to execute? What was
the effect of this? Add
a test?

[Xianzhu, 2016/08/09 18:51:48]

There might be a bug if background and shape-outside share the same image that
we would miss needed layout when shape-outside image changes. However this can't
be reproduced because we seem to always use different images for background and
shape-outside, perhaps because shape-outside's image request has different
referrer rule.

However, the change makes the code not depend on the special referrer rule.

@@ -1495,9 +1496,6 @@ void LayoutBox::imageChanged(WrappedImagePtr image, const IntRect*)
             markShapeOutsideDependentsForLayout();
         }
     }
-
-    if (!invalidatePaintOfLayerRectsForImage(image, style()->backgroundLayers(), true))
-        invalidatePaintOfLayerRectsForImage(image, style()->maskLayers(), false);
 }
 
 ResourcePriority LayoutBox::computeResourcePriority() const
@@ -1525,21 +1523,27 @@ ResourcePriority LayoutBox::computeResourcePriority() const
     return ResourcePriority(isVisible ? ResourcePriority::Visible : ResourcePriority::NotVisible, screenArea);
 }
 
-bool LayoutBox::invalidatePaintOfLayerRectsForImage(WrappedImagePtr image, const FillLayer& layers, bool drawingBackground)
+bool LayoutBox::invalidatePaintOfImageLayers(WrappedImagePtr image, const FillLayer& layers)
 {
-    if (drawingBackground && (isDocumentElement() || backgroundStolenForBeingBody()))
+    bool isBackground = &layers == &styleRef().backgroundLayers();

[eae, 2016/08/09 14:41:48]

NIT: Comparing references like this is a little odd; how about adding a ==
operator to the FillLayers calls?

[Xianzhu, 2016/08/09 18:51:48]

We have FillLayer::operator== that compares the values which is not desired
here.  

+    if (isBackground && (isDocumentElement() || backgroundStolenForBeingBody()))

[Stephen Chennney, 2016/08/09 14:22:31]

if (isBackground) {
  if (isDocumentElement() || ...
    return false;

  invalidateBackgroundObscurationStatus();
  ...
}

[Xianzhu, 2016/08/09 18:51:48]

Done.

         return false;
+
+    if (isBackground) {
+        invalidateBackgroundObscurationStatus();
+        if (backgroundIsKnownToBeObscured())
+            return false;
+    }
+
     for (const FillLayer* curLayer = &layers; curLayer; curLayer = curLayer->next()) {
         if (curLayer->image() && image == curLayer->image()->data()) {
             bool maybeAnimated = curLayer->image()->cachedImage() && curLayer->image()->cachedImage()->getImage() && curLayer->image()->cachedImage()->getImage()->maybeAnimated();
-            if (maybeAnimated && drawingBackground)
+            if (maybeAnimated && isBackground) {
                 setShouldDoFullPaintInvalidation(PaintInvalidationDelayedFull);
-            else
+            } else {
                 setShouldDoFullPaintInvalidation();
-
-            if (drawingBackground)
-                invalidateBackgroundObscurationStatus();
-            return true;
+                return true;
+            }
         }
     }
     return false;