Refactor the API for setting dynamic resource load priorities

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 4e6ea451ddf87c2f79d158ea61560174f8cdd6c7..27c8ef9d7ab8361aef3d9e47731f6074d123c2ce 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1351,6 +1351,31 @@ void LayoutBox::imageChanged(WrappedImagePtr image, const IntRect*)
         invalidatePaintOfLayerRectsForImage(image, style()->maskLayers(), false);
 }
 
+ResourcePriority LayoutBox::updatePriority(Resource*)

[Nate Chapin, 2015/10/07 19:40:40]

Merge the basically identical logic in LayoutImage and LayoutBlock here.

[esprehn, 2015/10/08 05:39:11]

You ignore the argument, why pass it at all?

This also doesn't actually update anything, it's a const computation.

updatePriority -> computeResourcePriority() const

[Nate Chapin, 2015/10/08 21:26:37]

I was thinking that the return value might depend on the Resource, but it
doesn't, and I forgot to remove it. Done.
Good point. Done.

+{
+    LayoutRect viewBounds = viewRect();
+    LayoutRect objectBounds = LayoutRect(absoluteContentBox());
+
+    // The object bounds might be empty right now, so intersects will fail since it doesn't deal
+    // with empty rects. Use LayoutRect::contains in that case.
+    bool isVisible;
+    if (!objectBounds.isEmpty())
+        isVisible =  viewBounds.intersects(objectBounds);
+    else
+        isVisible = viewBounds.contains(objectBounds);
+
+    LayoutRect screenRect;
+    if (!objectBounds.isEmpty()) {
+        screenRect = viewBounds;
+        screenRect.intersect(objectBounds);
+    }
+
+    int screenArea = 0;
+    if (!screenRect.isEmpty() && isVisible)
+        screenArea = static_cast<uint32_t>(screenRect.width() * screenRect.height());
+    return ResourcePriority(isVisible ? ResourcePriority::Visible : ResourcePriority::NotVisible, screenArea);
+}
+
 bool LayoutBox::invalidatePaintOfLayerRectsForImage(WrappedImagePtr image, const FillLayer& layers, bool drawingBackground)
 {
     if (drawingBackground && (isDocumentElement() || backgroundStolenForBeingBody()))