Raise the loading priority of in-viewport images.

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index 5f0eb9c7f4b07ca76caf9e01d55a68562f1ef96b..efd9f4de3810f43dacf8f36355d3b7e15b7d6d9a 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -32,6 +32,7 @@
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/editing/Editor.h"
 #include "core/editing/FrameSelection.h"
+#include "core/fetch/ResourceLoadPriorityOptimizer.h"
 #include "core/frame/Frame.h"
 #include "core/frame/FrameView.h"
 #include "core/page/Page.h"
@@ -58,6 +59,8 @@
 #include "core/rendering/RenderTheme.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/shapes/ShapeOutsideInfo.h"
+#include "core/rendering/style/ContentData.h"
+#include "core/rendering/style/RenderStyle.h"
 #include "platform/geometry/FloatQuad.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
@@ -1252,6 +1255,82 @@ void RenderBlock::layout()
     invalidateBackgroundObscurationStatus();
 }
 
+void RenderBlock::didLayout(ResourceLoadPriorityOptimizer& optimizer)
+{
+    RenderBox::didLayout(optimizer);
+    updateStyleImageLoadingPriorities(optimizer);
+}
+
+void RenderBlock::didScroll(ResourceLoadPriorityOptimizer& optimizer)
+{
+    RenderBox::didScroll(optimizer);
+    updateStyleImageLoadingPriorities(optimizer);
+}
+
+void RenderBlock::updateStyleImageLoadingPriorities(ResourceLoadPriorityOptimizer& optimizer)
+{
+    RenderStyle* blockStyle = style();
+    if (!blockStyle)
+        return;
+
+    Vector<ImageResource*> images;
+
+    for (const FillLayer* layer = blockStyle->backgroundLayers(); layer; layer = layer->next()) {

[eseidel, 2013/12/09 23:57:39]

These two loops look identical. Helper function?

[shatch, 2013/12/10 01:41:28]

Done.

+        if (layer->image()) {
+            ImageResource* img = layer->image()->cachedImage();
+            if (img) {
+                images.append(img);
+            }
+        }
+    }
+    for (const FillLayer* layer = blockStyle->maskLayers(); layer; layer = layer->next()) {
+        if (layer->image()) {
+            ImageResource* imageResource = layer->image()->cachedImage();
+            if (imageResource) {
+                images.append(imageResource);
+            }
+        }
+    }
+    ContentData* contentData = const_cast<ContentData*>(blockStyle->contentData());
+    if (contentData && contentData->isImage()) {
+        ImageContentData* imageContentData = static_cast<ImageContentData*>(contentData);
+        if (imageContentData->image() && imageContentData->image()->cachedImage())
+            images.append(imageContentData->image()->cachedImage());
+    }
+    if (blockStyle->boxReflect()) {
+        if (blockStyle->boxReflect()->mask().image()) {
+            if (blockStyle->boxReflect()->mask().image()->cachedImage()) {
+                images.append(blockStyle->boxReflect()->mask().image()->cachedImage());
+            }
+        }
+    }
+    if (blockStyle->listStyleImage() && blockStyle->listStyleImage()->cachedImage())
+        images.append(blockStyle->listStyleImage()->cachedImage());
+    if (blockStyle->borderImageSource() && blockStyle->borderImageSource()->cachedImage())
+        images.append(blockStyle->borderImageSource()->cachedImage());
+    if (blockStyle->maskBoxImageSource() && blockStyle->maskBoxImageSource()->cachedImage())

[eseidel, 2013/12/09 23:57:39]

I might have used a helper here too:

appendIfNotNull(images, blockStyle->maskBoxImageSource())

[shatch, 2013/12/10 01:41:28]

Done.

+        images.append(blockStyle->maskBoxImageSource()->cachedImage());
+
+    if (images.isEmpty())
+        return;
+
+    LayoutRect viewBounds = viewRect();
+    LayoutRect objectBounds = 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.

[eseidel, 2013/12/09 23:57:39]

What does contains do with an empty rect?  Are you sure this is what you want? 
Should contains just check the point then? Is that what it's doing?

I'm not convinced this if is helping you at all.

Maybe:
bool isVisible = objectBounds.isEmpty() ? viewBounds.intersects(objectBounds) :
true;
?

[shatch, 2013/12/10 01:41:28]

Yeah, it's pretty much just checking if the point is in the rect. The idea being
that if the rect's corner is in the view, most likely the image should be higher
priority. Assuming I'm reading that example right (did you mean
!objectBounds.isEmpty() ? ...), I think if we just mark everything with an empty
objectBounds as visible that we'll potentially end up bumping up priority on a
bunch of images that we shouldn't have.

+    bool isVisible;
+    if (!objectBounds.isEmpty())
+        isVisible =  viewBounds.intersects(objectBounds);
+    else
+        isVisible = viewBounds.contains(objectBounds);
+
+    ResourceLoadPriorityOptimizer::VisibilityStatus status = isVisible ?
+        ResourceLoadPriorityOptimizer::Visible : ResourceLoadPriorityOptimizer::NotVisible;
+
+    for (Vector<ImageResource*>::iterator it = images.begin(), end = images.end(); it != end; ++it)
+        optimizer.notifyImageResourceVisibility(*it, status);
+}
+
 void RenderBlock::relayoutShapeDescendantIfMoved(RenderBlock* child, LayoutSize offset)
 {
     LayoutUnit left = isHorizontalWritingMode() ? offset.width() : offset.height();