Raise the loading priority of in-viewport images.

Source/core/rendering/RenderImage.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011-2012. All rights reserved.
  *
@@ skipping 13 matching lines @@
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #include "config.h"
 #include "core/rendering/RenderImage.h"
 
 #include "HTMLNames.h"
 #include "core/editing/FrameSelection.h"
 #include "core/fetch/ImageResource.h"
+#include "core/fetch/ResourceLoadPriorityOptimizer.h"
+#include "core/fetch/ResourceLoader.h"
 #include "core/html/HTMLAreaElement.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLMapElement.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/frame/Frame.h"
 #include "core/rendering/HitTestResult.h"
 #include "core/rendering/LayoutRectRecorder.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderView.h"
@@ skipping 522 matching lines @@
         m_altText = toHTMLImageElement(node())->altText();
 }
 
 void RenderImage::layout()
 {
     LayoutRectRecorder recorder(*this);
     RenderReplaced::layout();
     updateInnerContentRect();
 }
 
+void RenderImage::didLayout(ResourceLoadPriorityOptimizer& optimizer)
+{
+    RenderReplaced::didLayout(optimizer);
+    updateImageLoadingPriority(optimizer);
+}
+
+void RenderImage::didScroll(ResourceLoadPriorityOptimizer& optimizer)
+{
+    RenderReplaced::didScroll(optimizer);
+    updateImageLoadingPriority(optimizer);
+}
+
+void RenderImage::updateImageLoadingPriority(ResourceLoadPriorityOptimizer& optimizer)
+{
+    if (!m_imageResource || !m_imageResource->cachedImage() || m_imageResource->cachedImage()->isLoaded())
+        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.
+    bool isVisible;

[eseidel, 2013/12/10 17:15:30]

Same problem.  I wouldn't bother making empty rects visible.  They can't have
any affect on rendering, no?

[shatch, 2013/12/10 18:56:19]

Per offline discussion: I don't have any data on this either way at the moment,
but I was sort of leaning towards the idea that the rect is empty, but the
position is still somewhat valid, so in that case we'd want to bump up the
priority. Either way, we should investigate more in the near future to figure
out what's best.

+    if (!objectBounds.isEmpty())
+        isVisible =  viewBounds.intersects(objectBounds);
+    else
+        isVisible = viewBounds.contains(objectBounds);
+
+    ResourceLoadPriorityOptimizer::VisibilityStatus status = isVisible ?
+        ResourceLoadPriorityOptimizer::Visible : ResourceLoadPriorityOptimizer::NotVisible;
+
+    optimizer.notifyImageResourceVisibility(m_imageResource->cachedImage(), status);
+}
+
 void RenderImage::computeIntrinsicRatioInformation(FloatSize& intrinsicSize, double& intrinsicRatio, bool& isPercentageIntrinsicSize) const
 {
     RenderReplaced::computeIntrinsicRatioInformation(intrinsicSize, intrinsicRatio, isPercentageIntrinsicSize);
 
     // Our intrinsicSize is empty if we're rendering generated images with relative width/height. Figure out the right intrinsic size to use.
     if (intrinsicSize.isEmpty() && (m_imageResource->imageHasRelativeWidth() || m_imageResource->imageHasRelativeHeight())) {
         RenderObject* containingBlock = isOutOfFlowPositioned() ? container() : this->containingBlock();
         if (containingBlock->isBox()) {
             RenderBox* box = toRenderBox(containingBlock);
             intrinsicSize.setWidth(box->availableLogicalWidth());
@@ skipping 20 matching lines @@
         return 0;
 
     ImageResource* cachedImage = m_imageResource->cachedImage();
     if (cachedImage && cachedImage->image() && cachedImage->image()->isSVGImage())
         return toSVGImage(cachedImage->image())->embeddedContentBox();
 
     return 0;
 }
 
 } // namespace WebCore