[S.P.] Don't draw frames of animated images that are offscreen.

Source/core/layout/LayoutImage.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 22 matching lines @@
 #include "core/fetch/ImageResource.h"
 #include "core/fetch/ResourceLoadPriorityOptimizer.h"
 #include "core/fetch/ResourceLoader.h"
 #include "core/frame/LocalFrame.h"
 #include "core/html/HTMLAreaElement.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLMapElement.h"
 #include "core/layout/HitTestResult.h"
 #include "core/layout/Layer.h"
+#include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/PaintInfo.h"
 #include "core/layout/TextRunConstructor.h"
 #include "core/page/Page.h"
 #include "core/paint/ImagePainter.h"
 #include "core/svg/graphics/SVGImage.h"
 #include "platform/fonts/Font.h"
 #include "platform/fonts/FontCache.h"
 
 namespace blink {
@@ skipping 116 matching lines @@
         // early. It may be that layout hasn't even taken place once yet.
         updateInnerContentRect();
     }
 
     setShouldDoFullPaintInvalidation();
 
     // Tell any potential compositing layers that the image needs updating.
     contentChanged(ImageChanged);
 }
 
+bool LayoutImage::rectIntersectsVisibleViewport(const LayoutRect& localRect)
+{
+    LayoutRect rect = localRect;
+    LayoutView* layoutView = view();
+    while (layoutView->frame()->ownerLayoutObject())
+        layoutView = layoutView->frame()->ownerLayoutObject()->view();
+    mapRectToPaintInvalidationBacking(layoutView, rect, 0);
+    return rect.intersects(LayoutRect(layoutView->frameView()->visualViewportRect()));
+}
+
+PaintInvalidationReason LayoutImage::invalidatePaintIfNeeded(const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
+{
+    if (!RuntimeEnabledFeatures::slimmingPaintEnabled())
+        return LayoutReplaced::invalidatePaintIfNeeded(paintInvalidationState, paintInvalidationContainer);
+
+    if (!imageResource() || !imageResource()->image() || !imageResource()->image()->maybeAnimated()
+        || rectIntersectsVisibleViewport(visualOverflowRect())) {
+        return LayoutReplaced::invalidatePaintIfNeeded(paintInvalidationState, paintInvalidationContainer);
+    }
+
+    return PaintInvalidationDelayedFull;

[chrishtr, 2015/03/16 23:07:41]

Since this method overrides invalidatePaintIfNeeded, in the case where this line
is reached all the code in LayoutObject::invalidatePaintIfNeeded never runs.
This means that no paint invalidation rects are issued at all, leading to no
paint and no raster.

[chrishtr, 2015/03/17 23:55:56]

Correct. That is the intention of the CL.

+}
+
+
 void LayoutImage::notifyFinished(Resource* newImage)
 {
     if (!m_imageResource)
         return;
 
     if (documentBeingDestroyed())
         return;
 
     invalidateBackgroundObscurationStatus();
 
@@ skipping 175 matching lines @@
         return 0;
 
     ImageResource* cachedImage = m_imageResource->cachedImage();
     if (cachedImage && cachedImage->image() && cachedImage->image()->isSVGImage())
         return toSVGImage(cachedImage->image())->embeddedContentBox();
 
     return 0;
 }
 
 } // namespace blink