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

Source/core/layout/LayoutImage.cpp

Index: Source/core/layout/LayoutImage.cpp
diff --git a/Source/core/layout/LayoutImage.cpp b/Source/core/layout/LayoutImage.cpp
index d93280a590121c736797572bd0154ec2b1a3282f..237c5aa70db2b5f54ce9f24aecacf901736ee274 100644
--- a/Source/core/layout/LayoutImage.cpp
+++ b/Source/core/layout/LayoutImage.cpp
@@ -39,6 +39,7 @@
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLMapElement.h"
 #include "core/layout/HitTestResult.h"
+#include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/PaintInfo.h"
 #include "core/layout/TextRunConstructor.h"
@@ -175,6 +176,30 @@ void LayoutImage::invalidatePaintAndMarkForLayoutIfNeeded()
     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);

[esprehn, 2015/03/20 06:52:32]

It might be nice to paint the first frame of an animated image, otherwise if you
scroll fast you might see the content behind the image in the prepaint area.

[chrishtr, 2015/03/20 16:44:45]

That is indeed a bug in this version, thanks for pointing it out. Will fix.

+    }
+
+    return PaintInvalidationDelayedFull;
+}
+
+
 void LayoutImage::notifyFinished(Resource* newImage)
 {
     if (!m_imageResource)