Clip PaintLayerScrollableArea::scrollIntoView return to layer bounds

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1398 matching lines @@
 
 LayoutRect PaintLayerScrollableArea::scrollIntoView(const LayoutRect& rect, const ScrollAlignment& alignX, const ScrollAlignment& alignY, ScrollType scrollType)
 {
     LayoutRect localExposeRect(box().absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms).boundingBox());
     localExposeRect.move(-box().borderLeft(), -box().borderTop());
     LayoutRect layerBounds(LayoutPoint(), LayoutSize(box().clientWidth(), box().clientHeight()));
     LayoutRect r = ScrollAlignment::getRectToExpose(layerBounds, localExposeRect, alignX, alignY);
 
     DoublePoint clampedScrollPosition = clampScrollPosition(scrollPositionDouble() + roundedIntSize(r.location()));
     if (clampedScrollPosition == scrollPositionDouble())
-        return rect;
+        return LayoutRect(box().localToAbsoluteQuad(FloatQuad(FloatRect(intersection(layerBounds, localExposeRect))), UseTransforms).boundingBox());

[bokan, 2016/08/24 18:02:18]

Taking the intersection now means we might end up with an empty rect (this can
happen if the layer isn't being drawn or other edge cases). You should probably
handle that in LayoutBox::scrollRectToVisible by returning if the returned
|newRect| is empty.

 
     DoubleSize oldScrollOffset = adjustedScrollOffset();
     scrollToPosition(clampedScrollPosition, ScrollOffsetUnclamped, ScrollBehaviorInstant, scrollType);
     DoubleSize scrollOffsetDifference = adjustedScrollOffset() - oldScrollOffset;
     localExposeRect.move(-LayoutSize(scrollOffsetDifference));
-    return LayoutRect(box().localToAbsoluteQuad(FloatQuad(FloatRect(localExposeRect)), UseTransforms).boundingBox());
+    return LayoutRect(box().localToAbsoluteQuad(FloatQuad(FloatRect(intersection(layerBounds, localExposeRect))), UseTransforms).boundingBox());
 }
 
 void PaintLayerScrollableArea::updateScrollableAreaSet(bool hasOverflow)
 {
     LocalFrame* frame = box().frame();
     if (!frame)
         return;
 
     FrameView* frameView = frame->view();
     if (!frameView)
@@ skipping 337 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollPositionClampScope::clampScrollableAreas()
 {
     for (auto& scrollableArea : *s_needsClamp)
         scrollableArea->clampScrollPositionsAfterLayout();
     delete s_needsClamp;
     s_needsClamp = nullptr;
 }
 
 } // namespace blink