third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp - chromium/src - Git at Google

 /*
  * 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@web.de>
  *   Randall Jesup <rjesup@wgate.com>
  *   Roland Mainz <roland.mainz@informatik.med.uni-giessen.de>
  *   Josh Soref <timeless@mac.com>
  *   Boris Zbarsky <bzbarsky@mit.edu>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  *
  * Alternatively, the contents of this file may be used under the terms
  * of either the Mozilla Public License Version 1.1, found at
  * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
  * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
  * (the "GPL"), in which case the provisions of the MPL or the GPL are
  * applicable instead of those above.  If you wish to allow use of your
  * version of this file only under the terms of one of those two
  * licenses (the MPL or the GPL) and not to allow others to use your
  * version of this file under the LGPL, indicate your decision by
  * deletingthe provisions above and replace them with the notice and
  * other provisions required by the MPL or the GPL, as the case may be.
  * If you do not delete the provisions above, a recipient may use your
  * version of this file under any of the LGPL, the MPL or the GPL.
  */

 #include "config.h"
 #include "core/paint/PaintLayerClipper.h"

 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/PaintLayer.h"

 namespace blink {

 static void adjustClipRectsForChildren(const LayoutObject& layoutObject, ClipRects& clipRects)
 {
     EPosition position = layoutObject.style()->position();
     // A fixed object is essentially the root of its containing block hierarchy, so when
     // we encounter such an object, we reset our clip rects to the fixedClipRect.
     if (position == FixedPosition) {
         clipRects.setPosClipRect(clipRects.fixedClipRect());
         clipRects.setOverflowClipRect(clipRects.fixedClipRect());
         clipRects.setFixed(true);
     } else if (position == RelativePosition) {
         clipRects.setPosClipRect(clipRects.overflowClipRect());
     } else if (position == AbsolutePosition) {
         clipRects.setOverflowClipRect(clipRects.posClipRect());
     }
 }

 static void applyClipRects(const ClipRectsContext& context, const LayoutObject& layoutObject, LayoutPoint offset, ClipRects& clipRects)
 {
     ASSERT(layoutObject.hasOverflowClip() || layoutObject.hasClip() || layoutObject.style()->containsPaint());
     LayoutView* view = layoutObject.view();
     ASSERT(view);
     if (clipRects.fixed() && context.rootLayer->layoutObject() == view)
         offset -= toIntSize(view->frameView()->scrollPosition());
     if (layoutObject.hasOverflowClip() || layoutObject.style()->containsPaint()) {
         ClipRect newOverflowClip = toLayoutBox(layoutObject).overflowClipRect(offset, context.scrollbarRelevancy);
         newOverflowClip.setHasRadius(layoutObject.style()->hasBorderRadius());
         clipRects.setOverflowClipRect(intersection(newOverflowClip, clipRects.overflowClipRect()));
         if (layoutObject.isPositioned())
             clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
         if (layoutObject.isLayoutView())
             clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
         if (layoutObject.style()->containsPaint()) {
             clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
             clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
         }
     }
     if (layoutObject.hasClip()) {
         LayoutRect newClip = toLayoutBox(layoutObject).clipRect(offset);
         clipRects.setPosClipRect(intersection(newClip, clipRects.posClipRect()).setIsClippedByClipCss());
         clipRects.setOverflowClipRect(intersection(newClip, clipRects.overflowClipRect()).setIsClippedByClipCss());
         clipRects.setFixedClipRect(intersection(newClip, clipRects.fixedClipRect()).setIsClippedByClipCss());

     }
 }

 PaintLayerClipper::PaintLayerClipper(const LayoutBoxModelObject& layoutObject)
     : m_layoutObject(layoutObject)
 {
 }

 ClipRects* PaintLayerClipper::clipRectsIfCached(const ClipRectsContext& context) const
 {
     ASSERT(context.usesCache());
     if (!m_cache)
         return 0;
     ClipRectsCache::Entry& entry = m_cache->get(context.cacheSlot());
     // FIXME: We used to ASSERT that we always got a consistent root layer.
     // We should add a test that has an inconsistent root. See
     // http://crbug.com/366118 for an example.
     if (context.rootLayer != entry.root)
         return 0;
     ASSERT(entry.scrollbarRelevancy == context.scrollbarRelevancy);
 #ifdef CHECK_CACHED_CLIP_RECTS
     // This code is useful to check cached clip rects, but is too expensive to leave enabled in debug builds by default.
     ClipRectsContext tempContext(context);
     tempContext.cacheSlot = UncachedClipRects;
     RefPtr<ClipRects> clipRects = ClipRects::create();
     calculateClipRects(tempContext, *clipRects);
     ASSERT(clipRects == *entry.clipRects);
 #endif
     return entry.clipRects.get();
 }
 ClipRects* PaintLayerClipper::storeClipRectsInCache(const ClipRectsContext& context, ClipRects* parentClipRects, const ClipRects& clipRects) const
 {
     ClipRectsCache::Entry& entry = cache().get(context.cacheSlot());
     entry.root = context.rootLayer;
 #if ENABLE(ASSERT)
     entry.scrollbarRelevancy = context.scrollbarRelevancy;
 #endif
     if (parentClipRects) {
         // If our clip rects match the clip rects of our parent, we share storage.
         if (clipRects == *parentClipRects) {
             entry.clipRects = parentClipRects;
             return parentClipRects;
         }
     }
     entry.clipRects = ClipRects::create(clipRects);
     return entry.clipRects.get();
 }
 ClipRects* PaintLayerClipper::getClipRects(const ClipRectsContext& context) const
 {
     if (ClipRects* result = clipRectsIfCached(context))
         return result;
     // Note that it's important that we call getClipRects on our parent
     // before we call calculateClipRects so that calculateClipRects will hit
     // the cache.
     ClipRects* parentClipRects = 0;
     if (context.rootLayer != m_layoutObject.layer() && m_layoutObject.layer()->parent())
         parentClipRects = m_layoutObject.layer()->parent()->clipper().getClipRects(context);
     RefPtr<ClipRects> clipRects = ClipRects::create();
     calculateClipRects(context, *clipRects);
     return storeClipRectsInCache(context, parentClipRects, *clipRects);
 }

 void PaintLayerClipper::clearClipRectsIncludingDescendants()
 {
     m_cache = nullptr;

     for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
         layer->clipper().clearClipRectsIncludingDescendants();
     }
 }

 void PaintLayerClipper::clearClipRectsIncludingDescendants(ClipRectsCacheSlot cacheSlot)
 {
     if (m_cache)
         m_cache->clear(cacheSlot);

     for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
         layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);
     }
 }


 LayoutRect PaintLayerClipper::localClipRect(const PaintLayer* clippingRootLayer) const
 {
     LayoutRect layerBounds;
     ClipRect backgroundRect, foregroundRect;
     ClipRectsContext context(clippingRootLayer, PaintingClipRects);
     calculateRects(context, LayoutRect(LayoutRect::infiniteIntRect()), layerBounds, backgroundRect, foregroundRect);

     LayoutRect clipRect = backgroundRect.rect();
     // TODO(chrishtr): avoid converting to IntRect and back.
     if (clipRect == LayoutRect(LayoutRect::infiniteIntRect()))
         return clipRect;

     LayoutPoint clippingRootOffset;
     m_layoutObject.layer()->convertToLayerCoords(clippingRootLayer, clippingRootOffset);
     clipRect.moveBy(-clippingRootOffset);

     return clipRect;
 }

 void PaintLayerClipper::calculateRects(const ClipRectsContext& context, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
     ClipRect& backgroundRect, ClipRect& foregroundRect, const LayoutPoint* offsetFromRoot) const
 {
     bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;

     if (!isClippingRoot && m_layoutObject.layer()->parent()) {
         backgroundRect = backgroundClipRect(context);
         backgroundRect.move(context.subPixelAccumulation);
         backgroundRect.intersect(paintDirtyRect);
     } else {
         backgroundRect = paintDirtyRect;
     }

     foregroundRect = backgroundRect;

     LayoutPoint offset;
     if (offsetFromRoot)
         offset = *offsetFromRoot;
     else
         m_layoutObject.layer()->convertToLayerCoords(context.rootLayer, offset);
     layerBounds = LayoutRect(offset, LayoutSize(m_layoutObject.layer()->size()));

     // Update the clip rects that will be passed to child layers.
     if ((m_layoutObject.hasOverflowClip() && shouldRespectOverflowClip(context)) || m_layoutObject.style()->containsPaint()) {
         foregroundRect.intersect(toLayoutBox(m_layoutObject).overflowClipRect(offset, context.scrollbarRelevancy));
         if (m_layoutObject.style()->hasBorderRadius())
             foregroundRect.setHasRadius(true);

         // FIXME: Does not do the right thing with columns yet, since we don't yet factor in the
         // individual column boxes as overflow.

         // The LayoutView is special since its overflow clipping rect may be larger than its box rect (crbug.com/492871).
         LayoutRect layerBoundsWithVisualOverflow = m_layoutObject.isLayoutView() ? toLayoutView(m_layoutObject).viewRect() : toLayoutBox(m_layoutObject).visualOverflowRect();
         toLayoutBox(m_layoutObject).flipForWritingMode(layerBoundsWithVisualOverflow); // PaintLayer are in physical coordinates, so the overflow has to be flipped.
         layerBoundsWithVisualOverflow.moveBy(offset);
         backgroundRect.intersect(layerBoundsWithVisualOverflow);
     }

     // CSS clip (different than clipping due to overflow) can clip to any box, even if it falls outside of the border box.
     if (m_layoutObject.hasClip()) {
         // Clip applies to *us* as well, so go ahead and update the damageRect.
         LayoutRect newPosClip = toLayoutBox(m_layoutObject).clipRect(offset);
         backgroundRect.intersect(newPosClip);
         backgroundRect.setIsClippedByClipCss();
         foregroundRect.intersect(newPosClip);
         foregroundRect.setIsClippedByClipCss();
     }
 }

 void PaintLayerClipper::calculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
 {
     bool rootLayerScrolls = m_layoutObject.document().settings() && m_layoutObject.document().settings()->rootLayerScrolls();
     if (!m_layoutObject.layer()->parent() && !rootLayerScrolls) {
         // The root layer's clip rect is always infinite.
         clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
         return;
     }

     bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;

     // For transformed layers, the root layer was shifted to be us, so there is no need to
     // examine the parent. We want to cache clip rects with us as the root.
     PaintLayer* parentLayer = !isClippingRoot ? m_layoutObject.layer()->parent() : 0;
     // Ensure that our parent's clip has been calculated so that we can examine the values.
     if (parentLayer) {
         // FIXME: Why don't we just call getClipRects here?
         if (context.usesCache() && parentLayer->clipper().cachedClipRects(context)) {
             clipRects = *parentLayer->clipper().cachedClipRects(context);
         } else {
             parentLayer->clipper().calculateClipRects(context, clipRects);
         }
     } else {
         clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
     }

     adjustClipRectsForChildren(m_layoutObject, clipRects);

     if ((m_layoutObject.hasOverflowClip() && shouldRespectOverflowClip(context)) || m_layoutObject.hasClip() || m_layoutObject.style()->containsPaint()) {
         // This offset cannot use convertToLayerCoords, because sometimes our rootLayer may be across
         // some transformed layer boundary, for example, in the PaintLayerCompositor overlapMap, where
         // clipRects are needed in view space.
         applyClipRects(context, m_layoutObject, roundedLayoutPoint(m_layoutObject.localToContainerPoint(FloatPoint(), context.rootLayer->layoutObject())), clipRects);
     }
 }

 static ClipRect backgroundClipRectForPosition(const ClipRects& parentRects, EPosition position)
 {
     if (position == FixedPosition)
         return parentRects.fixedClipRect();

     if (position == AbsolutePosition)
         return parentRects.posClipRect();

     return parentRects.overflowClipRect();
 }

 ClipRect PaintLayerClipper::backgroundClipRect(const ClipRectsContext& context) const
 {
     ASSERT(m_layoutObject.layer()->parent());
     ASSERT(m_layoutObject.view());

     RefPtr<ClipRects> parentClipRects = ClipRects::create();
     if (m_layoutObject.layer() == context.rootLayer)
         parentClipRects->reset(LayoutRect(LayoutRect::infiniteIntRect()));
     else
         m_layoutObject.layer()->parent()->clipper().getOrCalculateClipRects(context, *parentClipRects);

     ClipRect result = backgroundClipRectForPosition(*parentClipRects, m_layoutObject.style()->position());

     // Note: infinite clipRects should not be scrolled here, otherwise they will accidentally no longer be considered infinite.
     if (parentClipRects->fixed() && context.rootLayer->layoutObject() == m_layoutObject.view() && result != LayoutRect(LayoutRect::infiniteIntRect()))
         result.move(toIntSize(m_layoutObject.view()->frameView()->scrollPosition()));

     return result;
 }

 void PaintLayerClipper::getOrCalculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
 {
     if (context.usesCache())
         clipRects = *getClipRects(context);
     else
         calculateClipRects(context, clipRects);
 }

 bool PaintLayerClipper::shouldRespectOverflowClip(const ClipRectsContext& context) const
 {
     PaintLayer* layer = m_layoutObject.layer();
     if (layer != context.rootLayer)
         return true;

     if (context.respectOverflowClip == IgnoreOverflowClip)
         return false;

     if (layer->isRootLayer() && context.respectOverflowClipForViewport == IgnoreOverflowClip)
         return false;

     return true;
 }

 ClipRects* PaintLayerClipper::paintingClipRects(const PaintLayer* rootLayer, ShouldRespectOverflowClip respectOverflowClip, const LayoutSize& subpixelAccumulation) const
 {
     ClipRectsContext context(rootLayer, PaintingClipRects, IgnoreOverlayScrollbarSize, subpixelAccumulation);
     if (respectOverflowClip == IgnoreOverflowClip)
         context.setIgnoreOverflowClip();
     return getClipRects(context);
 }

 } // namespace blink
	/*
	* 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@web.de>
	* Randall Jesup <rjesup@wgate.com>
	* Roland Mainz <roland.mainz@informatik.med.uni-giessen.de>
	* Josh Soref <timeless@mac.com>
	* Boris Zbarsky <bzbarsky@mit.edu>
	*
	* This library is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* This library is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with this library; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	*
	* Alternatively, the contents of this file may be used under the terms
	* of either the Mozilla Public License Version 1.1, found at
	* http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
	* License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
	* (the "GPL"), in which case the provisions of the MPL or the GPL are
	* applicable instead of those above. If you wish to allow use of your
	* version of this file only under the terms of one of those two
	* licenses (the MPL or the GPL) and not to allow others to use your
	* version of this file under the LGPL, indicate your decision by
	* deletingthe provisions above and replace them with the notice and
	* other provisions required by the MPL or the GPL, as the case may be.
	* If you do not delete the provisions above, a recipient may use your
	* version of this file under any of the LGPL, the MPL or the GPL.
	*/

	#include "config.h"
	#include "core/paint/PaintLayerClipper.h"

	#include "core/frame/FrameView.h"
	#include "core/frame/Settings.h"
	#include "core/layout/LayoutView.h"
	#include "core/paint/PaintLayer.h"

	namespace blink {

	static void adjustClipRectsForChildren(const LayoutObject& layoutObject, ClipRects& clipRects)
	{
	EPosition position = layoutObject.style()->position();
	// A fixed object is essentially the root of its containing block hierarchy, so when
	// we encounter such an object, we reset our clip rects to the fixedClipRect.
	if (position == FixedPosition) {
	clipRects.setPosClipRect(clipRects.fixedClipRect());
	clipRects.setOverflowClipRect(clipRects.fixedClipRect());
	clipRects.setFixed(true);
	} else if (position == RelativePosition) {
	clipRects.setPosClipRect(clipRects.overflowClipRect());
	} else if (position == AbsolutePosition) {
	clipRects.setOverflowClipRect(clipRects.posClipRect());
	}
	}

	static void applyClipRects(const ClipRectsContext& context, const LayoutObject& layoutObject, LayoutPoint offset, ClipRects& clipRects)
	{
	ASSERT(layoutObject.hasOverflowClip() \|\| layoutObject.hasClip() \|\| layoutObject.style()->containsPaint());
	LayoutView* view = layoutObject.view();
	ASSERT(view);
	if (clipRects.fixed() && context.rootLayer->layoutObject() == view)
	offset -= toIntSize(view->frameView()->scrollPosition());
	if (layoutObject.hasOverflowClip() \|\| layoutObject.style()->containsPaint()) {
	ClipRect newOverflowClip = toLayoutBox(layoutObject).overflowClipRect(offset, context.scrollbarRelevancy);
	newOverflowClip.setHasRadius(layoutObject.style()->hasBorderRadius());
	clipRects.setOverflowClipRect(intersection(newOverflowClip, clipRects.overflowClipRect()));
	if (layoutObject.isPositioned())
	clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
	if (layoutObject.isLayoutView())
	clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
	if (layoutObject.style()->containsPaint()) {
	clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
	clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
	}
	}
	if (layoutObject.hasClip()) {
	LayoutRect newClip = toLayoutBox(layoutObject).clipRect(offset);
	clipRects.setPosClipRect(intersection(newClip, clipRects.posClipRect()).setIsClippedByClipCss());
	clipRects.setOverflowClipRect(intersection(newClip, clipRects.overflowClipRect()).setIsClippedByClipCss());
	clipRects.setFixedClipRect(intersection(newClip, clipRects.fixedClipRect()).setIsClippedByClipCss());

	}
	}

	PaintLayerClipper::PaintLayerClipper(const LayoutBoxModelObject& layoutObject)
	: m_layoutObject(layoutObject)
	{
	}

	ClipRects* PaintLayerClipper::clipRectsIfCached(const ClipRectsContext& context) const
	{
	ASSERT(context.usesCache());
	if (!m_cache)
	return 0;
	ClipRectsCache::Entry& entry = m_cache->get(context.cacheSlot());
	// FIXME: We used to ASSERT that we always got a consistent root layer.
	// We should add a test that has an inconsistent root. See
	// http://crbug.com/366118 for an example.
	if (context.rootLayer != entry.root)
	return 0;
	ASSERT(entry.scrollbarRelevancy == context.scrollbarRelevancy);
	#ifdef CHECK_CACHED_CLIP_RECTS
	// This code is useful to check cached clip rects, but is too expensive to leave enabled in debug builds by default.
	ClipRectsContext tempContext(context);
	tempContext.cacheSlot = UncachedClipRects;
	RefPtr<ClipRects> clipRects = ClipRects::create();
	calculateClipRects(tempContext, *clipRects);
	ASSERT(clipRects == *entry.clipRects);
	#endif
	return entry.clipRects.get();
	}
	ClipRects* PaintLayerClipper::storeClipRectsInCache(const ClipRectsContext& context, ClipRects* parentClipRects, const ClipRects& clipRects) const
	{
	ClipRectsCache::Entry& entry = cache().get(context.cacheSlot());
	entry.root = context.rootLayer;
	#if ENABLE(ASSERT)
	entry.scrollbarRelevancy = context.scrollbarRelevancy;
	#endif
	if (parentClipRects) {
	// If our clip rects match the clip rects of our parent, we share storage.
	if (clipRects == *parentClipRects) {
	entry.clipRects = parentClipRects;
	return parentClipRects;
	}
	}
	entry.clipRects = ClipRects::create(clipRects);
	return entry.clipRects.get();
	}
	ClipRects* PaintLayerClipper::getClipRects(const ClipRectsContext& context) const
	{
	if (ClipRects* result = clipRectsIfCached(context))
	return result;
	// Note that it's important that we call getClipRects on our parent
	// before we call calculateClipRects so that calculateClipRects will hit
	// the cache.
	ClipRects* parentClipRects = 0;
	if (context.rootLayer != m_layoutObject.layer() && m_layoutObject.layer()->parent())
	parentClipRects = m_layoutObject.layer()->parent()->clipper().getClipRects(context);
	RefPtr<ClipRects> clipRects = ClipRects::create();
	calculateClipRects(context, *clipRects);
	return storeClipRectsInCache(context, parentClipRects, *clipRects);
	}

	void PaintLayerClipper::clearClipRectsIncludingDescendants()
	{
	m_cache = nullptr;

	for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
	layer->clipper().clearClipRectsIncludingDescendants();
	}
	}

	void PaintLayerClipper::clearClipRectsIncludingDescendants(ClipRectsCacheSlot cacheSlot)
	{
	if (m_cache)
	m_cache->clear(cacheSlot);

	for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
	layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);
	}
	}


	LayoutRect PaintLayerClipper::localClipRect(const PaintLayer* clippingRootLayer) const
	{
	LayoutRect layerBounds;
	ClipRect backgroundRect, foregroundRect;
	ClipRectsContext context(clippingRootLayer, PaintingClipRects);
	calculateRects(context, LayoutRect(LayoutRect::infiniteIntRect()), layerBounds, backgroundRect, foregroundRect);

	LayoutRect clipRect = backgroundRect.rect();
	// TODO(chrishtr): avoid converting to IntRect and back.
	if (clipRect == LayoutRect(LayoutRect::infiniteIntRect()))
	return clipRect;

	LayoutPoint clippingRootOffset;
	m_layoutObject.layer()->convertToLayerCoords(clippingRootLayer, clippingRootOffset);
	clipRect.moveBy(-clippingRootOffset);

	return clipRect;
	}

	void PaintLayerClipper::calculateRects(const ClipRectsContext& context, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
	ClipRect& backgroundRect, ClipRect& foregroundRect, const LayoutPoint* offsetFromRoot) const
	{
	bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;

	if (!isClippingRoot && m_layoutObject.layer()->parent()) {
	backgroundRect = backgroundClipRect(context);
	backgroundRect.move(context.subPixelAccumulation);
	backgroundRect.intersect(paintDirtyRect);
	} else {
	backgroundRect = paintDirtyRect;
	}

	foregroundRect = backgroundRect;

	LayoutPoint offset;
	if (offsetFromRoot)
	offset = *offsetFromRoot;
	else
	m_layoutObject.layer()->convertToLayerCoords(context.rootLayer, offset);
	layerBounds = LayoutRect(offset, LayoutSize(m_layoutObject.layer()->size()));

	// Update the clip rects that will be passed to child layers.
	if ((m_layoutObject.hasOverflowClip() && shouldRespectOverflowClip(context)) \|\| m_layoutObject.style()->containsPaint()) {
	foregroundRect.intersect(toLayoutBox(m_layoutObject).overflowClipRect(offset, context.scrollbarRelevancy));
	if (m_layoutObject.style()->hasBorderRadius())
	foregroundRect.setHasRadius(true);

	// FIXME: Does not do the right thing with columns yet, since we don't yet factor in the
	// individual column boxes as overflow.

	// The LayoutView is special since its overflow clipping rect may be larger than its box rect (crbug.com/492871).
	LayoutRect layerBoundsWithVisualOverflow = m_layoutObject.isLayoutView() ? toLayoutView(m_layoutObject).viewRect() : toLayoutBox(m_layoutObject).visualOverflowRect();
	toLayoutBox(m_layoutObject).flipForWritingMode(layerBoundsWithVisualOverflow); // PaintLayer are in physical coordinates, so the overflow has to be flipped.
	layerBoundsWithVisualOverflow.moveBy(offset);
	backgroundRect.intersect(layerBoundsWithVisualOverflow);
	}

	// CSS clip (different than clipping due to overflow) can clip to any box, even if it falls outside of the border box.
	if (m_layoutObject.hasClip()) {
	// Clip applies to us as well, so go ahead and update the damageRect.
	LayoutRect newPosClip = toLayoutBox(m_layoutObject).clipRect(offset);
	backgroundRect.intersect(newPosClip);
	backgroundRect.setIsClippedByClipCss();
	foregroundRect.intersect(newPosClip);
	foregroundRect.setIsClippedByClipCss();
	}
	}

	void PaintLayerClipper::calculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
	{
	bool rootLayerScrolls = m_layoutObject.document().settings() && m_layoutObject.document().settings()->rootLayerScrolls();
	if (!m_layoutObject.layer()->parent() && !rootLayerScrolls) {
	// The root layer's clip rect is always infinite.
	clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
	return;
	}

	bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;

	// For transformed layers, the root layer was shifted to be us, so there is no need to
	// examine the parent. We want to cache clip rects with us as the root.
	PaintLayer* parentLayer = !isClippingRoot ? m_layoutObject.layer()->parent() : 0;
	// Ensure that our parent's clip has been calculated so that we can examine the values.
	if (parentLayer) {
	// FIXME: Why don't we just call getClipRects here?
	if (context.usesCache() && parentLayer->clipper().cachedClipRects(context)) {
	clipRects = *parentLayer->clipper().cachedClipRects(context);
	} else {
	parentLayer->clipper().calculateClipRects(context, clipRects);
	}
	} else {
	clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
	}

	adjustClipRectsForChildren(m_layoutObject, clipRects);

	if ((m_layoutObject.hasOverflowClip() && shouldRespectOverflowClip(context)) \|\| m_layoutObject.hasClip() \|\| m_layoutObject.style()->containsPaint()) {
	// This offset cannot use convertToLayerCoords, because sometimes our rootLayer may be across
	// some transformed layer boundary, for example, in the PaintLayerCompositor overlapMap, where
	// clipRects are needed in view space.
	applyClipRects(context, m_layoutObject, roundedLayoutPoint(m_layoutObject.localToContainerPoint(FloatPoint(), context.rootLayer->layoutObject())), clipRects);
	}
	}

	static ClipRect backgroundClipRectForPosition(const ClipRects& parentRects, EPosition position)
	{
	if (position == FixedPosition)
	return parentRects.fixedClipRect();

	if (position == AbsolutePosition)
	return parentRects.posClipRect();

	return parentRects.overflowClipRect();
	}

	ClipRect PaintLayerClipper::backgroundClipRect(const ClipRectsContext& context) const
	{
	ASSERT(m_layoutObject.layer()->parent());
	ASSERT(m_layoutObject.view());

	RefPtr<ClipRects> parentClipRects = ClipRects::create();
	if (m_layoutObject.layer() == context.rootLayer)
	parentClipRects->reset(LayoutRect(LayoutRect::infiniteIntRect()));
	else
	m_layoutObject.layer()->parent()->clipper().getOrCalculateClipRects(context, *parentClipRects);

	ClipRect result = backgroundClipRectForPosition(*parentClipRects, m_layoutObject.style()->position());

	// Note: infinite clipRects should not be scrolled here, otherwise they will accidentally no longer be considered infinite.
	if (parentClipRects->fixed() && context.rootLayer->layoutObject() == m_layoutObject.view() && result != LayoutRect(LayoutRect::infiniteIntRect()))
	result.move(toIntSize(m_layoutObject.view()->frameView()->scrollPosition()));

	return result;
	}

	void PaintLayerClipper::getOrCalculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
	{
	if (context.usesCache())
	clipRects = *getClipRects(context);
	else
	calculateClipRects(context, clipRects);
	}

	bool PaintLayerClipper::shouldRespectOverflowClip(const ClipRectsContext& context) const
	{
	PaintLayer* layer = m_layoutObject.layer();
	if (layer != context.rootLayer)
	return true;

	if (context.respectOverflowClip == IgnoreOverflowClip)
	return false;

	if (layer->isRootLayer() && context.respectOverflowClipForViewport == IgnoreOverflowClip)
	return false;

	return true;
	}

	ClipRects* PaintLayerClipper::paintingClipRects(const PaintLayer* rootLayer, ShouldRespectOverflowClip respectOverflowClip, const LayoutSize& subpixelAccumulation) const
	{
	ClipRectsContext context(rootLayer, PaintingClipRects, IgnoreOverlayScrollbarSize, subpixelAccumulation);
	if (respectOverflowClip == IgnoreOverflowClip)
	context.setIgnoreOverflowClip();
	return getClipRects(context);
	}

	} // namespace blink