Source/core/layout/LayoutScrollbar.cpp - chromium/blink - Git at Google

 /*
  * Copyright (C) 2008, 2009 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"
 #include "core/layout/LayoutScrollbar.h"

 #include "core/css/PseudoStyleRequest.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/layout/LayoutScrollbarTheme.h"
 #include "core/layout/LayoutView.h"
 #include "platform/graphics/GraphicsContext.h"

 namespace blink {

 PassRefPtrWillBeRawPtr<Scrollbar> LayoutScrollbar::createCustomScrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, Node* ownerNode, LocalFrame* owningFrame)
 {
     return adoptRefWillBeNoop(new LayoutScrollbar(scrollableArea, orientation, ownerNode, owningFrame));
 }

 LayoutScrollbar::LayoutScrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, Node* ownerNode, LocalFrame* owningFrame)
     : Scrollbar(scrollableArea, orientation, RegularScrollbar, LayoutScrollbarTheme::layoutScrollbarTheme())
     , m_owner(ownerNode)
     , m_owningFrame(owningFrame)
 {
     ASSERT(ownerNode || owningFrame);

     // FIXME: We need to do this because LayoutScrollbar::styleChanged is called as soon as the scrollbar is created.

     // Update the scrollbar size.
     IntRect rect(0, 0, 0, 0);
     updateScrollbarPart(ScrollbarBGPart);
     if (LayoutScrollbarPart* part = m_parts.get(ScrollbarBGPart)) {
         part->layout();
         rect.setSize(flooredIntSize(part->size()));
     } else if (this->orientation() == HorizontalScrollbar) {
         rect.setWidth(this->width());
     } else {
         rect.setHeight(this->height());
     }

     setFrameRect(rect);

 }

 LayoutScrollbar::~LayoutScrollbar()
 {
     if (m_parts.isEmpty())
         return;

     // When a scrollbar is detached from its parent (causing all parts removal) and
     // ready to be destroyed, its destruction can be delayed because of RefPtr
     // maintained in other classes such as EventHandler (m_lastScrollbarUnderMouse).
     // Meanwhile, we can have a call to updateScrollbarPart which recreates the
     // scrollbar part. So, we need to destroy these parts since we don't want them
     // to call on a destroyed scrollbar. See webkit bug 68009.
     updateScrollbarParts(true);
 }

 DEFINE_TRACE(LayoutScrollbar)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_owner);
     visitor->trace(m_owningFrame);
 #endif
     Scrollbar::trace(visitor);
 }

 LayoutBox* LayoutScrollbar::owningLayoutObject() const
 {
     if (m_owningFrame)
         return m_owningFrame->ownerLayoutObject();
     return m_owner && m_owner->layoutObject() ? m_owner->layoutObject()->enclosingBox() : 0;
 }

 LayoutBox* LayoutScrollbar::owningLayoutObjectWithinFrame() const
 {
     if (m_owningFrame)
         return m_owningFrame->contentLayoutObject();
     return owningLayoutObject();
 }

 void LayoutScrollbar::setParent(Widget* parent)
 {
     Scrollbar::setParent(parent);
     if (!parent) {
         // Destroy all of the scrollbar's LayoutBoxes.
         updateScrollbarParts(true);
     }
 }

 void LayoutScrollbar::setEnabled(bool e)
 {
     bool wasEnabled = enabled();
     Scrollbar::setEnabled(e);
     if (wasEnabled != e)
         updateScrollbarParts();
 }

 void LayoutScrollbar::styleChanged()
 {
     updateScrollbarParts();
 }

 void LayoutScrollbar::setHoveredPart(ScrollbarPart part)
 {
     if (part == m_hoveredPart)
         return;

     ScrollbarPart oldPart = m_hoveredPart;
     m_hoveredPart = part;

     updateScrollbarPart(oldPart);
     updateScrollbarPart(m_hoveredPart);

     updateScrollbarPart(ScrollbarBGPart);
     updateScrollbarPart(TrackBGPart);
 }

 void LayoutScrollbar::setPressedPart(ScrollbarPart part)
 {
     ScrollbarPart oldPart = m_pressedPart;
     Scrollbar::setPressedPart(part);

     updateScrollbarPart(oldPart);
     updateScrollbarPart(part);

     updateScrollbarPart(ScrollbarBGPart);
     updateScrollbarPart(TrackBGPart);
 }

 PassRefPtr<ComputedStyle> LayoutScrollbar::getScrollbarPseudoStyle(ScrollbarPart partType, PseudoId pseudoId)
 {
     if (!owningLayoutObject())
         return nullptr;

     RefPtr<ComputedStyle> result = owningLayoutObject()->getUncachedPseudoStyle(PseudoStyleRequest(pseudoId, this, partType), owningLayoutObject()->style());
     // Scrollbars for root frames should always have background color
     // unless explicitly specified as transparent. So we force it.
     // This is because WebKit assumes scrollbar to be always painted and missing background
     // causes visual artifact like non-paint invalidated dirty region.
     if (result && m_owningFrame && m_owningFrame->view() && !m_owningFrame->view()->isTransparent() && !result->hasBackground())
         result->setBackgroundColor(StyleColor(Color::white));

     return result;
 }

 void LayoutScrollbar::updateScrollbarParts(bool destroy)
 {
     updateScrollbarPart(ScrollbarBGPart, destroy);
     updateScrollbarPart(BackButtonStartPart, destroy);
     updateScrollbarPart(ForwardButtonStartPart, destroy);
     updateScrollbarPart(BackTrackPart, destroy);
     updateScrollbarPart(ThumbPart, destroy);
     updateScrollbarPart(ForwardTrackPart, destroy);
     updateScrollbarPart(BackButtonEndPart, destroy);
     updateScrollbarPart(ForwardButtonEndPart, destroy);
     updateScrollbarPart(TrackBGPart, destroy);

     if (destroy)
         return;

     // See if the scrollbar's thickness changed.  If so, we need to mark our owning object as needing a layout.
     bool isHorizontal = orientation() == HorizontalScrollbar;
     int oldThickness = isHorizontal ? height() : width();
     int newThickness = 0;
     LayoutScrollbarPart* part = m_parts.get(ScrollbarBGPart);
     if (part) {
         part->layout();
         newThickness = isHorizontal ? part->size().height() : part->size().width();
     }

     if (newThickness != oldThickness) {
         setFrameRect(IntRect(location(), IntSize(isHorizontal ? width() : newThickness, isHorizontal ? newThickness : height())));
         if (LayoutBox* box = owningLayoutObjectWithinFrame()) {
             if (box->isLayoutBlock())
                 toLayoutBlock(box)->notifyScrollbarThicknessChanged();
             box->setChildNeedsLayout();
             if (m_scrollableArea)
                 m_scrollableArea->invalidateScrollCorner(m_scrollableArea->scrollCornerRect());
         }
     }
 }

 static PseudoId pseudoForScrollbarPart(ScrollbarPart part)
 {
     switch (part) {
     case BackButtonStartPart:
     case ForwardButtonStartPart:
     case BackButtonEndPart:
     case ForwardButtonEndPart:
         return SCROLLBAR_BUTTON;
     case BackTrackPart:
     case ForwardTrackPart:
         return SCROLLBAR_TRACK_PIECE;
     case ThumbPart:
         return SCROLLBAR_THUMB;
     case TrackBGPart:
         return SCROLLBAR_TRACK;
     case ScrollbarBGPart:
         return SCROLLBAR;
     case NoPart:
     case AllParts:
         break;
     }
     ASSERT_NOT_REACHED();
     return SCROLLBAR;
 }

 void LayoutScrollbar::updateScrollbarPart(ScrollbarPart partType, bool destroy)
 {
     if (partType == NoPart)
         return;

     RefPtr<ComputedStyle> partStyle = !destroy ? getScrollbarPseudoStyle(partType,  pseudoForScrollbarPart(partType)) : PassRefPtr<ComputedStyle>(nullptr);

     bool needLayoutObject = !destroy && partStyle && partStyle->display() != NONE;

     if (needLayoutObject && partStyle->display() != BLOCK) {
         // See if we are a button that should not be visible according to OS settings.
         ScrollbarButtonsPlacement buttonsPlacement = theme()->buttonsPlacement();
         switch (partType) {
         case BackButtonStartPart:
             needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementSingle || buttonsPlacement == ScrollbarButtonsPlacementDoubleStart
                 || buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
             break;
         case ForwardButtonStartPart:
             needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementDoubleStart || buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
             break;
         case BackButtonEndPart:
             needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementDoubleEnd || buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
             break;
         case ForwardButtonEndPart:
             needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementSingle || buttonsPlacement == ScrollbarButtonsPlacementDoubleEnd
                 || buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
             break;
         default:
             break;
         }
     }

     LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
     if (!partLayoutObject && needLayoutObject) {
         partLayoutObject = LayoutScrollbarPart::createAnonymous(&owningLayoutObject()->document(), this, partType);
         m_parts.set(partType, partLayoutObject);
     } else if (partLayoutObject && !needLayoutObject) {
         m_parts.remove(partType);
         partLayoutObject->destroy();
         partLayoutObject = 0;
     }

     if (partLayoutObject)
         partLayoutObject->setStyle(partStyle.release());
 }

 IntRect LayoutScrollbar::buttonRect(ScrollbarPart partType)
 {
     LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
     if (!partLayoutObject)
         return IntRect();

     partLayoutObject->layout();

     bool isHorizontal = orientation() == HorizontalScrollbar;
     if (partType == BackButtonStartPart)
         return IntRect(location(), IntSize(isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(), isHorizontal ? height() : partLayoutObject->pixelSnappedHeight()));
     if (partType == ForwardButtonEndPart) {
         return IntRect(isHorizontal ? x() + width() - partLayoutObject->pixelSnappedWidth() : x(),
             isHorizontal ? y() : y() + height() - partLayoutObject->pixelSnappedHeight(),
             isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
             isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
     }

     if (partType == ForwardButtonStartPart) {
         IntRect previousButton = buttonRect(BackButtonStartPart);
         return IntRect(isHorizontal ? x() + previousButton.width() : x(),
             isHorizontal ? y() : y() + previousButton.height(),
             isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
             isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
     }

     IntRect followingButton = buttonRect(ForwardButtonEndPart);
     return IntRect(isHorizontal ? x() + width() - followingButton.width() - partLayoutObject->pixelSnappedWidth() : x(),
         isHorizontal ? y() : y() + height() - followingButton.height() - partLayoutObject->pixelSnappedHeight(),
         isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
         isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
 }

 IntRect LayoutScrollbar::trackRect(int startLength, int endLength)
 {
     LayoutScrollbarPart* part = m_parts.get(TrackBGPart);
     if (part)
         part->layout();

     if (orientation() == HorizontalScrollbar) {
         int marginLeft = part ? static_cast<int>(part->marginLeft()) : 0;
         int marginRight = part ? static_cast<int>(part->marginRight()) : 0;
         startLength += marginLeft;
         endLength += marginRight;
         int totalLength = startLength + endLength;
         return IntRect(x() + startLength, y(), width() - totalLength, height());
     }

     int marginTop = part ? static_cast<int>(part->marginTop()) : 0;
     int marginBottom = part ? static_cast<int>(part->marginBottom()) : 0;
     startLength += marginTop;
     endLength += marginBottom;
     int totalLength = startLength + endLength;

     return IntRect(x(), y() + startLength, width(), height() - totalLength);
 }

 IntRect LayoutScrollbar::trackPieceRectWithMargins(ScrollbarPart partType, const IntRect& oldRect)
 {
     LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
     if (!partLayoutObject)
         return oldRect;

     partLayoutObject->layout();

     IntRect rect = oldRect;
     if (orientation() == HorizontalScrollbar) {
         rect.setX(rect.x() + partLayoutObject->marginLeft());
         rect.setWidth(rect.width() - partLayoutObject->marginWidth());
     } else {
         rect.setY(rect.y() + partLayoutObject->marginTop());
         rect.setHeight(rect.height() - partLayoutObject->marginHeight());
     }
     return rect;
 }

 int LayoutScrollbar::minimumThumbLength()
 {
     LayoutScrollbarPart* partLayoutObject = m_parts.get(ThumbPart);
     if (!partLayoutObject)
         return 0;
     partLayoutObject->layout();
     return orientation() == HorizontalScrollbar ? partLayoutObject->size().width() : partLayoutObject->size().height();
 }

 void LayoutScrollbar::invalidateRect(const IntRect& rect)
 {
     Scrollbar::invalidateRect(rect);

     // FIXME: invalidate only the changed part.
     if (LayoutBox* owningLayoutObject = this->owningLayoutObject()) {
         for (auto& part : m_parts)
             owningLayoutObject->invalidateDisplayItemClientForNonCompositingDescendantsOf(*part.value);
     }
 }

 }
	/*
	* Copyright (C) 2008, 2009 Apple Inc. All Rights Reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"
	#include "core/layout/LayoutScrollbar.h"

	#include "core/css/PseudoStyleRequest.h"
	#include "core/frame/FrameView.h"
	#include "core/frame/LocalFrame.h"
	#include "core/layout/LayoutPart.h"
	#include "core/layout/LayoutScrollbarPart.h"
	#include "core/layout/LayoutScrollbarTheme.h"
	#include "core/layout/LayoutView.h"
	#include "platform/graphics/GraphicsContext.h"

	namespace blink {

	PassRefPtrWillBeRawPtr<Scrollbar> LayoutScrollbar::createCustomScrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, Node* ownerNode, LocalFrame* owningFrame)
	{
	return adoptRefWillBeNoop(new LayoutScrollbar(scrollableArea, orientation, ownerNode, owningFrame));
	}

	LayoutScrollbar::LayoutScrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, Node* ownerNode, LocalFrame* owningFrame)
	: Scrollbar(scrollableArea, orientation, RegularScrollbar, LayoutScrollbarTheme::layoutScrollbarTheme())
	, m_owner(ownerNode)
	, m_owningFrame(owningFrame)
	{
	ASSERT(ownerNode \|\| owningFrame);

	// FIXME: We need to do this because LayoutScrollbar::styleChanged is called as soon as the scrollbar is created.

	// Update the scrollbar size.
	IntRect rect(0, 0, 0, 0);
	updateScrollbarPart(ScrollbarBGPart);
	if (LayoutScrollbarPart* part = m_parts.get(ScrollbarBGPart)) {
	part->layout();
	rect.setSize(flooredIntSize(part->size()));
	} else if (this->orientation() == HorizontalScrollbar) {
	rect.setWidth(this->width());
	} else {
	rect.setHeight(this->height());
	}

	setFrameRect(rect);

	}

	LayoutScrollbar::~LayoutScrollbar()
	{
	if (m_parts.isEmpty())
	return;

	// When a scrollbar is detached from its parent (causing all parts removal) and
	// ready to be destroyed, its destruction can be delayed because of RefPtr
	// maintained in other classes such as EventHandler (m_lastScrollbarUnderMouse).
	// Meanwhile, we can have a call to updateScrollbarPart which recreates the
	// scrollbar part. So, we need to destroy these parts since we don't want them
	// to call on a destroyed scrollbar. See webkit bug 68009.
	updateScrollbarParts(true);
	}

	DEFINE_TRACE(LayoutScrollbar)
	{
	#if ENABLE(OILPAN)
	visitor->trace(m_owner);
	visitor->trace(m_owningFrame);
	#endif
	Scrollbar::trace(visitor);
	}

	LayoutBox* LayoutScrollbar::owningLayoutObject() const
	{
	if (m_owningFrame)
	return m_owningFrame->ownerLayoutObject();
	return m_owner && m_owner->layoutObject() ? m_owner->layoutObject()->enclosingBox() : 0;
	}

	LayoutBox* LayoutScrollbar::owningLayoutObjectWithinFrame() const
	{
	if (m_owningFrame)
	return m_owningFrame->contentLayoutObject();
	return owningLayoutObject();
	}

	void LayoutScrollbar::setParent(Widget* parent)
	{
	Scrollbar::setParent(parent);
	if (!parent) {
	// Destroy all of the scrollbar's LayoutBoxes.
	updateScrollbarParts(true);
	}
	}

	void LayoutScrollbar::setEnabled(bool e)
	{
	bool wasEnabled = enabled();
	Scrollbar::setEnabled(e);
	if (wasEnabled != e)
	updateScrollbarParts();
	}

	void LayoutScrollbar::styleChanged()
	{
	updateScrollbarParts();
	}

	void LayoutScrollbar::setHoveredPart(ScrollbarPart part)
	{
	if (part == m_hoveredPart)
	return;

	ScrollbarPart oldPart = m_hoveredPart;
	m_hoveredPart = part;

	updateScrollbarPart(oldPart);
	updateScrollbarPart(m_hoveredPart);

	updateScrollbarPart(ScrollbarBGPart);
	updateScrollbarPart(TrackBGPart);
	}

	void LayoutScrollbar::setPressedPart(ScrollbarPart part)
	{
	ScrollbarPart oldPart = m_pressedPart;
	Scrollbar::setPressedPart(part);

	updateScrollbarPart(oldPart);
	updateScrollbarPart(part);

	updateScrollbarPart(ScrollbarBGPart);
	updateScrollbarPart(TrackBGPart);
	}

	PassRefPtr<ComputedStyle> LayoutScrollbar::getScrollbarPseudoStyle(ScrollbarPart partType, PseudoId pseudoId)
	{
	if (!owningLayoutObject())
	return nullptr;

	RefPtr<ComputedStyle> result = owningLayoutObject()->getUncachedPseudoStyle(PseudoStyleRequest(pseudoId, this, partType), owningLayoutObject()->style());
	// Scrollbars for root frames should always have background color
	// unless explicitly specified as transparent. So we force it.
	// This is because WebKit assumes scrollbar to be always painted and missing background
	// causes visual artifact like non-paint invalidated dirty region.
	if (result && m_owningFrame && m_owningFrame->view() && !m_owningFrame->view()->isTransparent() && !result->hasBackground())
	result->setBackgroundColor(StyleColor(Color::white));

	return result;
	}

	void LayoutScrollbar::updateScrollbarParts(bool destroy)
	{
	updateScrollbarPart(ScrollbarBGPart, destroy);
	updateScrollbarPart(BackButtonStartPart, destroy);
	updateScrollbarPart(ForwardButtonStartPart, destroy);
	updateScrollbarPart(BackTrackPart, destroy);
	updateScrollbarPart(ThumbPart, destroy);
	updateScrollbarPart(ForwardTrackPart, destroy);
	updateScrollbarPart(BackButtonEndPart, destroy);
	updateScrollbarPart(ForwardButtonEndPart, destroy);
	updateScrollbarPart(TrackBGPart, destroy);

	if (destroy)
	return;

	// See if the scrollbar's thickness changed. If so, we need to mark our owning object as needing a layout.
	bool isHorizontal = orientation() == HorizontalScrollbar;
	int oldThickness = isHorizontal ? height() : width();
	int newThickness = 0;
	LayoutScrollbarPart* part = m_parts.get(ScrollbarBGPart);
	if (part) {
	part->layout();
	newThickness = isHorizontal ? part->size().height() : part->size().width();
	}

	if (newThickness != oldThickness) {
	setFrameRect(IntRect(location(), IntSize(isHorizontal ? width() : newThickness, isHorizontal ? newThickness : height())));
	if (LayoutBox* box = owningLayoutObjectWithinFrame()) {
	if (box->isLayoutBlock())
	toLayoutBlock(box)->notifyScrollbarThicknessChanged();
	box->setChildNeedsLayout();
	if (m_scrollableArea)
	m_scrollableArea->invalidateScrollCorner(m_scrollableArea->scrollCornerRect());
	}
	}
	}

	static PseudoId pseudoForScrollbarPart(ScrollbarPart part)
	{
	switch (part) {
	case BackButtonStartPart:
	case ForwardButtonStartPart:
	case BackButtonEndPart:
	case ForwardButtonEndPart:
	return SCROLLBAR_BUTTON;
	case BackTrackPart:
	case ForwardTrackPart:
	return SCROLLBAR_TRACK_PIECE;
	case ThumbPart:
	return SCROLLBAR_THUMB;
	case TrackBGPart:
	return SCROLLBAR_TRACK;
	case ScrollbarBGPart:
	return SCROLLBAR;
	case NoPart:
	case AllParts:
	break;
	}
	ASSERT_NOT_REACHED();
	return SCROLLBAR;
	}

	void LayoutScrollbar::updateScrollbarPart(ScrollbarPart partType, bool destroy)
	{
	if (partType == NoPart)
	return;

	RefPtr<ComputedStyle> partStyle = !destroy ? getScrollbarPseudoStyle(partType, pseudoForScrollbarPart(partType)) : PassRefPtr<ComputedStyle>(nullptr);

	bool needLayoutObject = !destroy && partStyle && partStyle->display() != NONE;

	if (needLayoutObject && partStyle->display() != BLOCK) {
	// See if we are a button that should not be visible according to OS settings.
	ScrollbarButtonsPlacement buttonsPlacement = theme()->buttonsPlacement();
	switch (partType) {
	case BackButtonStartPart:
	needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementSingle \|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleStart
	\|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
	break;
	case ForwardButtonStartPart:
	needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementDoubleStart \|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
	break;
	case BackButtonEndPart:
	needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementDoubleEnd \|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
	break;
	case ForwardButtonEndPart:
	needLayoutObject = (buttonsPlacement == ScrollbarButtonsPlacementSingle \|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleEnd
	\|\| buttonsPlacement == ScrollbarButtonsPlacementDoubleBoth);
	break;
	default:
	break;
	}
	}

	LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
	if (!partLayoutObject && needLayoutObject) {
	partLayoutObject = LayoutScrollbarPart::createAnonymous(&owningLayoutObject()->document(), this, partType);
	m_parts.set(partType, partLayoutObject);
	} else if (partLayoutObject && !needLayoutObject) {
	m_parts.remove(partType);
	partLayoutObject->destroy();
	partLayoutObject = 0;
	}

	if (partLayoutObject)
	partLayoutObject->setStyle(partStyle.release());
	}

	IntRect LayoutScrollbar::buttonRect(ScrollbarPart partType)
	{
	LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
	if (!partLayoutObject)
	return IntRect();

	partLayoutObject->layout();

	bool isHorizontal = orientation() == HorizontalScrollbar;
	if (partType == BackButtonStartPart)
	return IntRect(location(), IntSize(isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(), isHorizontal ? height() : partLayoutObject->pixelSnappedHeight()));
	if (partType == ForwardButtonEndPart) {
	return IntRect(isHorizontal ? x() + width() - partLayoutObject->pixelSnappedWidth() : x(),
	isHorizontal ? y() : y() + height() - partLayoutObject->pixelSnappedHeight(),
	isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
	isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
	}

	if (partType == ForwardButtonStartPart) {
	IntRect previousButton = buttonRect(BackButtonStartPart);
	return IntRect(isHorizontal ? x() + previousButton.width() : x(),
	isHorizontal ? y() : y() + previousButton.height(),
	isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
	isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
	}

	IntRect followingButton = buttonRect(ForwardButtonEndPart);
	return IntRect(isHorizontal ? x() + width() - followingButton.width() - partLayoutObject->pixelSnappedWidth() : x(),
	isHorizontal ? y() : y() + height() - followingButton.height() - partLayoutObject->pixelSnappedHeight(),
	isHorizontal ? partLayoutObject->pixelSnappedWidth() : width(),
	isHorizontal ? height() : partLayoutObject->pixelSnappedHeight());
	}

	IntRect LayoutScrollbar::trackRect(int startLength, int endLength)
	{
	LayoutScrollbarPart* part = m_parts.get(TrackBGPart);
	if (part)
	part->layout();

	if (orientation() == HorizontalScrollbar) {
	int marginLeft = part ? static_cast<int>(part->marginLeft()) : 0;
	int marginRight = part ? static_cast<int>(part->marginRight()) : 0;
	startLength += marginLeft;
	endLength += marginRight;
	int totalLength = startLength + endLength;
	return IntRect(x() + startLength, y(), width() - totalLength, height());
	}

	int marginTop = part ? static_cast<int>(part->marginTop()) : 0;
	int marginBottom = part ? static_cast<int>(part->marginBottom()) : 0;
	startLength += marginTop;
	endLength += marginBottom;
	int totalLength = startLength + endLength;

	return IntRect(x(), y() + startLength, width(), height() - totalLength);
	}

	IntRect LayoutScrollbar::trackPieceRectWithMargins(ScrollbarPart partType, const IntRect& oldRect)
	{
	LayoutScrollbarPart* partLayoutObject = m_parts.get(partType);
	if (!partLayoutObject)
	return oldRect;

	partLayoutObject->layout();

	IntRect rect = oldRect;
	if (orientation() == HorizontalScrollbar) {
	rect.setX(rect.x() + partLayoutObject->marginLeft());
	rect.setWidth(rect.width() - partLayoutObject->marginWidth());
	} else {
	rect.setY(rect.y() + partLayoutObject->marginTop());
	rect.setHeight(rect.height() - partLayoutObject->marginHeight());
	}
	return rect;
	}

	int LayoutScrollbar::minimumThumbLength()
	{
	LayoutScrollbarPart* partLayoutObject = m_parts.get(ThumbPart);
	if (!partLayoutObject)
	return 0;
	partLayoutObject->layout();
	return orientation() == HorizontalScrollbar ? partLayoutObject->size().width() : partLayoutObject->size().height();
	}

	void LayoutScrollbar::invalidateRect(const IntRect& rect)
	{
	Scrollbar::invalidateRect(rect);

	// FIXME: invalidate only the changed part.
	if (LayoutBox* owningLayoutObject = this->owningLayoutObject()) {
	for (auto& part : m_parts)
	owningLayoutObject->invalidateDisplayItemClientForNonCompositingDescendantsOf(*part.value);
	}
	}

	}