Source/WebCore/layout/FormattingContext.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2018 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. AND ITS CONTRIBUTORS ``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 ITS 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 "FormattingContext.h"

 #if ENABLE(LAYOUT_FORMATTING_CONTEXT)

 #include "DisplayBox.h"
 #include "FormattingState.h"
 #include "LayoutBox.h"
 #include "LayoutContainer.h"
 #include "LayoutDescendantIterator.h"
 #include "LayoutState.h"
 #include "Logging.h"
 #include <wtf/IsoMallocInlines.h>
 #include <wtf/text/TextStream.h>

 namespace WebCore {
 namespace Layout {

 WTF_MAKE_ISO_ALLOCATED_IMPL(FormattingContext);

 FormattingContext::FormattingContext(const Box& formattingContextRoot, FormattingState& formattingState)
     : m_root(makeWeakPtr(formattingContextRoot))
     , m_formattingState(formattingState)
 {
 #ifndef NDEBUG
     layoutState().registerFormattingContext(*this);
 #endif
 }

 FormattingContext::~FormattingContext()
 {
 #ifndef NDEBUG
     layoutState().deregisterFormattingContext(*this);
 #endif
 }

 LayoutState& FormattingContext::layoutState() const
 {
     return m_formattingState.layoutState();
 }

 void FormattingContext::computeOutOfFlowHorizontalGeometry(const Box& layoutBox) const
 {
     auto& layoutState = this->layoutState();
     auto containingBlockWidth = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).paddingBoxWidth();

     auto compute = [&](Optional<LayoutUnit> usedWidth) {
         auto usedValues = UsedHorizontalValues { containingBlockWidth, usedWidth, { } };
         return Geometry::outOfFlowHorizontalGeometry(layoutState, layoutBox, usedValues);
     };

     auto horizontalGeometry = compute({ });
     if (auto maxWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMaxWidth(), containingBlockWidth)) {
         auto maxHorizontalGeometry = compute(maxWidth);
         if (horizontalGeometry.widthAndMargin.width > maxHorizontalGeometry.widthAndMargin.width)
             horizontalGeometry = maxHorizontalGeometry;
     }

     if (auto minWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMinWidth(), containingBlockWidth)) {
         auto minHorizontalGeometry = compute(minWidth);
         if (horizontalGeometry.widthAndMargin.width < minHorizontalGeometry.widthAndMargin.width)
             horizontalGeometry = minHorizontalGeometry;
     }

     auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
     displayBox.setLeft(horizontalGeometry.left + horizontalGeometry.widthAndMargin.usedMargin.start);
     displayBox.setContentBoxWidth(horizontalGeometry.widthAndMargin.width);
     displayBox.setHorizontalMargin(horizontalGeometry.widthAndMargin.usedMargin);
     displayBox.setHorizontalComputedMargin(horizontalGeometry.widthAndMargin.computedMargin);
 }

 void FormattingContext::computeOutOfFlowVerticalGeometry(const Box& layoutBox) const
 {
     auto& layoutState = this->layoutState();

     auto compute = [&](UsedVerticalValues usedValues) {
         return Geometry::outOfFlowVerticalGeometry(layoutState, layoutBox, usedValues);
     };

     auto verticalGeometry = compute({ });
     if (auto maxHeight = Geometry::computedMaxHeight(layoutState, layoutBox)) {
         auto maxVerticalGeometry = compute({ *maxHeight });
         if (verticalGeometry.heightAndMargin.height > maxVerticalGeometry.heightAndMargin.height)
             verticalGeometry = maxVerticalGeometry;
     }

     if (auto minHeight = Geometry::computedMinHeight(layoutState, layoutBox)) {
         auto minVerticalGeometry = compute({ *minHeight });
         if (verticalGeometry.heightAndMargin.height < minVerticalGeometry.heightAndMargin.height)
             verticalGeometry = minVerticalGeometry;
     }

     auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
     auto nonCollapsedVerticalMargin = verticalGeometry.heightAndMargin.nonCollapsedMargin;
     displayBox.setTop(verticalGeometry.top + nonCollapsedVerticalMargin.before);
     displayBox.setContentBoxHeight(verticalGeometry.heightAndMargin.height);
     // Margins of absolutely positioned boxes do not collapse
     displayBox.setVerticalMargin({ nonCollapsedVerticalMargin, { } });
 }

 void FormattingContext::computeBorderAndPadding(const Box& layoutBox, Optional<UsedHorizontalValues> usedValues) const
 {
     auto& layoutState = this->layoutState();
     if (!usedValues)
         usedValues = UsedHorizontalValues { layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).contentBoxWidth() };
     auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
     displayBox.setBorder(Geometry::computedBorder(layoutBox));
     displayBox.setPadding(Geometry::computedPadding(layoutBox, *usedValues));
 }

 void FormattingContext::layoutOutOfFlowDescendants(const Box& layoutBox) const
 {
     if (!is<Container>(layoutBox))
         return;

     auto& container = downcast<Container>(layoutBox);
     if (!container.hasChild())
         return;

     auto& layoutState = this->layoutState();
     LOG_WITH_STREAM(FormattingContextLayout, stream << "Start: layout out-of-flow descendants -> context: " << &layoutState << " root: " << &root());

     for (auto& outOfFlowBox : container.outOfFlowDescendants()) {
         auto& layoutBox = *outOfFlowBox;

         ASSERT(layoutBox.establishesFormattingContext());

         computeBorderAndPadding(layoutBox);
         computeOutOfFlowHorizontalGeometry(layoutBox);

         layoutState.createFormattingContext(layoutBox)->layout();

         computeOutOfFlowVerticalGeometry(layoutBox);
         layoutOutOfFlowDescendants(layoutBox);
     }
     LOG_WITH_STREAM(FormattingContextLayout, stream << "End: layout out-of-flow descendants -> context: " << &layoutState << " root: " << &root());
 }

 static LayoutUnit mapHorizontalPositionToAncestor(const LayoutState& layoutState, LayoutUnit horizontalPosition, const Container& containingBlock, const Container& ancestor)
 {
     // "horizontalPosition" is in the coordinate system of the "containingBlock". -> map from containingBlock to ancestor.
     if (&containingBlock == &ancestor)
         return horizontalPosition;
     ASSERT(containingBlock.isContainingBlockDescendantOf(ancestor));
     for (auto* container = &containingBlock; container && container != &ancestor; container = container->containingBlock())
         horizontalPosition += layoutState.displayBoxForLayoutBox(*container).left();
     return horizontalPosition;
 }

 // FIXME: turn these into templates.
 LayoutUnit FormattingContext::mapLeftToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
 {
     ASSERT(layoutBox.containingBlock());
     return mapHorizontalPositionToAncestor(layoutState, layoutState.displayBoxForLayoutBox(layoutBox).left(), *layoutBox.containingBlock(), ancestor);
 }

 LayoutUnit FormattingContext::mapRightToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
 {
     ASSERT(layoutBox.containingBlock());
     return mapHorizontalPositionToAncestor(layoutState, layoutState.displayBoxForLayoutBox(layoutBox).right(), *layoutBox.containingBlock(), ancestor);
 }

 Display::Box FormattingContext::mapBoxToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
 {
     ASSERT(layoutBox.isContainingBlockDescendantOf(ancestor));
     auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
     auto topLeft = displayBox.topLeft();
     for (auto* containingBlock = layoutBox.containingBlock(); containingBlock && containingBlock != &ancestor; containingBlock = containingBlock->containingBlock())
         topLeft.moveBy(layoutState.displayBoxForLayoutBox(*containingBlock).topLeft());

     auto mappedDisplayBox = Display::Box(displayBox);
     mappedDisplayBox.setTopLeft(topLeft);
     return mappedDisplayBox;
 }

 LayoutUnit FormattingContext::mapTopToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
 {
     ASSERT(layoutBox.isContainingBlockDescendantOf(ancestor));
     auto top = layoutState.displayBoxForLayoutBox(layoutBox).top();
     for (auto* container = layoutBox.containingBlock(); container && container != &ancestor; container = container->containingBlock())
         top += layoutState.displayBoxForLayoutBox(*container).top();
     return top;
 }

 Point FormattingContext::mapPointToAncestor(const LayoutState& layoutState, Point position, const Container& from, const Container& to)
 {
     if (&from == &to)
         return position;
     ASSERT(from.isContainingBlockDescendantOf(to));
     auto mappedPosition = position;
     for (auto* container = &from; container && container != &to; container = container->containingBlock())
         mappedPosition.moveBy(layoutState.displayBoxForLayoutBox(*container).topLeft());
     return mappedPosition;
 }

 Point FormattingContext::mapPointToDescendent(const LayoutState& layoutState, Point point, const Container& from, const Container& to)
 {
     // "point" is in the coordinate system of the "from" container.
     if (&from == &to)
         return point;
     ASSERT(to.isContainingBlockDescendantOf(from));
     for (auto* container = &to; container && container != &from; container = container->containingBlock())
         point.moveBy(-layoutState.displayBoxForLayoutBox(*container).topLeft());
     return point;
 }

 #ifndef NDEBUG
 void FormattingContext::validateGeometryConstraintsAfterLayout() const
 {
     if (!is<Container>(root()))
         return;
     auto& formattingContextRoot = downcast<Container>(root());
     auto& layoutState = this->layoutState();
     // FIXME: add a descendantsOfType<> flavor that stops at nested formatting contexts
     for (auto& layoutBox : descendantsOfType<Box>(formattingContextRoot)) {
         if (&layoutBox.formattingContextRoot() != &formattingContextRoot)
             continue;
         auto& containingBlockDisplayBox = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock());
         auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);

         // 10.3.3 Block-level, non-replaced elements in normal flow
         // 10.3.7 Absolutely positioned, non-replaced elements
         if ((layoutBox.isBlockLevelBox() || layoutBox.isOutOfFlowPositioned()) && !layoutBox.replaced()) {
             // margin-left + border-left-width + padding-left + width + padding-right + border-right-width + margin-right = width of containing block
             auto containingBlockWidth = containingBlockDisplayBox.contentBoxWidth();
             ASSERT(displayBox.marginStart() + displayBox.borderLeft() + displayBox.paddingLeft().valueOr(0) + displayBox.contentBoxWidth()
                 + displayBox.paddingRight().valueOr(0) + displayBox.borderRight() + displayBox.marginEnd() == containingBlockWidth);
         }

         // 10.6.4 Absolutely positioned, non-replaced elements
         if (layoutBox.isOutOfFlowPositioned() && !layoutBox.replaced()) {
             // top + margin-top + border-top-width + padding-top + height + padding-bottom + border-bottom-width + margin-bottom + bottom = height of containing block
             auto containingBlockHeight = containingBlockDisplayBox.contentBoxHeight();
             ASSERT(displayBox.top() + displayBox.marginBefore() + displayBox.borderTop() + displayBox.paddingTop().valueOr(0) + displayBox.contentBoxHeight()
                 + displayBox.paddingBottom().valueOr(0) + displayBox.borderBottom() + displayBox.marginAfter() == containingBlockHeight);
         }
     }
 }
 #endif

 }
 }
 #endif
	/*
	* Copyright (C) 2018 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. AND ITS CONTRIBUTORS ``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 ITS 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 "FormattingContext.h"

	#if ENABLE(LAYOUT_FORMATTING_CONTEXT)

	#include "DisplayBox.h"
	#include "FormattingState.h"
	#include "LayoutBox.h"
	#include "LayoutContainer.h"
	#include "LayoutDescendantIterator.h"
	#include "LayoutState.h"
	#include "Logging.h"
	#include <wtf/IsoMallocInlines.h>
	#include <wtf/text/TextStream.h>

	namespace WebCore {
	namespace Layout {

	WTF_MAKE_ISO_ALLOCATED_IMPL(FormattingContext);

	FormattingContext::FormattingContext(const Box& formattingContextRoot, FormattingState& formattingState)
	: m_root(makeWeakPtr(formattingContextRoot))
	, m_formattingState(formattingState)
	{
	#ifndef NDEBUG
	layoutState().registerFormattingContext(*this);
	#endif
	}

	FormattingContext::~FormattingContext()
	{
	#ifndef NDEBUG
	layoutState().deregisterFormattingContext(*this);
	#endif
	}

	LayoutState& FormattingContext::layoutState() const
	{
	return m_formattingState.layoutState();
	}

	void FormattingContext::computeOutOfFlowHorizontalGeometry(const Box& layoutBox) const
	{
	auto& layoutState = this->layoutState();
	auto containingBlockWidth = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).paddingBoxWidth();

	auto compute = [&](Optional<LayoutUnit> usedWidth) {
	auto usedValues = UsedHorizontalValues { containingBlockWidth, usedWidth, { } };
	return Geometry::outOfFlowHorizontalGeometry(layoutState, layoutBox, usedValues);
	};

	auto horizontalGeometry = compute({ });
	if (auto maxWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMaxWidth(), containingBlockWidth)) {
	auto maxHorizontalGeometry = compute(maxWidth);
	if (horizontalGeometry.widthAndMargin.width > maxHorizontalGeometry.widthAndMargin.width)
	horizontalGeometry = maxHorizontalGeometry;
	}

	if (auto minWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMinWidth(), containingBlockWidth)) {
	auto minHorizontalGeometry = compute(minWidth);
	if (horizontalGeometry.widthAndMargin.width < minHorizontalGeometry.widthAndMargin.width)
	horizontalGeometry = minHorizontalGeometry;
	}

	auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
	displayBox.setLeft(horizontalGeometry.left + horizontalGeometry.widthAndMargin.usedMargin.start);
	displayBox.setContentBoxWidth(horizontalGeometry.widthAndMargin.width);
	displayBox.setHorizontalMargin(horizontalGeometry.widthAndMargin.usedMargin);
	displayBox.setHorizontalComputedMargin(horizontalGeometry.widthAndMargin.computedMargin);
	}

	void FormattingContext::computeOutOfFlowVerticalGeometry(const Box& layoutBox) const
	{
	auto& layoutState = this->layoutState();

	auto compute = [&](UsedVerticalValues usedValues) {
	return Geometry::outOfFlowVerticalGeometry(layoutState, layoutBox, usedValues);
	};

	auto verticalGeometry = compute({ });
	if (auto maxHeight = Geometry::computedMaxHeight(layoutState, layoutBox)) {
	auto maxVerticalGeometry = compute({ *maxHeight });
	if (verticalGeometry.heightAndMargin.height > maxVerticalGeometry.heightAndMargin.height)
	verticalGeometry = maxVerticalGeometry;
	}

	if (auto minHeight = Geometry::computedMinHeight(layoutState, layoutBox)) {
	auto minVerticalGeometry = compute({ *minHeight });
	if (verticalGeometry.heightAndMargin.height < minVerticalGeometry.heightAndMargin.height)
	verticalGeometry = minVerticalGeometry;
	}

	auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
	auto nonCollapsedVerticalMargin = verticalGeometry.heightAndMargin.nonCollapsedMargin;
	displayBox.setTop(verticalGeometry.top + nonCollapsedVerticalMargin.before);
	displayBox.setContentBoxHeight(verticalGeometry.heightAndMargin.height);
	// Margins of absolutely positioned boxes do not collapse
	displayBox.setVerticalMargin({ nonCollapsedVerticalMargin, { } });
	}

	void FormattingContext::computeBorderAndPadding(const Box& layoutBox, Optional<UsedHorizontalValues> usedValues) const
	{
	auto& layoutState = this->layoutState();
	if (!usedValues)
	usedValues = UsedHorizontalValues { layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).contentBoxWidth() };
	auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
	displayBox.setBorder(Geometry::computedBorder(layoutBox));
	displayBox.setPadding(Geometry::computedPadding(layoutBox, *usedValues));
	}

	void FormattingContext::layoutOutOfFlowDescendants(const Box& layoutBox) const
	{
	if (!is<Container>(layoutBox))
	return;

	auto& container = downcast<Container>(layoutBox);
	if (!container.hasChild())
	return;

	auto& layoutState = this->layoutState();
	LOG_WITH_STREAM(FormattingContextLayout, stream << "Start: layout out-of-flow descendants -> context: " << &layoutState << " root: " << &root());

	for (auto& outOfFlowBox : container.outOfFlowDescendants()) {
	auto& layoutBox = *outOfFlowBox;

	ASSERT(layoutBox.establishesFormattingContext());

	computeBorderAndPadding(layoutBox);
	computeOutOfFlowHorizontalGeometry(layoutBox);

	layoutState.createFormattingContext(layoutBox)->layout();

	computeOutOfFlowVerticalGeometry(layoutBox);
	layoutOutOfFlowDescendants(layoutBox);
	}
	LOG_WITH_STREAM(FormattingContextLayout, stream << "End: layout out-of-flow descendants -> context: " << &layoutState << " root: " << &root());
	}

	static LayoutUnit mapHorizontalPositionToAncestor(const LayoutState& layoutState, LayoutUnit horizontalPosition, const Container& containingBlock, const Container& ancestor)
	{
	// "horizontalPosition" is in the coordinate system of the "containingBlock". -> map from containingBlock to ancestor.
	if (&containingBlock == &ancestor)
	return horizontalPosition;
	ASSERT(containingBlock.isContainingBlockDescendantOf(ancestor));
	for (auto* container = &containingBlock; container && container != &ancestor; container = container->containingBlock())
	horizontalPosition += layoutState.displayBoxForLayoutBox(*container).left();
	return horizontalPosition;
	}

	// FIXME: turn these into templates.
	LayoutUnit FormattingContext::mapLeftToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
	{
	ASSERT(layoutBox.containingBlock());
	return mapHorizontalPositionToAncestor(layoutState, layoutState.displayBoxForLayoutBox(layoutBox).left(), *layoutBox.containingBlock(), ancestor);
	}

	LayoutUnit FormattingContext::mapRightToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
	{
	ASSERT(layoutBox.containingBlock());
	return mapHorizontalPositionToAncestor(layoutState, layoutState.displayBoxForLayoutBox(layoutBox).right(), *layoutBox.containingBlock(), ancestor);
	}

	Display::Box FormattingContext::mapBoxToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
	{
	ASSERT(layoutBox.isContainingBlockDescendantOf(ancestor));
	auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
	auto topLeft = displayBox.topLeft();
	for (auto* containingBlock = layoutBox.containingBlock(); containingBlock && containingBlock != &ancestor; containingBlock = containingBlock->containingBlock())
	topLeft.moveBy(layoutState.displayBoxForLayoutBox(*containingBlock).topLeft());

	auto mappedDisplayBox = Display::Box(displayBox);
	mappedDisplayBox.setTopLeft(topLeft);
	return mappedDisplayBox;
	}

	LayoutUnit FormattingContext::mapTopToAncestor(const LayoutState& layoutState, const Box& layoutBox, const Container& ancestor)
	{
	ASSERT(layoutBox.isContainingBlockDescendantOf(ancestor));
	auto top = layoutState.displayBoxForLayoutBox(layoutBox).top();
	for (auto* container = layoutBox.containingBlock(); container && container != &ancestor; container = container->containingBlock())
	top += layoutState.displayBoxForLayoutBox(*container).top();
	return top;
	}

	Point FormattingContext::mapPointToAncestor(const LayoutState& layoutState, Point position, const Container& from, const Container& to)
	{
	if (&from == &to)
	return position;
	ASSERT(from.isContainingBlockDescendantOf(to));
	auto mappedPosition = position;
	for (auto* container = &from; container && container != &to; container = container->containingBlock())
	mappedPosition.moveBy(layoutState.displayBoxForLayoutBox(*container).topLeft());
	return mappedPosition;
	}

	Point FormattingContext::mapPointToDescendent(const LayoutState& layoutState, Point point, const Container& from, const Container& to)
	{
	// "point" is in the coordinate system of the "from" container.
	if (&from == &to)
	return point;
	ASSERT(to.isContainingBlockDescendantOf(from));
	for (auto* container = &to; container && container != &from; container = container->containingBlock())
	point.moveBy(-layoutState.displayBoxForLayoutBox(*container).topLeft());
	return point;
	}

	#ifndef NDEBUG
	void FormattingContext::validateGeometryConstraintsAfterLayout() const
	{
	if (!is<Container>(root()))
	return;
	auto& formattingContextRoot = downcast<Container>(root());
	auto& layoutState = this->layoutState();
	// FIXME: add a descendantsOfType<> flavor that stops at nested formatting contexts
	for (auto& layoutBox : descendantsOfType<Box>(formattingContextRoot)) {
	if (&layoutBox.formattingContextRoot() != &formattingContextRoot)
	continue;
	auto& containingBlockDisplayBox = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock());
	auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);

	// 10.3.3 Block-level, non-replaced elements in normal flow
	// 10.3.7 Absolutely positioned, non-replaced elements
	if ((layoutBox.isBlockLevelBox() \|\| layoutBox.isOutOfFlowPositioned()) && !layoutBox.replaced()) {
	// margin-left + border-left-width + padding-left + width + padding-right + border-right-width + margin-right = width of containing block
	auto containingBlockWidth = containingBlockDisplayBox.contentBoxWidth();
	ASSERT(displayBox.marginStart() + displayBox.borderLeft() + displayBox.paddingLeft().valueOr(0) + displayBox.contentBoxWidth()
	+ displayBox.paddingRight().valueOr(0) + displayBox.borderRight() + displayBox.marginEnd() == containingBlockWidth);
	}

	// 10.6.4 Absolutely positioned, non-replaced elements
	if (layoutBox.isOutOfFlowPositioned() && !layoutBox.replaced()) {
	// top + margin-top + border-top-width + padding-top + height + padding-bottom + border-bottom-width + margin-bottom + bottom = height of containing block
	auto containingBlockHeight = containingBlockDisplayBox.contentBoxHeight();
	ASSERT(displayBox.top() + displayBox.marginBefore() + displayBox.borderTop() + displayBox.paddingTop().valueOr(0) + displayBox.contentBoxHeight()
	+ displayBox.paddingBottom().valueOr(0) + displayBox.borderBottom() + displayBox.marginAfter() == containingBlockHeight);
	}
	}
	}
	#endif

	}
	}
	#endif