| /* |
| * 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 "BlockFormattingContext.h" |
| |
| #if ENABLE(LAYOUT_FORMATTING_CONTEXT) |
| |
| #include "BlockFormattingState.h" |
| #include "DisplayBox.h" |
| #include "FloatingContext.h" |
| #include "FloatingState.h" |
| #include "LayoutBox.h" |
| #include "LayoutContainer.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(BlockFormattingContext); |
| |
| BlockFormattingContext::BlockFormattingContext(const Box& formattingContextRoot, BlockFormattingState& formattingState) |
| : FormattingContext(formattingContextRoot, formattingState) |
| { |
| } |
| |
| void BlockFormattingContext::layout() const |
| { |
| // 9.4.1 Block formatting contexts |
| // In a block formatting context, boxes are laid out one after the other, vertically, beginning at the top of a containing block. |
| // The vertical distance between two sibling boxes is determined by the 'margin' properties. |
| // Vertical margins between adjacent block-level boxes in a block formatting context collapse. |
| if (!is<Container>(root())) |
| return; |
| |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[Start] -> block formatting context -> formatting root(" << &root() << ")"); |
| |
| auto& formattingRoot = downcast<Container>(root()); |
| LayoutQueue layoutQueue; |
| FloatingContext floatingContext(formattingState().floatingState()); |
| // This is a post-order tree traversal layout. |
| // The root container layout is done in the formatting context it lives in, not that one it creates, so let's start with the first child. |
| if (auto* firstChild = formattingRoot.firstInFlowOrFloatingChild()) |
| layoutQueue.append(firstChild); |
| // 1. Go all the way down to the leaf node |
| // 2. Compute static position and width as we traverse down |
| // 3. As we climb back on the tree, compute height and finialize position |
| // (Any subtrees with new formatting contexts need to layout synchronously) |
| while (!layoutQueue.isEmpty()) { |
| // Traverse down on the descendants and compute width/static position until we find a leaf node. |
| while (true) { |
| auto& layoutBox = *layoutQueue.last(); |
| |
| if (layoutBox.establishesFormattingContext()) { |
| layoutFormattingContextRoot(floatingContext, layoutBox); |
| layoutQueue.removeLast(); |
| // Since this box is a formatting context root, it takes care of its entire subtree. |
| // Continue with next sibling if exists. |
| if (!layoutBox.nextInFlowOrFloatingSibling()) |
| break; |
| layoutQueue.append(layoutBox.nextInFlowOrFloatingSibling()); |
| continue; |
| } |
| |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[Compute] -> [Position][Border][Padding][Width][Margin] -> for layoutBox(" << &layoutBox << ")"); |
| computeBorderAndPadding(layoutBox); |
| computeWidthAndMargin(layoutBox); |
| computeStaticPosition(floatingContext, layoutBox); |
| if (!is<Container>(layoutBox) || !downcast<Container>(layoutBox).hasInFlowOrFloatingChild()) |
| break; |
| layoutQueue.append(downcast<Container>(layoutBox).firstInFlowOrFloatingChild()); |
| } |
| |
| // Climb back on the ancestors and compute height/final position. |
| while (!layoutQueue.isEmpty()) { |
| // All inflow descendants (if there are any) are laid out by now. Let's compute the box's height. |
| auto& layoutBox = *layoutQueue.takeLast(); |
| |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[Compute] -> [Height][Margin] -> for layoutBox(" << &layoutBox << ")"); |
| // Formatting root boxes are special-cased and they don't come here. |
| ASSERT(!layoutBox.establishesFormattingContext()); |
| computeHeightAndMargin(layoutBox); |
| // Move in-flow positioned children to their final position. |
| placeInFlowPositionedChildren(layoutBox); |
| if (auto* nextSibling = layoutBox.nextInFlowOrFloatingSibling()) { |
| layoutQueue.append(nextSibling); |
| break; |
| } |
| } |
| } |
| // Place the inflow positioned children. |
| placeInFlowPositionedChildren(formattingRoot); |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[End] -> block formatting context -> formatting root(" << &root() << ")"); |
| } |
| |
| void BlockFormattingContext::layoutFormattingContextRoot(FloatingContext& floatingContext, const Box& layoutBox) const |
| { |
| // Start laying out this formatting root in the formatting contenxt it lives in. |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[Compute] -> [Position][Border][Padding][Width][Margin] -> for layoutBox(" << &layoutBox << ")"); |
| computeBorderAndPadding(layoutBox); |
| computeWidthAndMargin(layoutBox); |
| computeStaticPosition(floatingContext, layoutBox); |
| // Swich over to the new formatting context (the one that the root creates). |
| auto formattingContext = layoutState().createFormattingContext(layoutBox); |
| formattingContext->layout(); |
| |
| // Come back and finalize the root's geometry. |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "[Compute] -> [Height][Margin] -> for layoutBox(" << &layoutBox << ")"); |
| computeHeightAndMargin(layoutBox); |
| |
| // Float related final positioning. |
| if (layoutBox.isFloatingPositioned()) { |
| computeFloatingPosition(floatingContext, layoutBox); |
| floatingContext.floatingState().append(layoutBox); |
| } else if (layoutBox.establishesBlockFormattingContext()) |
| computePositionToAvoidFloats(floatingContext, layoutBox); |
| |
| // Now that we computed the root's height, we can go back and layout the out-of-flow descedants (if any). |
| formattingContext->layoutOutOfFlowDescendants(layoutBox); |
| } |
| |
| void BlockFormattingContext::placeInFlowPositionedChildren(const Box& layoutBox) const |
| { |
| if (!is<Container>(layoutBox)) |
| return; |
| |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "Start: move in-flow positioned children -> parent: " << &layoutBox); |
| auto& container = downcast<Container>(layoutBox); |
| for (auto& childBox : childrenOfType<Box>(container)) { |
| if (!childBox.isInFlowPositioned()) |
| continue; |
| |
| auto computeInFlowPositionedPosition = [&] { |
| auto& layoutState = this->layoutState(); |
| auto positionOffset = Geometry::inFlowPositionedPositionOffset(layoutState, childBox); |
| |
| auto& displayBox = layoutState.displayBoxForLayoutBox(childBox); |
| auto topLeft = displayBox.topLeft(); |
| |
| topLeft.move(positionOffset); |
| |
| displayBox.setTopLeft(topLeft); |
| }; |
| |
| computeInFlowPositionedPosition(); |
| } |
| LOG_WITH_STREAM(FormattingContextLayout, stream << "End: move in-flow positioned children -> parent: " << &layoutBox); |
| } |
| |
| void BlockFormattingContext::computeStaticPosition(const FloatingContext& floatingContext, const Box& layoutBox) const |
| { |
| auto& layoutState = this->layoutState(); |
| layoutState.displayBoxForLayoutBox(layoutBox).setTopLeft(Geometry::staticPosition(layoutState, layoutBox)); |
| if (layoutBox.hasFloatClear()) |
| computeEstimatedVerticalPositionForFloatClear(floatingContext, layoutBox); |
| else if (layoutBox.establishesFormattingContext()) |
| computeEstimatedVerticalPositionForFormattingRoot(layoutBox); |
| } |
| |
| void BlockFormattingContext::computeEstimatedVerticalPosition(const Box& layoutBox) const |
| { |
| auto& layoutState = this->layoutState(); |
| auto estimatedMarginBefore = MarginCollapse::estimatedMarginBefore(layoutState, layoutBox); |
| setEstimatedMarginBefore(layoutBox, estimatedMarginBefore); |
| |
| auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox); |
| auto nonCollapsedValues = UsedVerticalMargin::NonCollapsedValues { estimatedMarginBefore.nonCollapsedValue, { } }; |
| auto collapsedValues = UsedVerticalMargin::CollapsedValues { estimatedMarginBefore.collapsedValue, { }, estimatedMarginBefore.isCollapsedThrough }; |
| auto verticalMargin = UsedVerticalMargin { nonCollapsedValues, collapsedValues }; |
| displayBox.setVerticalMargin(verticalMargin); |
| displayBox.setTop(verticalPositionWithMargin(layoutBox, verticalMargin)); |
| #if !ASSERT_DISABLED |
| displayBox.setHasEstimatedMarginBefore(); |
| #endif |
| } |
| |
| void BlockFormattingContext::computeEstimatedVerticalPositionForAncestors(const Box& layoutBox) const |
| { |
| // We only need to estimate margin top for float related layout (formatting context roots avoid floats). |
| ASSERT(layoutBox.isFloatingPositioned() || layoutBox.hasFloatClear() || layoutBox.establishesBlockFormattingContext() || layoutBox.establishesInlineFormattingContext()); |
| |
| // In order to figure out whether a box should avoid a float, we need to know the final positions of both (ignore relative positioning for now). |
| // In block formatting context the final position for a normal flow box includes |
| // 1. the static position and |
| // 2. the corresponding (non)collapsed margins. |
| // Now the vertical margins are computed when all the descendants are finalized, because the margin values might be depending on the height of the box |
| // (and the height might be based on the content). |
| // So when we get to the point where we intersect the box with the float to decide if the box needs to move, we don't yet have the final vertical position. |
| // |
| // The idea here is that as long as we don't cross the block formatting context boundary, we should be able to pre-compute the final top position. |
| for (auto* ancestor = layoutBox.containingBlock(); ancestor && !ancestor->establishesBlockFormattingContext(); ancestor = ancestor->containingBlock()) { |
| // FIXME: with incremental layout, we might actually have a valid (non-estimated) margin top as well. |
| if (hasEstimatedMarginBefore(*ancestor)) |
| return; |
| computeEstimatedVerticalPosition(*ancestor); |
| } |
| } |
| |
| void BlockFormattingContext::computeEstimatedVerticalPositionForFormattingRoot(const Box& layoutBox) const |
| { |
| ASSERT(layoutBox.establishesFormattingContext()); |
| ASSERT(!layoutBox.hasFloatClear()); |
| |
| auto avoidsFloats = layoutBox.isFloatingPositioned() || layoutBox.establishesBlockFormattingContext(); |
| if (avoidsFloats) |
| computeEstimatedVerticalPositionForAncestors(layoutBox); |
| |
| // If the inline formatting root is also the root for the floats (happens when the root box also establishes a block formatting context) |
| // the floats are in the coordinate system of this root. No need to find the final vertical position. |
| auto inlineContextInheritsFloats = layoutBox.establishesInlineFormattingContext() && !layoutBox.establishesBlockFormattingContext(); |
| if (inlineContextInheritsFloats) { |
| computeEstimatedVerticalPosition(layoutBox); |
| computeEstimatedVerticalPositionForAncestors(layoutBox); |
| } |
| } |
| |
| void BlockFormattingContext::computeEstimatedVerticalPositionForFloatClear(const FloatingContext& floatingContext, const Box& layoutBox) const |
| { |
| ASSERT(layoutBox.hasFloatClear()); |
| if (floatingContext.floatingState().isEmpty()) |
| return; |
| // The static position with clear requires margin esitmation to see if clearance is needed. |
| computeEstimatedVerticalPosition(layoutBox); |
| computeEstimatedVerticalPositionForAncestors(layoutBox); |
| auto verticalPositionAndClearance = floatingContext.verticalPositionWithClearance(layoutBox); |
| if (!verticalPositionAndClearance.position) { |
| ASSERT(!verticalPositionAndClearance.clearance); |
| return; |
| } |
| |
| auto& displayBox = layoutState().displayBoxForLayoutBox(layoutBox); |
| ASSERT(*verticalPositionAndClearance.position >= displayBox.top()); |
| displayBox.setTop(*verticalPositionAndClearance.position); |
| if (verticalPositionAndClearance.clearance) |
| displayBox.setHasClearance(); |
| } |
| |
| #ifndef NDEBUG |
| bool BlockFormattingContext::hasPrecomputedMarginBefore(const Box& layoutBox) const |
| { |
| for (auto* ancestor = layoutBox.containingBlock(); ancestor && !ancestor->establishesBlockFormattingContext(); ancestor = ancestor->containingBlock()) { |
| if (hasEstimatedMarginBefore(*ancestor)) |
| continue; |
| return false; |
| } |
| return true; |
| } |
| #endif |
| |
| void BlockFormattingContext::computeFloatingPosition(const FloatingContext& floatingContext, const Box& layoutBox) const |
| { |
| ASSERT(layoutBox.isFloatingPositioned()); |
| ASSERT(hasPrecomputedMarginBefore(layoutBox)); |
| layoutState().displayBoxForLayoutBox(layoutBox).setTopLeft(floatingContext.positionForFloat(layoutBox)); |
| } |
| |
| void BlockFormattingContext::computePositionToAvoidFloats(const FloatingContext& floatingContext, const Box& layoutBox) const |
| { |
| auto& layoutState = this->layoutState(); |
| // Formatting context roots avoid floats. |
| ASSERT(layoutBox.establishesBlockFormattingContext()); |
| ASSERT(!layoutBox.isFloatingPositioned()); |
| ASSERT(!layoutBox.hasFloatClear()); |
| ASSERT(hasPrecomputedMarginBefore(layoutBox)); |
| |
| if (floatingContext.floatingState().isEmpty()) |
| return; |
| |
| if (auto adjustedPosition = floatingContext.positionForFormattingContextRoot(layoutBox)) |
| layoutState.displayBoxForLayoutBox(layoutBox).setTopLeft(*adjustedPosition); |
| } |
| |
| void BlockFormattingContext::computeWidthAndMargin(const Box& layoutBox) const |
| { |
| auto& layoutState = this->layoutState(); |
| auto containingBlockWidth = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).contentBoxWidth(); |
| |
| auto compute = [&](Optional<LayoutUnit> usedWidth) -> WidthAndMargin { |
| auto usedValues = UsedHorizontalValues { containingBlockWidth, usedWidth, { } }; |
| if (layoutBox.isInFlow()) |
| return Geometry::inFlowWidthAndMargin(layoutState, layoutBox, usedValues); |
| |
| if (layoutBox.isFloatingPositioned()) |
| return Geometry::floatingWidthAndMargin(layoutState, layoutBox, usedValues); |
| |
| ASSERT_NOT_REACHED(); |
| return { }; |
| }; |
| |
| auto widthAndMargin = compute({ }); |
| |
| if (auto maxWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMaxWidth(), containingBlockWidth)) { |
| auto maxWidthAndMargin = compute(maxWidth); |
| if (widthAndMargin.width > maxWidthAndMargin.width) |
| widthAndMargin = maxWidthAndMargin; |
| } |
| |
| auto minWidth = Geometry::computedValueIfNotAuto(layoutBox.style().logicalMinWidth(), containingBlockWidth).valueOr(0); |
| auto minWidthAndMargin = compute(minWidth); |
| if (widthAndMargin.width < minWidthAndMargin.width) |
| widthAndMargin = minWidthAndMargin; |
| |
| auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox); |
| displayBox.setContentBoxWidth(widthAndMargin.width); |
| displayBox.setHorizontalMargin(widthAndMargin.usedMargin); |
| displayBox.setHorizontalComputedMargin(widthAndMargin.computedMargin); |
| } |
| |
| void BlockFormattingContext::computeHeightAndMargin(const Box& layoutBox) const |
| { |
| auto& layoutState = this->layoutState(); |
| |
| auto compute = [&](UsedVerticalValues usedValues) -> HeightAndMargin { |
| |
| if (layoutBox.isInFlow()) |
| return Geometry::inFlowHeightAndMargin(layoutState, layoutBox, usedValues); |
| |
| if (layoutBox.isFloatingPositioned()) |
| return Geometry::floatingHeightAndMargin(layoutState, layoutBox, usedValues, UsedHorizontalValues { layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock()).contentBoxWidth() }); |
| |
| ASSERT_NOT_REACHED(); |
| return { }; |
| }; |
| |
| auto heightAndMargin = compute({ }); |
| if (auto maxHeight = Geometry::computedMaxHeight(layoutState, layoutBox)) { |
| if (heightAndMargin.height > *maxHeight) { |
| auto maxHeightAndMargin = compute({ *maxHeight }); |
| // Used height should remain the same. |
| ASSERT((layoutState.inQuirksMode() && (layoutBox.isBodyBox() || layoutBox.isDocumentBox())) || maxHeightAndMargin.height == *maxHeight); |
| heightAndMargin = { *maxHeight, maxHeightAndMargin.nonCollapsedMargin }; |
| } |
| } |
| |
| if (auto minHeight = Geometry::computedMinHeight(layoutState, layoutBox)) { |
| if (heightAndMargin.height < *minHeight) { |
| auto minHeightAndMargin = compute({ *minHeight }); |
| // Used height should remain the same. |
| ASSERT((layoutState.inQuirksMode() && (layoutBox.isBodyBox() || layoutBox.isDocumentBox())) || minHeightAndMargin.height == *minHeight); |
| heightAndMargin = { *minHeight, minHeightAndMargin.nonCollapsedMargin }; |
| } |
| } |
| |
| // 1. Compute collapsed margins. |
| // 2. Adjust vertical position using the collapsed values |
| // 3. Adjust previous in-flow sibling margin after using this margin. |
| auto collapsedMargin = MarginCollapse::collapsedVerticalValues(layoutState, layoutBox, heightAndMargin.nonCollapsedMargin); |
| auto verticalMargin = UsedVerticalMargin { heightAndMargin.nonCollapsedMargin, collapsedMargin }; |
| auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox); |
| |
| // Out of flow boxes don't need vertical adjustment after margin collapsing. |
| if (layoutBox.isOutOfFlowPositioned()) { |
| ASSERT(!hasEstimatedMarginBefore(layoutBox)); |
| displayBox.setContentBoxHeight(heightAndMargin.height); |
| displayBox.setVerticalMargin(verticalMargin); |
| return; |
| } |
| |
| ASSERT(!hasEstimatedMarginBefore(layoutBox) || estimatedMarginBefore(layoutBox).usedValue() == verticalMargin.before()); |
| removeEstimatedMarginBefore(layoutBox); |
| displayBox.setTop(verticalPositionWithMargin(layoutBox, verticalMargin)); |
| displayBox.setContentBoxHeight(heightAndMargin.height); |
| displayBox.setVerticalMargin(verticalMargin); |
| |
| MarginCollapse::updatePositiveNegativeMarginValues(layoutState, layoutBox); |
| // Adjust the previous sibling's margin bottom now that this box's vertical margin is computed. |
| MarginCollapse::updateMarginAfterForPreviousSibling(layoutState, layoutBox); |
| } |
| |
| void BlockFormattingContext::computeIntrinsicWidthConstraints() const |
| { |
| auto& layoutState = this->layoutState(); |
| auto& formattingRoot = root(); |
| auto& formattingStateForRoot = layoutState.formattingStateForBox(formattingRoot); |
| ASSERT(!formattingStateForRoot.intrinsicWidthConstraints(formattingRoot)); |
| |
| // Can we just compute them without checking the children? |
| if (!Geometry::intrinsicWidthConstraintsNeedChildrenWidth(formattingRoot)) |
| return formattingStateForRoot.setIntrinsicWidthConstraints(formattingRoot, Geometry::intrinsicWidthConstraints(layoutState, formattingRoot)); |
| |
| // Visit the in-flow descendants and compute their min/max intrinsic width if needed. |
| // 1. Go all the way down to the leaf node |
| // 2. Check if actually need to visit all the boxes as we traverse down (already computed, container's min/max does not depend on descendants etc) |
| // 3. As we climb back on the tree, compute min/max intrinsic width |
| // (Any subtrees with new formatting contexts need to layout synchronously) |
| Vector<const Box*> queue; |
| ASSERT(is<Container>(formattingRoot)); |
| if (auto* firstChild = downcast<Container>(formattingRoot).firstInFlowOrFloatingChild()) |
| queue.append(firstChild); |
| |
| auto& formattingState = this->formattingState(); |
| while (!queue.isEmpty()) { |
| while (true) { |
| auto& childBox = *queue.last(); |
| auto childIntrinsicWidthConstraints = formattingState.intrinsicWidthConstraints(childBox); |
| auto skipDescendants = childIntrinsicWidthConstraints || !Geometry::intrinsicWidthConstraintsNeedChildrenWidth(childBox) || childBox.establishesFormattingContext(); |
| |
| if (skipDescendants) { |
| if (!childIntrinsicWidthConstraints) { |
| if (!Geometry::intrinsicWidthConstraintsNeedChildrenWidth(childBox)) |
| formattingState.setIntrinsicWidthConstraints(childBox, Geometry::intrinsicWidthConstraints(layoutState, childBox)); |
| else if (childBox.establishesFormattingContext()) |
| layoutState.createFormattingContext(childBox)->computeIntrinsicWidthConstraints(); |
| else |
| ASSERT_NOT_REACHED(); |
| } |
| queue.removeLast(); |
| if (!childBox.nextInFlowOrFloatingSibling()) |
| break; |
| queue.append(childBox.nextInFlowOrFloatingSibling()); |
| // Skip descendants |
| continue; |
| } |
| } |
| |
| // Compute min/max intrinsic width bottom up. |
| while (!queue.isEmpty()) { |
| auto& childBox = *queue.takeLast(); |
| formattingState.setIntrinsicWidthConstraints(childBox, Geometry::intrinsicWidthConstraints(layoutState, childBox)); |
| // Move over to the next sibling or take the next box in the queue. |
| if (!is<Container>(childBox) || !downcast<Container>(childBox).nextInFlowOrFloatingSibling()) |
| continue; |
| queue.append(downcast<Container>(childBox).nextInFlowOrFloatingSibling()); |
| } |
| } |
| formattingStateForRoot.setIntrinsicWidthConstraints(formattingRoot, Geometry::intrinsicWidthConstraints(layoutState, formattingRoot)); |
| } |
| |
| LayoutUnit BlockFormattingContext::verticalPositionWithMargin(const Box& layoutBox, const UsedVerticalMargin& verticalMargin) const |
| { |
| ASSERT(!layoutBox.isOutOfFlowPositioned()); |
| // Now that we've computed the final margin before, let's shift the box's vertical position if needed. |
| // 1. Check if the box has clearance. If so, we've already precomputed/finalized the top value and vertical margin does not impact it anymore. |
| // 2. Check if the margin before collapses with the previous box's margin after. if not -> return previous box's bottom including margin after + marginBefore |
| // 3. Check if the previous box's margins collapse through. If not -> return previous box' bottom excluding margin after + marginBefore (they are supposed to be equal) |
| // 4. Go to previous box and start from step #1 until we hit the parent box. |
| auto& layoutState = this->layoutState(); |
| auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox); |
| if (displayBox.hasClearance()) |
| return displayBox.top(); |
| |
| auto* currentLayoutBox = &layoutBox; |
| while (currentLayoutBox) { |
| if (!currentLayoutBox->previousInFlowSibling()) |
| break; |
| auto& previousInFlowSibling = *currentLayoutBox->previousInFlowSibling(); |
| if (!MarginCollapse::marginBeforeCollapsesWithPreviousSiblingMarginAfter(layoutState, *currentLayoutBox)) { |
| auto& previousDisplayBox = layoutState.displayBoxForLayoutBox(previousInFlowSibling); |
| return previousDisplayBox.rectWithMargin().bottom() + verticalMargin.before(); |
| } |
| |
| if (!MarginCollapse::marginsCollapseThrough(layoutState, previousInFlowSibling)) { |
| auto& previousDisplayBox = layoutState.displayBoxForLayoutBox(previousInFlowSibling); |
| return previousDisplayBox.bottom() + verticalMargin.before(); |
| } |
| currentLayoutBox = &previousInFlowSibling; |
| } |
| |
| auto& containingBlock = *layoutBox.containingBlock(); |
| auto containingBlockContentBoxTop = layoutState.displayBoxForLayoutBox(containingBlock).contentBoxTop(); |
| // Adjust vertical position depending whether this box directly or indirectly adjoins with its parent. |
| auto directlyAdjoinsParent = !layoutBox.previousInFlowSibling(); |
| if (directlyAdjoinsParent) { |
| // If the top and bottom margins of a box are adjoining, then it is possible for margins to collapse through it. |
| // In this case, the position of the element depends on its relationship with the other elements whose margins are being collapsed. |
| if (verticalMargin.collapsedValues().isCollapsedThrough) { |
| // If the element's margins are collapsed with its parent's top margin, the top border edge of the box is defined to be the same as the parent's. |
| if (MarginCollapse::marginBeforeCollapsesWithParentMarginBefore(layoutState, layoutBox)) |
| return containingBlockContentBoxTop; |
| // Otherwise, either the element's parent is not taking part in the margin collapsing, or only the parent's bottom margin is involved. |
| // The position of the element's top border edge is the same as it would have been if the element had a non-zero bottom border. |
| auto beforeMarginWithBottomBorder = MarginCollapse::marginBeforeIgnoringCollapsingThrough(layoutState, layoutBox, verticalMargin.nonCollapsedValues()); |
| return containingBlockContentBoxTop + beforeMarginWithBottomBorder; |
| } |
| // Non-collapsed through box vertical position depending whether the margin collapses. |
| if (MarginCollapse::marginBeforeCollapsesWithParentMarginBefore(layoutState, layoutBox)) |
| return containingBlockContentBoxTop; |
| |
| return containingBlockContentBoxTop + verticalMargin.before(); |
| } |
| // At this point this box indirectly (via collapsed through previous in-flow siblings) adjoins the parent. Let's check if it margin collapses with the parent. |
| ASSERT(containingBlock.firstInFlowChild()); |
| ASSERT(containingBlock.firstInFlowChild() != &layoutBox); |
| if (MarginCollapse::marginBeforeCollapsesWithParentMarginBefore(layoutState, *containingBlock.firstInFlowChild())) |
| return containingBlockContentBoxTop; |
| |
| return containingBlockContentBoxTop + verticalMargin.before(); |
| } |
| |
| void BlockFormattingContext::setEstimatedMarginBefore(const Box& layoutBox, const EstimatedMarginBefore& estimatedMarginBefore) const |
| { |
| // Can't cross formatting context boundary. |
| ASSERT(&layoutState().formattingStateForBox(layoutBox) == &formattingState()); |
| m_estimatedMarginBeforeList.set(&layoutBox, estimatedMarginBefore); |
| } |
| |
| bool BlockFormattingContext::hasEstimatedMarginBefore(const Box& layoutBox) const |
| { |
| // Can't cross formatting context boundary. |
| ASSERT(&layoutState().formattingStateForBox(layoutBox) == &formattingState()); |
| return m_estimatedMarginBeforeList.contains(&layoutBox); |
| } |
| |
| } |
| } |
| |
| #endif |
