BlockFormattingContextGeometry.cpp   [plain text]

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#include "config.h"
#include "BlockFormattingContext.h"

#if ENABLE(LAYOUT_FORMATTING_CONTEXT)

#include "FormattingContext.h"
#include "InlineFormattingState.h"
#include "LayoutChildIterator.h"
#include "Logging.h"
#include <wtf/text/TextStream.h>

namespace WebCore {
namespace Layout {

HeightAndMargin BlockFormattingContext::Geometry::inFlowNonReplacedHeightAndMargin(const LayoutState& layoutState, const Box& layoutBox, Optional<LayoutUnit> usedHeight)
{
    ASSERT(layoutBox.isInFlow() && !layoutBox.replaced());
    ASSERT(layoutBox.isOverflowVisible());

    auto compute = [&]() -> HeightAndMargin {

        // 10.6.3 Block-level non-replaced elements in normal flow when 'overflow' computes to 'visible'
        //
        // If 'margin-top', or 'margin-bottom' are 'auto', their used value is 0.
        // If 'height' is 'auto', the height depends on whether the element has any block-level children and whether it has padding or borders:
        // The element's height is the distance from its top content edge to the first applicable of the following:
        // 1. the bottom edge of the last line box, if the box establishes a inline formatting context with one or more lines
        // 2. the bottom edge of the bottom (possibly collapsed) margin of its last in-flow child, if the child's bottom margin
        //    does not collapse with the element's bottom margin
        // 3. the bottom border edge of the last in-flow child whose top margin doesn't collapse with the element's bottom margin
        // 4. zero, otherwise
        // Only children in the normal flow are taken into account (i.e., floating boxes and absolutely positioned boxes are ignored,
        // and relatively positioned boxes are considered without their offset). Note that the child box may be an anonymous block box.

        auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);
        auto computedVerticalMargin = Geometry::computedVerticalMargin(layoutState, layoutBox);
        auto nonCollapsedMargin = UsedVerticalMargin::NonCollapsedValues { computedVerticalMargin.before.valueOr(0), computedVerticalMargin.after.valueOr(0) }; 
        auto borderAndPaddingTop = displayBox.borderTop() + displayBox.paddingTop().valueOr(0);

        auto height = usedHeight ? usedHeight.value() : computedHeightValue(layoutState, layoutBox, HeightType::Normal);
        if (height)
            return { height.value(), nonCollapsedMargin };

        if (!is<Container>(layoutBox) || !downcast<Container>(layoutBox).hasInFlowChild())
            return { 0, nonCollapsedMargin };

        // 1. the bottom edge of the last line box, if the box establishes a inline formatting context with one or more lines
        if (layoutBox.establishesInlineFormattingContext()) {
            // This is temp and will be replaced by the correct display box once inline runs move over to the display tree.
            auto& inlineRuns = downcast<InlineFormattingState>(layoutState.establishedFormattingState(layoutBox)).inlineRuns();
            auto bottomEdge = inlineRuns.isEmpty() ? LayoutUnit() : inlineRuns.last().logicalBottom();
            return { bottomEdge, nonCollapsedMargin };
        }

        // 2. the bottom edge of the bottom (possibly collapsed) margin of its last in-flow child, if the child's bottom margin...
        auto* lastInFlowChild = downcast<Container>(layoutBox).lastInFlowChild();
        ASSERT(lastInFlowChild);
        if (!MarginCollapse::marginAfterCollapsesWithParentMarginAfter(layoutState, *lastInFlowChild)) {
            auto& lastInFlowDisplayBox = layoutState.displayBoxForLayoutBox(*lastInFlowChild);
            return { lastInFlowDisplayBox.bottom() + lastInFlowDisplayBox.marginAfter() - borderAndPaddingTop, nonCollapsedMargin };
        }

        // 3. the bottom border edge of the last in-flow child whose top margin doesn't collapse with the element's bottom margin
        auto* inFlowChild = lastInFlowChild;
        while (inFlowChild && MarginCollapse::marginBeforeCollapsesWithParentMarginAfter(layoutState, *inFlowChild))
            inFlowChild = inFlowChild->previousInFlowSibling();
        if (inFlowChild) {
            auto& inFlowDisplayBox = layoutState.displayBoxForLayoutBox(*inFlowChild);
            return { inFlowDisplayBox.top() + inFlowDisplayBox.borderBox().height() - borderAndPaddingTop, nonCollapsedMargin };
        }

        // 4. zero, otherwise
        return { 0, nonCollapsedMargin };
    };

    auto heightAndMargin = compute();

    LOG_WITH_STREAM(FormattingContextLayout, stream << "[Height][Margin] -> inflow non-replaced -> height(" << heightAndMargin.height << "px) margin(" << heightAndMargin.nonCollapsedMargin.before << "px, " << heightAndMargin.nonCollapsedMargin.after << "px) -> layoutBox(" << &layoutBox << ")");
    return heightAndMargin;
}

WidthAndMargin BlockFormattingContext::Geometry::inFlowNonReplacedWidthAndMargin(const LayoutState& layoutState, const Box& layoutBox, Optional<LayoutUnit> usedWidth)
{
    ASSERT(layoutBox.isInFlow() && !layoutBox.replaced());

    auto compute = [&]() {

        // 10.3.3 Block-level, non-replaced elements in normal flow
        //
        // The following constraints must hold among the used values of the other properties:
        // 'margin-left' + 'border-left-width' + 'padding-left' + 'width' + 'padding-right' + 'border-right-width' + 'margin-right' = width of containing block
        //
        // 1. If 'width' is not 'auto' and 'border-left-width' + 'padding-left' + 'width' + 'padding-right' + 'border-right-width' 
        //    (plus any of 'margin-left' or 'margin-right' that are not 'auto') is larger than the width of the containing block, then
        //    any 'auto' values for 'margin-left' or 'margin-right' are, for the following rules, treated as zero.
        //
        // 2. If all of the above have a computed value other than 'auto', the values are said to be "over-constrained" and one of the used values will
        //    have to be different from its computed value. If the 'direction' property of the containing block has the value 'ltr', the specified value
        //    of 'margin-right' is ignored and the value is calculated so as to make the equality true. If the value of 'direction' is 'rtl',
        //    this happens to 'margin-left' instead.
        //
        // 3. If there is exactly one value specified as 'auto', its used value follows from the equality.
        //
        // 4. If 'width' is set to 'auto', any other 'auto' values become '0' and 'width' follows from the resulting equality.
        //
        // 5. If both 'margin-left' and 'margin-right' are 'auto', their used values are equal. This horizontally centers the element with respect to the
        //    edges of the containing block.

        auto& style = layoutBox.style();
        auto* containingBlock = layoutBox.containingBlock();
        auto containingBlockWidth = layoutState.displayBoxForLayoutBox(*containingBlock).contentBoxWidth();
        auto& displayBox = layoutState.displayBoxForLayoutBox(layoutBox);

        auto width = computedValueIfNotAuto(usedWidth ? Length { usedWidth.value(), Fixed } : style.logicalWidth(), containingBlockWidth);
        auto computedHorizontalMargin = Geometry::computedHorizontalMargin(layoutState, layoutBox);
        UsedHorizontalMargin usedHorizontalMargin;
        auto borderLeft = displayBox.borderLeft();
        auto borderRight = displayBox.borderRight();
        auto paddingLeft = displayBox.paddingLeft().valueOr(0);
        auto paddingRight = displayBox.paddingRight().valueOr(0);

        // #1
        if (width) {
            auto horizontalSpaceForMargin = containingBlockWidth - (computedHorizontalMargin.start.valueOr(0) + borderLeft + paddingLeft + *width + paddingRight + borderRight + computedHorizontalMargin.end.valueOr(0));
            if (horizontalSpaceForMargin < 0)
                usedHorizontalMargin = { computedHorizontalMargin.start.valueOr(0), computedHorizontalMargin.end.valueOr(0) };
        }

        // #2
        if (width && computedHorizontalMargin.start && computedHorizontalMargin.end) {
            if (containingBlock->style().isLeftToRightDirection()) {
                usedHorizontalMargin.start = *computedHorizontalMargin.start;
                usedHorizontalMargin.end = containingBlockWidth - (usedHorizontalMargin.start + borderLeft + paddingLeft  + *width + paddingRight + borderRight);
            } else {
                usedHorizontalMargin.end = *computedHorizontalMargin.end;
                usedHorizontalMargin.start = containingBlockWidth - (borderLeft + paddingLeft + *width + paddingRight + borderRight + usedHorizontalMargin.end);
            }
        }

        // #3
        if (!computedHorizontalMargin.start && width && computedHorizontalMargin.end) {
            usedHorizontalMargin.end = *computedHorizontalMargin.end;
            usedHorizontalMargin.start = containingBlockWidth - (borderLeft + paddingLeft  + *width + paddingRight + borderRight + usedHorizontalMargin.end);
        } else if (computedHorizontalMargin.start && !width && computedHorizontalMargin.end) {
            usedHorizontalMargin = { *computedHorizontalMargin.start, *computedHorizontalMargin.end };
            width = containingBlockWidth - (usedHorizontalMargin.start + borderLeft + paddingLeft + paddingRight + borderRight + usedHorizontalMargin.end);
        } else if (computedHorizontalMargin.start && width && !computedHorizontalMargin.end) {
            usedHorizontalMargin.start = *computedHorizontalMargin.start;
            usedHorizontalMargin.end = containingBlockWidth - (usedHorizontalMargin.start + borderLeft + paddingLeft + *width + paddingRight + borderRight);
        }

        // #4
        if (!width) {
            usedHorizontalMargin = { computedHorizontalMargin.start.valueOr(0), computedHorizontalMargin.end.valueOr(0) };
            width = containingBlockWidth - (usedHorizontalMargin.start + borderLeft + paddingLeft + paddingRight + borderRight + usedHorizontalMargin.end);
        }

        // #5
        if (!computedHorizontalMargin.start && !computedHorizontalMargin.end) {
            auto horizontalSpaceForMargin = containingBlockWidth - (borderLeft + paddingLeft  + *width + paddingRight + borderRight);
            usedHorizontalMargin = { horizontalSpaceForMargin / 2, horizontalSpaceForMargin / 2 };
        }

        ASSERT(width);

        return WidthAndMargin { *width, usedHorizontalMargin, computedHorizontalMargin };
    };

    auto widthAndMargin = compute();
    LOG_WITH_STREAM(FormattingContextLayout, stream << "[Width][Margin] -> inflow non-replaced -> width(" << widthAndMargin.width << "px) margin(" << widthAndMargin.usedMargin.start << "px, " << widthAndMargin.usedMargin.end << "px) -> layoutBox(" << &layoutBox << ")");
    return widthAndMargin;
}

WidthAndMargin BlockFormattingContext::Geometry::inFlowReplacedWidthAndMargin(const LayoutState& layoutState, const Box& layoutBox, Optional<LayoutUnit> usedWidth)
{
    ASSERT(layoutBox.isInFlow() && layoutBox.replaced());

    // 10.3.4 Block-level, replaced elements in normal flow
    //
    // 1. The used value of 'width' is determined as for inline replaced elements.
    // 2. Then the rules for non-replaced block-level elements are applied to determine the margins.

    // #1
    auto width = inlineReplacedWidthAndMargin(layoutState, layoutBox, usedWidth).width;
    // #2
    auto nonReplacedWidthAndMargin = inFlowNonReplacedWidthAndMargin(layoutState, layoutBox, width);

    LOG_WITH_STREAM(FormattingContextLayout, stream << "[Width][Margin] -> inflow replaced -> width(" << width << "px) margin(" << nonReplacedWidthAndMargin.usedMargin.start << "px, " << nonReplacedWidthAndMargin.usedMargin.end << "px) -> layoutBox(" << &layoutBox << ")");
    return { width, nonReplacedWidthAndMargin.usedMargin, nonReplacedWidthAndMargin.computedMargin };
}

Point BlockFormattingContext::Geometry::staticPosition(const LayoutState& layoutState, const Box& layoutBox)
{
    // https://www.w3.org/TR/CSS22/visuren.html#block-formatting
    // 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.
    // In a block formatting context, each box's left outer edge touches the left edge of the containing block (for right-to-left formatting, right edges touch).

    LayoutUnit top;
    auto& containingBlockDisplayBox = layoutState.displayBoxForLayoutBox(*layoutBox.containingBlock());
    if (auto* previousInFlowSibling = layoutBox.previousInFlowSibling()) {
        auto& previousInFlowDisplayBox = layoutState.displayBoxForLayoutBox(*previousInFlowSibling);
        top = previousInFlowDisplayBox.bottom() + previousInFlowDisplayBox.marginAfter();
    } else
        top = containingBlockDisplayBox.contentBoxTop();

    auto left = containingBlockDisplayBox.contentBoxLeft();
    LOG_WITH_STREAM(FormattingContextLayout, stream << "[Position] -> static -> top(" << top << "px) left(" << left << "px) layoutBox(" << &layoutBox << ")");
    return { left, top };
}

HeightAndMargin BlockFormattingContext::Geometry::inFlowHeightAndMargin(const LayoutState& layoutState, const Box& layoutBox, Optional<LayoutUnit> usedHeight)
{
    ASSERT(layoutBox.isInFlow());

    // 10.6.2 Inline replaced elements, block-level replaced elements in normal flow, 'inline-block'
    // replaced elements in normal flow and floating replaced elements
    if (layoutBox.replaced())
        return inlineReplacedHeightAndMargin(layoutState, layoutBox, usedHeight);

    HeightAndMargin heightAndMargin;
    // TODO: Figure out the case for the document element. Let's just complicated-case it for now.
    if (layoutBox.isOverflowVisible() && !layoutBox.isDocumentBox())
        heightAndMargin = inFlowNonReplacedHeightAndMargin(layoutState, layoutBox, usedHeight);
    else {
        // 10.6.6 Complicated cases
        // Block-level, non-replaced elements in normal flow when 'overflow' does not compute to 'visible' (except if the 'overflow' property's value has been propagated to the viewport).
        heightAndMargin = complicatedCases(layoutState, layoutBox, usedHeight);
    }

    if (!Quirks::needsStretching(layoutState, layoutBox))
        return heightAndMargin;

    heightAndMargin = Quirks::stretchedHeight(layoutState, layoutBox, heightAndMargin);

    LOG_WITH_STREAM(FormattingContextLayout, stream << "[Height][Margin] -> inflow non-replaced -> streched to viewport -> height(" << heightAndMargin.height << "px) margin(" << heightAndMargin.nonCollapsedMargin.before << "px, " << heightAndMargin.nonCollapsedMargin.after << "px) -> layoutBox(" << &layoutBox << ")");
    return heightAndMargin;
}

WidthAndMargin BlockFormattingContext::Geometry::inFlowWidthAndMargin(const LayoutState& layoutState, const Box& layoutBox, Optional<LayoutUnit> usedWidth)
{
    ASSERT(layoutBox.isInFlow());

    if (!layoutBox.replaced())
        return inFlowNonReplacedWidthAndMargin(layoutState, layoutBox, usedWidth);
    return inFlowReplacedWidthAndMargin(layoutState, layoutBox, usedWidth);
}

bool BlockFormattingContext::Geometry::instrinsicWidthConstraintsNeedChildrenWidth(const Box& layoutBox)
{
    if (!is<Container>(layoutBox) || !downcast<Container>(layoutBox).hasInFlowOrFloatingChild())
        return false;
    return layoutBox.style().width().isAuto();
}

FormattingContext::InstrinsicWidthConstraints BlockFormattingContext::Geometry::instrinsicWidthConstraints(const LayoutState& layoutState, const Box& layoutBox)
{
    auto& style = layoutBox.style();
    if (auto width = fixedValue(style.logicalWidth()))
        return { *width, *width };

    // Minimum/maximum width can't be depending on the containing block's width.
    if (!style.logicalWidth().isAuto())
        return { };

    if (!is<Container>(layoutBox))
        return { };

    LayoutUnit minimumIntrinsicWidth;
    LayoutUnit maximumIntrinsicWidth;

    for (auto& child : childrenOfType<Box>(downcast<Container>(layoutBox))) {
        if (child.isOutOfFlowPositioned())
            continue;
        auto& formattingState = layoutState.formattingStateForBox(child);
        ASSERT(formattingState.isBlockFormattingState());
        auto childInstrinsicWidthConstraints = formattingState.instrinsicWidthConstraints(child);
        ASSERT(childInstrinsicWidthConstraints);
        
        auto& style = child.style();
        auto horizontalMarginBorderAndPadding = fixedValue(style.marginStart()).valueOr(0)
            + LayoutUnit { style.borderLeftWidth() }
            + fixedValue(style.paddingLeft()).valueOr(0)
            + fixedValue(style.paddingRight()).valueOr(0)
            + LayoutUnit { style.borderRightWidth() }
            + fixedValue(style.marginEnd()).valueOr(0);

        minimumIntrinsicWidth = std::max(minimumIntrinsicWidth, childInstrinsicWidthConstraints->minimum + horizontalMarginBorderAndPadding); 
        maximumIntrinsicWidth = std::max(maximumIntrinsicWidth, childInstrinsicWidthConstraints->maximum + horizontalMarginBorderAndPadding); 
    }

    return { minimumIntrinsicWidth, maximumIntrinsicWidth };
}

LayoutUnit BlockFormattingContext::Geometry::estimatedMarginBefore(const LayoutState& layoutState, const Box& layoutBox)
{
    ASSERT(layoutBox.isBlockLevelBox());
    // Can't estimate vertical margins for out of flow boxes (and we shouldn't need to do it for float boxes).
    ASSERT(layoutBox.isInFlow());
    // Can't cross block formatting context boundary.
    ASSERT(!layoutBox.establishesBlockFormattingContext());

    // Let's just use the normal path for now.
    return MarginCollapse::marginBefore(layoutState, layoutBox);
}

LayoutUnit BlockFormattingContext::Geometry::estimatedMarginAfter(const LayoutState& layoutState, const Box& layoutBox)
{
    ASSERT(layoutBox.isBlockLevelBox());
    // Can't estimate vertical margins for out of flow boxes (and we shouldn't need to do it for float boxes).
    ASSERT(layoutBox.isInFlow());
    // Can't cross block formatting context boundary.
    ASSERT(!layoutBox.establishesBlockFormattingContext());

    // Let's just use the normal path for now.
    return MarginCollapse::marginAfter(layoutState, layoutBox);
}

}
}

#endif