Source/WebCore/layout/blockformatting/BlockFormattingContext.cpp

/*
 * Copyright (C) 2018 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
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#include "config.h"
#include "BlockFormattingContext.h"

#if ENABLE(LAYOUT_FORMATTING_CONTEXT)

#include "BlockFormattingState.h"
#include "FloatingContext.h"
#include "FloatingState.h"
#include "LayoutBox.h"
#include "LayoutContainer.h"
#include "LayoutContext.h"
#include <wtf/IsoMallocInlines.h>

namespace WebCore {
namespace Layout {

WTF_MAKE_ISO_ALLOCATED_IMPL(BlockFormattingContext);

BlockFormattingContext::BlockFormattingContext(const Box& formattingContextRoot, LayoutContext& layoutContext)
    : FormattingContext(formattingContextRoot, layoutContext)
{
}

void BlockFormattingContext::layout(LayoutContext& layoutContext, FormattingState& formattingState) 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;
    auto& formattingRoot = downcast<Container>(root());
    Vector<const Box*> 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 (formattingRoot.hasInFlowOrFloatingChild())
        layoutQueue.append(formattingRoot.firstInFlowOrFloatingChild());
    // 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();
            computeWidth(layoutBox);
            computeStaticPosition(layoutBox);
            if (layoutBox.establishesFormattingContext()) {
                auto formattingContext = layoutContext.formattingContext(layoutBox);
                formattingContext->layout(layoutContext, layoutContext.establishedFormattingState(layoutBox, *formattingContext));
                break;
            }
            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();
            computeHeight(layoutBox);
            // Adjust position now that we have all the previous floats placed in this context -if needed.
            floatingContext.computePosition(layoutBox);
            if (!is<Container>(layoutBox))
                continue;
            auto& container = downcast<Container>(layoutBox);
            // Move in-flow positioned children to their final position.
            placeInFlowPositionedChildren(container);
            if (auto* nextSibling = container.nextInFlowOrFloatingSibling()) {
                layoutQueue.append(nextSibling);
                break;
            }
        }
    }
    // Place the inflow positioned children.
    placeInFlowPositionedChildren(formattingRoot);
    // And take care of out-of-flow boxes as the final step.
    layoutOutOfFlowDescendants();
}

std::unique_ptr<FormattingState> BlockFormattingContext::createFormattingState(Ref<FloatingState>&& floatingState) const
{
    return std::make_unique<BlockFormattingState>(WTFMove(floatingState));
}

Ref<FloatingState> BlockFormattingContext::createOrFindFloatingState() const
{
    // Block formatting context always establishes a new floating state.
    return FloatingState::create();
}

void BlockFormattingContext::computeStaticPosition(const Box&) const
{
}

void BlockFormattingContext::computeWidth(const Box&) const
{
}

void BlockFormattingContext::computeHeight(const Box&) const
{
}

LayoutUnit BlockFormattingContext::marginTop(const Box&) const
{
    return 0;
}

LayoutUnit BlockFormattingContext::marginBottom(const Box&) const
{
    return 0;
}

}
}

#endif