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serenity/Libraries/LibWeb/Layout/LayoutBlock.h
Andreas Kling c7d9229a0f LibWeb: Reorganize layout algorithm
Previously, layout recursively performed these steps (roughly):

1. Compute own width
2. Compute own position
3. Layout in-flow children
4. Compute own height
5. Layout absolutely positioned descendants

However, step (2) was pretty inconsistent. Some things computed their
own position, others had their parent do it for them, etc.
To get closer to CSS spec language, and make things easier in general,
this patch reorganizes the algorithm into:

1. Compute own width & height
2. Compute width & height of in-flow managed descendants
3. Move in-flow managed descendants to their final position
4. Layout absolutely positioned descendants

Block layout is now driven by the containing block, which will iterate
the descendants it's responsible for. There are a lot of inefficient
patterns in this logic right now, but they can easily be replaced with
better iteration functions once we settle on a long-term architecture.

Since the ICB (LayoutDocument) is at (0, 0), it doesn't rely on a
containing block to move it into place.

This code is still evolving along with my understanding of CSS layout,
so it's likely that we'll reorganize this again sooner or later. :^)
2020-06-14 19:01:54 +02:00

117 lines
4 KiB
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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* 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 THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT HOLDER 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.
*/
#pragma once
#include <LibWeb/Layout/LayoutBox.h>
#include <LibWeb/Layout/LineBox.h>
namespace Web {
class Element;
class LayoutBlock : public LayoutBox {
public:
LayoutBlock(const Node*, NonnullRefPtr<StyleProperties>);
virtual ~LayoutBlock() override;
virtual const char* class_name() const override { return "LayoutBlock"; }
virtual void layout(LayoutMode = LayoutMode::Default) override;
virtual void render(RenderingContext&) override;
virtual LayoutNode& inline_wrapper() override;
Vector<LineBox>& line_boxes() { return m_line_boxes; }
const Vector<LineBox>& line_boxes() const { return m_line_boxes; }
LineBox& ensure_last_line_box();
LineBox& add_line_box();
virtual HitTestResult hit_test(const Gfx::IntPoint&) const override;
LayoutBlock* previous_sibling() { return to<LayoutBlock>(LayoutNode::previous_sibling()); }
const LayoutBlock* previous_sibling() const { return to<LayoutBlock>(LayoutNode::previous_sibling()); }
LayoutBlock* next_sibling() { return to<LayoutBlock>(LayoutNode::next_sibling()); }
const LayoutBlock* next_sibling() const { return to<LayoutBlock>(LayoutNode::next_sibling()); }
template<typename Callback>
void for_each_fragment(Callback);
template<typename Callback>
void for_each_fragment(Callback) const;
virtual void split_into_lines(LayoutBlock& container, LayoutMode) override;
protected:
void compute_width();
void compute_height();
void layout_absolutely_positioned_descendants();
private:
virtual bool is_block() const override { return true; }
void place_block_level_non_replaced_element_in_normal_flow(LayoutBlock&);
void place_block_level_replaced_element_in_normal_flow(LayoutReplaced&);
void layout_absolutely_positioned_descendant(LayoutBox&);
NonnullRefPtr<StyleProperties> style_for_anonymous_block() const;
void layout_inside(LayoutMode);
void layout_inline_children(LayoutMode);
void layout_contained_boxes(LayoutMode);
Vector<LineBox> m_line_boxes;
};
template<typename Callback>
void LayoutBlock::for_each_fragment(Callback callback)
{
for (auto& line_box : line_boxes()) {
for (auto& fragment : line_box.fragments()) {
if (callback(fragment) == IterationDecision::Break)
return;
}
}
}
template<typename Callback>
void LayoutBlock::for_each_fragment(Callback callback) const
{
for (auto& line_box : line_boxes()) {
for (auto& fragment : line_box.fragments()) {
if (callback(fragment) == IterationDecision::Break)
return;
}
}
}
template<>
inline bool is<LayoutBlock>(const LayoutNode& node)
{
return node.is_block();
}
}