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/*
* Copyright (C) 2007 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. ``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
* 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.
*/
#ifndef LayoutState_h
#define LayoutState_h
#include "platform/geometry/LayoutRect.h"
#include "wtf/Allocator.h"
#include "wtf/HashMap.h"
#include "wtf/Noncopyable.h"
namespace blink {
class LayoutBox;
class LayoutFlowThread;
class LayoutObject;
class LayoutView;
// LayoutState is an optimization used during layout.
//
// LayoutState's purpose is to cache information as we walk down the container
// block chain during layout. In particular, the absolute layout offset for the
// current LayoutObject is O(1) when using LayoutState, when it is
// O(depthOfTree) without it (thus potentially making layout O(N^2)).
// LayoutState incurs some memory overhead and is pretty intrusive (see next
// paragraphs about those downsides).
//
// To use LayoutState, the layout() functions have to allocate a new LayoutSTate
// object on the stack whenever the LayoutObject creates a new coordinate system
// (which is pretty much all objects but LayoutTableRow).
//
// LayoutStates are linked together with a single linked list, acting in
// practice like a stack that we push / pop. LayoutView holds the top-most
// pointer to this stack.
//
// See the layout() functions on how to set it up during layout.
// See e.g LayoutBox::offsetFromLogicalTopOfFirstPage on how to use LayoutState
// for computations.
class LayoutState {
// LayoutState is always allocated on the stack.
// The reason is that it is scoped to layout, thus we can avoid expensive
// mallocs.
DISALLOW_NEW();
WTF_MAKE_NONCOPYABLE(LayoutState);
public:
// Constructor for root LayoutState created by LayoutView
explicit LayoutState(LayoutView&);
// Constructor for sub-tree layout and orthogonal writing-mode roots
explicit LayoutState(LayoutObject& root);
LayoutState(LayoutBox&,
bool containingBlockLogicalWidthChanged = false);
~LayoutState();
bool isPaginated() const { return m_isPaginated; }
// The page logical offset is the object's offset from the top of the page in
// the page progression direction (so an x-offset in vertical text and a
// y-offset for horizontal text).
LayoutUnit pageLogicalOffset(const LayoutBox&,
const LayoutUnit& childLogicalOffset) const;
const LayoutSize& paginationOffset() const { return m_paginationOffset; }
bool containingBlockLogicalWidthChanged() const {
return m_containingBlockLogicalWidthChanged;
}
bool paginationStateChanged() const { return m_paginationStateChanged; }
void setPaginationStateChanged() { m_paginationStateChanged = true; }
LayoutState* next() const { return m_next; }
LayoutFlowThread* flowThread() const { return m_flowThread; }
LayoutObject& layoutObject() const { return m_layoutObject; }
private:
// Do not add anything apart from bitfields until after m_flowThread. See
// https://bugs.webkit.org/show_bug.cgi?id=100173
bool m_isPaginated : 1;
bool m_containingBlockLogicalWidthChanged : 1;
bool m_paginationStateChanged : 1;
LayoutFlowThread* m_flowThread;
LayoutState* m_next;
// x/y offset from the logical top / start of the first page. Does not include
// relative positioning or scroll offsets.
LayoutSize m_paginationOffset;
LayoutObject& m_layoutObject;
};
} // namespace blink
#endif // LayoutState_h
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