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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "core/layout/ScrollAnchor.h"
#include "core/frame/FrameView.h"
#include "core/layout/LayoutView.h"
#include "core/layout/line/InlineTextBox.h"
#include "core/paint/PaintLayerScrollableArea.h"
namespace blink {
using Corner = ScrollAnchor::Corner;
ScrollAnchor::ScrollAnchor(ScrollableArea* scroller)
: m_scroller(scroller)
, m_anchorObject(nullptr)
, m_corner(Corner::TopLeft)
{
ASSERT(m_scroller);
ASSERT(m_scroller->isFrameView() || m_scroller->isPaintLayerScrollableArea());
}
ScrollAnchor::~ScrollAnchor()
{
}
static LayoutBox* scrollerLayoutBox(const ScrollableArea* scroller)
{
LayoutBox* box = scroller->isFrameView()
? toFrameView(scroller)->layoutView()
: &toPaintLayerScrollableArea(scroller)->box();
ASSERT(box);
return box;
}
static Corner cornerFromCandidateRect(LayoutRect candidateRect, LayoutRect visibleRect)
{
if (visibleRect.contains(candidateRect.minXMinYCorner()))
return Corner::TopLeft;
if (visibleRect.contains(candidateRect.maxXMinYCorner()))
return Corner::TopRight;
if (visibleRect.contains(candidateRect.minXMaxYCorner()))
return Corner::BottomLeft;
if (visibleRect.contains(candidateRect.maxXMaxYCorner()))
return Corner::BottomRight;
return Corner::TopLeft;
}
static LayoutPoint cornerPointOfRect(LayoutRect rect, Corner whichCorner)
{
switch (whichCorner) {
case Corner::TopLeft: return rect.minXMinYCorner();
case Corner::TopRight: return rect.maxXMinYCorner();
case Corner::BottomLeft: return rect.minXMaxYCorner();
case Corner::BottomRight: return rect.maxXMaxYCorner();
}
ASSERT_NOT_REACHED();
return LayoutPoint();
}
// Bounds of the LayoutObject relative to the scroller's visible content rect.
static LayoutRect relativeBounds(const LayoutObject* layoutObject, const ScrollableArea* scroller)
{
LayoutRect localBounds;
if (layoutObject->isBox()) {
localBounds = toLayoutBox(layoutObject)->borderBoxRect();
} else if (layoutObject->isText()) {
// TODO(skobes): Use first and last InlineTextBox only?
for (InlineTextBox* box = toLayoutText(layoutObject)->firstTextBox(); box; box = box->nextTextBox())
localBounds.unite(box->calculateBoundaries());
} else {
// Only LayoutBox and LayoutText are supported.
ASSERT_NOT_REACHED();
}
LayoutRect relativeBounds = LayoutRect(layoutObject->localToAncestorQuad(
FloatRect(localBounds), scrollerLayoutBox(scroller)).boundingBox());
if (scroller->isFrameView())
relativeBounds.moveBy(-LayoutPoint(scroller->scrollPositionDouble()));
return relativeBounds;
}
static LayoutPoint computeRelativeOffset(const LayoutObject* layoutObject, const ScrollableArea* scroller, Corner corner)
{
return cornerPointOfRect(relativeBounds(layoutObject, scroller), corner);
}
static bool candidateMovesWithScroller(const LayoutObject* candidate, const ScrollableArea* scroller)
{
if (candidate->style() && candidate->style()->hasViewportConstrainedPosition())
return false;
bool skippedByContainerLookup = false;
candidate->container(scrollerLayoutBox(scroller), &skippedByContainerLookup);
return !skippedByContainerLookup;
}
ScrollAnchor::ExamineResult ScrollAnchor::examine(const LayoutObject* candidate) const
{
if (candidate->isLayoutInline())
return ExamineResult(Continue);
if (!candidate->isText() && !candidate->isBox())
return ExamineResult(Skip);
if (!candidateMovesWithScroller(candidate, m_scroller))
return ExamineResult(Skip);
LayoutRect candidateRect = relativeBounds(candidate, m_scroller);
LayoutRect visibleRect = scrollerLayoutBox(m_scroller)->overflowClipRect(LayoutPoint());
bool occupiesSpace = candidateRect.width() > 0 && candidateRect.height() > 0;
if (occupiesSpace && visibleRect.intersects(candidateRect)) {
return ExamineResult(
visibleRect.contains(candidateRect) ? Return : Constrain,
cornerFromCandidateRect(candidateRect, visibleRect));
} else {
return ExamineResult(Skip);
}
}
void ScrollAnchor::findAnchor()
{
LayoutObject* stayWithin = scrollerLayoutBox(m_scroller);
LayoutObject* candidate = stayWithin->nextInPreOrder(stayWithin);
while (candidate) {
ExamineResult result = examine(candidate);
if (result.viable) {
m_anchorObject = candidate;
m_corner = result.corner;
}
switch (result.status) {
case Skip:
candidate = candidate->nextInPreOrderAfterChildren(stayWithin);
break;
case Constrain:
stayWithin = candidate;
// fall through
case Continue:
candidate = candidate->nextInPreOrder(stayWithin);
break;
case Return:
return;
}
}
}
void ScrollAnchor::save()
{
if (m_scroller->scrollPosition() == IntPoint::zero()) {
clear();
return;
}
if (m_anchorObject)
return;
findAnchor();
if (!m_anchorObject)
return;
m_anchorObject->setIsScrollAnchorObject();
m_savedRelativeOffset = computeRelativeOffset(m_anchorObject, m_scroller, m_corner);
}
void ScrollAnchor::restore()
{
if (!m_anchorObject)
return;
LayoutSize adjustment = computeRelativeOffset(m_anchorObject, m_scroller, m_corner) - m_savedRelativeOffset;
if (!adjustment.isZero()) {
m_scroller->setScrollPosition(
m_scroller->scrollPositionDouble() + DoubleSize(adjustment),
AnchoringScroll);
}
}
void ScrollAnchor::clear()
{
LayoutObject* anchorObject = m_anchorObject;
m_anchorObject = nullptr;
if (anchorObject)
anchorObject->maybeClearIsScrollAnchorObject();
}
} // namespace blink
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