Compute snap offsets according to CSS Scroll Snap Spec Level 1

third_party/WebKit/Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 38 matching lines @@
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutReplica.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/layout/LayoutTableCell.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/api/LineLayoutBox.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/layout/shapes/ShapeOutsideInfo.h"
 #include "core/page/AutoscrollController.h"
 #include "core/page/Page.h"
+#include "core/page/scrolling/SnapCoordinator.h"
 #include "core/paint/BackgroundImageGeometry.h"
 #include "core/paint/BoxPainter.h"
 #include "core/paint/PaintLayer.h"
 #include "core/style/ShadowList.h"
 #include "platform/LengthFunctions.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/FloatQuad.h"
 #include "platform/geometry/FloatRoundedRect.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/graphics/GraphicsContext.h"
@@ skipping 69 matching lines @@
         unmarkOrthogonalWritingModeRoot();
 
     ShapeOutsideInfo::removeInfo(*this);
 
     LayoutBoxModelObject::willBeDestroyed();
 }
 
 void LayoutBox::insertedIntoTree()
 {
     LayoutBoxModelObject::insertedIntoTree();
+    addScrollSnapMapping();
 
     if (isOrthogonalWritingModeRoot())
         markOrthogonalWritingModeRoot();
 }
 
 void LayoutBox::willBeRemovedFromTree()
 {
     if (!documentBeingDestroyed() && isOrthogonalWritingModeRoot())
         unmarkOrthogonalWritingModeRoot();
 
+    clearScrollSnapMapping();
     LayoutBoxModelObject::willBeRemovedFromTree();
 }
 
 void LayoutBox::removeFloatingOrPositionedChildFromBlockLists()
 {
     ASSERT(isFloatingOrOutOfFlowPositioned());
 
     if (documentBeingDestroyed())
         return;
 
@@ skipping 126 matching lines @@
 
     if (LayoutMultiColumnSpannerPlaceholder* placeholder = this->spannerPlaceholder())
         placeholder->layoutObjectInFlowThreadStyleDidChange(oldStyle);
 
     updateBackgroundAttachmentFixedStatusAfterStyleChange();
 
     if (oldStyle) {
         LayoutFlowThread* flowThread = flowThreadContainingBlock();
         if (flowThread && flowThread != this)
             flowThread->flowThreadDescendantStyleDidChange(this, diff, *oldStyle);
+
+        updateScrollSnapMappingAfterStyleChange(&newStyle, oldStyle);
     }
 
     ASSERT(!isInline() || isAtomicInlineLevel()); // Non-atomic inlines should be LayoutInline or LayoutText, not LayoutBox.
 }
 
 void LayoutBox::updateBackgroundAttachmentFixedStatusAfterStyleChange()
 {
     if (!frameView())
         return;
 
@@ skipping 52 matching lines @@
         && oldStyle->gridRowEnd() == style()->gridRowEnd()
         && oldStyle->order() == style()->order()
         && oldStyle->hasOutOfFlowPosition() == style()->hasOutOfFlowPosition())
         return;
 
     // It should be possible to not dirty the grid in some cases (like moving an explicitly placed grid item).
     // For now, it's more simple to just always recompute the grid.
     toLayoutGrid(parent())->dirtyGrid();
 }
 
+void LayoutBox::updateScrollSnapMappingAfterStyleChange(const ComputedStyle* newStyle, const ComputedStyle* oldStyle)
+{
+    SnapCoordinator* snapCoordinator = document().snapCoordinator();
+    if (!snapCoordinator)
+        return;
+
+    // Scroll snap type has no effect on the viewport defining element instead
+    // they are handled by the LayoutView.
+    bool allowsSnapContainer = node() != document().viewportDefiningElement();
+
+    ScrollSnapType oldSnapType = oldStyle ? oldStyle->getScrollSnapType() : ScrollSnapTypeNone;
+    ScrollSnapType newSnapType = newStyle && allowsSnapContainer ? newStyle->getScrollSnapType() : ScrollSnapTypeNone;
+    if (oldSnapType != newSnapType)
+        snapCoordinator->snapContainerDidChange(*this, newSnapType);
+
+    Vector<LengthPoint> emptyVector;
+    const Vector<LengthPoint>& oldSnapCoordinate = oldStyle ? oldStyle->scrollSnapCoordinate() : emptyVector;
+    const Vector<LengthPoint>& newSnapCoordinate = newStyle ? newStyle->scrollSnapCoordinate() : emptyVector;
+    if (oldSnapCoordinate != newSnapCoordinate)
+        snapCoordinator->snapAreaDidChange(*this, newSnapCoordinate);
+}
+
+void LayoutBox::addScrollSnapMapping()
+{
+    updateScrollSnapMappingAfterStyleChange(style(), nullptr);
+}
+
+void LayoutBox::clearScrollSnapMapping()
+{
+    updateScrollSnapMappingAfterStyleChange(nullptr, style());
+}
+
 void LayoutBox::updateFromStyle()
 {
     LayoutBoxModelObject::updateFromStyle();
 
     const ComputedStyle& styleToUse = styleRef();
     setFloating(!isOutOfFlowPositioned() && styleToUse.isFloating());
     setHasTransformRelatedProperty(styleToUse.hasTransformRelatedProperty());
     setHasReflection(styleToUse.boxReflect());
 }
 
@@ skipping 4463 matching lines @@
     LayoutFlowThread* flowThread = flowThreadContainingBlock();
     if (!flowThread) {
         // If there's no flow thread, we're not nested. All pages have the same height. Give up.
         return strutToNextPage;
     }
     // Start searching for a suitable offset at the top of the next page or column.
     LayoutUnit flowThreadOffset = offsetFromLogicalTopOfFirstPage() + nextPageLogicalTop;
     return strutToNextPage + flowThread->nextLogicalTopForUnbreakableContent(flowThreadOffset, contentLogicalHeight) - flowThreadOffset;
 }
 
+LayoutBox* LayoutBox::snapContainer() const
+{
+    return m_rareData ? m_rareData->m_snapContainer : nullptr;
+}
+
+void LayoutBox::setSnapContainer(LayoutBox* newContainer)
+{
+    LayoutBox* oldContainer = snapContainer();
+    if (oldContainer == newContainer)
+        return;
+
+    if (oldContainer)
+        oldContainer->removeSnapArea(*this);
+
+    ensureRareData().m_snapContainer = newContainer;
+
+    if (newContainer)
+        newContainer->addSnapArea(*this);
+}
+
+void LayoutBox::clearSnapAreas()
+{
+    if (SnapAreaSet* areas = snapAreas()) {
+        for (auto& snapArea : *areas)
+            snapArea->m_rareData->m_snapContainer = nullptr;
+        areas->clear();
+    }
+}
+
+void LayoutBox::addSnapArea(const LayoutBox& snapArea)
+{
+    ensureRareData().ensureSnapAreas().add(&snapArea);
+}
+
+void LayoutBox::removeSnapArea(const LayoutBox& snapArea)
+{
+    if (m_rareData && m_rareData->m_snapAreas) {
+        m_rareData->m_snapAreas->remove(&snapArea);
+    }
+}
+
+SnapAreaSet* LayoutBox::snapAreas() const
+{
+    return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
+}
+
 } // namespace blink