Compute snap offsets (both repeat and element based)

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 31 matching lines @@
 enum OverlayScrollbarSizeRelevancy { IgnoreOverlayScrollbarSize, IncludeOverlayScrollbarSize };
 enum MarginDirection { BlockDirection, InlineDirection };
 
 enum ShouldComputePreferred { ComputeActual, ComputePreferred };
 
 enum ScrollOffsetClamping {
     ScrollOffsetUnclamped,
     ScrollOffsetClamped
 };
 
+using SnapAreaSet = HashSet<const LayoutBox*>;
+
 struct LayoutBoxRareData {
     WTF_MAKE_NONCOPYABLE(LayoutBoxRareData); USING_FAST_MALLOC(LayoutBoxRareData);
 public:
     LayoutBoxRareData()
         : m_spannerPlaceholder(nullptr)
         , m_overrideLogicalContentHeight(-1)
         , m_overrideLogicalContentWidth(-1)
         , m_previousBorderBoxSize(LayoutUnit(-1), LayoutUnit(-1))
         , m_percentHeightContainer(nullptr)
+        , m_snapContainer(nullptr)
+        , m_snapAreas(nullptr)
     {
     }
 
     // For spanners, the spanner placeholder that lays us out within the multicol container.
     LayoutMultiColumnSpannerPlaceholder* m_spannerPlaceholder;
 
     LayoutUnit m_overrideLogicalContentHeight;
     LayoutUnit m_overrideLogicalContentWidth;
 
     // Set by LayoutBox::savePreviousBoxSizesIfNeeded().
     LayoutSize m_previousBorderBoxSize;
     LayoutRect m_previousContentBoxRect;
     LayoutRect m_previousLayoutOverflowRect;
 
     LayoutUnit m_pageLogicalOffset;
 
     LayoutUnit m_paginationStrut;
 
     LayoutBlock* m_percentHeightContainer;
+    // For snap area, the owning snap container.
+    LayoutBox* m_snapContainer;
+    // For snap container, the descendant snap areas that contribute snap
+    // points.
+    OwnPtr<SnapAreaSet> m_snapAreas;
+
+    SnapAreaSet& ensureSnapAreas()
+    {
+        if (!m_snapAreas)
+            m_snapAreas = adoptPtr(new SnapAreaSet);
+
+        return *m_snapAreas;
+    }
 };
 
 // LayoutBox implements the full CSS box model.
 //
 // LayoutBoxModelObject only introduces some abstractions for LayoutInline and
 // LayoutBox. The logic for the model is in LayoutBox, e.g. the storage for the
 // rectangle and offset forming the CSS box (m_frameRect) and the getters for
 // the different boxes.
 //
 // LayoutBox is also the uppermost class to support scrollbars, however the
@@ skipping 798 matching lines @@
 
     void mapLocalToAncestor(const LayoutBoxModelObject* ancestor, TransformState&, MapCoordinatesFlags = ApplyContainerFlip, bool* wasFixed = nullptr, const PaintInvalidationState* = nullptr) const override;
     void mapAncestorToLocal(const LayoutBoxModelObject*, TransformState&, MapCoordinatesFlags) const override;
 
     void clearPreviousPaintInvalidationRects() override;
 
     LayoutBlock* percentHeightContainer() const { return m_rareData ? m_rareData->m_percentHeightContainer : nullptr; }
     void setPercentHeightContainer(LayoutBlock*);
     void removeFromPercentHeightContainer();
     void clearPercentHeightDescendants();
+    // For snap areas, returns the snap container that owns us.
+    LayoutBox* snapContainer() const;
+    void setSnapContainer(LayoutBox*);
+    // For snap containers, returns all associated snap areas.
+    SnapAreaSet* snapAreas() const;
+    void clearSnapAreas();
 
 protected:
     void willBeDestroyed() override;
 
     void insertedIntoTree() override;
     void willBeRemovedFromTree() override;
 
     void styleWillChange(StyleDifference, const ComputedStyle& newStyle) override;
     void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
     void updateFromStyle() override;
@@ skipping 41 matching lines @@
 
 private:
     bool mustInvalidateBackgroundOrBorderPaintOnHeightChange() const;
     bool mustInvalidateBackgroundOrBorderPaintOnWidthChange() const;
     inline bool mustInvalidateFillLayersPaintOnWidthChange(const FillLayer&) const;
 
     void invalidatePaintRectClippedByOldAndNewBounds(const LayoutBoxModelObject& paintInvalidationContainer, const LayoutRect&, const LayoutRect& oldBounds, const LayoutRect& newBounds);
 
     void updateShapeOutsideInfoAfterStyleChange(const ComputedStyle&, const ComputedStyle* oldStyle);
     void updateGridPositionAfterStyleChange(const ComputedStyle*);
+    void updateScrollSnapMappingAfterStyleChange(const ComputedStyle*, const ComputedStyle* oldStyle);
+    void clearScrollSnapMapping();
+    void addScrollSnapMapping();
 
     bool autoWidthShouldFitContent() const;
     LayoutUnit shrinkToFitLogicalWidth(LayoutUnit availableLogicalWidth, LayoutUnit bordersPlusPadding) const;
 
     // Returns true if we queued up a paint invalidation.
     bool invalidatePaintOfLayerRectsForImage(WrappedImagePtr, const FillLayer&, bool drawingBackground);
 
     bool stretchesToViewportInQuirksMode() const;
     bool skipContainingBlockForPercentHeightCalculation(const LayoutBox* containingBlock) const;
 
@@ skipping 64 matching lines @@
 
     // Our intrinsic height, used for min-height: min-content etc. Maintained by
     // updateLogicalHeight. This is logicalHeight() before it is clamped to
     // min/max.
     mutable LayoutUnit m_intrinsicContentLogicalHeight;
 
     void inflatePaintInvalidationRectForReflectionAndFilter(LayoutRect&) const;
 
     LayoutRectOutsets m_marginBoxOutsets;
 
+    void addSnapArea(const LayoutBox&);
+    void removeSnapArea(const LayoutBox&);
+
 protected:
     // The logical width of the element if it were to break its lines at every
     // possible opportunity.
     //
     // See LayoutObject::minPreferredLogicalWidth() for more details.
     LayoutUnit m_minPreferredLogicalWidth;
 
     // The logical width of the element if it never breaks any lines at all.
     //
     // See LayoutObject::maxPreferredLogicalWidth() for more details.
@@ skipping 78 matching lines @@
         if (UNLIKELY(m_inlineBoxWrapper != nullptr))
             deleteLineBoxWrapper();
     }
 
     m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace blink
 
 #endif // LayoutBox_h