Compute snap offsets (both repeat and element based)

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 37 matching lines @@
 #include "core/layout/LayoutListMarker.h"
 #include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/layout/LayoutTableCell.h"
 #include "core/layout/LayoutView.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 43 matching lines @@
         return OverflowClipPaintLayer;
 
     return NoPaintLayer;
 }
 
 void LayoutBox::willBeDestroyed()
 {
     clearOverrideSize();
     clearContainingBlockOverrideSize();
     clearExtraInlineAndBlockOffests();
+    clearScrollSnapMapping();
 
     LayoutBlock::removePercentHeightDescendantIfNeeded(this);
 
     ShapeOutsideInfo::removeInfo(*this);
 
     LayoutBoxModelObject::willBeDestroyed();
 }
 
+void LayoutBox::insertedIntoTree()
+{
+    LayoutObject::insertedIntoTree();
+    addScrollSnapMapping();
+}
+
 void LayoutBox::removeFloatingOrPositionedChildFromBlockLists()
 {
     ASSERT(isFloatingOrOutOfFlowPositioned());
 
     if (documentBeingDestroyed())
         return;
 
     if (isFloating()) {
         LayoutBlockFlow* parentBlockFlow = nullptr;
         for (LayoutObject* curr = parent(); curr && !curr->isLayoutView(); curr = curr->parent()) {
@@ skipping 114 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);

[esprehn, 2015/12/01 18:31:11]

newStyle should be a reference, don't do & here.

[majidvp, 2015/12/03 17:54:16]

Good point. I have now changed the code to make |addScrollSnapMapping|
and |clearScrollSnapMapping| more symmetrical and both using 
|updateScrollSnapMappingAfterStyleChange|. This is cleaner and 
addresses an small issue I noticed too.

To do this, I am using the fact that newStyle is a pointer and can be null.

     }
 }
 
 void LayoutBox::updateBackgroundAttachmentFixedStatusAfterStyleChange()
 {
     if (!frameView())
         return;
 
     // On low-powered/mobile devices, preventing blitting on a scroll can cause noticeable delays
     // when scrolling a page with a fixed background image. As an optimization, assuming there are
@@ skipping 50 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;
+
+    ScrollSnapType oldSnapType = oldStyle ? oldStyle->scrollSnapType() :  ScrollSnapTypeNone;
+    ScrollSnapType newSnapType = newStyle ? newStyle->scrollSnapType() :  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;

[esprehn, 2015/12/01 18:31:11]

newStyle can't be null, you don't need the null check.

[majidvp, 2015/12/03 17:54:16]

See above.

+    if (oldSnapCoordinate != newSnapCoordinate)
+        snapCoordinator->snapAreaDidChange(*this, newSnapCoordinate);
+}
+
+void LayoutBox::addScrollSnapMapping()
+{
+    updateScrollSnapMappingAfterStyleChange(style(), nullptr);
+}
+
+void LayoutBox::clearScrollSnapMapping()
+{
+    if (SnapAreaSet* areas = snapAreas()) {
+        for (auto& snapArea : *areas)
+            snapArea->m_rareData->m_snapContainer = nullptr;
+        areas->clear();
+    }
+
+    this->setSnapContainer(nullptr);

[esprehn, 2015/12/01 18:31:11]

Why do you need this-> ?

[majidvp, 2015/12/03 17:54:16]

Done.

+}
+
 void LayoutBox::updateFromStyle()
 {
     LayoutBoxModelObject::updateFromStyle();
 
     const ComputedStyle& styleToUse = styleRef();
     bool isViewObject = isLayoutView();
     bool rootLayerScrolls = document().settings() && document().settings()->rootLayerScrolls();
 
     // LayoutView of the main frame is resposible from painting base background.
     if (isViewObject && !document().ownerElement())
@@ skipping 4495 matching lines @@
 
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender() && borderImage->isLoaded();
 }
 
 ShapeOutsideInfo* LayoutBox::shapeOutsideInfo() const
 {
     return ShapeOutsideInfo::isEnabledFor(*this) ? ShapeOutsideInfo::info(*this) : nullptr;
 }
 
+LayoutBox* LayoutBox::snapContainer() const
+{
+    return m_rareData ? m_rareData->m_snapContainer : nullptr;
+}
+
+void LayoutBox::setSnapContainer(LayoutBox* container)
+{
+    if (LayoutBox* currentContainer = snapContainer())
+        currentContainer->removeSnapArea(*this);
+
+    ensureRareData().m_snapContainer = container;
+
+    if (container)
+        container->addSnapArea(*this);
+}
+
+
+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