Compute snap offsets (both repeat and element based)

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 68af23e2104623ab7161b1d3d3d92e123197ecf8..c8b85eeb4d8e3f748d80c68fb86af57391c9a677 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -116,6 +116,7 @@
 #include "core/page/scrolling/ScrollCustomizationCallbacks.h"
 #include "core/page/scrolling/ScrollState.h"
 #include "core/page/scrolling/ScrollStateCallback.h"
+#include "core/page/scrolling/SnapCoordinator.h"
 #include "core/paint/PaintLayer.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGElement.h"
@@ -1530,7 +1531,9 @@ void Element::attach(const AttachContext& context)
     if (!isActiveInsertionPoint(*this))
         LayoutTreeBuilderForElement(*this, context.resolvedStyle).createLayoutObjectIfNeeded();
 
-    addCallbackSelectors();
+    const ComputedStyle* style = computedStyle();
+    addCallbackSelectors(style);
+    addScrollSnapMapping(style);
 
     if (hasRareData() && !layoutObject()) {
         if (ElementAnimations* elementAnimations = elementRareData()->elementAnimations()) {
@@ -1562,7 +1565,11 @@ void Element::detach(const AttachContext& context)
 {
     HTMLFrameOwnerElement::UpdateSuspendScope suspendWidgetHierarchyUpdates;
     cancelFocusAppearanceUpdate();
-    removeCallbackSelectors();
+
+    const ComputedStyle* style = computedStyle();
+    removeCallbackSelectors(style);
+    removeScrollSnapMapping(style);
+
     if (hasRareData()) {
         ElementRareData* data = elementRareData();
         data->clearPseudoElements();
@@ -1772,8 +1779,10 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change)
 
     ASSERT(oldStyle);
 
-    if (localChange != NoChange)
+    if (localChange != NoChange) {
         updateCallbackSelectors(oldStyle.get(), newStyle.get());
+        updateScrollSnapMapping(oldStyle.get(), newStyle.get());
+    }
 
     if (LayoutObject* layoutObject = this->layoutObject()) {
         if (localChange != NoChange || pseudoStyleCacheIsInvalid(oldStyle.get(), newStyle.get()) || svgFilterNeedsLayerUpdate()) {
@@ -1817,16 +1826,45 @@ void Element::updateCallbackSelectors(const ComputedStyle* oldStyle, const Compu
         CSSSelectorWatch::from(document()).updateSelectorMatches(oldCallbackSelectors, newCallbackSelectors);
 }
 
-void Element::addCallbackSelectors()
+void Element::addCallbackSelectors(const ComputedStyle* style)
+{
+    updateCallbackSelectors(0, style);
+}
+
+void Element::removeCallbackSelectors(const ComputedStyle* style)
+{
+    updateCallbackSelectors(style, 0);
+}
+
+void Element::updateScrollSnapMapping(const ComputedStyle* oldStyle, const ComputedStyle* newStyle)
 {
-    updateCallbackSelectors(0, computedStyle());
+    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;
+    Vector<LengthPoint> oldSnapCoordinate = oldStyle ? oldStyle->scrollSnapCoordinate() :  emptyVector;
+    Vector<LengthPoint> newSnapCoordinate = newStyle ? newStyle->scrollSnapCoordinate() :  emptyVector;

[esprehn, 2015/10/20 21:03:35]

This means making copies all the time, I think you want const refs to the
vectors

+    if (oldSnapCoordinate != newSnapCoordinate)
+        snapCoordinator->snapElementDidChange(*this, newSnapCoordinate);
 }
 
-void Element::removeCallbackSelectors()
+void Element::addScrollSnapMapping(const ComputedStyle* style)
 {
-    updateCallbackSelectors(computedStyle(), 0);
+    updateScrollSnapMapping(0, style);
 }
 
+void Element::removeScrollSnapMapping(const ComputedStyle* style)
+{
+    updateScrollSnapMapping(style, 0);
+}
+
+
 ElementShadow* Element::shadow() const
 {
     return hasRareData() ? elementRareData()->shadow() : nullptr;