Adapt and reland old position sticky implementation

Source/core/page/scrolling/ScrollingConstraints.cpp

Index: Source/core/page/scrolling/ScrollingConstraints.cpp
diff --git a/Source/core/page/scrolling/ScrollingConstraints.cpp b/Source/core/page/scrolling/ScrollingConstraints.cpp
index 0e59a00cdb3e4b03e77fb82564dc83ada4d4b827..89badd279ae44d2fd9067e74a709977b2558aefc 100644
--- a/Source/core/page/scrolling/ScrollingConstraints.cpp
+++ b/Source/core/page/scrolling/ScrollingConstraints.cpp
@@ -28,9 +28,9 @@
 
 namespace blink {
 
-FloatPoint FixedPositionViewportConstraints::layerPositionForViewportRect(const FloatRect& viewportRect) const
+LayoutPoint FixedPositionViewportConstraints::layerPositionForViewportRect(const LayoutRect& viewportRect) const
 {
-    FloatSize offset;
+    LayoutSize offset;
 
     if (hasAnchorEdge(AnchorEdgeLeft))
         offset.setWidth(viewportRect.x() - m_viewportRectAtLastLayout.x());
@@ -45,4 +45,57 @@ FloatPoint FixedPositionViewportConstraints::layerPositionForViewportRect(const
     return m_layerPositionAtLastLayout + offset;
 }
 
+LayoutSize StickyPositionViewportConstraints::computeStickyOffset(const LayoutRect& viewportRect) const
+{
+    LayoutRect boxRect = m_absoluteStickyBoxRect;
+
+    if (hasAnchorEdge(AnchorEdgeRight)) {
+        LayoutUnit rightLimit = viewportRect.maxX() - m_rightOffset;
+        LayoutUnit rightDelta = std::min<LayoutUnit>(0, rightLimit - m_absoluteStickyBoxRect.maxX());
+        LayoutUnit availableSpace = std::min<LayoutUnit>(0, m_absoluteContainingBlockRect.x() - m_absoluteStickyBoxRect.x());
+        if (rightDelta < availableSpace)
+            rightDelta = availableSpace;
+
+        boxRect.move(rightDelta, 0);
+    }
+
+    if (hasAnchorEdge(AnchorEdgeLeft)) {
+        LayoutUnit leftLimit = viewportRect.x() + m_leftOffset;
+        LayoutUnit leftDelta = std::max<LayoutUnit>(0, leftLimit - m_absoluteStickyBoxRect.x());
+        LayoutUnit availableSpace = std::max<LayoutUnit>(0, m_absoluteContainingBlockRect.maxX() - m_absoluteStickyBoxRect.maxX());
+        if (leftDelta > availableSpace)
+            leftDelta = availableSpace;
+
+        boxRect.move(leftDelta, 0);
+    }
+
+    if (hasAnchorEdge(AnchorEdgeBottom)) {
+        LayoutUnit bottomLimit = viewportRect.maxY() - m_bottomOffset;
+        LayoutUnit bottomDelta = std::min<LayoutUnit>(0, bottomLimit - m_absoluteStickyBoxRect.maxY());
+        LayoutUnit availableSpace = std::min<LayoutUnit>(0, m_absoluteContainingBlockRect.y() - m_absoluteStickyBoxRect.y());
+        if (bottomDelta < availableSpace)
+            bottomDelta = availableSpace;
+
+        boxRect.move(0, bottomDelta);
+    }
+
+    if (hasAnchorEdge(AnchorEdgeTop)) {
+        LayoutUnit topLimit = viewportRect.y() + m_topOffset;
+        LayoutUnit topDelta = std::max<LayoutUnit>(0, topLimit - m_absoluteStickyBoxRect.y());
+        LayoutUnit availableSpace = std::max<LayoutUnit>(0, m_absoluteContainingBlockRect.maxY() - m_absoluteStickyBoxRect.maxY());
+        if (topDelta > availableSpace)
+            topDelta = availableSpace;
+
+        boxRect.move(0, topDelta);
+    }
+
+    return boxRect.location() - m_absoluteStickyBoxRect.location();
+}
+
+LayoutPoint StickyPositionViewportConstraints::layerPositionForViewportRect(const LayoutRect& viewportRect) const
+{
+    LayoutSize offset = computeStickyOffset(viewportRect);
+    return m_layerPositionAtLastLayout + offset - m_stickyOffsetAtLastLayout;
+}
+
 } // namespace blink