Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h

Index: third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h b/third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h
index 6b3dca6ed15f4f13cb52653d392476c18f874ecc..87ba070f3d7988d5580916e66cec36dbcf370658 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingConstraints.h
@@ -26,19 +26,19 @@
 #ifndef ScrollingConstraints_h

[chrishtr, 2015/12/11 02:06:12]

Rename this file ViewportConstraints and add a new one for
StickyPositionViewportConstraints.

[flackr, 2016/01/19 15:40:48]

Done.

 #define ScrollingConstraints_h
 
-#include "platform/geometry/FloatRect.h"
+#include "platform/geometry/LayoutRect.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 // ViewportConstraints classes encapsulate data and logic required to reposition elements whose layout
-// depends on the viewport rect (i.e., position fixed), when scrolling and zooming.
+// depends on the viewport rect (positioned fixed and sticky), when scrolling and zooming.
 class ViewportConstraints {
     STACK_ALLOCATED();
 public:
-    // FIXME: Simplify this code now that position: sticky doesn't exist.
     enum ConstraintType {
         FixedPositionConstaint,
+        StickyPositionConstraint,
     };
 
     enum AnchorEdgeFlags {
@@ -63,15 +63,15 @@ public:
     void addAnchorEdge(AnchorEdgeFlags edgeFlag) { m_anchorEdges |= edgeFlag; }
     void setAnchorEdges(AnchorEdges edges) { m_anchorEdges = edges; }
 
-    FloatSize alignmentOffset() const { return m_alignmentOffset; }

[chrishtr, 2015/12/11 02:06:12]

Why the change from float to layout units here? This affects fixed-position
also, if it needs to be changed please break it out into another patch and
commit that first.

[flackr, 2016/01/19 15:40:48]

Undone. At the time I thought it'd made for fewer conversions but I'm not sure.

-    void setAlignmentOffset(const FloatSize& offset) { m_alignmentOffset = offset; }
+    LayoutSize alignmentOffset() const { return m_alignmentOffset; }
+    void setAlignmentOffset(const LayoutSize& offset) { m_alignmentOffset = offset; }
 
 protected:
     ViewportConstraints()
         : m_anchorEdges(0)
     { }
 
-    FloatSize m_alignmentOffset;
+    LayoutSize m_alignmentOffset;
     AnchorEdges m_anchorEdges;
 };
 
@@ -84,33 +84,76 @@ public:
 
     FixedPositionViewportConstraints(const FixedPositionViewportConstraints& other)
         : ViewportConstraints(other)
-        , m_viewportRectAtLastLayout(other.m_viewportRectAtLastLayout)
-        , m_layerPositionAtLastLayout(other.m_layerPositionAtLastLayout)
     { }
 
-    FloatPoint layerPositionForViewportRect(const FloatRect& viewportRect) const;
-
-    const FloatRect& viewportRectAtLastLayout() const { return m_viewportRectAtLastLayout; }
-    void setViewportRectAtLastLayout(const FloatRect& rect) { m_viewportRectAtLastLayout = rect; }
-
-    const FloatPoint& layerPositionAtLastLayout() const { return m_layerPositionAtLastLayout; }
-    void setLayerPositionAtLastLayout(const FloatPoint& point) { m_layerPositionAtLastLayout = point; }
-
     bool operator==(const FixedPositionViewportConstraints& other) const
     {
         return m_alignmentOffset == other.m_alignmentOffset
-            && m_anchorEdges == other.m_anchorEdges
-            && m_viewportRectAtLastLayout == other.m_viewportRectAtLastLayout
-            && m_layerPositionAtLastLayout == other.m_layerPositionAtLastLayout;
+            && m_anchorEdges == other.m_anchorEdges;
     }
 
     bool operator!=(const FixedPositionViewportConstraints& other) const { return !(*this == other); }
 
 private:
     ConstraintType constraintType() const override { return FixedPositionConstaint; }
+};
+
+class StickyPositionViewportConstraints final : public ViewportConstraints {
+public:
+    StickyPositionViewportConstraints()
+        : m_leftOffset(0)
+        , m_rightOffset(0)
+        , m_topOffset(0)
+        , m_bottomOffset(0)
+    { }
+
+    StickyPositionViewportConstraints(const StickyPositionViewportConstraints& other)
+        : ViewportConstraints(other)
+        , m_leftOffset(other.m_leftOffset)
+        , m_rightOffset(other.m_rightOffset)
+        , m_topOffset(other.m_topOffset)
+        , m_bottomOffset(other.m_bottomOffset)
+        , m_absoluteContainingBlockRect(other.m_absoluteContainingBlockRect)
+        , m_absoluteStickyBoxRect(other.m_absoluteStickyBoxRect)
+    { }
 
-    FloatRect m_viewportRectAtLastLayout;
-    FloatPoint m_layerPositionAtLastLayout;
+    LayoutSize computeStickyOffset(const LayoutRect& viewportRect) const;
+
+    LayoutUnit leftOffset() const { return m_leftOffset; }
+    LayoutUnit rightOffset() const { return m_rightOffset; }
+    LayoutUnit topOffset() const { return m_topOffset; }
+    LayoutUnit bottomOffset() const { return m_bottomOffset; }
+
+    void setLeftOffset(LayoutUnit offset) { m_leftOffset = offset; }
+    void setRightOffset(LayoutUnit offset) { m_rightOffset = offset; }
+    void setTopOffset(LayoutUnit offset) { m_topOffset = offset; }
+    void setBottomOffset(LayoutUnit offset) { m_bottomOffset = offset; }
+
+    void setAbsoluteContainingBlockRect(const LayoutRect& rect) { m_absoluteContainingBlockRect = rect; }
+
+    void setAbsoluteStickyBoxRect(const LayoutRect& rect) { m_absoluteStickyBoxRect = rect; }
+
+    bool operator==(const StickyPositionViewportConstraints& other) const
+    {
+        return m_leftOffset == other.m_leftOffset
+            && m_rightOffset == other.m_rightOffset
+            && m_topOffset == other.m_topOffset
+            && m_bottomOffset == other.m_bottomOffset
+            && m_absoluteContainingBlockRect == other.m_absoluteContainingBlockRect
+            && m_absoluteStickyBoxRect == other.m_absoluteStickyBoxRect;
+    }
+
+    bool operator!=(const StickyPositionViewportConstraints& other) const { return !(*this == other); }
+
+private:
+    ConstraintType constraintType() const override { return StickyPositionConstraint; }
+
+    LayoutUnit m_leftOffset;
+    LayoutUnit m_rightOffset;
+    LayoutUnit m_topOffset;
+    LayoutUnit m_bottomOffset;
+    LayoutRect m_absoluteContainingBlockRect;
+    LayoutRect m_absoluteStickyBoxRect;
 };
 
 } // namespace blink