Bug 63895 (Part 1) - Add helper methods for retrieving overflow areas in the frame's local coordinate space. r=dbaron

layout/generic/nsFrame.cpp

@@ -5118,12 +5118,39 @@ nsIFrame::GetOverflowAreas() const
                          nsRect(nsPoint(0, 0), GetSize()));
 }
 
+nsOverflowAreas
+nsIFrame::GetOverflowAreasRelativeToSelf() const
+{
+  if (IsTransformed()) {
+    nsOverflowAreas* preTransformOverflows = static_cast<nsOverflowAreas*>
+      (Properties().Get(PreTransformOverflowAreasProperty()));
+    if (preTransformOverflows) {
+      return nsOverflowAreas(preTransformOverflows->VisualOverflow(),
+                             preTransformOverflows->ScrollableOverflow());
+    }
+  }
+  return nsOverflowAreas(GetVisualOverflowRect(),
+                         GetScrollableOverflowRect());
+}
+
 nsRect
 nsIFrame::GetScrollableOverflowRectRelativeToParent() const
 {
   return GetScrollableOverflowRect() + mRect.TopLeft();
 }
 
+nsRect
+nsIFrame::GetScrollableOverflowRectRelativeToSelf() const
+{
+  if (IsTransformed()) {
+    nsOverflowAreas* preTransformOverflows = static_cast<nsOverflowAreas*>
+      (Properties().Get(PreTransformOverflowAreasProperty()));
+    if (preTransformOverflows)
+      return preTransformOverflows->ScrollableOverflow();
+  }
+  return GetScrollableOverflowRect();
+}
+
 nsRect
 nsIFrame::GetVisualOverflowRectRelativeToSelf() const
 {

layout/generic/nsIFrame.h

@@ -2280,6 +2280,15 @@ public:
 
   nsOverflowAreas GetOverflowAreas() const;
 
+  /**
+   * Same as GetOverflowAreas, except in this frame's coordinate
+   * system (before transforms are applied).
+   *
+   * @return the overflow areas relative to this frame, before any CSS transforms have
+   * been applied, i.e. in this frame's coordinate system
+   */
+  nsOverflowAreas GetOverflowAreasRelativeToSelf() const;
+
   /**
    * Same as GetScrollableOverflowRect, except relative to the parent
    * frame.
@@ -2289,6 +2298,15 @@ public:
    */
   nsRect GetScrollableOverflowRectRelativeToParent() const;
 
+  /**
+   * Same as GetScrollableOverflowRect, except in this frame's coordinate
+   * system (before transforms are applied).
+   *
+   * @return the rect relative to this frame, before any CSS transforms have
+   * been applied, i.e. in this frame's coordinate system
+   */
+  nsRect GetScrollableOverflowRectRelativeToSelf() const;
+
   /**
    * Like GetVisualOverflowRect, except in this frame's
    * coordinate system (before transforms are applied).