Allow objects without scrollbars to be scrollable

Source/core/platform/ScrollableArea.h

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 114 matching lines @@
         return scrollbar->Widget::convertToContainingView(scrollbarPoint);
     }
     virtual IntPoint convertFromContainingViewToScrollbar(const Scrollbar* scrollbar, const IntPoint& parentPoint) const
     {
         return scrollbar->Widget::convertFromContainingView(parentPoint);
     }
 
     virtual Scrollbar* horizontalScrollbar() const { return 0; }
     virtual Scrollbar* verticalScrollbar() const { return 0; }
 
-    virtual IntPoint scrollPosition() const;
+    virtual IntPoint scrollPosition() const = 0;
     virtual IntPoint minimumScrollPosition() const;
     virtual IntPoint maximumScrollPosition() const;
 
     enum VisibleContentRectIncludesScrollbars { ExcludeScrollbars, IncludeScrollbars };
     virtual IntRect visibleContentRect(VisibleContentRectIncludesScrollbars = ExcludeScrollbars) const;
     virtual int visibleHeight() const = 0;
     virtual int visibleWidth() const = 0;
     virtual IntSize contentsSize() const = 0;
     virtual IntSize overhangAmount() const { return IntSize(); }
     virtual IntPoint lastKnownMousePosition() const { return IntPoint(); }
@@ skipping 22 matching lines @@
     // Let subclasses provide a way of asking for and servicing scroll
     // animations.
     virtual bool scheduleAnimation() { return false; }
     void serviceScrollAnimations();
 
     virtual bool usesCompositedScrolling() const { return false; }
     virtual void updateNeedsCompositedScrolling() { }
 
     virtual void reportMemoryUsage(MemoryObjectInfo*) const;
 
+    virtual bool isHorizontallyScrollable() const = 0;

[aelias_OOO_until_Jul13, 2013/06/18 00:54:47]

Instead of making each subclass implement this, how about just checking if
visibleContentRect().size() is smaller than scrollSize()?

[bokan, 2013/06/18 23:03:27]

The meaning of this method is more "is the object allowed to scroll?", rather
than "is there overflow?". E.g. A RenderLayer isHorizontallyScrollable if it's
overflowX style is OAUTO or OSCROLL (and later if we want scrollable input text
boxes we'd add an "or isTextInputBox()"). I think it'll be different for each
subclass - though I think maybe renaming the method to something like
horizontalScrollEnabled() will reflect that better.

[aelias_OOO_until_Jul13, 2013/06/19 02:55:24]

So it really means scrollable by user input events.  Maybe rename to "bool
userInputScrollable(Orientation orientation)"?

[bokan, 2013/06/19 18:57:00]

Done.

+    virtual bool isVerticallyScrollable() const = 0;
+
     // Convenience functions
     int scrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? scrollPosition().x() : scrollPosition().y(); }
     int minimumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? minimumScrollPosition().x() : minimumScrollPosition().y(); }
     int maximumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? maximumScrollPosition().x() : maximumScrollPosition().y(); }
     int clampScrollPosition(ScrollbarOrientation orientation, int pos)  { return std::max(std::min(pos, maximumScrollPosition(orientation)), minimumScrollPosition(orientation)); }
 
 protected:
     ScrollableArea();
     virtual ~ScrollableArea();
 
@@ skipping 10 matching lines @@
     virtual GraphicsLayer* layerForScrollCorner() const { return 0; }
 #if ENABLE(RUBBER_BANDING)
     virtual GraphicsLayer* layerForOverhangAreas() const { return 0; }
 #endif
     bool hasLayerForHorizontalScrollbar() const;
     bool hasLayerForVerticalScrollbar() const;
     bool hasLayerForScrollCorner() const;
 
 private:
     void scrollPositionChanged(const IntPoint&);
+
+    bool isScrollable(ScrollbarOrientation orientation) const { return orientation == HorizontalScrollbar ? isHorizontallyScrollable() : isVerticallyScrollable(); }
     
     // NOTE: Only called from the ScrollAnimator.
     friend class ScrollAnimator;
     void setScrollOffsetFromAnimation(const IntPoint&);
 
     // This function should be overriden by subclasses to perform the actual
     // scroll of the content.
     virtual void setScrollOffset(const IntPoint&) = 0;
 
     mutable OwnPtr<ScrollAnimator> m_scrollAnimator;
@@ skipping 18 matching lines @@
     // vertical-lr / ltr            NO                      NO
     // vertical-lr / rtl            NO                      YES
     // vertical-rl / ltr            YES                     NO
     // vertical-rl / rtl            YES                     YES
     IntPoint m_scrollOrigin;
 };
 
 } // namespace WebCore
 
 #endif // ScrollableArea_h