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 22 matching lines @@
 
 class FloatPoint;
 class GraphicsContext;
 class GraphicsLayer;
 class PlatformGestureEvent;
 class PlatformWheelEvent;
 class ScrollAnimator;
 
 class ScrollableArea {
 public:
+    static int pixelsPerLineStep() { return 40; }
+    static float minFractionToStepWhenPaging() { return 0.875f; }
+    static int maxOverlapBetweenPages();
+
     bool scroll(ScrollDirection, ScrollGranularity, float multiplier = 1);
     void scrollToOffsetWithoutAnimation(const FloatPoint&);
     void scrollToOffsetWithoutAnimation(ScrollbarOrientation, float offset);
 
     // Should be called when the scroll position changes externally, for example if the scroll layer position
     // is updated on the scrolling thread and we need to notify the main thread.
     void notifyScrollPositionChanged(const IntPoint&);
 
     // Allows subclasses to handle scroll position updates themselves. If this member function
     // returns true, the scrollable area won't actually update the scroll position and instead
@@ skipping 42 matching lines @@
     ScrollAnimator* scrollAnimator() const;
 
     // This getter will return null if the ScrollAnimator hasn't been created yet.
     ScrollAnimator* existingScrollAnimator() const { return m_scrollAnimator.get(); }
 
     const IntPoint& scrollOrigin() const { return m_scrollOrigin; }
     bool scrollOriginChanged() const { return m_scrollOriginChanged; }
 
     virtual bool isActive() const = 0;
     virtual int scrollSize(ScrollbarOrientation) const = 0;
     virtual int scrollPosition(Scrollbar*) const = 0;

[aelias_OOO_until_Jul13, 2013/06/19 22:25:12]

It's no longer appropriate for this call to take a Scrollbar pointer, and this
is also redundant with the other scrollPosition().

Even worse, looking at the implementations, scrollPosition(ScrollBar*) is
relative to scrollOrigin whereas scrollPosition(void) is not.  FYI, scrollOrigin
expresses the top-left origin of the initial containing block.  Because RTL
pages initialize scrolled to the right, scrollOrigin().x() can be positive and
minimumScrollPosition().x() can be negative on RTL pages (but on non-RTL pages,
it will always be zero).

It looks like the only caller is in Scrollbar.cpp.  So please delete this method
and add a private method in Scrollbar.cpp:

int Scrollbar::currentPos() {
    if (!m_scrollableArea)
        return 0;
    if (m_orientation == HorizontalScrollbar) {
        m_scrollableArea->scrollPosition().x() +
m_scrollableArea.scrollOrigin().x();
    } else if (m_orientation == VerticalScrollbar) {
        m_scrollableArea->scrollPosition().y() +
m_scrollableArea.scrollOrigin().y();
    }
    return 0;
}

[bokan, 2013/06/19 23:50:58]

Done (there's an existing currentPos() accessor for m_currentPos, I called the
new method scrollableAreaCurrentPos()). 

Question about scroll origin: If the page is RTL, does that mean that
scrollOffsets are negative and maximumScrollPosition is 0?

[aelias_OOO_until_Jul13, 2013/06/20 00:04:14]

Not quite; it means maximumScrollPosition.x() == viewportWidth and
minimumScrollPosition.x() == -(contentsWidth - viewportWidth).

[aelias_OOO_until_Jul13, 2013/06/20 00:09:40]

Err, actually what you said was correct, since we are talking about maximum
scroll position; I meant the right side of the scrollable bounds is
viewportWidth.

     virtual void invalidateScrollbar(Scrollbar*, const IntRect&);
     virtual bool isScrollCornerVisible() const = 0;
     virtual IntRect scrollCornerRect() const = 0;
     virtual void invalidateScrollCorner(const IntRect&);
     virtual void getTickmarks(Vector<IntRect>&) const { }
 
     // Convert points and rects between the scrollbar and its containing view.
     // The client needs to implement these in order to be aware of layout effects
     // like CSS transforms.
     virtual IntRect convertFromScrollbarToContainingView(const Scrollbar* scrollbar, const IntRect& scrollbarRect) const
     {
         return scrollbar->Widget::convertToContainingView(scrollbarRect);
     }
     virtual IntRect convertFromContainingViewToScrollbar(const Scrollbar* scrollbar, const IntRect& parentRect) const
     {
         return scrollbar->Widget::convertFromContainingView(parentRect);
     }
     virtual IntPoint convertFromScrollbarToContainingView(const Scrollbar* scrollbar, const IntPoint& scrollbarPoint) const
     {
         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 userInputScrollable(ScrollbarOrientation) 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:
+

[aelias_OOO_until_Jul13, 2013/06/19 22:25:12]

nit: accidental newline

[bokan, 2013/06/19 23:50:58]

Done.

     ScrollableArea();
     virtual ~ScrollableArea();
 
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }
 
     virtual void invalidateScrollbarRect(Scrollbar*, const IntRect&) = 0;
     virtual void invalidateScrollCornerRect(const IntRect&) = 0;
 
     friend class ScrollingCoordinator;
     virtual GraphicsLayer* layerForScrolling() const { return 0; }
     virtual GraphicsLayer* layerForHorizontalScrollbar() const { return 0; }
     virtual GraphicsLayer* layerForVerticalScrollbar() const { return 0; }
     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&);
-    
+
     // 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;
 
+    virtual int lineStep(ScrollbarOrientation) const;
+    virtual int pageStep(ScrollbarOrientation) const;
+    virtual int documentStep(ScrollbarOrientation) const;
+    virtual float pixelStep(ScrollbarOrientation) const;
+
     mutable OwnPtr<ScrollAnimator> m_scrollAnimator;
     unsigned m_constrainsScrollingToContentEdge : 1;
 
     unsigned m_inLiveResize : 1;
 
     unsigned m_verticalScrollElasticity : 2; // ScrollElasticity
     unsigned m_horizontalScrollElasticity : 2; // ScrollElasticity
 
     unsigned m_scrollbarOverlayStyle : 2; // ScrollbarOverlayStyle
 
     unsigned m_scrollOriginChanged : 1;
 
     // There are 8 possible combinations of writing mode and direction. Scroll origin will be non-zero in the x or y axis
     // if there is any reversed direction or writing-mode. The combinations are:
     // writing-mode / direction     scrollOrigin.x() set    scrollOrigin.y() set
     // horizontal-tb / ltr          NO                      NO
     // horizontal-tb / rtl          YES                     NO
     // horizontal-bt / ltr          NO                      YES
     // horizontal-bt / rtl          YES                     YES
     // 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