Preserve fractional scroll offset for JS scrolling API

Source/core/rendering/RenderLayerScrollableArea.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 73 matching lines @@
     virtual void invalidateScrollCornerRect(const IntRect&) override;
     virtual bool isActive() const override;
     virtual bool isScrollCornerVisible() const override;
     virtual IntRect scrollCornerRect() const override;
     virtual IntRect convertFromScrollbarToContainingView(const Scrollbar*, const IntRect&) const override;
     virtual IntRect convertFromContainingViewToScrollbar(const Scrollbar*, const IntRect&) const override;
     virtual IntPoint convertFromScrollbarToContainingView(const Scrollbar*, const IntPoint&) const override;
     virtual IntPoint convertFromContainingViewToScrollbar(const Scrollbar*, const IntPoint&) const override;
     virtual int scrollSize(ScrollbarOrientation) const override;
     virtual void setScrollOffset(const IntPoint&) override;
+    virtual void setScrollOffset(const DoublePoint&) override;
     virtual IntPoint scrollPosition() const override;
+    virtual DoublePoint scrollPositionDouble() const override;
     virtual IntPoint minimumScrollPosition() const override;
     virtual IntPoint maximumScrollPosition() const override;
     virtual IntRect visibleContentRect(IncludeScrollbarsInRect) const override;
     virtual int visibleHeight() const override;
     virtual int visibleWidth() const override;
     virtual IntSize contentsSize() const override;
     virtual IntSize overhangAmount() const override;
     virtual IntPoint lastKnownMousePosition() const override;
     virtual bool shouldSuspendScrollAnimations() const override;
     virtual bool scrollbarsCanBeActive() const override;
     virtual IntRect scrollableAreaBoundingBox() const override;
     virtual bool userInputScrollable(ScrollbarOrientation) const override;
     virtual bool shouldPlaceVerticalScrollbarOnLeft() const override;
     virtual int pageStep(ScrollbarOrientation) const override;
 
-    int scrollXOffset() const { return m_scrollOffset.width() + scrollOrigin().x(); }
-    int scrollYOffset() const { return m_scrollOffset.height() + scrollOrigin().y(); }
+    double scrollXOffset() const { return m_scrollOffset.width() + scrollOrigin().x(); }
+    double scrollYOffset() const { return m_scrollOffset.height() + scrollOrigin().y(); }
 
-    IntSize scrollOffset() const { return m_scrollOffset; }
+    DoubleSize scrollOffset() const { return m_scrollOffset; }
 
     // FIXME: We shouldn't allow access to m_overflowRect outside this class.
     LayoutRect overflowRect() const { return m_overflowRect; }
 
-    void scrollToOffset(const IntSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped);
-    void scrollToXOffset(int x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(IntSize(x, scrollYOffset()), clamp); }
-    void scrollToYOffset(int y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(IntSize(scrollXOffset(), y), clamp); }
+    void scrollToOffset(const DoubleSize& scrollOffset, ScrollOffsetClamping = ScrollOffsetUnclamped);
+    void scrollToXOffset(double x, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(DoubleSize(x, scrollYOffset()), clamp); }
+    void scrollToYOffset(double y, ScrollOffsetClamping clamp = ScrollOffsetUnclamped) { scrollToOffset(DoubleSize(scrollXOffset(), y), clamp); }
 
     void updateAfterLayout();
     void updateAfterStyleChange(const RenderStyle*);
     void updateAfterOverflowRecalc();
 
     virtual bool updateAfterCompositingChange() override;
 
     bool hasScrollbar() const { return m_hBar || m_vBar; }
 
     // FIXME: This should be removed.
@@ skipping 11 matching lines @@
     }
 
     LayoutUnit scrollWidth() const;
     LayoutUnit scrollHeight() const;
     int pixelSnappedScrollWidth() const;
     int pixelSnappedScrollHeight() const;
 
     int verticalScrollbarWidth(OverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize) const;
     int horizontalScrollbarHeight(OverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize) const;
 
-    IntSize adjustedScrollOffset() const { return IntSize(scrollXOffset(), scrollYOffset()); }
+    DoubleSize adjustedScrollOffset() const { return DoubleSize(scrollXOffset(), scrollYOffset()); }
 
     void paintResizer(GraphicsContext*, const IntPoint& paintOffset, const IntRect& damageRect);
     void paintOverflowControls(GraphicsContext*, const IntPoint& paintOffset, const IntRect& damageRect, bool paintingOverlayControls);
     void paintScrollCorner(GraphicsContext*, const IntPoint&, const IntRect& damageRect);
 
     void positionOverflowControls(const IntSize& offsetFromRoot);
 
     // isPointInResizeControl() is used for testing if a pointer/touch position is in the resize control
     // area.
     bool isPointInResizeControl(const IntPoint& absolutePoint, ResizerHitTestType) const;
@@ skipping 20 matching lines @@
     RenderLayer* topmostScrollChild() const { ASSERT(!m_nextTopmostScrollChild); return m_topmostScrollChild; }
 
 private:
     bool hasHorizontalOverflow() const;
     bool hasVerticalOverflow() const;
     bool hasScrollableHorizontalOverflow() const;
     bool hasScrollableVerticalOverflow() const;
 
     void computeScrollDimensions();
 
-    IntSize clampScrollOffset(const IntSize&) const;
+    DoubleSize clampScrollOffset(const DoubleSize&) const;
 
     IntRect rectForHorizontalScrollbar(const IntRect& borderBoxRect) const;
     IntRect rectForVerticalScrollbar(const IntRect& borderBoxRect) const;
     LayoutUnit verticalScrollbarStart(int minX, int maxX) const;
     LayoutUnit horizontalScrollbarStart(int minX) const;
     IntSize scrollbarOffset(const Scrollbar*) const;
 
     PassRefPtr<Scrollbar> createScrollbar(ScrollbarOrientation);
     void destroyScrollbar(ScrollbarOrientation);
 
@@ skipping 29 matching lines @@
     RenderLayer* m_topmostScrollChild;
 
     // FIXME: once cc can handle composited scrolling with clip paths, we will
     // no longer need this bit.
     unsigned m_needsCompositedScrolling : 1;
 
     // The width/height of our scrolled area.
     LayoutRect m_overflowRect;
 
     // This is the (scroll) offset from scrollOrigin().
-    IntSize m_scrollOffset;
+    DoubleSize m_scrollOffset;
 
     IntPoint m_cachedOverlayScrollbarOffset;
 
     // For areas with overflow, we have a pair of scrollbars.
     RefPtr<Scrollbar> m_hBar;
     RefPtr<Scrollbar> m_vBar;
 
     // Renderers to hold our custom scroll corner.
     RawPtrWillBePersistent<RenderScrollbarPart> m_scrollCorner;
 
     // Renderers to hold our custom resizer.
     RawPtrWillBePersistent<RenderScrollbarPart> m_resizer;
 };
 
 } // namespace blink
 
 #endif // RenderLayerScrollableArea_h