Preserve fractional scroll offset for JS scrolling API

Source/core/rendering/RenderLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 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 107 matching lines @@
         }
     }
 
     if (box().frame() && box().frame()->page()) {
         if (ScrollingCoordinator* scrollingCoordinator = box().frame()->page()->scrollingCoordinator())
             scrollingCoordinator->willDestroyScrollableArea(this);
     }
 
     if (!box().documentBeingDestroyed()) {
         Node* node = box().node();
+        // FIXME: Make setSavedLayerScrollOffset take DoubleSize. crbug.com/414283.
         if (node && node->isElementNode())
-            toElement(node)->setSavedLayerScrollOffset(m_scrollOffset);
+            toElement(node)->setSavedLayerScrollOffset(flooredIntSize(m_scrollOffset));
     }
 
     if (LocalFrame* frame = box().frame()) {
         if (FrameView* frameView = frame->view())
             frameView->removeResizerArea(box());
     }
 
     destroyScrollbar(HorizontalScrollbar);
     destroyScrollbar(VerticalScrollbar);
 
@@ skipping 197 matching lines @@
 }
 
 int RenderLayerScrollableArea::scrollSize(ScrollbarOrientation orientation) const
 {
     IntSize scrollDimensions = maximumScrollPosition() - minimumScrollPosition();
     return (orientation == HorizontalScrollbar) ? scrollDimensions.width() : scrollDimensions.height();
 }
 
 void RenderLayerScrollableArea::setScrollOffset(const IntPoint& newScrollOffset)
 {
+    setScrollOffset(DoublePoint(newScrollOffset));
+}
+
+void RenderLayerScrollableArea::setScrollOffset(const DoublePoint& newScrollOffset)
+{
     if (!box().isMarquee()) {
         // Ensure that the dimensions will be computed if they need to be (for overflow:hidden blocks).
         if (m_scrollDimensionsDirty)
             computeScrollDimensions();
     }
 
-    if (scrollOffset() == toIntSize(newScrollOffset))
+    if (scrollOffset() == toDoubleSize(newScrollOffset))
         return;
 
-    m_scrollOffset = toIntSize(newScrollOffset);
+    m_scrollOffset = toDoubleSize(newScrollOffset);
 
     LocalFrame* frame = box().frame();
     ASSERT(frame);
 
     RefPtr<FrameView> frameView = box().frameView();
 
     TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "ScrollLayer", "data", InspectorScrollLayerEvent::data(&box()));
     // FIXME(361045): remove InspectorInstrumentation calls once DevTools Timeline migrates to tracing.
     InspectorInstrumentation::willScrollLayer(&box());
 
@@ skipping 43 matching lines @@
         box().node()->document().enqueueScrollEventForNode(box().node());
 
     if (AXObjectCache* cache = box().document().existingAXObjectCache())
         cache->handleScrollPositionChanged(&box());
 
     InspectorInstrumentation::didScrollLayer(&box());
 }
 
 IntPoint RenderLayerScrollableArea::scrollPosition() const
 {
-    return IntPoint(m_scrollOffset);
+    return IntPoint(flooredIntSize(m_scrollOffset));
+}
+
+DoublePoint RenderLayerScrollableArea::scrollPositionDouble() const
+{
+    return DoublePoint(m_scrollOffset);
 }
 
 IntPoint RenderLayerScrollableArea::minimumScrollPosition() const
 {
     return -scrollOrigin();
 }
 
 IntPoint RenderLayerScrollableArea::maximumScrollPosition() const
 {
     if (!box().hasOverflowClip())
@@ skipping 124 matching lines @@
     m_scrollDimensionsDirty = false;
 
     m_overflowRect = box().layoutOverflowRect();
     box().flipForWritingMode(m_overflowRect);
 
     int scrollableLeftOverflow = m_overflowRect.x() - box().borderLeft() - (box().style()->shouldPlaceBlockDirectionScrollbarOnLogicalLeft() ? box().verticalScrollbarWidth() : 0);
     int scrollableTopOverflow = m_overflowRect.y() - box().borderTop();
     setScrollOrigin(IntPoint(-scrollableLeftOverflow, -scrollableTopOverflow));
 }
 
-void RenderLayerScrollableArea::scrollToOffset(const IntSize& scrollOffset, ScrollOffsetClamping clamp)
+void RenderLayerScrollableArea::scrollToOffset(const DoubleSize& scrollOffset, ScrollOffsetClamping clamp)
 {
-    IntSize newScrollOffset = clamp == ScrollOffsetClamped ? clampScrollOffset(scrollOffset) : scrollOffset;
-    if (newScrollOffset != adjustedScrollOffset())
-        scrollToOffsetWithoutAnimation(-scrollOrigin() + newScrollOffset);
+    DoubleSize newScrollOffset = clamp == ScrollOffsetClamped ? clampScrollOffset(scrollOffset) : scrollOffset;
+    if (newScrollOffset != adjustedScrollOffset()) {
+        DoublePoint origin(scrollOrigin());
+        // FIXME: Make scrollToOffsetWithoutAnimation take DoublePoint. crbug.com/414283.
+        scrollToOffsetWithoutAnimation(toFloatPoint(-origin + newScrollOffset));
+    }
 }
 
 void RenderLayerScrollableArea::updateAfterLayout()
 {
     m_scrollDimensionsDirty = true;
-    IntSize originalScrollOffset = adjustedScrollOffset();
+    DoubleSize originalScrollOffset = adjustedScrollOffset();
 
     computeScrollDimensions();
 
     if (!box().isMarquee()) {
         // Layout may cause us to be at an invalid scroll position. In this case we need
         // to pull our scroll offsets back to the max (or push them up to the min).
-        IntSize clampedScrollOffset = clampScrollOffset(adjustedScrollOffset());
+        DoubleSize clampedScrollOffset = clampScrollOffset(adjustedScrollOffset());
         if (clampedScrollOffset != adjustedScrollOffset())
             scrollToOffset(clampedScrollOffset);
     }
 
-    if (originalScrollOffset != adjustedScrollOffset())
-        scrollToOffsetWithoutAnimation(-scrollOrigin() + adjustedScrollOffset());
+    if (originalScrollOffset != adjustedScrollOffset()) {
+        DoublePoint origin(scrollOrigin());
+        scrollToOffsetWithoutAnimation(toFloatPoint(-origin + adjustedScrollOffset()));
+    }
 
     bool hasHorizontalOverflow = this->hasHorizontalOverflow();
     bool hasVerticalOverflow = this->hasVerticalOverflow();
 
     {
         // Hits in compositing/overflow/automatically-opt-into-composited-scrolling-after-style-change.html.
         DisableCompositingQueryAsserts disabler;
 
         // overflow:scroll should just enable/disable.
         if (box().style()->overflowX() == OSCROLL)
@@ skipping 174 matching lines @@
     }
 
     bool hasHorizontalOverflow = this->hasHorizontalOverflow();
     bool hasVerticalOverflow = this->hasVerticalOverflow();
     bool autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
     bool autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
     if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)
         box().setNeedsLayoutAndFullPaintInvalidation();
 }
 
-IntSize RenderLayerScrollableArea::clampScrollOffset(const IntSize& scrollOffset) const
+DoubleSize RenderLayerScrollableArea::clampScrollOffset(const DoubleSize& scrollOffset) const
 {
     int maxX = scrollWidth() - box().pixelSnappedClientWidth();
     int maxY = scrollHeight() - box().pixelSnappedClientHeight();
 
-    int x = std::max(std::min(scrollOffset.width(), maxX), 0);
-    int y = std::max(std::min(scrollOffset.height(), maxY), 0);
-    return IntSize(x, y);
+    double x = std::max(std::min(scrollOffset.width(), static_cast<double>(maxX)), 0.0);
+    double y = std::max(std::min(scrollOffset.height(), static_cast<double>(maxY)), 0.0);
+    return DoubleSize(x, y);
 }
 
 IntRect RenderLayerScrollableArea::rectForHorizontalScrollbar(const IntRect& borderBoxRect) const
 {
     if (!m_hBar)
         return IntRect();
 
     const IntRect& scrollCorner = scrollCornerRect();
 
     return IntRect(horizontalScrollbarStart(borderBoxRect.x()),
@@ skipping 582 matching lines @@
 
     // FIXME (Radar 4118564): We should also autoscroll the window as necessary to keep the point under the cursor in view.
 }
 
 LayoutRect RenderLayerScrollableArea::exposeRect(const LayoutRect& rect, const ScrollAlignment& alignX, const ScrollAlignment& alignY)
 {
     LayoutRect localExposeRect(box().absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms).boundingBox());
     LayoutRect layerBounds(0, 0, box().clientWidth(), box().clientHeight());
     LayoutRect r = ScrollAlignment::getRectToExpose(layerBounds, localExposeRect, alignX, alignY);
 
-    IntSize clampedScrollOffset = clampScrollOffset(adjustedScrollOffset() + toIntSize(roundedIntRect(r).location()));
+    DoubleSize clampedScrollOffset = clampScrollOffset(adjustedScrollOffset() + toIntSize(roundedIntRect(r).location()));
     if (clampedScrollOffset == adjustedScrollOffset())
         return rect;
 
-    IntSize oldScrollOffset = adjustedScrollOffset();
+    DoubleSize oldScrollOffset = adjustedScrollOffset();
     scrollToOffset(clampedScrollOffset);
-    IntSize scrollOffsetDifference = adjustedScrollOffset() - oldScrollOffset;
-    localExposeRect.move(-scrollOffsetDifference);
+    DoubleSize scrollOffsetDifference = adjustedScrollOffset() - oldScrollOffset;
+    localExposeRect.move(-LayoutSize(scrollOffsetDifference));
     return LayoutRect(box().localToAbsoluteQuad(FloatQuad(FloatRect(localExposeRect)), UseTransforms).boundingBox());
 }
 
 void RenderLayerScrollableArea::updateScrollableAreaSet(bool hasOverflow)
 {
     LocalFrame* frame = box().frame();
     if (!frame)
         return;
 
     FrameView* frameView = frame->view();
@@ skipping 64 matching lines @@
 void RenderLayerScrollableArea::setTopmostScrollChild(RenderLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink