Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.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@gmail.com>
@@ skipping 193 matching lines @@
   visitor->trace(m_scrollAnchor);
   ScrollableArea::trace(visitor);
 }
 
 HostWindow* PaintLayerScrollableArea::getHostWindow() const {
   if (Page* page = box().frame()->page())
     return &page->chromeClient();
   return nullptr;
 }
 
+ProgrammaticScrollCoordinator*
+PaintLayerScrollableArea::getProgrammaticScrollCoordinator() const {
+  if (Page* page = box().frame()->page())
+    return page->scrollingCoordinator()->programmaticScrollCoordinator();
+  return nullptr;
+}
+
 GraphicsLayer* PaintLayerScrollableArea::layerForScrolling() const {
   return layer()->hasCompositedLayerMapping()
              ? layer()->compositedLayerMapping()->scrollingContentsLayer()
              : 0;
 }
 
 GraphicsLayer* PaintLayerScrollableArea::layerForHorizontalScrollbar() const {
   // See crbug.com/343132.
   DisableCompositingQueryAsserts disabler;
 
@@ skipping 1399 matching lines @@
   document.updateStyleAndLayout();
 
   // FIXME (Radar 4118564): We should also autoscroll the window as necessary to
   // keep the point under the cursor in view.
 }
 
 LayoutRect PaintLayerScrollableArea::scrollIntoView(
     const LayoutRect& rect,
     const ScrollAlignment& alignX,
     const ScrollAlignment& alignY,
-    ScrollType scrollType) {
+    ScrollType scrollType,
+    ScrollBehavior scrollBehavior) {
   LayoutRect localExposeRect(
       box()
           .absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms)
           .boundingBox());
   localExposeRect.move(-box().borderLeft(), -box().borderTop());
   LayoutRect layerBounds(LayoutPoint(),
                          LayoutSize(box().clientWidth(), box().clientHeight()));
   LayoutRect r = ScrollAlignment::getRectToExpose(layerBounds, localExposeRect,
                                                   alignX, alignY);
 
   ScrollOffset oldScrollOffset = getScrollOffset();
   ScrollOffset newScrollOffset(clampScrollOffset(roundedIntSize(
       toScrollOffset(FloatPoint(r.location()) + oldScrollOffset))));
-  setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  if (scrollType == ProgrammaticScroll &&
+      scrollBehavior == ScrollBehaviorSmooth) {
+    getProgrammaticScrollCoordinator()->queueAnimation(this, newScrollOffset);

[bokan, 2017/02/02 22:51:50]

Hmm, maybe I'm missing something obvious here, but why do we need this new
ProgrammaticScrollCoordinator rather than using the existing path for
Element::scrollTo that just calls setScrollOffset with smooth behavior? Is it
because scrollIntoView can cause coordinated scrolling between many boxes and we
need to a way to queue those up and play them back linearly?

[sunyunjia, 2017/02/10 23:25:20]

Right! See here:
https://docs.google.com/a/chromium.org/document/d/1EeGvVnlHjIVVKwU-Y-A4uYtB-B...

[bokan, 2017/02/21 21:33:00]

Got it. I think the name makes it sound like it's related to
ScrollingCoordinator which it isn't. I think SmoothScrollSequencer or something
similar might be better.

+  } else {
+    setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  }
   ScrollOffset scrollOffsetDifference = getScrollOffset() - oldScrollOffset;
   localExposeRect.move(-LayoutSize(scrollOffsetDifference));
 
   LayoutRect intersect =
       localToAbsolute(box(), intersection(layerBounds, localExposeRect));
   if (intersect.isEmpty() && !layerBounds.isEmpty() &&
       !localExposeRect.isEmpty()) {
     return localToAbsolute(box(), localExposeRect);
   }
   return intersect;
@@ skipping 459 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink