Refactor ScrollableArea::setScrollPosition.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 32054fb3d7af13061465e7b559e9ec93b3931750..3f89d3f1e5672e1be5a266bccba3a61b653a58b0 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -114,9 +114,10 @@ PaintLayerScrollableArea::PaintLayerScrollableArea(PaintLayer& layer)
     // We save and restore only the scrollOffset as the other scroll values are recalculated.
     Element* element = toElement(node);
     m_scrollOffset = element->savedLayerScrollOffset();
-    if (!m_scrollOffset.isZero())
+    if (!m_scrollOffset.isZero()) {
       scrollAnimator().setCurrentPosition(
           FloatPoint(m_scrollOffset.width(), m_scrollOffset.height()));
+    }
     element->setSavedLayerScrollOffset(IntSize());
   }
   updateResizerAreaSet();
@@ -148,9 +149,10 @@ void PaintLayerScrollableArea::dispose() {
   if (!box().documentBeingDestroyed()) {
     Node* node = box().node();
     // FIXME: Make setSavedLayerScrollOffset take DoubleSize. crbug.com/414283.
-    if (node && node->isElementNode())
+    if (node && node->isElementNode()) {
       toElement(node)->setSavedLayerScrollOffset(
           flooredIntSize(m_scrollOffset));
+    }
   }
 
   if (LocalFrame* frame = box().frame()) {
@@ -498,8 +500,9 @@ IntRect PaintLayerScrollableArea::visibleContentRect(
             : 0;
   }
 
+  // TODO(szager): Handle fractional scroll offsets correctly.
   return IntRect(
-      IntPoint(scrollXOffset(), scrollYOffset()),
+      IntPoint(flooredIntSize(adjustedScrollOffset())),
       IntSize(max(0, layer()->size().width() - verticalScrollbarWidth),
               max(0, layer()->size().height() - horizontalScrollbarHeight)));
 }
@@ -635,17 +638,11 @@ void PaintLayerScrollableArea::updateScrollDimensions() {
   updateScrollOrigin();
 }
 
-void PaintLayerScrollableArea::scrollToPosition(
-    const DoublePoint& scrollPosition,
-    ScrollOffsetClamping clamp,
-    ScrollBehavior scrollBehavior,
+void PaintLayerScrollableArea::setScrollPositionUnconditionally(
+    const DoublePoint& position,
     ScrollType scrollType) {
-  DoublePoint newScrollPosition = clamp == ScrollOffsetClamped
-                                      ? clampScrollPosition(scrollPosition)
-                                      : scrollPosition;
-  if (newScrollPosition != scrollPositionDouble())
-    ScrollableArea::setScrollPosition(newScrollPosition, scrollType,
-                                      scrollBehavior);
+  cancelScrollAnimation();

[skobes, 2016/10/04 22:25:26]

Is this what happened before? (cancelling the animation)

[szager1, 2016/10/04 22:54:13]

Yes, it's the same thing that
ProgrammaticScrollAnimator::scrollToOffsetWithoutAnimation() does.

+  scrollPositionChanged(position, scrollType);
 }
 
 void PaintLayerScrollableArea::updateAfterLayout() {
@@ -806,9 +803,13 @@ void PaintLayerScrollableArea::clampScrollPositionsAfterLayout() {
   if (shouldPerformScrollAnchoring())
     m_scrollAnchor.restore();
 
-  DoublePoint clamped = clampScrollPosition(scrollPositionDouble());
-  if (clamped != scrollPositionDouble() || scrollOriginChanged())
-    ScrollableArea::setScrollPosition(clamped, ProgrammaticScroll);
+  if (scrollOriginChanged()) {
+    setScrollPositionUnconditionally(
+        clampScrollPosition(scrollPositionDouble()));
+  } else {
+    ScrollableArea::setScrollPosition(scrollPositionDouble(),

[bokan, 2016/10/04 22:17:25]

Why not just ScrollableArea::setScrollPosition

[szager1, 2016/10/04 22:54:14]

I don't understand the question; maybe you're asking why
ScrollableArea::setScrollPosition() instead of just setScrollPosition()?  If so,
the answer is: PLSA::setScrollPosition takes an adjusted scroll position
argument, SA::setScrollPosition takes an un-adjusted scroll position argument.

Which is really just awful, hence my eagerness to rename these suckers.

[bokan, 2016/10/04 22:56:51]

What I meant was, since ScrollableArea::setScrollPosition clamps, why the
setScrollPositionUnconditionally to the clamped position above? Couldn't we just
remove the branch and call SA::SetScrollPosition(scrollPositionDouble()) in all
cases?

[szager1, 2016/10/04 23:37:37]

No, this is necessary for the case where the scroll position hasn't changed, but
the scroll origin has changed.  With this patch,
ScrollableArea::setScrollPosition will early return if the scroll position
hasn't changed, but when the scroll origin changes, we need all of the
post-scroll-position-update code to run (i.e., everything in
SA::scrollOffsetChanged(), which calls into PLSA::updateScrollOffset()).

[bokan, 2016/10/04 23:38:38]

Got it, thanks.

+                                      ProgrammaticScroll);
+  }
 
   setNeedsScrollPositionClamp(false);
   resetScrollOriginChanged();
@@ -1563,17 +1564,17 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
 
   DoublePoint clampedScrollPosition = clampScrollPosition(
       scrollPositionDouble() + roundedIntSize(r.location()));
-  if (clampedScrollPosition == scrollPositionDouble())
+  if (clampedScrollPosition == scrollPositionDouble()) {
     return LayoutRect(
         box()
             .localToAbsoluteQuad(FloatQuad(FloatRect(intersection(
                                      layerBounds, localExposeRect))),
                                  UseTransforms)
             .boundingBox());
+  }
 
   DoubleSize oldScrollOffset = adjustedScrollOffset();
-  scrollToPosition(clampedScrollPosition, ScrollOffsetUnclamped,
-                   ScrollBehaviorInstant, scrollType);
+  setScrollPosition(clampedScrollPosition, scrollType, ScrollBehaviorInstant);
   DoubleSize scrollOffsetDifference = adjustedScrollOffset() - oldScrollOffset;
   localExposeRect.move(-LayoutSize(scrollOffsetDifference));
   return LayoutRect(