Port fix for VSP floating-point hang from 4.8 (#4979)

src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/VirtualizingStackPanel.cs

@@ -931,16 +931,19 @@ private void OnAnchorOperation(bool isAnchorOperationPending)
  // situations where the viewport size has changed)
  if (!success)
  {
+ double computedOffset, maxOffset;
  if (isHorizontal)
  {
- success = DoubleUtil.GreaterThanOrClose(_scrollData._computedOffset.X,
-  _scrollData._extent.Width - _scrollData._viewport.Width);
+ computedOffset = _scrollData._computedOffset.X;
+ maxOffset = _scrollData._extent.Width - _scrollData._viewport.Width;
  }
  else
  {
- success = DoubleUtil.GreaterThanOrClose(_scrollData._computedOffset.Y,
-  _scrollData._extent.Height - _scrollData._viewport.Height);
+ computedOffset = _scrollData._computedOffset.Y;
+ maxOffset = _scrollData._extent.Height - _scrollData._viewport.Height;
  }
+ success = LayoutDoubleUtil.LessThan(maxOffset, computedOffset) ||
+ LayoutDoubleUtil.AreClose(maxOffset, computedOffset);
  }
  }
  }
@@ -973,21 +976,22 @@ private void OnAnchorOperation(bool isAnchorOperationPending)
  else
  {
  bool remeasure = false;
- double actualOffset, expectedOffset;
+ double actualOffset, expectedOffset, maxOffset;
 
  if (isHorizontal)
  {
  _scrollData._computedOffset.X = prevFirstContainerOffset - prevFirstContainerOffsetFromViewport;
 
  actualOffset = _scrollData._computedOffset.X + actualDistanceBetweenViewports;
  expectedOffset = _scrollData._computedOffset.X + _scrollData._expectedDistanceBetweenViewports;
+ maxOffset = _scrollData._extent.Width - _scrollData._viewport.Width;
 
- if (DoubleUtil.LessThan(expectedOffset, 0) || DoubleUtil.GreaterThan(expectedOffset, _scrollData._extent.Width - _scrollData._viewport.Width))
+ if (LayoutDoubleUtil.LessThan(expectedOffset, 0) || LayoutDoubleUtil.LessThan(maxOffset, expectedOffset))
  {
  // the condition can fail due to estimated sizes in subtrees that contribute
  // to FindScrollOffset(_scrollData._firstContainerInViewport) but not to
  // _scrollData._extent. If that happens, remeasure.
- if (DoubleUtil.AreClose(actualOffset, 0) || DoubleUtil.AreClose(actualOffset, _scrollData._extent.Width - _scrollData._viewport.Width))
+ if (LayoutDoubleUtil.AreClose(actualOffset, 0) || LayoutDoubleUtil.AreClose(actualOffset, maxOffset))
  {
  _scrollData._computedOffset.X = actualOffset;
  _scrollData._offset.X = actualOffset;
@@ -1010,13 +1014,14 @@ private void OnAnchorOperation(bool isAnchorOperationPending)
 
  actualOffset = _scrollData._computedOffset.Y + actualDistanceBetweenViewports;
  expectedOffset = _scrollData._computedOffset.Y + _scrollData._expectedDistanceBetweenViewports;
+ maxOffset = _scrollData._extent.Height - _scrollData._viewport.Height;
 
- if (DoubleUtil.LessThan(expectedOffset, 0) || DoubleUtil.GreaterThan(expectedOffset, _scrollData._extent.Height - _scrollData._viewport.Height))
+ if (LayoutDoubleUtil.LessThan(expectedOffset, 0) || LayoutDoubleUtil.LessThan(maxOffset, expectedOffset))
  {
  // the condition can fail due to estimated sizes in subtrees that contribute
  // to FindScrollOffset(_scrollData._firstContainerInViewport) but not to
  // _scrollData._extent. If that happens, remeasure.
- if (DoubleUtil.AreClose(actualOffset, 0) || DoubleUtil.AreClose(actualOffset, _scrollData._extent.Height - _scrollData._viewport.Height))
+ if (LayoutDoubleUtil.AreClose(actualOffset, 0) || LayoutDoubleUtil.AreClose(actualOffset, maxOffset))
  {
  _scrollData._computedOffset.Y = actualOffset;
  _scrollData._offset.Y = actualOffset;
@@ -2824,11 +2829,11 @@ private Size MeasureOverrideImpl(Size constraint,
  ref scrollGeneration);
 
  if (ItemsChangedDuringMeasure)
-  {
-  // if the Items collection changed, our state is now invalid. Start over.
-  remeasure = true;
-  goto EscapeMeasure;
-  }
+ {
+ // if the Items collection changed, our state is now invalid. Start over.
+ remeasure = true;
+ goto EscapeMeasure;
+ }
  }
  }
 
@@ -2873,11 +2878,11 @@ private Size MeasureOverrideImpl(Size constraint,
  ref scrollGeneration);
 
  if (ItemsChangedDuringMeasure)
-  {
-  // if the Items collection changed, our state is now invalid. Start over.
-  remeasure = true;
-  goto EscapeMeasure;
-  }
+ {
+ // if the Items collection changed, our state is now invalid. Start over.
+ remeasure = true;
+ goto EscapeMeasure;
+ }
  }
  }
 
@@ -12321,6 +12326,12 @@ private void IdentifyTrace(ItemsControl ic, VirtualizingStackPanel vsp)
  "ScrollUnit:", VirtualizingPanel.GetScrollUnit(ic),
  "CacheLen:", VirtualizingPanel.GetCacheLength(ic), VirtualizingPanel.GetCacheLengthUnit(ic));
 
+ DpiScale dpiScale = vsp.GetDpi();
+ AddTrace(null, ScrollTraceOp.ID, _nullInfo,
+ "DPIScale:", dpiScale.DpiScaleX, dpiScale.DpiScaleY,
+ "UseLayoutRounding:", vsp.UseLayoutRounding,
+ "Rounding Quantum:", 1.0/dpiScale.DpiScaleY);
+
  AddTrace(null, ScrollTraceOp.ID, _nullInfo,
  "CanContentScroll:", ScrollViewer.GetCanContentScroll(ic),
  "IsDeferredScrolling:", ScrollViewer.GetIsDeferredScrollingEnabled(ic),