diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index b70e0bf77f..54645e461e 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -68,7 +68,7 @@ jobs:
     inputs:
       script: |
         brew update
-        brew install castxml
+        brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/8a004a91a7fcd3f6620d5b01b6541ff0a640ffba/Formula/castxml.rb
 
   - task: CmdLine@2
     displayName: 'Install Nuke'
diff --git a/packages/Avalonia/Avalonia.csproj b/packages/Avalonia/Avalonia.csproj
index 9f7593b702..2c5a09bee7 100644
--- a/packages/Avalonia/Avalonia.csproj
+++ b/packages/Avalonia/Avalonia.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-      <TargetFrameworks>netstandard2.0;net461;netcoreapp3.1</TargetFrameworks>
+      <TargetFrameworks>netstandard2.0;net461;netcoreapp2.0</TargetFrameworks>
       <PackageId>Avalonia</PackageId>
   </PropertyGroup>
 
@@ -20,8 +20,8 @@
                          Platform=$(Platform)" />
 
     <ItemGroup>
-      <_PackageFiles Include="$(DesignerHostAppPath)/Avalonia.Designer.HostApp/bin/$(Configuration)/netcoreapp3.1/Avalonia.Designer.HostApp.dll">
-        <PackagePath>tools/netcoreapp3.1/designer</PackagePath>
+      <_PackageFiles Include="$(DesignerHostAppPath)/Avalonia.Designer.HostApp/bin/$(Configuration)/netcoreapp2.0/Avalonia.Designer.HostApp.dll">
+        <PackagePath>tools/netcoreapp2.0/designer</PackagePath>
         <Visible>false</Visible>
         <BuildAction>None</BuildAction>
       </_PackageFiles>
diff --git a/packages/Avalonia/Avalonia.props b/packages/Avalonia/Avalonia.props
index 99d53c1e03..6f21971d3d 100644
--- a/packages/Avalonia/Avalonia.props
+++ b/packages/Avalonia/Avalonia.props
@@ -1,6 +1,6 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <AvaloniaPreviewerNetCoreToolPath>$(MSBuildThisFileDirectory)\..\tools\netcoreapp3.1\designer\Avalonia.Designer.HostApp.dll</AvaloniaPreviewerNetCoreToolPath>
+    <AvaloniaPreviewerNetCoreToolPath>$(MSBuildThisFileDirectory)\..\tools\netcoreapp2.0\designer\Avalonia.Designer.HostApp.dll</AvaloniaPreviewerNetCoreToolPath>
     <AvaloniaPreviewerNetFullToolPath>$(MSBuildThisFileDirectory)\..\tools\net461\designer\Avalonia.Designer.HostApp.exe</AvaloniaPreviewerNetFullToolPath>
     <AvaloniaBuildTasksLocation>$(MSBuildThisFileDirectory)\..\tools\netstandard2.0\Avalonia.Build.Tasks.dll</AvaloniaBuildTasksLocation>
     <AvaloniaUseExternalMSBuild>false</AvaloniaUseExternalMSBuild>
diff --git a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
index ba68b113e3..ba1921a185 100644
--- a/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
+++ b/samples/ControlCatalog/Pages/DialogsPage.xaml.cs
@@ -1,4 +1,7 @@
+using System;
 using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
 #pragma warning disable 4014
@@ -34,7 +37,9 @@ namespace ControlCatalog.Pages
                 new OpenFileDialog()
                 {
                     Title = "Open file",
-                    Filters = GetFilters()
+                    Filters = GetFilters(),
+                    // Almost guaranteed to exist
+                    InitialFileName = Assembly.GetEntryAssembly()?.GetModules().FirstOrDefault()?.FullyQualifiedName
                 }.ShowAsync(GetWindow());
             };
             this.FindControl<Button>("SaveFile").Click += delegate
diff --git a/scripts/ReplaceNugetCache.sh b/scripts/ReplaceNugetCache.sh
index e1c0487d60..7ac601571d 100755
--- a/scripts/ReplaceNugetCache.sh
+++ b/scripts/ReplaceNugetCache.sh
@@ -1,8 +1,8 @@
  #!/usr/bin/env bash
  
- cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp2.0/Avalonia**.dll ~/.nuget/packages/avalonia/$1/lib/netcoreapp2.0/
- cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp2.0/Avalonia**.dll ~/.nuget/packages/avalonia/$1/lib/netstandard2.0/
- cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp2.0/Avalonia**.dll ~/.nuget/packages/avalonia.skia/$1/lib/netstandard2.0/
- cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp2.0/Avalonia**.dll ~/.nuget/packages/avalonia.native/$1/lib/netstandard2.0/
+ cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp3.1/Avalonia**.dll ~/.nuget/packages/avalonia/$1/lib/netcoreapp3.1/
+ cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp3.1/Avalonia**.dll ~/.nuget/packages/avalonia/$1/lib/netstandard2.0/
+ cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp3.1/Avalonia**.dll ~/.nuget/packages/avalonia.skia/$1/lib/netstandard2.0/
+ cp ../samples/ControlCatalog.NetCore/bin/Debug/netcoreapp3.1/Avalonia**.dll ~/.nuget/packages/avalonia.native/$1/lib/netstandard2.0/
  
  
diff --git a/src/Avalonia.Controls/AutoCompleteBox.cs b/src/Avalonia.Controls/AutoCompleteBox.cs
index bf177d64cd..9bc7ba9e2f 100644
--- a/src/Avalonia.Controls/AutoCompleteBox.cs
+++ b/src/Avalonia.Controls/AutoCompleteBox.cs
@@ -1630,7 +1630,7 @@ namespace Avalonia.Controls
         /// </summary>
         /// <param name="sender">The source object.</param>
         /// <param name="e">The event data.</param>
-        private void DropDownPopup_Closed(object sender, EventArgs e)
+        private void DropDownPopup_Closed(object sender, PopupClosedEventArgs e)
         {
             // Force the drop down dependency property to be false.
             if (IsDropDownOpen)
@@ -1638,6 +1638,11 @@ namespace Avalonia.Controls
                 IsDropDownOpen = false;
             }
 
+            if (e.CloseEvent is PointerEventArgs pointerEvent)
+            {
+                pointerEvent.Handled = true;
+            }
+
             // Fire the DropDownClosed event
             if (_popupHasOpened)
             {
diff --git a/src/Avalonia.Controls/Calendar/DatePicker.cs b/src/Avalonia.Controls/Calendar/DatePicker.cs
index 07e42c64e4..b4e4ad1452 100644
--- a/src/Avalonia.Controls/Calendar/DatePicker.cs
+++ b/src/Avalonia.Controls/Calendar/DatePicker.cs
@@ -895,12 +895,17 @@ namespace Avalonia.Controls
                 _ignoreButtonClick = false;
             }
         }
-        private void PopUp_Closed(object sender, EventArgs e)
+        private void PopUp_Closed(object sender, PopupClosedEventArgs e)
         {
             IsDropDownOpen = false;
 
             if(!_isPopupClosing)
             {
+                if (e.CloseEvent is PointerEventArgs pointerEvent)
+                {
+                    pointerEvent.Handled = true;
+                }
+
                 _isPopupClosing = true;
                 Threading.Dispatcher.UIThread.InvokeAsync(() => _isPopupClosing = false);
             }
diff --git a/src/Avalonia.Controls/ComboBox.cs b/src/Avalonia.Controls/ComboBox.cs
index 4b7d931d80..1daa6a5630 100644
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@@ -242,11 +242,16 @@ namespace Avalonia.Controls
             }
         }
 
-        private void PopupClosed(object sender, EventArgs e)
+        private void PopupClosed(object sender, PopupClosedEventArgs e)
         {
             _subscriptionsOnOpen?.Dispose();
             _subscriptionsOnOpen = null;
 
+            if (e.CloseEvent is PointerEventArgs pointerEvent)
+            {
+                pointerEvent.Handled = true;
+            }
+
             if (CanFocus(this))
             {
                 Focus();
diff --git a/src/Avalonia.Controls/Primitives/Popup.cs b/src/Avalonia.Controls/Primitives/Popup.cs
index f069903e05..66f2153b6c 100644
--- a/src/Avalonia.Controls/Primitives/Popup.cs
+++ b/src/Avalonia.Controls/Primitives/Popup.cs
@@ -95,7 +95,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Raised when the popup closes.
         /// </summary>
-        public event EventHandler? Closed;
+        public event EventHandler<PopupClosedEventArgs>? Closed;
 
         /// <summary>
         /// Raised when the popup opens.
@@ -270,7 +270,7 @@ namespace Avalonia.Controls.Primitives
 
                 if (parentPopupRoot?.Parent is Popup popup)
                 {
-                    DeferCleanup(SubscribeToEventHandler<Popup, EventHandler>(popup, ParentClosed,
+                    DeferCleanup(SubscribeToEventHandler<Popup, EventHandler<PopupClosedEventArgs>>(popup, ParentClosed,
                         (x, handler) => x.Closed += handler,
                         (x, handler) => x.Closed -= handler));
                 }
@@ -306,28 +306,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Closes the popup.
         /// </summary>
-        public void Close()
-        {
-            if (_openState is null)
-            {
-                using (BeginIgnoringIsOpen())
-                {
-                    IsOpen = false;
-                }
-
-                return;
-            }
-
-            _openState.Dispose();
-            _openState = null;
-
-            using (BeginIgnoringIsOpen())
-            {
-                IsOpen = false;
-            }
-
-            Closed?.Invoke(this, EventArgs.Empty);
-        }
+        public void Close() => CloseCore(null);
 
         /// <summary>
         /// Measures the control.
@@ -389,22 +368,44 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        private void CloseCore(EventArgs? closeEvent)
+        {
+            if (_openState is null)
+            {
+                using (BeginIgnoringIsOpen())
+                {
+                    IsOpen = false;
+                }
+
+                return;
+            }
+
+            _openState.Dispose();
+            _openState = null;
+
+            using (BeginIgnoringIsOpen())
+            {
+                IsOpen = false;
+            }
+
+            Closed?.Invoke(this, new PopupClosedEventArgs(closeEvent));
+        }
+
         private void ListenForNonClientClick(RawInputEventArgs e)
         {
             var mouse = e as RawPointerEventArgs;
 
             if (!StaysOpen && mouse?.Type == RawPointerEventType.NonClientLeftButtonDown)
             {
-                Close();
+                CloseCore(e);
             }
         }
 
         private void PointerPressedOutside(object sender, PointerPressedEventArgs e)
         {
-            if (!StaysOpen && !IsChildOrThis((IVisual)e.Source))
+            if (!StaysOpen && e.Source is IVisual v && !IsChildOrThis(v))
             {
-                Close();
-                e.Handled = true;
+                CloseCore(e);
             }
         }
 
diff --git a/src/Avalonia.Controls/Primitives/PopupClosedEventArgs.cs b/src/Avalonia.Controls/Primitives/PopupClosedEventArgs.cs
new file mode 100644
index 0000000000..c51543438c
--- /dev/null
+++ b/src/Avalonia.Controls/Primitives/PopupClosedEventArgs.cs
@@ -0,0 +1,33 @@
+using System;
+using Avalonia.Interactivity;
+
+#nullable enable
+
+namespace Avalonia.Controls.Primitives
+{
+    /// <summary>
+    /// Holds data for the <see cref="Popup.Closed"/> event.
+    /// </summary>
+    public class PopupClosedEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PopupClosedEventArgs"/> class.
+        /// </summary>
+        /// <param name="closeEvent"></param>
+        public PopupClosedEventArgs(EventArgs? closeEvent)
+        {
+            CloseEvent = closeEvent;
+        }
+
+        /// <summary>
+        /// Gets the event that closed the popup, if any.
+        /// </summary>
+        /// <remarks>
+        /// If <see cref="Popup.StaysOpen"/> is false, then this property will hold details of the
+        /// interaction that caused the popup to close if the close was caused by e.g. a pointer press
+        /// outside the popup. It can be used to mark the event as handled if the event should not
+        /// be propagated.
+        /// </remarks>
+        public EventArgs? CloseEvent { get; }
+    }
+}
diff --git a/src/Avalonia.Controls/Primitives/PopupRoot.cs b/src/Avalonia.Controls/Primitives/PopupRoot.cs
index 4c84d32637..788fe03162 100644
--- a/src/Avalonia.Controls/Primitives/PopupRoot.cs
+++ b/src/Avalonia.Controls/Primitives/PopupRoot.cs
@@ -117,20 +117,41 @@ namespace Avalonia.Controls.Primitives
             });
         }
 
-        /// <summary>
-        /// Carries out the arrange pass of the window.
-        /// </summary>
-        /// <param name="finalSize">The final window size.</param>
-        /// <returns>The <paramref name="finalSize"/> parameter unchanged.</returns>
-        protected override Size ArrangeOverride(Size finalSize)
+        protected override Size MeasureOverride(Size availableSize)
+        {
+            var measured = base.MeasureOverride(availableSize);
+            var width = measured.Width;
+            var height = measured.Height;
+            var widthCache = Width;
+            var heightCache = Height;
+
+            if (!double.IsNaN(widthCache))
+            {
+                width = widthCache;
+            }
+
+            width = Math.Min(width, MaxWidth);
+            width = Math.Max(width, MinWidth);
+
+            if (!double.IsNaN(heightCache))
+            {
+                height = heightCache;
+            }
+
+            height = Math.Min(height, MaxHeight);
+            height = Math.Max(height, MinHeight);
+
+            return new Size(width, height);
+        }
+
+        protected override sealed Size ArrangeSetBounds(Size size)
         {
             using (BeginAutoSizing())
             {
-                _positionerParameters.Size = finalSize;
+                _positionerParameters.Size = size;
                 UpdatePosition();
+                return ClientSize;
             }
-
-            return base.ArrangeOverride(PlatformImpl?.ClientSize ?? default(Size));
         }
     }
 }
diff --git a/src/Avalonia.Controls/ScrollChangedEventArgs.cs b/src/Avalonia.Controls/ScrollChangedEventArgs.cs
new file mode 100644
index 0000000000..fed23964f5
--- /dev/null
+++ b/src/Avalonia.Controls/ScrollChangedEventArgs.cs
@@ -0,0 +1,45 @@
+using Avalonia.Interactivity;
+
+namespace Avalonia.Controls
+{
+    /// <summary>
+    /// Describes a change in scrolling state.
+    /// </summary>
+    public class ScrollChangedEventArgs : RoutedEventArgs
+    {
+        public ScrollChangedEventArgs(
+            Vector extentDelta,
+            Vector offsetDelta,
+            Vector viewportDelta)
+            : this(ScrollViewer.ScrollChangedEvent, extentDelta, offsetDelta, viewportDelta)
+        {
+        }
+
+        public ScrollChangedEventArgs(
+            RoutedEvent routedEvent,
+            Vector extentDelta,
+            Vector offsetDelta,
+            Vector viewportDelta)
+            : base(routedEvent)
+        {
+            ExtentDelta = extentDelta;
+            OffsetDelta = offsetDelta;
+            ViewportDelta = viewportDelta;
+        }
+
+        /// <summary>
+        /// Gets the change to the value of <see cref="ScrollViewer.Extent"/>.
+        /// </summary>
+        public Vector ExtentDelta { get; }
+
+        /// <summary>
+        /// Gets the change to the value of <see cref="ScrollViewer.Offset"/>.
+        /// </summary>
+        public Vector OffsetDelta { get; }
+
+        /// <summary>
+        /// Gets the change to the value of <see cref="ScrollViewer.Viewport"/>.
+        /// </summary>
+        public Vector ViewportDelta { get; }
+    }
+}
diff --git a/src/Avalonia.Controls/ScrollViewer.cs b/src/Avalonia.Controls/ScrollViewer.cs
index 8bfcc1f9db..c3f0dc0056 100644
--- a/src/Avalonia.Controls/ScrollViewer.cs
+++ b/src/Avalonia.Controls/ScrollViewer.cs
@@ -2,6 +2,7 @@ using System;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
+using Avalonia.Interactivity;
 
 namespace Avalonia.Controls
 {
@@ -165,6 +166,14 @@ namespace Avalonia.Controls
                 nameof(VerticalScrollBarVisibility),
                 ScrollBarVisibility.Auto);
 
+        /// <summary>
+        /// Defines the <see cref="ScrollChanged"/> event.
+        /// </summary>
+        public static readonly RoutedEvent<ScrollChangedEventArgs> ScrollChangedEvent =
+            RoutedEvent.Register<ScrollViewer, ScrollChangedEventArgs>(
+                nameof(ScrollChanged),
+                RoutingStrategies.Bubble);
+
         internal const double DefaultSmallChange = 16;
 
         private IDisposable _childSubscription;
@@ -191,6 +200,15 @@ namespace Avalonia.Controls
         {
         }
 
+        /// <summary>
+        /// Occurs when changes are detected to the scroll position, extent, or viewport size.
+        /// </summary>
+        public event EventHandler<ScrollChangedEventArgs> ScrollChanged
+        {
+            add => AddHandler(ScrollChangedEvent, value);
+            remove => RemoveHandler(ScrollChangedEvent, value);
+        }
+
         /// <summary>
         /// Gets the extent of the scrollable content.
         /// </summary>
@@ -203,9 +221,11 @@ namespace Avalonia.Controls
 
             private set
             {
+                var old = _extent;
+
                 if (SetAndRaise(ExtentProperty, ref _extent, value))
                 {
-                    CalculatedPropertiesChanged();
+                    CalculatedPropertiesChanged(extentDelta: value - old);
                 }
             }
         }
@@ -222,11 +242,13 @@ namespace Avalonia.Controls
 
             set
             {
+                var old = _offset;
+
                 value = ValidateOffset(this, value);
 
                 if (SetAndRaise(OffsetProperty, ref _offset, value))
                 {
-                    CalculatedPropertiesChanged();
+                    CalculatedPropertiesChanged(offsetDelta: value - old);
                 }
             }
         }
@@ -243,9 +265,11 @@ namespace Avalonia.Controls
 
             private set
             {
+                var old = _viewport;
+
                 if (SetAndRaise(ViewportProperty, ref _viewport, value))
                 {
-                    CalculatedPropertiesChanged();
+                    CalculatedPropertiesChanged(viewportDelta: value - old);
                 }
             }
         }
@@ -525,7 +549,10 @@ namespace Avalonia.Controls
             }
         }
 
-        private void CalculatedPropertiesChanged()
+        private void CalculatedPropertiesChanged(
+            Size extentDelta = default,
+            Vector offsetDelta = default,
+            Size viewportDelta = default)
         {
             // Pass old values of 0 here because we don't have the old values at this point,
             // and it shouldn't matter as only the template uses these properies.
@@ -546,6 +573,20 @@ namespace Avalonia.Controls
                 SetAndRaise(SmallChangeProperty, ref _smallChange, new Size(DefaultSmallChange, DefaultSmallChange));
                 SetAndRaise(LargeChangeProperty, ref _largeChange, Viewport);
             }
+
+            if (extentDelta != default || offsetDelta != default || viewportDelta != default)
+            {
+                using var route = BuildEventRoute(ScrollChangedEvent);
+
+                if (route.HasHandlers)
+                {
+                    var e = new ScrollChangedEventArgs(
+                        new Vector(extentDelta.Width, extentDelta.Height),
+                        offsetDelta,
+                        new Vector(viewportDelta.Width, viewportDelta.Height));
+                    route.RaiseEvent(this, e);
+                }
+            }
         }
 
         protected override void OnKeyDown(KeyEventArgs e)
diff --git a/src/Avalonia.Controls/Window.cs b/src/Avalonia.Controls/Window.cs
index 387bf0adb8..ee596432f7 100644
--- a/src/Avalonia.Controls/Window.cs
+++ b/src/Avalonia.Controls/Window.cs
@@ -313,22 +313,7 @@ namespace Avalonia.Controls
         /// Should be called from left mouse button press event handler
         /// </summary>
         public void BeginResizeDrag(WindowEdge edge, PointerPressedEventArgs e) => PlatformImpl?.BeginResizeDrag(edge, e);
-        
-        /// <summary>
-        /// Carries out the arrange pass of the window.
-        /// </summary>
-        /// <param name="finalSize">The final window size.</param>
-        /// <returns>The <paramref name="finalSize"/> parameter unchanged.</returns>
-        protected override Size ArrangeOverride(Size finalSize)
-        {
-            using (BeginAutoSizing())
-            {
-                PlatformImpl?.Resize(finalSize);
-            }
 
-            return base.ArrangeOverride(PlatformImpl?.ClientSize ?? default(Size));
-        }
-        
         /// <inheritdoc/>
         Size ILayoutRoot.MaxClientSize => _maxPlatformClientSize;
 
@@ -450,6 +435,19 @@ namespace Avalonia.Controls
 
             EnsureInitialized();
             IsVisible = true;
+
+            var initialSize = new Size(
+                double.IsNaN(Width) ? ClientSize.Width : Width,
+                double.IsNaN(Height) ? ClientSize.Height : Height);
+
+            if (initialSize != ClientSize)
+            {
+                using (BeginAutoSizing())
+                {
+                    PlatformImpl?.Resize(initialSize);
+                }
+            }
+
             LayoutManager.ExecuteInitialLayoutPass(this);
 
             using (BeginAutoSizing())
@@ -569,38 +567,60 @@ namespace Avalonia.Controls
             }
         }
 
-        /// <inheritdoc/>
         protected override Size MeasureOverride(Size availableSize)
         {
             var sizeToContent = SizeToContent;
             var clientSize = ClientSize;
-            var constraint = availableSize;
+            var constraint = clientSize;
 
-            if ((sizeToContent & SizeToContent.Width) != 0)
+            if (sizeToContent.HasFlagCustom(SizeToContent.Width))
             {
                 constraint = constraint.WithWidth(double.PositiveInfinity);
             }
 
-            if ((sizeToContent & SizeToContent.Height) != 0)
+            if (sizeToContent.HasFlagCustom(SizeToContent.Height))
             {
                 constraint = constraint.WithHeight(double.PositiveInfinity);
             }
 
             var result = base.MeasureOverride(constraint);
 
-            if ((sizeToContent & SizeToContent.Width) == 0)
+            if (!sizeToContent.HasFlagCustom(SizeToContent.Width))
             {
-                result = result.WithWidth(clientSize.Width);
+                if (!double.IsInfinity(availableSize.Width))
+                {
+                    result = result.WithWidth(availableSize.Width);
+                }
+                else
+                {
+                    result = result.WithWidth(clientSize.Width);
+                }
             }
 
-            if ((sizeToContent & SizeToContent.Height) == 0)
+            if (!sizeToContent.HasFlagCustom(SizeToContent.Height))
             {
-                result = result.WithHeight(clientSize.Height);
+                if (!double.IsInfinity(availableSize.Height))
+                {
+                    result = result.WithHeight(availableSize.Height);
+                }
+                else
+                {
+                    result = result.WithHeight(clientSize.Height);
+                }
             }
 
             return result;
         }
 
+        protected sealed override Size ArrangeSetBounds(Size size)
+        {
+            using (BeginAutoSizing())
+            {
+                PlatformImpl?.Resize(size);
+                return ClientSize;
+            }
+        }
+
         protected sealed override void HandleClosed()
         {
             RaiseEvent(new RoutedEventArgs(WindowClosedEvent));
@@ -616,6 +636,9 @@ namespace Avalonia.Controls
                 SizeToContent = SizeToContent.Manual;
             }
 
+            Width = clientSize.Width;
+            Height = clientSize.Height;
+
             base.HandleResized(clientSize);
         }
 
diff --git a/src/Avalonia.Controls/WindowBase.cs b/src/Avalonia.Controls/WindowBase.cs
index 63eabb32f4..bb63d1b353 100644
--- a/src/Avalonia.Controls/WindowBase.cs
+++ b/src/Avalonia.Controls/WindowBase.cs
@@ -224,16 +224,54 @@ namespace Avalonia.Controls
         /// <param name="clientSize">The new client size.</param>
         protected override void HandleResized(Size clientSize)
         {
-            if (!AutoSizing)
-            {
-                Width = clientSize.Width;
-                Height = clientSize.Height;
-            }
             ClientSize = clientSize;
             LayoutManager.ExecuteLayoutPass();
             Renderer?.Resized(clientSize);
         }
 
+        /// <summary>
+        /// Overrides the core measure logic for windows.
+        /// </summary>
+        /// <param name="availableSize">The available size.</param>
+        /// <returns>The measured size.</returns>
+        /// <remarks>
+        /// The layout logic for top-level windows is different than for other controls because
+        /// they don't have a parent, meaning that many layout properties handled by the default
+        /// MeasureCore (such as margins and alignment) make no sense.
+        /// </remarks>
+        protected override Size MeasureCore(Size availableSize)
+        {
+            ApplyStyling();
+            ApplyTemplate();
+
+            var constraint = LayoutHelper.ApplyLayoutConstraints(this, availableSize);
+
+            return MeasureOverride(constraint);
+        }
+
+        /// <summary>
+        /// Overrides the core arrange logic for windows.
+        /// </summary>
+        /// <param name="finalRect">The final arrange rect.</param>
+        /// <remarks>
+        /// The layout logic for top-level windows is different than for other controls because
+        /// they don't have a parent, meaning that many layout properties handled by the default
+        /// ArrangeCore (such as margins and alignment) make no sense.
+        /// </remarks>
+        protected override void ArrangeCore(Rect finalRect)
+        {
+            var constraint = ArrangeSetBounds(finalRect.Size);
+            var arrangeSize = ArrangeOverride(constraint);
+            Bounds = new Rect(arrangeSize);
+        }
+
+        /// <summary>
+        /// Called durung the arrange pass to set the size of the window.
+        /// </summary>
+        /// <param name="size">The requested size of the window.</param>
+        /// <returns>The actual size of the window.</returns>
+        protected virtual Size ArrangeSetBounds(Size size) => size;
+
         /// <summary>
         /// Handles a window position change notification from 
         /// <see cref="IWindowBaseImpl.PositionChanged"/>.
diff --git a/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj b/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
index 3dcf7c9681..c0e46416c1 100644
--- a/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
+++ b/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net461;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net461;netcoreapp2.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Avalonia.Dialogs/ManagedFileChooser.xaml b/src/Avalonia.Dialogs/ManagedFileChooser.xaml
index af0c91e7bd..8a0451f982 100644
--- a/src/Avalonia.Dialogs/ManagedFileChooser.xaml
+++ b/src/Avalonia.Dialogs/ManagedFileChooser.xaml
@@ -58,7 +58,7 @@
             <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="10">
                 <StackPanel.Styles>
                     <Style Selector="Button">
-                        <Setter Property="Margin">4</Setter>
+                        <Setter Property="Margin" Value="4"/>
                     </Style>
                 </StackPanel.Styles>
                 <Button Command="{Binding Ok}">OK</Button>
diff --git a/src/Avalonia.Input/Raw/RawPointerEventArgs.cs b/src/Avalonia.Input/Raw/RawPointerEventArgs.cs
index bbd5515da0..62a1dd5d84 100644
--- a/src/Avalonia.Input/Raw/RawPointerEventArgs.cs
+++ b/src/Avalonia.Input/Raw/RawPointerEventArgs.cs
@@ -63,7 +63,7 @@ namespace Avalonia.Input.Raw
         /// <summary>
         /// Gets the type of the event.
         /// </summary>
-        public RawPointerEventType Type { get; private set; }
+        public RawPointerEventType Type { get; set; }
 
         /// <summary>
         /// Gets the input modifiers.
diff --git a/src/Avalonia.Layout/LayoutHelper.cs b/src/Avalonia.Layout/LayoutHelper.cs
index af7d8ee52e..2b61de00a7 100644
--- a/src/Avalonia.Layout/LayoutHelper.cs
+++ b/src/Avalonia.Layout/LayoutHelper.cs
@@ -1,4 +1,5 @@
 using System;
+using Avalonia.Utilities;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Layout
@@ -19,16 +20,11 @@ namespace Avalonia.Layout
         /// <returns>The control's size.</returns>
         public static Size ApplyLayoutConstraints(ILayoutable control, Size constraints)
         {
-            var controlWidth = control.Width;
-            var controlHeight = control.Height;
-
-            double width = (controlWidth > 0) ? controlWidth : constraints.Width;
-            double height = (controlHeight > 0) ? controlHeight : constraints.Height;
-            width = Math.Min(width, control.MaxWidth);
-            width = Math.Max(width, control.MinWidth);
-            height = Math.Min(height, control.MaxHeight);
-            height = Math.Max(height, control.MinHeight);
-            return new Size(width, height);
+            var minmax = new MinMax(control);
+
+            return new Size(
+                MathUtilities.Clamp(constraints.Width, minmax.MinWidth, minmax.MaxWidth),
+                MathUtilities.Clamp(constraints.Height, minmax.MinHeight, minmax.MaxHeight));
         }
 
         public static Size MeasureChild(ILayoutable control, Size availableSize, Thickness padding,
@@ -85,5 +81,39 @@ namespace Avalonia.Layout
 
             InnerInvalidateMeasure(control);
         }
+
+        /// <summary>
+        /// Calculates the min and max height for a control. Ported from WPF.
+        /// </summary>
+        private readonly struct MinMax
+        {
+            public MinMax(ILayoutable e)
+            {
+                MaxHeight = e.MaxHeight;
+                MinHeight = e.MinHeight;
+                double l = e.Height;
+
+                double height = (double.IsNaN(l) ? double.PositiveInfinity : l);
+                MaxHeight = Math.Max(Math.Min(height, MaxHeight), MinHeight);
+
+                height = (double.IsNaN(l) ? 0 : l);
+                MinHeight = Math.Max(Math.Min(MaxHeight, height), MinHeight);
+
+                MaxWidth = e.MaxWidth;
+                MinWidth = e.MinWidth;
+                l = e.Width;
+
+                double width = (double.IsNaN(l) ? double.PositiveInfinity : l);
+                MaxWidth = Math.Max(Math.Min(width, MaxWidth), MinWidth);
+
+                width = (double.IsNaN(l) ? 0 : l);
+                MinWidth = Math.Max(Math.Min(MaxWidth, width), MinWidth);
+            }
+
+            public double MinWidth { get; }
+            public double MaxWidth { get; }
+            public double MinHeight { get; }
+            public double MaxHeight { get; }
+        }
     }
 }
diff --git a/src/Avalonia.ReactiveUI/AppBuilderExtensions.cs b/src/Avalonia.ReactiveUI/AppBuilderExtensions.cs
index 485aaf1c26..6771d3e179 100644
--- a/src/Avalonia.ReactiveUI/AppBuilderExtensions.cs
+++ b/src/Avalonia.ReactiveUI/AppBuilderExtensions.cs
@@ -15,7 +15,7 @@ namespace Avalonia.ReactiveUI
         public static TAppBuilder UseReactiveUI<TAppBuilder>(this TAppBuilder builder)
             where TAppBuilder : AppBuilderBase<TAppBuilder>, new()
         {
-            return builder.AfterSetup(_ =>
+            return builder.AfterPlatformServicesSetup(_ =>
             {
                 RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;
                 Locator.CurrentMutable.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
index b4bf4c799a..b2e827fa26 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Rendering.SceneGraph
     /// </summary>
     public class Scene : IDisposable
     {
-        private Dictionary<IVisual, IVisualNode> _index;
+        private readonly Dictionary<IVisual, IVisualNode> _index;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Scene"/> class.
@@ -83,7 +83,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>The cloned scene.</returns>
         public Scene CloneScene()
         {
-            var index = new Dictionary<IVisual, IVisualNode>();
+            var index = new Dictionary<IVisual, IVisualNode>(_index.Count);
             var root = Clone((VisualNode)Root, null, index);
 
             var result = new Scene(root, index, Layers.Clone(), Generation + 1)
@@ -162,9 +162,18 @@ namespace Avalonia.Rendering.SceneGraph
 
             index.Add(result.Visual, result);
 
-            foreach (var child in source.Children)
+            int childCount = source.Children.Count;
+
+            if (childCount > 0)
             {
-                result.AddChild(Clone((VisualNode)child, result, index));
+                Span<IVisualNode> children = result.AddChildrenSpan(childCount);
+
+                for (var i = 0; i < childCount; i++)
+                {
+                    var child = source.Children[i];
+
+                    children[i] = Clone((VisualNode)child, result, index);
+                }
             }
 
             return result;
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
index 5960b4f560..25f7383a1a 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
@@ -11,16 +11,28 @@ namespace Avalonia.Rendering.SceneGraph
     public class SceneLayers : IEnumerable<SceneLayer>
     {
         private readonly IVisual _root;
-        private readonly List<SceneLayer> _inner = new List<SceneLayer>();
-        private readonly Dictionary<IVisual, SceneLayer> _index = new Dictionary<IVisual, SceneLayer>();
+        private readonly List<SceneLayer> _inner;
+        private readonly Dictionary<IVisual, SceneLayer> _index;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="SceneLayers"/> class.
         /// </summary>
         /// <param name="root">The scene's root visual.</param>
-        public SceneLayers(IVisual root)
+        public SceneLayers(IVisual root) : this(root, 0)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SceneLayers"/> class.
+        /// </summary>
+        /// <param name="root">The scene's root visual.</param>
+        /// <param name="capacity">Initial layer capacity.</param>
+        public SceneLayers(IVisual root, int capacity)
         {
             _root = root;
+
+            _inner = new List<SceneLayer>(capacity);
+            _index = new Dictionary<IVisual, SceneLayer>(capacity);
         }
 
         /// <summary>
@@ -84,7 +96,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>The cloned layers.</returns>
         public SceneLayers Clone()
         {
-            var result = new SceneLayers(_root);
+            var result = new SceneLayers(_root, Count);
 
             foreach (var src in _inner)
             {
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
index 82444a0c29..8cd1a47795 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reactive.Disposables;
+using Avalonia.Collections.Pooled;
 using Avalonia.Media;
 using Avalonia.Platform;
 using Avalonia.Utilities;
@@ -19,8 +20,8 @@ namespace Avalonia.Rendering.SceneGraph
 
         private Rect? _bounds;
         private double _opacity;
-        private List<IVisualNode> _children;
-        private List<IRef<IDrawOperation>> _drawOperations;
+        private PooledList<IVisualNode> _children;
+        private PooledList<IRef<IDrawOperation>> _drawOperations;
         private IRef<IDisposable> _drawOperationsRefCounter;
         private bool _drawOperationsCloned;
         private Matrix transformRestore;
@@ -349,6 +350,18 @@ namespace Avalonia.Rendering.SceneGraph
             context.Transform = transformRestore;
         }
 
+        /// <summary>
+        /// Inserts default constructed children into collection and returns a span for the newly created range.
+        /// </summary>
+        /// <param name="count">Count of children that will be added.</param>
+        /// <returns></returns>
+        internal Span<IVisualNode> AddChildrenSpan(int count)
+        {
+            EnsureChildrenCreated(count);
+
+            return _children.AddSpan(count);
+        }
+
         private Rect CalculateBounds()
         {
             var result = new Rect();
@@ -362,11 +375,11 @@ namespace Avalonia.Rendering.SceneGraph
             return result;
         }
 
-        private void EnsureChildrenCreated()
+        private void EnsureChildrenCreated(int capacity = 0)
         {
             if (_children == null)
             {
-                _children = new List<IVisualNode>();
+                _children = new PooledList<IVisualNode>(capacity);
             }
         }
 
@@ -377,13 +390,21 @@ namespace Avalonia.Rendering.SceneGraph
         {
             if (_drawOperations == null)
             {
-                _drawOperations = new List<IRef<IDrawOperation>>();
+                _drawOperations = new PooledList<IRef<IDrawOperation>>();
                 _drawOperationsRefCounter = RefCountable.Create(CreateDisposeDrawOperations(_drawOperations));
                 _drawOperationsCloned = false;
             }
             else if (_drawOperationsCloned)
             {
-                _drawOperations = new List<IRef<IDrawOperation>>(_drawOperations.Select(op => op.Clone()));
+                var oldDrawOperations = _drawOperations;
+
+                _drawOperations = new PooledList<IRef<IDrawOperation>>(oldDrawOperations.Count);
+
+                foreach (var drawOperation in oldDrawOperations)
+                {
+                    _drawOperations.Add(drawOperation.Clone());
+                }
+
                 _drawOperationsRefCounter.Dispose();
                 _drawOperationsRefCounter = RefCountable.Create(CreateDisposeDrawOperations(_drawOperations));
                 _drawOperationsCloned = false;
@@ -397,14 +418,16 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         /// <param name="drawOperations">Draw operations that need to be disposed.</param>
         /// <returns>Disposable for given draw operations.</returns>
-        private static IDisposable CreateDisposeDrawOperations(List<IRef<IDrawOperation>> drawOperations)
+        private static IDisposable CreateDisposeDrawOperations(PooledList<IRef<IDrawOperation>> drawOperations)
         {
-            return Disposable.Create(() =>
+            return Disposable.Create(drawOperations, operations =>
             {
-                foreach (var operation in drawOperations)
+                foreach (var operation in operations)
                 {
                     operation.Dispose();
                 }
+
+                operations.Dispose();
             });
         }
 
@@ -414,6 +437,8 @@ namespace Avalonia.Rendering.SceneGraph
         {
             _drawOperationsRefCounter?.Dispose();
 
+            _children?.Dispose();
+
             Disposed = true;
         }
     }
diff --git a/src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs b/src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs
index 492f5f824f..5c9a0c992a 100644
--- a/src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs
+++ b/src/Avalonia.X11/NativeDialogs/GtkNativeFileDialogs.cs
@@ -91,7 +91,13 @@ namespace Avalonia.X11.NativeDialogs
                 gtk_dialog_add_button(dlg, open, GtkResponseType.Cancel);
             if (initialFileName != null)
                 using (var fn = new Utf8Buffer(initialFileName))
-                    gtk_file_chooser_set_current_name(dlg, fn);
+                {
+                    if (action == GtkFileChooserAction.Save)
+                        gtk_file_chooser_set_current_name(dlg, fn);
+                    else
+                        gtk_file_chooser_set_filename(dlg, fn);
+                }
+
             gtk_window_present(dlg);
             return tcs.Task;
         }
diff --git a/src/Avalonia.X11/X11ImmediateRendererProxy.cs b/src/Avalonia.X11/X11ImmediateRendererProxy.cs
index f7bc7f9711..7280567bb3 100644
--- a/src/Avalonia.X11/X11ImmediateRendererProxy.cs
+++ b/src/Avalonia.X11/X11ImmediateRendererProxy.cs
@@ -11,6 +11,7 @@ namespace Avalonia.X11
         private readonly IRenderLoop _loop;
         private ImmediateRenderer _renderer;
         private bool _invalidated;
+        private bool _running;
         private object _lock = new object();
 
         public X11ImmediateRendererProxy(IVisual root, IRenderLoop loop)
@@ -22,6 +23,7 @@ namespace Avalonia.X11
 
         public void Dispose()
         {
+            _running = false;
             _renderer.Dispose();
         }
 
@@ -78,12 +80,14 @@ namespace Avalonia.X11
 
         public void Start()
         {
+            _running = true;
             _loop.Add(this);
             _renderer.Start();
         }
 
         public void Stop()
         {
+            _running = false;
             _loop.Remove(this);
             _renderer.Stop();
         }
@@ -100,7 +104,11 @@ namespace Avalonia.X11
             {
                 lock (_lock)
                     _invalidated = false;
-                Dispatcher.UIThread.Post(() => Paint(new Rect(0, 0, 100000, 100000)));
+                Dispatcher.UIThread.Post(() =>
+                {
+                    if (_running)
+                        Paint(new Rect(0, 0, 100000, 100000));
+                });
             }
         }
     }
diff --git a/src/Avalonia.X11/X11Window.cs b/src/Avalonia.X11/X11Window.cs
index 60fd0346a3..3a919e2bc4 100644
--- a/src/Avalonia.X11/X11Window.cs
+++ b/src/Avalonia.X11/X11Window.cs
@@ -442,7 +442,7 @@ namespace Avalonia.X11
                             updatedSizeViaScaling = UpdateScaling();
                         }
 
-                        if (changedSize && !updatedSizeViaScaling)
+                        if (changedSize && !updatedSizeViaScaling && !_popup)
                             Resized?.Invoke(ClientSize);
 
                         Dispatcher.UIThread.RunJobs(DispatcherPriority.Layout);
@@ -649,7 +649,27 @@ namespace Avalonia.X11
             ScheduleInput(args);
         }
 
-        public void ScheduleInput(RawInputEventArgs args)
+        public void ScheduleXI2Input(RawInputEventArgs args)
+        {
+            if (args is RawPointerEventArgs pargs)
+            {
+                if ((pargs.Type == RawPointerEventType.TouchBegin
+                     || pargs.Type == RawPointerEventType.TouchUpdate
+                     || pargs.Type == RawPointerEventType.LeftButtonDown
+                     || pargs.Type == RawPointerEventType.RightButtonDown
+                     || pargs.Type == RawPointerEventType.MiddleButtonDown
+                     || pargs.Type == RawPointerEventType.NonClientLeftButtonDown)
+                    && ActivateTransientChildIfNeeded())
+                    return;
+                if (pargs.Type == RawPointerEventType.TouchEnd
+                    && ActivateTransientChildIfNeeded())
+                    pargs.Type = RawPointerEventType.TouchCancel;
+            }
+
+            ScheduleInput(args);
+        }
+        
+        private void ScheduleInput(RawInputEventArgs args)
         {
             if (args is RawPointerEventArgs mouse)
                 mouse.Position = mouse.Position / Scaling;
diff --git a/src/Avalonia.X11/XI2Manager.cs b/src/Avalonia.X11/XI2Manager.cs
index ac14efe133..0734532d92 100644
--- a/src/Avalonia.X11/XI2Manager.cs
+++ b/src/Avalonia.X11/XI2Manager.cs
@@ -196,7 +196,7 @@ namespace Avalonia.X11
                     (ev.Type == XiEventType.XI_TouchUpdate ?
                         RawPointerEventType.TouchUpdate :
                         RawPointerEventType.TouchEnd);
-                client.ScheduleInput(new RawTouchEventArgs(client.TouchDevice,
+                client.ScheduleXI2Input(new RawTouchEventArgs(client.TouchDevice,
                     ev.Timestamp, client.InputRoot, type, ev.Position, ev.Modifiers, ev.Detail));
                 return;
             }
@@ -230,10 +230,10 @@ namespace Avalonia.X11
                 }
 
                 if (scrollDelta != default)
-                    client.ScheduleInput(new RawMouseWheelEventArgs(client.MouseDevice, ev.Timestamp,
+                    client.ScheduleXI2Input(new RawMouseWheelEventArgs(client.MouseDevice, ev.Timestamp,
                         client.InputRoot, ev.Position, scrollDelta, ev.Modifiers));
                 if (_pointerDevice.HasMotion(ev))
-                    client.ScheduleInput(new RawPointerEventArgs(client.MouseDevice, ev.Timestamp, client.InputRoot,
+                    client.ScheduleXI2Input(new RawPointerEventArgs(client.MouseDevice, ev.Timestamp, client.InputRoot,
                         RawPointerEventType.Move, ev.Position, ev.Modifiers));
             }
 
@@ -250,7 +250,7 @@ namespace Avalonia.X11
                     _ => (RawPointerEventType?)null
                 };
                 if (type.HasValue)
-                    client.ScheduleInput(new RawPointerEventArgs(client.MouseDevice, ev.Timestamp, client.InputRoot,
+                    client.ScheduleXI2Input(new RawPointerEventArgs(client.MouseDevice, ev.Timestamp, client.InputRoot,
                         type.Value, ev.Position, ev.Modifiers));
             }
             
@@ -313,7 +313,7 @@ namespace Avalonia.X11
     interface IXI2Client
     {
         IInputRoot InputRoot { get; }
-        void ScheduleInput(RawInputEventArgs args);
+        void ScheduleXI2Input(RawInputEventArgs args);
         IMouseDevice MouseDevice { get; }
         TouchDevice TouchDevice { get; }
     }
diff --git a/src/Skia/Avalonia.Skia/FormattedTextImpl.cs b/src/Skia/Avalonia.Skia/FormattedTextImpl.cs
index 9612fa3d9b..d0157815a9 100644
--- a/src/Skia/Avalonia.Skia/FormattedTextImpl.cs
+++ b/src/Skia/Avalonia.Skia/FormattedTextImpl.cs
@@ -140,25 +140,17 @@ namespace Avalonia.Skia
 
         public Rect HitTestTextPosition(int index)
         {
+            if (string.IsNullOrEmpty(Text))
+            {
+                var alignmentOffset = TransformX(0, 0, _paint.TextAlign);
+                return new Rect(alignmentOffset, 0, 0, _lineHeight);
+            }
             var rects = GetRects();
-
-            if (index < 0 || index >= rects.Count)
+            if (index >= Text.Length || index < 0)
             {
                 var r = rects.LastOrDefault();
                 return new Rect(r.X + r.Width, r.Y, 0, _lineHeight);
             }
-
-            if (rects.Count == 0)
-            {
-                return new Rect(0, 0, 1, _lineHeight);
-            }
-
-            if (index == rects.Count)
-            {
-                var lr = rects[rects.Count - 1];
-                return new Rect(new Point(lr.X + lr.Width, lr.Y), rects[index - 1].Size);
-            }
-
             return rects[index];
         }
 
diff --git a/src/tools/Avalonia.Designer.HostApp/Avalonia.Designer.HostApp.csproj b/src/tools/Avalonia.Designer.HostApp/Avalonia.Designer.HostApp.csproj
index 372cb8476b..1c7077870a 100644
--- a/src/tools/Avalonia.Designer.HostApp/Avalonia.Designer.HostApp.csproj
+++ b/src/tools/Avalonia.Designer.HostApp/Avalonia.Designer.HostApp.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>net461;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net461;netcoreapp2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\Avalonia.DesignerSupport\Avalonia.DesignerSupport.csproj" />
diff --git a/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs b/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
index 5a47a86e51..28e87dd671 100644
--- a/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
@@ -209,16 +209,17 @@ namespace Avalonia.Controls.UnitTests
             screenImpl.Setup(x => x.ScreenCount).Returns(1);
             screenImpl.Setup(X => X.AllScreens).Returns( new[] { new Screen(1, screen, screen, true) });
 
-            popupImpl = MockWindowingPlatform.CreatePopupMock();
+            var windowImpl = MockWindowingPlatform.CreateWindowMock();
+            popupImpl = MockWindowingPlatform.CreatePopupMock(windowImpl.Object);
             popupImpl.SetupGet(x => x.Scaling).Returns(1);
+            windowImpl.Setup(x => x.CreatePopup()).Returns(popupImpl.Object);
 
-            var windowImpl = MockWindowingPlatform.CreateWindowMock(() => popupImpl.Object);
             windowImpl.Setup(x => x.Screen).Returns(screenImpl.Object);
 
             var services = TestServices.StyledWindow.With(
                                         inputManager: new InputManager(),
                                         windowImpl: windowImpl.Object,
-                                        windowingPlatform: new MockWindowingPlatform(() => windowImpl.Object, () => popupImpl.Object));
+                                        windowingPlatform: new MockWindowingPlatform(() => windowImpl.Object, x => popupImpl.Object));
 
             return UnitTestApplication.Start(services);
         }
diff --git a/tests/Avalonia.Controls.UnitTests/Primitives/PopupRootTests.cs b/tests/Avalonia.Controls.UnitTests/Primitives/PopupRootTests.cs
index 501c0455d0..a61d313c8c 100644
--- a/tests/Avalonia.Controls.UnitTests/Primitives/PopupRootTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/Primitives/PopupRootTests.cs
@@ -2,11 +2,14 @@ using System;
 using System.Linq;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
+using Avalonia.Controls.Primitives.PopupPositioning;
 using Avalonia.Controls.Templates;
 using Avalonia.LogicalTree;
+using Avalonia.Platform;
 using Avalonia.Styling;
 using Avalonia.UnitTests;
 using Avalonia.VisualTree;
+using Moq;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests.Primitives
@@ -172,9 +175,146 @@ namespace Avalonia.Controls.UnitTests.Primitives
             }
         }
 
-        private PopupRoot CreateTarget(TopLevel popupParent)
+        [Fact]
+        public void Child_Should_Be_Measured_With_Infinity()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new ChildControl();
+                var window = new Window();
+                var target = CreateTarget(window);
+                
+                target.Content = child;
+                target.Show();
+
+                Assert.Equal(Size.Infinity, child.MeasureSize);
+            }
+        }
+
+        [Fact]
+        public void Child_Should_Be_Measured_With_Width_Height_When_Set()
         {
-            var result = new PopupRoot(popupParent, popupParent.PlatformImpl.CreatePopup())
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new ChildControl();
+                var window = new Window();
+                var target = CreateTarget(window);
+
+                target.Width = 500;
+                target.Height = 600;
+                target.Content = child;
+                target.Show();
+
+                Assert.Equal(new Size(500, 600), child.MeasureSize);
+            }
+        }
+
+        [Fact]
+        public void Child_Should_Be_Measured_With_MaxWidth_MaxHeight_When_Set()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new ChildControl();
+                var window = new Window();
+                var target = CreateTarget(window);
+
+                target.MaxWidth = 500;
+                target.MaxHeight = 600;
+                target.Content = child;
+                target.Show();
+
+                Assert.Equal(new Size(500, 600), child.MeasureSize);
+            }
+        }
+
+        [Fact]
+        public void Should_Not_Have_Offset_On_Bounds_When_Content_Larger_Than_Max_Window_Size()
+        {
+            // Issue #3784.
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = new Window();
+                var popupImpl = MockWindowingPlatform.CreatePopupMock(window.PlatformImpl);
+
+                var child = new Canvas
+                {
+                    Width = 400,
+                    Height = 1344,
+                };
+
+                var target = CreateTarget(window, popupImpl.Object);
+                target.Content = child;
+
+                target.Show();
+
+                Assert.Equal(new Size(400, 1024), target.Bounds.Size);
+
+                // Issue #3784 causes this to be (0, 160) which makes no sense as Window has no
+                // parent control to be offset against.
+                Assert.Equal(new Point(0, 0), target.Bounds.Position);
+            }
+        }
+
+        [Fact]
+        public void MinWidth_MinHeight_Should_Be_Respected()
+        {
+            // Issue #3796
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = new Window();
+                var popupImpl = MockWindowingPlatform.CreatePopupMock(window.PlatformImpl);
+
+                var target = CreateTarget(window, popupImpl.Object);
+                target.MinWidth = 400;
+                target.MinHeight = 800;
+                target.Content = new Border
+                {
+                    Width = 100,
+                    Height = 100,
+                };
+
+                target.Show();
+
+                Assert.Equal(new Rect(0, 0, 400, 800), target.Bounds);
+                Assert.Equal(new Size(400, 800), target.ClientSize);
+                Assert.Equal(new Size(400, 800), target.PlatformImpl.ClientSize);
+            }
+        }
+
+        [Fact]
+        public void Setting_Width_Should_Resize_WindowImpl()
+        {
+            // Issue #3796
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = new Window();
+                var popupImpl = MockWindowingPlatform.CreatePopupMock(window.PlatformImpl);
+                var positioner = new Mock<IPopupPositioner>();
+                popupImpl.Setup(x => x.PopupPositioner).Returns(positioner.Object);
+
+                var target = CreateTarget(window, popupImpl.Object);
+                target.Width = 400;
+                target.Height = 800;
+
+                target.Show();
+
+                Assert.Equal(400, target.Width);
+                Assert.Equal(800, target.Height);
+
+                target.Width = 410;
+                target.LayoutManager.ExecuteLayoutPass();
+
+                positioner.Verify(x => 
+                    x.Update(It.Is<PopupPositionerParameters>(x => x.Size.Width == 410)));
+                Assert.Equal(410, target.Width);
+            }
+        }
+
+        private PopupRoot CreateTarget(TopLevel popupParent, IPopupImpl impl = null)
+        {
+            impl ??= popupParent.PlatformImpl.CreatePopup();
+
+            var result = new PopupRoot(popupParent, impl)
             {
                 Template = new FuncControlTemplate<PopupRoot>((parent, scope) =>
                     new ContentPresenter
@@ -217,5 +357,16 @@ namespace Avalonia.Controls.UnitTests.Primitives
                 Popup = (Popup)this.GetVisualChildren().Single();
             }
         }
+
+        private class ChildControl : Control
+        {
+            public Size MeasureSize { get; private set; }
+
+            protected override Size MeasureOverride(Size availableSize)
+            {
+                MeasureSize = availableSize;
+                return base.MeasureOverride(availableSize);
+            }
+        }
     }
 }
diff --git a/tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs b/tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs
index a4c0fa054b..0b9c94f850 100644
--- a/tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/Primitives/PopupTests.cs
@@ -298,13 +298,6 @@ namespace Avalonia.Controls.UnitTests.Primitives
             }
         }
 
-        Window PreparedWindow(object content = null)
-        {
-            var w = new Window {Content = content};
-            w.ApplyTemplate();
-            return w;
-        }
-
         [Fact]
         public void DataContextBeginUpdate_Should_Not_Be_Called_For_Controls_That_Dont_Inherit()
         {
@@ -351,18 +344,88 @@ namespace Avalonia.Controls.UnitTests.Primitives
             }
         }
 
+        [Fact]
+        public void StaysOpen_False_Should_Not_Handle_Closing_Click()
+        {
+            using (CreateServices())
+            {
+                var window = PreparedWindow();
+                var target = new Popup() 
+                { 
+                    PlacementTarget = window ,
+                    StaysOpen = false,
+                };
+
+                target.Open();
+
+                var e = CreatePointerPressedEventArgs(window);
+                window.RaiseEvent(e);
+
+                Assert.False(e.Handled);
+            }
+        }
+
+        [Fact]
+        public void Should_Pass_Closing_Click_To_Closed_Event()
+        {
+            using (CreateServices())
+            {
+                var window = PreparedWindow();
+                var target = new Popup()
+                {
+                    PlacementTarget = window,
+                    StaysOpen = false,
+                };
+
+                target.Open();
+
+                var press = CreatePointerPressedEventArgs(window);
+                var raised = 0;
+
+                target.Closed += (s, e) =>
+                {
+                    Assert.Same(press, e.CloseEvent);
+                    ++raised;
+                };
+
+                window.RaiseEvent(press);
+
+                Assert.Equal(1, raised);
+            }
+        }
+
         private IDisposable CreateServices()
         {
             return UnitTestApplication.Start(TestServices.StyledWindow.With(windowingPlatform:
                 new MockWindowingPlatform(null,
-                    () =>
+                    x =>
                     {
                         if(UsePopupHost)
                             return null;
-                        return MockWindowingPlatform.CreatePopupMock().Object;
+                        return MockWindowingPlatform.CreatePopupMock(x).Object;
                     })));
         }
 
+        private PointerPressedEventArgs CreatePointerPressedEventArgs(Window source)
+        {
+            var pointer = new Pointer(Pointer.GetNextFreeId(), PointerType.Mouse, true);
+            return new PointerPressedEventArgs(
+                source,
+                pointer,
+                source,
+                default,
+                0,
+                new PointerPointProperties(RawInputModifiers.None, PointerUpdateKind.LeftButtonPressed),
+                KeyModifiers.None);
+        }
+
+        private Window PreparedWindow(object content = null)
+        {
+            var w = new Window { Content = content };
+            w.ApplyTemplate();
+            return w;
+        }
+
         private static IControl PopupContentControlTemplate(PopupContentControl control, INameScope scope)
         {
             return new Popup
diff --git a/tests/Avalonia.Controls.UnitTests/ScrollViewerTests.cs b/tests/Avalonia.Controls.UnitTests/ScrollViewerTests.cs
index 5375a244c9..8da1e26f0d 100644
--- a/tests/Avalonia.Controls.UnitTests/ScrollViewerTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ScrollViewerTests.cs
@@ -4,7 +4,6 @@ using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Layout;
-using Avalonia.LogicalTree;
 using Moq;
 using Xunit;
 
@@ -147,6 +146,78 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(new Size(45, 67), target.LargeChange);
         }
 
+        [Fact]
+        public void Changing_Extent_Should_Raise_ScrollChanged()
+        {
+            var target = new ScrollViewer();
+            var raised = 0;
+
+            target.SetValue(ScrollViewer.ExtentProperty, new Size(100, 100));
+            target.SetValue(ScrollViewer.ViewportProperty, new Size(50, 50));
+            target.Offset = new Vector(10, 10);
+
+            target.ScrollChanged += (s, e) =>
+            {
+                Assert.Equal(new Vector(11, 12), e.ExtentDelta);
+                Assert.Equal(default, e.OffsetDelta);
+                Assert.Equal(default, e.ViewportDelta);
+                ++raised;
+            };
+
+            target.SetValue(ScrollViewer.ExtentProperty, new Size(111, 112));
+
+            Assert.Equal(1, raised);
+
+        }
+
+        [Fact]
+        public void Changing_Offset_Should_Raise_ScrollChanged()
+        {
+            var target = new ScrollViewer();
+            var raised = 0;
+
+            target.SetValue(ScrollViewer.ExtentProperty, new Size(100, 100));
+            target.SetValue(ScrollViewer.ViewportProperty, new Size(50, 50));
+            target.Offset = new Vector(10, 10);
+
+            target.ScrollChanged += (s, e) =>
+            {
+                Assert.Equal(default, e.ExtentDelta);
+                Assert.Equal(new Vector(12, 14), e.OffsetDelta);
+                Assert.Equal(default, e.ViewportDelta);
+                ++raised;
+            };
+
+            target.Offset = new Vector(22, 24);
+
+            Assert.Equal(1, raised);
+
+        }
+
+        [Fact]
+        public void Changing_Viewport_Should_Raise_ScrollChanged()
+        {
+            var target = new ScrollViewer();
+            var raised = 0;
+
+            target.SetValue(ScrollViewer.ExtentProperty, new Size(100, 100));
+            target.SetValue(ScrollViewer.ViewportProperty, new Size(50, 50));
+            target.Offset = new Vector(10, 10);
+
+            target.ScrollChanged += (s, e) =>
+            {
+                Assert.Equal(default, e.ExtentDelta);
+                Assert.Equal(default, e.OffsetDelta);
+                Assert.Equal(new Vector(6, 8), e.ViewportDelta);
+                ++raised;
+            };
+
+            target.SetValue(ScrollViewer.ViewportProperty, new Size(56, 58));
+
+            Assert.Equal(1, raised);
+
+        }
+
         private Control CreateTemplate(ScrollViewer control, INameScope scope)
         {
             return new Grid
diff --git a/tests/Avalonia.Controls.UnitTests/WindowTests.cs b/tests/Avalonia.Controls.UnitTests/WindowTests.cs
index fed63fc683..cf2920998a 100644
--- a/tests/Avalonia.Controls.UnitTests/WindowTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/WindowTests.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Avalonia.Layout;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.UnitTests;
@@ -351,7 +352,30 @@ namespace Avalonia.Controls.UnitTests
 
                 target.Show();
 
-                Assert.Equal(new Size(100, 50), child.MeasureSize);
+                Assert.Equal(1, child.MeasureSizes.Count);
+                Assert.Equal(new Size(100, 50), child.MeasureSizes[0]);
+            }
+        }
+
+        [Fact]
+        public void Child_Should_Be_Measured_With_ClientSize_If_SizeToContent_Is_Manual_And_No_Width_Height_Specified()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var windowImpl = MockWindowingPlatform.CreateWindowMock();
+                windowImpl.Setup(x => x.ClientSize).Returns(new Size(550, 450));
+
+                var child = new ChildControl();
+                var target = new Window(windowImpl.Object)
+                {
+                    SizeToContent = SizeToContent.Manual,
+                    Content = child
+                };
+
+                target.Show();
+
+                Assert.Equal(1, child.MeasureSizes.Count);
+                Assert.Equal(new Size(550, 450), child.MeasureSizes[0]);
             }
         }
 
@@ -371,7 +395,151 @@ namespace Avalonia.Controls.UnitTests
 
                 target.Show();
 
-                Assert.Equal(Size.Infinity, child.MeasureSize);
+                Assert.Equal(1, child.MeasureSizes.Count);
+                Assert.Equal(Size.Infinity, child.MeasureSizes[0]);
+            }
+        }
+
+        [Fact]
+        public void Should_Not_Have_Offset_On_Bounds_When_Content_Larger_Than_Max_Window_Size()
+        {
+            // Issue #3784.
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var windowImpl = MockWindowingPlatform.CreateWindowMock();
+                var clientSize = new Size(200, 200);
+                var maxClientSize = new Size(480, 480);
+
+                windowImpl.Setup(x => x.Resize(It.IsAny<Size>())).Callback<Size>(size =>
+                {
+                    clientSize = size.Constrain(maxClientSize);
+                    windowImpl.Object.Resized?.Invoke(clientSize);
+                });
+
+                windowImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
+
+                var child = new Canvas
+                {
+                    Width = 400,
+                    Height = 800,
+                };
+                var target = new Window(windowImpl.Object)
+                {
+                    SizeToContent = SizeToContent.WidthAndHeight,
+                    Content = child
+                };
+
+                target.Show();
+
+                Assert.Equal(new Size(400, 480), target.Bounds.Size);
+
+                // Issue #3784 causes this to be (0, 160) which makes no sense as Window has no
+                // parent control to be offset against.
+                Assert.Equal(new Point(0, 0), target.Bounds.Position);
+            }
+        }
+
+        [Fact]
+        public void Width_Height_Should_Not_Be_NaN_After_Show_With_SizeToContent_WidthAndHeight()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new Canvas
+                {
+                    Width = 400,
+                    Height = 800,
+                };
+
+                var target = new Window()
+                {
+                    SizeToContent = SizeToContent.WidthAndHeight,
+                    Content = child
+                };
+
+                target.Show();
+
+                Assert.Equal(400, target.Width);
+                Assert.Equal(800, target.Height);
+            }
+        }
+
+        [Fact]
+        public void SizeToContent_Should_Not_Be_Lost_On_Show()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new Canvas
+                {
+                    Width = 400,
+                    Height = 800,
+                };
+
+                var target = new Window()
+                {
+                    SizeToContent = SizeToContent.WidthAndHeight,
+                    Content = child
+                };
+
+                target.Show();
+
+                Assert.Equal(SizeToContent.WidthAndHeight, target.SizeToContent);
+            }
+        }
+
+        [Fact]
+        public void Width_Height_Should_Be_Updated_When_SizeToContent_Is_WidthAndHeight()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var child = new Canvas
+                {
+                    Width = 400,
+                    Height = 800,
+                };
+
+                var target = new Window()
+                {
+                    SizeToContent = SizeToContent.WidthAndHeight,
+                    Content = child
+                };
+
+                target.Show();
+
+                Assert.Equal(400, target.Width);
+                Assert.Equal(800, target.Height);
+
+                child.Width = 410;
+                target.LayoutManager.ExecuteLayoutPass();
+
+                Assert.Equal(410, target.Width);
+                Assert.Equal(800, target.Height);
+                Assert.Equal(SizeToContent.WidthAndHeight, target.SizeToContent);
+            }
+        }
+
+        [Fact]
+        public void Setting_Width_Should_Resize_WindowImpl()
+        {
+            // Issue #3796
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var target = new Window()
+                {
+                    Width = 400,
+                    Height = 800,
+                };
+
+                target.Show();
+
+                Assert.Equal(400, target.Width);
+                Assert.Equal(800, target.Height);
+
+                target.Width = 410;
+                target.LayoutManager.ExecuteLayoutPass();
+
+                var windowImpl = Mock.Get(target.PlatformImpl);
+                windowImpl.Verify(x => x.Resize(new Size(410, 800)));
+                Assert.Equal(410, target.Width);
             }
         }
 
@@ -384,11 +552,11 @@ namespace Avalonia.Controls.UnitTests
 
         private class ChildControl : Control
         {
-            public Size MeasureSize { get; private set; }
+            public List<Size> MeasureSizes { get; } = new List<Size>();
 
             protected override Size MeasureOverride(Size availableSize)
             {
-                MeasureSize = availableSize;
+                MeasureSizes.Add(availableSize);
                 return base.MeasureOverride(availableSize);
             }
         }
diff --git a/tests/Avalonia.DesignerSupport.Tests/DesignerSupportTests.cs b/tests/Avalonia.DesignerSupport.Tests/DesignerSupportTests.cs
index 319e91d2ba..dd704bc775 100644
--- a/tests/Avalonia.DesignerSupport.Tests/DesignerSupportTests.cs
+++ b/tests/Avalonia.DesignerSupport.Tests/DesignerSupportTests.cs
@@ -18,7 +18,7 @@ namespace Avalonia.DesignerSupport.Tests
 {
     public class DesignerSupportTests
     {
-        private const string DesignerAppPath = "../../../../../src/tools/Avalonia.Designer.HostApp/bin/$BUILD/netcoreapp3.1/Avalonia.Designer.HostApp.dll";
+        private const string DesignerAppPath = "../../../../../src/tools/Avalonia.Designer.HostApp/bin/$BUILD/netcoreapp2.0/Avalonia.Designer.HostApp.dll";
         private readonly Xunit.Abstractions.ITestOutputHelper outputHelper;
 
         public DesignerSupportTests(Xunit.Abstractions.ITestOutputHelper outputHelper)
diff --git a/tests/Avalonia.Layout.UnitTests/FullLayoutTests.cs b/tests/Avalonia.Layout.UnitTests/FullLayoutTests.cs
index 69eff0b65d..dcc29a9716 100644
--- a/tests/Avalonia.Layout.UnitTests/FullLayoutTests.cs
+++ b/tests/Avalonia.Layout.UnitTests/FullLayoutTests.cs
@@ -1,25 +1,12 @@
-using System.Diagnostics;
-using System.IO;
 using System.Linq;
-using Moq;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
-using Avalonia.Diagnostics;
-using Avalonia.Input;
-using Avalonia.Platform;
-using Avalonia.Rendering;
-using Avalonia.Shared.PlatformSupport;
 using Avalonia.Styling;
-using Avalonia.Themes.Default;
+using Avalonia.UnitTests;
 using Avalonia.VisualTree;
 using Xunit;
-using Avalonia.Media;
-using System;
-using System.Collections.Generic;
-using Avalonia.Controls.UnitTests;
-using Avalonia.UnitTests;
 
 namespace Avalonia.Layout.UnitTests
 {
@@ -28,10 +15,8 @@ namespace Avalonia.Layout.UnitTests
         [Fact]
         public void Grandchild_Size_Changed()
         {
-            using (var context = AvaloniaLocator.EnterScope())
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                RegisterServices();
-
                 Border border;
                 TextBlock textBlock;
 
@@ -55,7 +40,6 @@ namespace Avalonia.Layout.UnitTests
                 };
 
                 window.Show();
-                window.LayoutManager.ExecuteInitialLayoutPass(window);
 
                 Assert.Equal(new Size(400, 400), border.Bounds.Size);
                 textBlock.Width = 200;
@@ -68,10 +52,8 @@ namespace Avalonia.Layout.UnitTests
         [Fact]
         public void Test_ScrollViewer_With_TextBlock()
         {
-            using (var context = AvaloniaLocator.EnterScope())
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                RegisterServices();
-
                 ScrollViewer scrollViewer;
                 TextBlock textBlock;
 
@@ -79,7 +61,6 @@ namespace Avalonia.Layout.UnitTests
                 {
                     Width = 800,
                     Height = 600,
-                    SizeToContent = SizeToContent.WidthAndHeight,
                     Content = scrollViewer = new ScrollViewer
                     {
                         Width = 200,
@@ -99,7 +80,6 @@ namespace Avalonia.Layout.UnitTests
                 window.Resources["ScrollBarThickness"] = 10.0;
 
                 window.Show();
-                window.LayoutManager.ExecuteInitialLayoutPass(window);
 
                 Assert.Equal(new Size(800, 600), window.Bounds.Size);
                 Assert.Equal(new Size(200, 200), scrollViewer.Bounds.Size);
@@ -131,87 +111,5 @@ namespace Avalonia.Layout.UnitTests
         {
             return v.Bounds.Position;
         }
-
-        class FormattedTextMock : IFormattedTextImpl
-        {
-            public FormattedTextMock(string text)
-            {
-                Text = text;
-            }
-
-            public Size Constraint { get; set; }
-
-            public string Text { get; }
-
-            public Rect Bounds => Rect.Empty;
-
-            public void Dispose()
-            {
-            }
-
-            public IEnumerable<FormattedTextLine> GetLines() => new FormattedTextLine[0];
-
-            public TextHitTestResult HitTestPoint(Point point) => new TextHitTestResult();
-
-            public Rect HitTestTextPosition(int index) => new Rect();
-
-            public IEnumerable<Rect> HitTestTextRange(int index, int length) => new Rect[0];
-
-            public Size Measure() => Constraint;
-        }
-
-        private void RegisterServices()
-        {
-            var globalStyles = new Mock<IGlobalStyles>();
-            var globalStylesResources = globalStyles.As<IResourceNode>();
-            var outObj = (object)10;
-            globalStylesResources.Setup(x => x.TryGetResource("FontSizeNormal", out outObj)).Returns(true);
-
-            var renderInterface = new Mock<IPlatformRenderInterface>();
-            renderInterface.Setup(x =>
-                x.CreateFormattedText(
-                    It.IsAny<string>(),
-                    It.IsAny<Typeface>(),
-                    It.IsAny<double>(),
-                    It.IsAny<TextAlignment>(),
-                    It.IsAny<TextWrapping>(),
-                    It.IsAny<Size>(),
-                    It.IsAny<IReadOnlyList<FormattedTextStyleSpan>>()))
-                .Returns(new FormattedTextMock("TEST"));
-
-            var streamGeometry = new Mock<IStreamGeometryImpl>();
-            streamGeometry.Setup(x =>
-                    x.Open())
-                .Returns(new Mock<IStreamGeometryContextImpl>().Object);
-
-            renderInterface.Setup(x =>
-                    x.CreateStreamGeometry())
-                .Returns(streamGeometry.Object);
-
-            var windowImpl = new Mock<IWindowImpl>();
-
-            Size clientSize = default(Size);
-
-            windowImpl.SetupGet(x => x.ClientSize).Returns(() => clientSize);
-            windowImpl.Setup(x => x.Resize(It.IsAny<Size>())).Callback<Size>(s => clientSize = s);
-            windowImpl.Setup(x => x.MaxClientSize).Returns(new Size(1024, 1024));
-            windowImpl.SetupGet(x => x.Scaling).Returns(1);
-
-            AvaloniaLocator.CurrentMutable
-                .Bind<IStandardCursorFactory>().ToConstant(new CursorFactoryMock())
-                .Bind<IAssetLoader>().ToConstant(new AssetLoader())
-                .Bind<IInputManager>().ToConstant(new Mock<IInputManager>().Object)
-                .Bind<IGlobalStyles>().ToConstant(globalStyles.Object)
-                .Bind<IRuntimePlatform>().ToConstant(new AppBuilder().RuntimePlatform)
-                .Bind<IPlatformRenderInterface>().ToConstant(renderInterface.Object)
-                .Bind<IStyler>().ToConstant(new Styler())
-                .Bind<IFontManagerImpl>().ToConstant(new MockFontManagerImpl())
-                .Bind<ITextShaperImpl>().ToConstant(new MockTextShaperImpl())
-                .Bind<IWindowingPlatform>().ToConstant(new Avalonia.Controls.UnitTests.WindowingPlatformMock(() => windowImpl.Object));
-
-            var theme = new DefaultTheme();
-            globalStyles.Setup(x => x.IsStylesInitialized).Returns(true);
-            globalStyles.Setup(x => x.Styles).Returns(theme);
-        }
     }
 }
diff --git a/tests/Avalonia.UnitTests/MockWindowingPlatform.cs b/tests/Avalonia.UnitTests/MockWindowingPlatform.cs
index 782e4a0974..b3e4b4edbc 100644
--- a/tests/Avalonia.UnitTests/MockWindowingPlatform.cs
+++ b/tests/Avalonia.UnitTests/MockWindowingPlatform.cs
@@ -8,65 +8,122 @@ namespace Avalonia.UnitTests
 {
     public class MockWindowingPlatform : IWindowingPlatform
     {
+        private static readonly Size s_screenSize = new Size(1280, 1024);
         private readonly Func<IWindowImpl> _windowImpl;
-        private readonly Func<IPopupImpl> _popupImpl;
+        private readonly Func<IWindowBaseImpl, IPopupImpl> _popupImpl;
 
-        public MockWindowingPlatform(Func<IWindowImpl> windowImpl = null, Func<IPopupImpl> popupImpl = null )
+        public MockWindowingPlatform(
+            Func<IWindowImpl> windowImpl = null,
+            Func<IWindowBaseImpl, IPopupImpl> popupImpl = null )
         {
             _windowImpl = windowImpl;
             _popupImpl = popupImpl;
         }
 
-        public static Mock<IWindowImpl> CreateWindowMock(Func<IPopupImpl> popupImpl = null)
+        public static Mock<IWindowImpl> CreateWindowMock()
         {
-            var win = Mock.Of<IWindowImpl>(x => x.Scaling == 1);
-            var mock = Mock.Get(win);
-            mock.Setup(x => x.Show()).Callback(() =>
+            var windowImpl = new Mock<IWindowImpl>();
+            var position = new PixelPoint();
+            var clientSize = new Size(800, 600);
+
+            windowImpl.SetupAllProperties();
+            windowImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
+            windowImpl.Setup(x => x.Scaling).Returns(1);
+            windowImpl.Setup(x => x.Screen).Returns(CreateScreenMock().Object);
+            windowImpl.Setup(x => x.Position).Returns(() => position);
+            SetupToplevel(windowImpl);
+
+            windowImpl.Setup(x => x.CreatePopup()).Returns(() =>
             {
-                mock.Object.Activated?.Invoke();
+                return CreatePopupMock(windowImpl.Object).Object;
             });
-            mock.Setup(x => x.CreatePopup()).Returns(() =>
+
+            windowImpl.Setup(x => x.Dispose()).Callback(() =>
             {
-                if (popupImpl != null)
-                    return popupImpl();
-                return CreatePopupMock().Object;
+                windowImpl.Object.Closed?.Invoke();
+            });
+
+            windowImpl.Setup(x => x.Move(It.IsAny<PixelPoint>())).Callback<PixelPoint>(x =>
+            {
+                position = x;
+                windowImpl.Object.PositionChanged?.Invoke(x);
+            });
 
+            windowImpl.Setup(x => x.Resize(It.IsAny<Size>())).Callback<Size>(x =>
+            {
+                clientSize = x.Constrain(s_screenSize);
+                windowImpl.Object.Resized?.Invoke(clientSize);
             });
-            mock.Setup(x => x.Dispose()).Callback(() =>
+
+            windowImpl.Setup(x => x.Show()).Callback(() =>
             {
-                mock.Object.Closed?.Invoke();
+                windowImpl.Object.Activated?.Invoke();
             });
-            PixelPoint pos = default;
-            mock.SetupGet(x => x.Position).Returns(() => pos);
-            mock.Setup(x => x.Move(It.IsAny<PixelPoint>())).Callback(new Action<PixelPoint>(np => pos = np));
-            SetupToplevel(mock);
-            return mock;
+
+            return windowImpl;
         }
 
-        static void SetupToplevel<T>(Mock<T> mock) where T : class, ITopLevelImpl
+        public static Mock<IPopupImpl> CreatePopupMock(IWindowBaseImpl parent)
         {
-            mock.SetupGet(x => x.MouseDevice).Returns(new MouseDevice());
+            var popupImpl = new Mock<IPopupImpl>();
+            var clientSize = new Size();
+
+            var positionerHelper = new ManagedPopupPositionerPopupImplHelper(parent, (pos, size, scale) =>
+            {
+                clientSize = size.Constrain(s_screenSize);
+                popupImpl.Object.PositionChanged?.Invoke(pos);
+                popupImpl.Object.Resized?.Invoke(clientSize);
+            });
+            
+            var positioner = new ManagedPopupPositioner(positionerHelper);
+
+            popupImpl.SetupAllProperties();
+            popupImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
+            popupImpl.Setup(x => x.Scaling).Returns(1);
+            popupImpl.Setup(x => x.PopupPositioner).Returns(positioner);
+            
+            SetupToplevel(popupImpl);
+            
+            return popupImpl;
         }
 
-        public static Mock<IPopupImpl> CreatePopupMock()
+        public static Mock<IScreenImpl> CreateScreenMock()
         {
-            var positioner = Mock.Of<IPopupPositioner>();
-            var popup = Mock.Of<IPopupImpl>(x => x.Scaling == 1);
-            var mock = Mock.Get(popup);
-            mock.SetupGet(x => x.PopupPositioner).Returns(positioner);
-            SetupToplevel(mock);
-            
-            return mock;
+            var screenImpl = new Mock<IScreenImpl>();
+            var bounds = new PixelRect(0, 0, (int)s_screenSize.Width, (int)s_screenSize.Height);
+            var screen = new Screen(96, bounds, bounds, true);
+            screenImpl.Setup(x => x.AllScreens).Returns(new[] { screen });
+            screenImpl.Setup(x => x.ScreenCount).Returns(1);
+            return screenImpl;
         }
 
         public IWindowImpl CreateWindow()
         {
-            return _windowImpl?.Invoke() ?? CreateWindowMock(_popupImpl).Object;
+            if (_windowImpl is object)
+            {
+                return _windowImpl();
+            }
+            else
+            {
+                var mock = CreateWindowMock();
+
+                if (_popupImpl is object)
+                {
+                    mock.Setup(x => x.CreatePopup()).Returns(() => _popupImpl(mock.Object));
+                }
+
+                return mock.Object;
+            }
         }
 
         public IEmbeddableWindowImpl CreateEmbeddableWindow()
         {
             throw new NotImplementedException();
         }
+
+        private static void SetupToplevel<T>(Mock<T> mock) where T : class, ITopLevelImpl
+        {
+            mock.SetupGet(x => x.MouseDevice).Returns(new MouseDevice());
+        }
     }
 }