Merge branch 'master' into feature/tabindex

5 years ago · fdcb744455
39 changed files with 567 additions and 257 deletions
--- a/native/Avalonia.Native/src/OSX/window.h
+++ b/native/Avalonia.Native/src/OSX/window.h
@ -10,6 +10,8 @@ class WindowBaseImpl;
 -(void) setSwRenderedFrame: (AvnFramebuffer* _Nonnull) fb dispose: (IUnknown* _Nonnull) dispose;
 -(void) onClosed;
 -(AvnPixelSize) getPixelSize;
+-(AvnPlatformResizeReason) getResizeReason;
+-(void) setResizeReason:(AvnPlatformResizeReason)reason;
@end

@interface AutoFitContentView : NSView
@ -34,6 +36,7 @@ class WindowBaseImpl;
 -(double) getScaling;
 -(double) getExtendedTitleBarHeight;
 -(void) setIsExtended:(bool)value;
+-(bool) isDialog;
@end

 struct INSWindowHolder
@ -50,4 +53,23 @@ struct IWindowStateChanged
    virtual AvnWindowState WindowState () = 0;
 };

+class ResizeScope
+{
+public:
+    ResizeScope(AvnView* _Nonnull view, AvnPlatformResizeReason reason)
+    {
+        _view = view;
+        _restore = [view getResizeReason];
+        [view setResizeReason:reason];
+    }
+    
+    ~ResizeScope()
+    {
+        [_view setResizeReason:_restore];
+    }
+private:
+    AvnView* _Nonnull _view;
+    AvnPlatformResizeReason _restore;
+};
+
 #endif /* window_h */
--- a/native/Avalonia.Native/src/OSX/window.mm
+++ b/native/Avalonia.Native/src/OSX/window.mm
@ -52,6 +52,7 @@ public:
        [Window setBackingType:NSBackingStoreBuffered];
        
        [Window setOpaque:false];
+        [Window setContentView: StandardContainer];
    }
    
    virtual HRESULT ObtainNSWindowHandle(void** ret) override
@ -115,7 +116,7 @@ public:
        return Window;
    }
    
-    virtual HRESULT Show(bool activate) override
+    virtual HRESULT Show(bool activate, bool isDialog) override
    {
        START_COM_CALL;
        
@ -124,7 +125,6 @@ public:
            SetPosition(lastPositionSet);
            UpdateStyle();
            
-            [Window setContentView: StandardContainer];
            [Window setTitle:_lastTitle];
            
            if(ShouldTakeFocusOnShow() && activate)
@ -277,7 +277,7 @@ public:
        }
    }
    
-    virtual HRESULT Resize(double x, double y) override
+    virtual HRESULT Resize(double x, double y, AvnPlatformResizeReason reason) override
    {
        if(_inResize)
        {
@ -287,6 +287,7 @@ public:
        _inResize = true;
        
        START_COM_CALL;
+        auto resizeBlock = ResizeScope(View, reason);
        
        @autoreleasepool
        {
@ -317,7 +318,7 @@ public:
            {
                if(!_shown)
                {
-                    BaseEvents->Resized(AvnSize{x,y});
+                    BaseEvents->Resized(AvnSize{x,y}, reason);
                }
                
                [Window setContentSize:NSSize{x, y}];
@ -577,6 +578,11 @@ public:
        return S_OK;
    }

+    virtual bool IsDialog()
+    {
+        return false;
+    }
+    
 protected:
    virtual NSWindowStyleMask GetStyle()
    {
@ -607,6 +613,7 @@ private:
    NSRect _preZoomSize;
    bool _transitioningWindowState;
    bool _isClientAreaExtended;
+    bool _isDialog;
    AvnExtendClientAreaChromeHints _extendClientHints;
    
    FORWARD_IUNKNOWN()
@ -667,13 +674,14 @@ private:
        }
    }
    
-    virtual HRESULT Show (bool activate) override
+    virtual HRESULT Show (bool activate, bool isDialog) override
    {
        START_COM_CALL;
        
        @autoreleasepool
        {
-            WindowBaseImpl::Show(activate);
+            _isDialog = isDialog;
+            WindowBaseImpl::Show(activate, isDialog);
            
            HideOrShowTrafficLights();
            
@ -1213,6 +1221,11 @@ private:
        }
    }
    
+    virtual bool IsDialog() override
+    {
+        return _isDialog;
+    }
+    
 protected:
    virtual NSWindowStyleMask GetStyle() override
    {
@ -1373,6 +1386,7 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    bool _lastKeyHandled;
    AvnPixelSize _lastPixelSize;
    NSObject<IRenderTarget>* _renderTarget;
+    AvnPlatformResizeReason _resizeReason;
 }

 - (void)onClosed
@ -1484,7 +1498,8 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
        _lastPixelSize.Height = (int)fsize.height;
        [self updateRenderTarget];
    
-        _parent->BaseEvents->Resized(AvnSize{newSize.width, newSize.height});
+        auto reason = [self inLiveResize] ? ResizeUser : _resizeReason;
+        _parent->BaseEvents->Resized(AvnSize{newSize.width, newSize.height}, reason);
    }
 }

@ -1983,6 +1998,16 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    
 }

+- (AvnPlatformResizeReason)getResizeReason
+{
+    return _resizeReason;
+}
+
+- (void)setResizeReason:(AvnPlatformResizeReason)reason
+{
+    _resizeReason = reason;
+}
+
@end


@ -2002,6 +2027,11 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    _isExtended = value;
 }

+-(bool) isDialog
+{
+    return _parent->IsDialog();
+}
+
 -(double) getScaling
 {
    return _lastScaling;
@ -2180,7 +2210,22 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent

 -(BOOL)canBecomeKeyWindow
 {
-    return _canBecomeKeyAndMain;
+    if (_canBecomeKeyAndMain)
+    {
+        // If the window has a child window being shown as a dialog then don't allow it to become the key window.
+        for(NSWindow* uch in [self childWindows])
+        {
+            auto ch = objc_cast<AvnWindow>(uch);
+            if(ch == nil)
+                continue;
+            if (ch.isDialog)
+                return false;
+        }
+        
+        return true;
+    }
+    
+    return false;
 }

 -(BOOL)canBecomeMainWindow
@ -2188,22 +2233,6 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    return _canBecomeKeyAndMain;
 }

-(bool) activateAppropriateChild: (bool)activating
-{
-    for(NSWindow* uch in [self childWindows])
-    {
-        auto ch = objc_cast<AvnWindow>(uch);
-        if(ch == nil)
-            continue;
-        [ch activateAppropriateChild:false];
-        return FALSE;
-    }
-    
-    if(!activating)
-        [self makeKeyAndOrderFront:self];
-    return TRUE;
-}
-
 -(bool)shouldTryToHandleEvents
 {
    return _isEnabled;
@ -2214,26 +2243,15 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    _isEnabled = enable;
 }

-(void)makeKeyWindow
-{
-    if([self activateAppropriateChild: true])
-    {
-        [super makeKeyWindow];
-    }
-}
-
 -(void)becomeKeyWindow
 {
    [self showWindowMenuWithAppMenu];
    
-    if([self activateAppropriateChild: true])
+    if(_parent != nullptr)
    {
-        if(_parent != nullptr)
-        {
-            _parent->BaseEvents->Activated();
-        }
+        _parent->BaseEvents->Activated();
    }
-    
+
    [super becomeKeyWindow];
 }

@ -2243,7 +2261,6 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    if(parent != nil)
    {
        [parent removeChildWindow:self];
-        [parent activateAppropriateChild: false];
    }
 }

@ -2378,7 +2395,7 @@ protected:
        return NSWindowStyleMaskBorderless;
    }
    
-    virtual HRESULT Resize(double x, double y) override
+    virtual HRESULT Resize(double x, double y, AvnPlatformResizeReason reason) override
    {
        START_COM_CALL;
        
--- a/src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs
+++ b/src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs
@ -67,7 +67,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform

        public Action<Rect> Paint { get; set; }

-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }

        public Action<double> ScalingChanged { get; set; }

@ -134,7 +134,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform

        protected virtual void OnResized(Size size)
        {
-            Resized?.Invoke(size);
+            Resized?.Invoke(size, PlatformResizeReason.Unspecified);
        }

        class ViewImpl : InvalidationAwareSurfaceView, ISurfaceHolderCallback, IInitEditorInfo
--- a/src/Avalonia.Controls/ApiCompatBaseline.txt
+++ b/src/Avalonia.Controls/ApiCompatBaseline.txt
@ -30,15 +30,29 @@ MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownV
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.OldValue.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Boolean> Avalonia.StyledProperty<System.Boolean> Avalonia.Controls.ScrollViewer.AllowAutoHideProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.Controls.Viewbox.StretchProperty' does not exist in the implementation but it does exist in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<System.ComponentModel.CancelEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<System.ComponentModel.CancelEventArgs>)' is present in the implementation but not in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.remove_ShutdownRequested(System.EventHandler<System.ComponentModel.CancelEventArgs>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.remove_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
+MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.get()' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty Avalonia.AvaloniaProperty Avalonia.Controls.Notifications.NotificationCard.CloseOnClickProperty' does not exist in the implementation but it does exist in the contract.
 EnumValuesMustMatch : Enum value 'Avalonia.Platform.ExtendClientAreaChromeHints Avalonia.Platform.ExtendClientAreaChromeHints.Default' is (System.Int32)2 in the implementation but (System.Int32)1 in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize.get()' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.Action<Avalonia.Size, Avalonia.Platform.PlatformResizeReason> Avalonia.Platform.ITopLevelImpl.Resized.get()' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.Action<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.Resized.get()' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.Resized.get()' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size, Avalonia.Platform.PlatformResizeReason>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size>)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.ICursorImpl)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' is present in the contract but not in the implementation.
 MembersMustExist : Member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
-Total Issues: 42
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean)' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean, System.Boolean)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size, Avalonia.Platform.PlatformResizeReason)' is present in the implementation but not in the contract.
+Total Issues: 56
--- a/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
+++ b/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
@ -48,7 +48,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
        public event EventHandler<ControlledApplicationLifetimeStartupEventArgs> Startup;

        /// <inheritdoc/>
-        public event EventHandler<CancelEventArgs> ShutdownRequested;
+        public event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;

        /// <inheritdoc/>
        public event EventHandler<ControlledApplicationLifetimeExitEventArgs> Exit;
@ -134,7 +134,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
                _activeLifetime = null;
        }
        
-        private void OnShutdownRequested(object sender, CancelEventArgs e)
+        private void OnShutdownRequested(object sender, ShutdownRequestedEventArgs e)
        {
            ShutdownRequested?.Invoke(this, e);

--- a/src/Avalonia.Controls/ApplicationLifetimes/IClassicDesktopStyleApplicationLifetime.cs
+++ b/src/Avalonia.Controls/ApplicationLifetimes/IClassicDesktopStyleApplicationLifetime.cs
@ -37,14 +37,21 @@ namespace Avalonia.Controls.ApplicationLifetimes
        IReadOnlyList<Window> Windows { get; }

        /// <summary>
-        /// Raised by the platform when a shutdown is requested.
+        /// Raised by the platform when an application shutdown is requested.
        /// </summary>
        /// <remarks>
-        /// Raised on on OSX via the Quit menu or right-clicking on the application icon and selecting Quit. This event
-        /// provides a first-chance to cancel application shutdown; if shutdown is not canceled at this point the application
+        /// Application Shutdown can be requested for various reasons like OS shutdown.
+        /// 
+        /// On Windows this will be called when an OS Session (logout or shutdown) terminates. Cancelling the eventargs will 
+        /// block OS shutdown.
+        /// 
+        /// On OSX this has the same behavior as on Windows and in addition:
+        /// This event is raised via the Quit menu or right-clicking on the application icon and selecting Quit. 
+        /// 
+        /// This event provides a first-chance to cancel application shutdown; if shutdown is not canceled at this point the application
        /// will try to close each non-owned open window, invoking the <see cref="Window.Closing"/> event on each and allowing
-        /// each window to cancel the shutdown.
+        /// each window to cancel the shutdown of the application. Windows cannot however prevent OS shutdown.
        /// </remarks>
-        event EventHandler<CancelEventArgs> ShutdownRequested;
+        event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
    }
 }
--- a/src/Avalonia.Controls/ApplicationLifetimes/ShutdownRequestedEventArgs.cs
+++ b/src/Avalonia.Controls/ApplicationLifetimes/ShutdownRequestedEventArgs.cs
@ -0,0 +1,9 @@
+using System.ComponentModel;
+
+namespace Avalonia.Controls.ApplicationLifetimes
+{
+    public class ShutdownRequestedEventArgs : CancelEventArgs
+    {
+
+    }
+}
--- a/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevelImpl.cs
+++ b/src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevelImpl.cs
@ -31,7 +31,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
            set
            {
                _clientSize = value;
-                Resized?.Invoke(value);
+                Resized?.Invoke(value, PlatformResizeReason.Unspecified);
            }
        }

@ -49,7 +49,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
        
        public Action<RawInputEventArgs> Input { get; set; }
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        public Action<double> ScalingChanged { get; set; }

        public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
--- a/src/Avalonia.Controls/Platform/IPlatformLifetimeEventsImpl.cs
+++ b/src/Avalonia.Controls/Platform/IPlatformLifetimeEventsImpl.cs
@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using Avalonia.Controls.ApplicationLifetimes;

 namespace Avalonia.Platform
 {
@ -11,6 +12,6 @@ namespace Avalonia.Platform
        /// <remarks>
        /// Raised on on OSX via the Quit menu or right-clicking on the application icon and selecting Quit.
        /// </remarks>
-        event EventHandler<CancelEventArgs> ShutdownRequested;
+        event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
    }
 }
--- a/src/Avalonia.Controls/Platform/ITopLevelImpl.cs
+++ b/src/Avalonia.Controls/Platform/ITopLevelImpl.cs
@ -3,11 +3,46 @@ using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
+using Avalonia.Layout;
 using Avalonia.Rendering;
 using JetBrains.Annotations;

 namespace Avalonia.Platform
 {
+    /// <summary>
+    /// Describes the reason for a <see cref="ITopLevelImpl.Resized"/> message.
+    /// </summary>
+    public enum PlatformResizeReason
+    {
+        /// <summary>
+        /// The resize reason is unknown or unspecified.
+        /// </summary>
+        Unspecified,
+
+        /// <summary>
+        /// The resize was due to the user resizing the window, for example by dragging the
+        /// window frame.
+        /// </summary>
+        User,
+
+        /// <summary>
+        /// The resize was initiated by the application, for example by setting one of the sizing-
+        /// related properties on <see cref="Window"/> such as <see cref="Layoutable.Width"/> or
+        /// <see cref="Layoutable.Height"/>.
+        /// </summary>
+        Application,
+
+        /// <summary>
+        /// The resize was initiated by the layout system.
+        /// </summary>
+        Layout,
+
+        /// <summary>
+        /// The resize was due to a change in DPI.
+        /// </summary>
+        DpiChange,
+    }
+
    /// <summary>
    /// Defines a platform-specific top-level window implementation.
    /// </summary>
@ -57,7 +92,7 @@ namespace Avalonia.Platform
        /// <summary>
        /// Gets or sets a method called when the toplevel is resized.
        /// </summary>
-        Action<Size> Resized { get; set; }
+        Action<Size, PlatformResizeReason> Resized { get; set; }

        /// <summary>
        /// Gets or sets a method called when the toplevel's scaling changes.
--- a/src/Avalonia.Controls/Platform/IWindowBaseImpl.cs
+++ b/src/Avalonia.Controls/Platform/IWindowBaseImpl.cs
@ -7,7 +7,9 @@ namespace Avalonia.Platform
        /// <summary>
        /// Shows the window.
        /// </summary>
-        void Show(bool activate);
+        /// <param name="activate">Whether to activate the shown window.</param>
+        /// <param name="isDialog">Whether the window is being shown as a dialog.</param>
+        void Show(bool activate, bool isDialog);

        /// <summary>
        /// Hides the window.
--- a/src/Avalonia.Controls/Platform/IWindowImpl.cs
+++ b/src/Avalonia.Controls/Platform/IWindowImpl.cs
@ -110,7 +110,9 @@ namespace Avalonia.Platform
        /// <summary>
        /// Sets the client size of the top level.
        /// </summary>
-        void Resize(Size clientSize);
+        /// <param name="clientSize">The new client size.</param>
+        /// <param name="reason">The reason for the resize.</param>
+        void Resize(Size clientSize, PlatformResizeReason reason = PlatformResizeReason.Application);

        /// <summary>
        /// Sets the client size of the top level.
--- a/src/Avalonia.Controls/Primitives/PopupRoot.cs
+++ b/src/Avalonia.Controls/Primitives/PopupRoot.cs
@ -161,12 +161,9 @@ namespace Avalonia.Controls.Primitives

        protected override sealed Size ArrangeSetBounds(Size size)
        {
-            using (BeginAutoSizing())
-            {
-                _positionerParameters.Size = size;
-                UpdatePosition();
-                return ClientSize;
-            }
+            _positionerParameters.Size = size;
+            UpdatePosition();
+            return ClientSize;
        }
    }
 }
--- a/src/Avalonia.Controls/TopLevel.cs
+++ b/src/Avalonia.Controls/TopLevel.cs
@ -377,11 +377,15 @@ namespace Avalonia.Controls
            LayoutManager?.Dispose();
        }

+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected virtual void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
        /// <summary>
        /// Handles a resize notification from <see cref="ITopLevelImpl.Resized"/>.
        /// </summary>
        /// <param name="clientSize">The new client size.</param>
-        protected virtual void HandleResized(Size clientSize)
+        /// <param name="reason">The reason for the resize.</param>
+        protected virtual void HandleResized(Size clientSize, PlatformResizeReason reason)
        {
            ClientSize = clientSize;
            FrameSize = PlatformImpl.FrameSize;
--- a/src/Avalonia.Controls/Window.cs
+++ b/src/Avalonia.Controls/Window.cs
@ -244,7 +244,7 @@ namespace Avalonia.Controls
            impl.WindowStateChanged = HandleWindowStateChanged;
            _maxPlatformClientSize = PlatformImpl?.MaxAutoSizeHint ?? default(Size);
            impl.ExtendClientAreaToDecorationsChanged = ExtendClientAreaToDecorationsChanged;            
-            this.GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl?.Resize(x));
+            this.GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl?.Resize(x, PlatformResizeReason.Application));

            PlatformImpl?.ShowTaskbarIcon(ShowInTaskbar);
        }
@ -258,6 +258,18 @@ namespace Avalonia.Controls
        /// <summary>
        /// Gets or sets a value indicating how the window will size itself to fit its content.
        /// </summary>
+        /// <remarks>
+        /// If <see cref="SizeToContent"/> has a value other than <see cref="SizeToContent.Manual"/>,
+        /// <see cref="SizeToContent"/> is automatically set to <see cref="SizeToContent.Manual"/>
+        /// if a user resizes the window by using the resize grip or dragging the border.
+        /// 
+        /// NOTE: Because of a limitation of X11, <see cref="SizeToContent"/> will be reset on X11 to
+        /// <see cref="SizeToContent.Manual"/> on any resize - including the resize that happens when
+        /// the window is first shown. This is because X11 resize notifications are asynchronous and
+        /// there is no way to know whether a resize came from the user or the layout system. To avoid
+        /// this, consider setting <see cref="CanResize"/> to false, which will disable user resizing
+        /// of the window.
+        /// </remarks>
        public SizeToContent SizeToContent
        {
            get { return GetValue(SizeToContentProperty); }
@ -583,28 +595,23 @@ namespace Avalonia.Controls
                return;
            }

-            using (BeginAutoSizing())
-            {
-                Renderer?.Stop();
+            Renderer?.Stop();

-                if (Owner is Window owner)
-                {
-                    owner.RemoveChild(this);
-                }
+            if (Owner is Window owner)
+            {
+                owner.RemoveChild(this);
+            }

-                if (_children.Count > 0)
+            if (_children.Count > 0)
+            {
+                foreach (var child in _children.ToArray())
                {
-                    foreach (var child in _children.ToArray())
-                    {
-                        child.child.Hide();
-                    }
+                    child.child.Hide();
                }
-
-                Owner = null;
-
-                PlatformImpl?.Hide();
            }

+            Owner = null;
+            PlatformImpl?.Hide();
            IsVisible = false;
        }

@ -675,29 +682,23 @@ namespace Avalonia.Controls

            if (initialSize != ClientSize)
            {
-                using (BeginAutoSizing())
-                {
-                    PlatformImpl?.Resize(initialSize);
-                }
+                PlatformImpl?.Resize(initialSize, PlatformResizeReason.Layout);
            }

            LayoutManager.ExecuteInitialLayoutPass();

-            using (BeginAutoSizing())
+            if (parent != null)
            {
-                if (parent != null)
-                {
-                    PlatformImpl?.SetParent(parent.PlatformImpl);
-                }
-                
-                Owner = parent;
-                parent?.AddChild(this, false);
-                
-                SetWindowStartupLocation(Owner?.PlatformImpl);
-                
-                PlatformImpl?.Show(ShowActivated);
-                Renderer?.Start();                
+                PlatformImpl?.SetParent(parent.PlatformImpl);
            }
+
+            Owner = parent;
+            parent?.AddChild(this, false);
+
+            SetWindowStartupLocation(Owner?.PlatformImpl);
+
+            PlatformImpl?.Show(ShowActivated, false);
+            Renderer?.Start();
            OnOpened(EventArgs.Empty);
        }

@ -760,41 +761,34 @@ namespace Avalonia.Controls

            if (initialSize != ClientSize)
            {
-                using (BeginAutoSizing())
-                {
-                    PlatformImpl?.Resize(initialSize);
-                }
+                PlatformImpl?.Resize(initialSize, PlatformResizeReason.Layout);
            }

            LayoutManager.ExecuteInitialLayoutPass();

            var result = new TaskCompletionSource<TResult>();

-            using (BeginAutoSizing())
-            {
-                PlatformImpl?.SetParent(owner.PlatformImpl);
-                Owner = owner;
-                owner.AddChild(this, true);
-                
-                SetWindowStartupLocation(owner.PlatformImpl);
-                
-                PlatformImpl?.Show(ShowActivated);
+            PlatformImpl?.SetParent(owner.PlatformImpl);
+            Owner = owner;
+            owner.AddChild(this, true);

-                Renderer?.Start();
+            SetWindowStartupLocation(owner.PlatformImpl);

-                Observable.FromEventPattern<EventHandler, EventArgs>(
-                        x => Closed += x,
-                        x => Closed -= x)
-                    .Take(1)
-                    .Subscribe(_ =>
-                    {
-                        owner.Activate();
-                        result.SetResult((TResult)(_dialogResult ?? default(TResult)));
-                    });
+            PlatformImpl?.Show(ShowActivated, true);

-                OnOpened(EventArgs.Empty);
-            }
+            Renderer?.Start();
+
+            Observable.FromEventPattern<EventHandler, EventArgs>(
+                    x => Closed += x,
+                    x => Closed -= x)
+                .Take(1)
+                .Subscribe(_ =>
+                {
+                    owner.Activate();
+                    result.SetResult((TResult)(_dialogResult ?? default(TResult)));
+                });

+            OnOpened(EventArgs.Empty);
            return result.Task;
        }

@ -937,11 +931,8 @@ namespace Avalonia.Controls

        protected sealed override Size ArrangeSetBounds(Size size)
        {
-            using (BeginAutoSizing())
-            {
-                PlatformImpl?.Resize(size);
-                return ClientSize;
-            }
+            PlatformImpl?.Resize(size, PlatformResizeReason.Layout);
+            return ClientSize;
        }

        protected sealed override void HandleClosed()
@ -958,18 +949,36 @@ namespace Avalonia.Controls
            Owner = null;
        }

+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected sealed override void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
        /// <inheritdoc/>
-        protected sealed override void HandleResized(Size clientSize)
+        protected sealed override void HandleResized(Size clientSize, PlatformResizeReason reason)
        {
-            if (!AutoSizing)
+            if (ClientSize == clientSize)
+                return;
+
+            var sizeToContent = SizeToContent;
+
+            // If auto-sizing is enabled, and the resize came from a user resize (or the reason was
+            // unspecified) then turn off auto-resizing for any window dimension that is not equal
+            // to the requested size.
+            if (sizeToContent != SizeToContent.Manual &&
+                CanResize &&
+                reason == PlatformResizeReason.Unspecified ||  
+                reason == PlatformResizeReason.User)
            {
-                SizeToContent = SizeToContent.Manual;
+                if (clientSize.Width != ClientSize.Width)
+                    sizeToContent &= ~SizeToContent.Width;
+                if (clientSize.Height != ClientSize.Height)
+                    sizeToContent &= ~SizeToContent.Height;
+                SizeToContent = sizeToContent;
            }

            Width = clientSize.Width;
            Height = clientSize.Height;

-            base.HandleResized(clientSize);
+            base.HandleResized(clientSize, reason);
        }

        /// <summary>
--- a/src/Avalonia.Controls/WindowBase.cs
+++ b/src/Avalonia.Controls/WindowBase.cs
@ -39,7 +39,6 @@ namespace Avalonia.Controls
        public static readonly StyledProperty<bool> TopmostProperty =
            AvaloniaProperty.Register<WindowBase, bool>(nameof(Topmost));

-        private int _autoSizing;
        private bool _hasExecutedInitialLayoutPass;
        private bool _isActive;
        private bool _ignoreVisibilityChange;
@ -95,10 +94,8 @@ namespace Avalonia.Controls
        
        public Screens Screens { get; private set; }

-        /// <summary>
-        /// Whether an auto-size operation is in progress.
-        /// </summary>
-        protected bool AutoSizing => _autoSizing > 0;
+        [Obsolete("No longer used. Always returns false.")]
+        protected bool AutoSizing => false;

        /// <summary>
        /// Gets or sets the owner of the window.
@ -162,7 +159,7 @@ namespace Avalonia.Controls
                    LayoutManager.ExecuteInitialLayoutPass();
                    _hasExecutedInitialLayoutPass = true;
                }
-                PlatformImpl?.Show(true);
+                PlatformImpl?.Show(true, false);
                Renderer?.Start();
                OnOpened(EventArgs.Empty);
            }
@ -172,20 +169,9 @@ namespace Avalonia.Controls
            }
        }

-        /// <summary>
-        /// Begins an auto-resize operation.
-        /// </summary>
-        /// <returns>A disposable used to finish the operation.</returns>
-        /// <remarks>
-        /// When an auto-resize operation is in progress any resize events received will not be
-        /// cause the new size to be written to the <see cref="Layoutable.Width"/> and
-        /// <see cref="Layoutable.Height"/> properties.
-        /// </remarks>
-        protected IDisposable BeginAutoSizing()
-        {
-            ++_autoSizing;
-            return Disposable.Create(() => --_autoSizing);
-        }
+
+        [Obsolete("No longer used. Has no effect.")]
+        protected IDisposable BeginAutoSizing() => Disposable.Empty;

        /// <summary>
        /// Ensures that the window is initialized.
@ -215,11 +201,15 @@ namespace Avalonia.Controls
            }
        }

+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected override void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
        /// <summary>
        /// Handles a resize notification from <see cref="ITopLevelImpl.Resized"/>.
        /// </summary>
        /// <param name="clientSize">The new client size.</param>
-        protected override void HandleResized(Size clientSize)
+        /// <param name="reason">The reason for the resize.</param>
+        protected override void HandleResized(Size clientSize, PlatformResizeReason reason)
        {
            ClientSize = clientSize;
            FrameSize = PlatformImpl.FrameSize;
--- a/src/Avalonia.DesignerSupport/Remote/PreviewerWindowImpl.cs
+++ b/src/Avalonia.DesignerSupport/Remote/PreviewerWindowImpl.cs
@ -20,7 +20,7 @@ namespace Avalonia.DesignerSupport.Remote
            ClientSize = new Size(1, 1);
        }

-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
        {
        }

@ -58,7 +58,7 @@ namespace Avalonia.DesignerSupport.Remote
            base.OnMessage(transport, obj);
        }
        
-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
        {
            _transport.Send(new RequestViewportResizeMessage
            {
@ -99,10 +99,6 @@ namespace Avalonia.DesignerSupport.Remote
        {
        }

-        public void ShowDialog(IWindowImpl parent)
-        {
-        }
-
        public void SetSystemDecorations(SystemDecorations enabled)
        {
        }
--- a/src/Avalonia.DesignerSupport/Remote/Stubs.cs
+++ b/src/Avalonia.DesignerSupport/Remote/Stubs.cs
@ -27,7 +27,7 @@ namespace Avalonia.DesignerSupport.Remote
        public IEnumerable<object> Surfaces { get; }
        public Action<RawInputEventArgs> Input { get; set; }
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        public Action<double> ScalingChanged { get; set; }
        public Func<bool> Closing { get; set; }
        public Action Closed { get; set; }
@ -54,7 +54,7 @@ namespace Avalonia.DesignerSupport.Remote
                PopupPositioner = new ManagedPopupPositioner(new ManagedPopupPositionerPopupImplHelper(parent,
                    (_, size, __) =>
                    {
-                        Resize(size);
+                        Resize(size, PlatformResizeReason.Unspecified);
                    }));
        }

@ -78,7 +78,7 @@ namespace Avalonia.DesignerSupport.Remote
        {
        }

-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
        {
        }

@ -98,7 +98,7 @@ namespace Avalonia.DesignerSupport.Remote
        {
        }

-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
        {
        }

--- a/src/Avalonia.Headless/HeadlessWindowImpl.cs
+++ b/src/Avalonia.Headless/HeadlessWindowImpl.cs
@ -47,7 +47,7 @@ namespace Avalonia.Headless
        public IEnumerable<object> Surfaces { get; }
        public Action<RawInputEventArgs> Input { get; set; }
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        public Action<double> ScalingChanged { get; set; }

        public IRenderer CreateRenderer(IRenderRoot root)
@ -76,7 +76,7 @@ namespace Avalonia.Headless
        public Action Closed { get; set; }
        public IMouseDevice MouseDevice { get; }

-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
        {
            if (activate)
                Dispatcher.UIThread.Post(() => Activated?.Invoke(), DispatcherPriority.Input);
@ -108,7 +108,7 @@ namespace Avalonia.Headless
        public Action Activated { get; set; }
        public IPlatformHandle Handle { get; } = new PlatformHandle(IntPtr.Zero, "STUB");
        public Size MaxClientSize { get; } = new Size(1920, 1280);
-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
        {
            // Emulate X11 behavior here
            if (IsPopup)
@ -126,7 +126,7 @@ namespace Avalonia.Headless
            if (ClientSize != clientSize)
            {
                ClientSize = clientSize;
-                Resized?.Invoke(clientSize);
+                Resized?.Invoke(clientSize, PlatformResizeReason.Unspecified);
            }
        }

@ -148,11 +148,6 @@ namespace Avalonia.Headless

        }

-        public void ShowDialog(IWindowImpl parent)
-        {
-            Show(true);
-        }
-
        public void SetSystemDecorations(bool enabled)
        {

--- a/src/Avalonia.Input/TappedEventArgs.cs
+++ b/src/Avalonia.Input/TappedEventArgs.cs
@ -13,6 +13,10 @@ namespace Avalonia.Input
            this.lastPointerEventArgs = lastPointerEventArgs;
        }

+        public IPointer Pointer => lastPointerEventArgs.Pointer;
+        public KeyModifiers KeyModifiers => lastPointerEventArgs.KeyModifiers;
+        public ulong Timestamp => lastPointerEventArgs.Timestamp;
+        
        public Point GetPosition(IVisual? relativeTo) => lastPointerEventArgs.GetPosition(relativeTo);
    }
 }
--- a/src/Avalonia.Native/AvaloniaNativeApplicationPlatform.cs
+++ b/src/Avalonia.Native/AvaloniaNativeApplicationPlatform.cs
@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Native.Interop;
 using Avalonia.Platform;

@ -7,7 +8,7 @@ namespace Avalonia.Native
 {
    internal class AvaloniaNativeApplicationPlatform : CallbackBase, IAvnApplicationEvents, IPlatformLifetimeEventsImpl
    {
-        public event EventHandler<CancelEventArgs> ShutdownRequested;
+        public event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
        
        void IAvnApplicationEvents.FilesOpened(IAvnStringArray urls)
        {
@ -17,7 +18,7 @@ namespace Avalonia.Native
        public int TryShutdown()
        {
            if (ShutdownRequested is null) return 1;
-            var e = new CancelEventArgs();
+            var e = new ShutdownRequestedEventArgs();
            ShutdownRequested(this, e);
            return (!e.Cancel).AsComBool();
        }
--- a/src/Avalonia.Native/PopupImpl.cs
+++ b/src/Avalonia.Native/PopupImpl.cs
@ -32,7 +32,7 @@ namespace Avalonia.Native
        private void MoveResize(PixelPoint position, Size size, double scaling)
        {
            Position = position;
-            Resize(size);
+            Resize(size, PlatformResizeReason.Layout);
            //TODO: We ignore the scaling override for now
        }

@ -60,14 +60,14 @@ namespace Avalonia.Native
            }
        }

-        public override void Show(bool activate)
+        public override void Show(bool activate, bool isDialog)
        {
            var parent = _parent;
            while (parent is PopupImpl p) 
                parent = p._parent;
            if (parent is WindowImpl w)
                w.Native.TakeFocusFromChildren();
-            base.Show(false);
+            base.Show(false, isDialog);
        }

        public override IPopupImpl CreatePopup() => new PopupImpl(_factory, _opts, _glFeature, this);
--- a/src/Avalonia.Native/WindowImplBase.cs
+++ b/src/Avalonia.Native/WindowImplBase.cs
@ -87,7 +87,7 @@ namespace Avalonia.Native
            var monitor = Screen.AllScreens.OrderBy(x => x.PixelDensity)
                    .FirstOrDefault(m => m.Bounds.Contains(Position));

-            Resize(new Size(monitor.WorkingArea.Width * 0.75d, monitor.WorkingArea.Height * 0.7d));
+            Resize(new Size(monitor.WorkingArea.Width * 0.75d, monitor.WorkingArea.Height * 0.7d), PlatformResizeReason.Layout);
        }

        public Size ClientSize 
@ -146,7 +146,7 @@ namespace Avalonia.Native
        public Action LostFocus { get; set; }
        
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        public Action Closed { get; set; }
        public IMouseDevice MouseDevice => _mouse;
        public abstract IPopupImpl CreatePopup();
@ -186,13 +186,13 @@ namespace Avalonia.Native
                _parent.Paint?.Invoke(new Rect(0, 0, s.Width, s.Height));
            }

-            void IAvnWindowBaseEvents.Resized(AvnSize* size)
+            void IAvnWindowBaseEvents.Resized(AvnSize* size, AvnPlatformResizeReason reason)
            {
                if (_parent?._native != null)
                {
                    var s = new Size(size->Width, size->Height);
                    _parent._savedLogicalSize = s;
-                    _parent.Resized?.Invoke(s);
+                    _parent.Resized?.Invoke(s, (PlatformResizeReason)reason);
                }
            }

@ -320,9 +320,9 @@ namespace Avalonia.Native
            }
        }

-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
        {
-            _native.Resize(clientSize.Width, clientSize.Height);
+            _native.Resize(clientSize.Width, clientSize.Height, (AvnPlatformResizeReason)reason);
        }

        public IRenderer CreateRenderer(IRenderRoot root)
@ -365,9 +365,9 @@ namespace Avalonia.Native
        }


-        public virtual void Show(bool activate)
+        public virtual void Show(bool activate, bool isDialog)
        {
-            _native.Show(activate.AsComBool());
+            _native.Show(activate.AsComBool(), isDialog.AsComBool());
        }


--- a/src/Avalonia.Native/avn.idl
+++ b/src/Avalonia.Native/avn.idl
@ -400,6 +400,15 @@ enum AvnExtendClientAreaChromeHints
    AvnDefaultChrome = AvnPreferSystemChrome,
 }

+enum AvnPlatformResizeReason
+{
+    ResizeUnspecified,
+    ResizeUser,
+    ResizeApplication,
+    ResizeLayout,
+    ResizeDpiChange,
+}
+
 [uuid(809c652e-7396-11d2-9771-00a0c9b4d50c)]
 interface IAvaloniaNativeFactory : IUnknown
 {
@ -430,7 +439,7 @@ interface IAvnString : IUnknown
 [uuid(e5aca675-02b7-4129-aa79-d6e417210bda)]
 interface IAvnWindowBase : IUnknown
 {
-     HRESULT Show(bool activate);
+     HRESULT Show(bool activate, bool isDialog);
     HRESULT Hide();
     HRESULT Close();
     HRESULT Activate();
@ -438,7 +447,7 @@ interface IAvnWindowBase : IUnknown
     HRESULT GetFrameSize(AvnSize*ret);
     HRESULT GetScaling(double*ret);
     HRESULT SetMinMaxSize(AvnSize minSize, AvnSize maxSize);
-     HRESULT Resize(double width, double height);
+     HRESULT Resize(double width, double height, AvnPlatformResizeReason reason);
     HRESULT Invalidate(AvnRect rect);
     HRESULT BeginMoveDrag();
     HRESULT BeginResizeDrag(AvnWindowEdge edge);
@ -492,7 +501,7 @@ interface IAvnWindowBaseEvents : IUnknown
     void Closed();
     void Activated();
     void Deactivated();
-     void Resized([const] AvnSize& size);
+     void Resized([const] AvnSize& size, AvnPlatformResizeReason reason);
     void PositionChanged(AvnPoint position);
     void RawMouseEvent(AvnRawMouseEventType type,
                                uint timeStamp,
--- a/src/Avalonia.Visuals/Media/DrawingGroup.cs
+++ b/src/Avalonia.Visuals/Media/DrawingGroup.cs
@ -12,6 +12,12 @@ namespace Avalonia.Media
        public static readonly StyledProperty<Transform> TransformProperty =
            AvaloniaProperty.Register<DrawingGroup, Transform>(nameof(Transform));

+        public static readonly StyledProperty<Geometry> ClipGeometryProperty =
+            AvaloniaProperty.Register<DrawingGroup, Geometry>(nameof(ClipGeometry));
+
+        public static readonly StyledProperty<IBrush> OpacityMaskProperty =
+            AvaloniaProperty.Register<DrawingGroup, IBrush>(nameof(OpacityMask));
+
        public double Opacity
        {
            get => GetValue(OpacityProperty);
@ -24,6 +30,18 @@ namespace Avalonia.Media
            set => SetValue(TransformProperty, value);
        }

+        public Geometry ClipGeometry
+        {
+            get => GetValue(ClipGeometryProperty);
+            set => SetValue(ClipGeometryProperty, value);
+        }
+
+        public IBrush OpacityMask
+        {
+            get => GetValue(OpacityMaskProperty);
+            set => SetValue(OpacityMaskProperty, value);
+        }
+
        [Content]
        public AvaloniaList<Drawing> Children { get; } = new AvaloniaList<Drawing>();

@ -31,6 +49,8 @@ namespace Avalonia.Media
        {
            using (context.PushPreTransform(Transform?.Value ?? Matrix.Identity))
            using (context.PushOpacity(Opacity))
+            using (ClipGeometry != null ? context.PushGeometryClip(ClipGeometry) : default(DrawingContext.PushedState))
+            using (OpacityMask != null ? context.PushOpacityMask(OpacityMask, GetBounds()) : default(DrawingContext.PushedState))
            {
                foreach (var drawing in Children)
                {
--- a/src/Avalonia.X11/X11Window.cs
+++ b/src/Avalonia.X11/X11Window.cs
@ -336,7 +336,7 @@ namespace Avalonia.X11
        public IEnumerable<object> Surfaces { get; }
        public Action<RawInputEventArgs> Input { get; set; }
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        //TODO
        public Action<double> ScalingChanged { get; set; }
        public Action Deactivated { get; set; }
@ -510,7 +510,7 @@ namespace Avalonia.X11
                        UpdateImePosition();

                        if (changedSize && !updatedSizeViaScaling && !_popup)
-                            Resized?.Invoke(ClientSize);
+                            Resized?.Invoke(ClientSize, PlatformResizeReason.Unspecified);

                        Dispatcher.UIThread.RunJobs(DispatcherPriority.Layout);
                    }, DispatcherPriority.Layout);
@ -565,7 +565,7 @@ namespace Avalonia.X11
                    UpdateImePosition();
                    SetMinMaxSize(_scaledMinMaxSize.minSize, _scaledMinMaxSize.maxSize);
                    if(!skipResize)
-                        Resize(oldScaledSize, true);
+                        Resize(oldScaledSize, true, PlatformResizeReason.DpiChange);
                    return true;
                }

@ -616,7 +616,7 @@ namespace Avalonia.X11
            {
                // Occurs once the window has been mapped, which is the earliest the extents
                // can be retrieved, so invoke event to force update of TopLevel.FrameSize.
-                Resized.Invoke(ClientSize);
+                Resized.Invoke(ClientSize, PlatformResizeReason.Unspecified);
            }

            if (atom == _x11.Atoms._NET_WM_STATE)
@ -839,7 +839,7 @@ namespace Avalonia.X11
                XSetTransientForHint(_x11.Display, _handle, parent.Handle.Handle);
        }

-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
        {
            _wasMappedAtLeastOnce = true;
            XMapWindow(_x11.Display, _handle);
@ -862,19 +862,19 @@ namespace Avalonia.X11
        }


-        public void Resize(Size clientSize) => Resize(clientSize, false);
+        public void Resize(Size clientSize, PlatformResizeReason reason) => Resize(clientSize, false, reason);
        public void Move(PixelPoint point) => Position = point;
        private void MoveResize(PixelPoint position, Size size, double scaling)
        {
            Move(position);
            _scalingOverride = scaling;
            UpdateScaling(true);
-            Resize(size, true);
+            Resize(size, true, PlatformResizeReason.Layout);
        }

        PixelSize ToPixelSize(Size size) => new PixelSize((int)(size.Width * RenderScaling), (int)(size.Height * RenderScaling));
        
-        void Resize(Size clientSize, bool force)
+        void Resize(Size clientSize, bool force, PlatformResizeReason reason)
        {
            if (!force && clientSize == ClientSize)
                return;
@ -891,7 +891,7 @@ namespace Avalonia.X11
            if (force || !_wasMappedAtLeastOnce || (_popup && needImmediatePopupResize))
            {
                _realSize = pixelSize;
-                Resized?.Invoke(ClientSize);
+                Resized?.Invoke(ClientSize, reason);
            }
        }
        
@ -1024,15 +1024,22 @@ namespace Avalonia.X11
                side = NetWmMoveResize._NET_WM_MOVERESIZE_SIZE_BOTTOMLEFT;
            BeginMoveResize(side, e);
        }
-        
+
        public void SetTitle(string title)
        {
-            var data = Encoding.UTF8.GetBytes(title);
-            fixed (void* pdata = data)
+            if (string.IsNullOrEmpty(title))
            {
-                XChangeProperty(_x11.Display, _handle, _x11.Atoms._NET_WM_NAME, _x11.Atoms.UTF8_STRING, 8,
-                    PropertyMode.Replace, pdata, data.Length);
-                XStoreName(_x11.Display, _handle, title);
+                XDeleteProperty(_x11.Display, _handle, _x11.Atoms._NET_WM_NAME);
+            }
+            else
+            {
+                var data = Encoding.UTF8.GetBytes(title);
+                fixed (void* pdata = data)
+                {
+                    XChangeProperty(_x11.Display, _handle, _x11.Atoms._NET_WM_NAME, _x11.Atoms.UTF8_STRING, 8,
+                        PropertyMode.Replace, pdata, data.Length);
+                    XStoreName(_x11.Display, _handle, title);
+                }
            }
        }

--- a/src/Linux/Avalonia.LinuxFramebuffer/FramebufferToplevelImpl.cs
+++ b/src/Linux/Avalonia.LinuxFramebuffer/FramebufferToplevelImpl.cs
@ -69,7 +69,7 @@ namespace Avalonia.LinuxFramebuffer
        public IEnumerable<object> Surfaces { get; }
        public Action<RawInputEventArgs> Input { get; set; }
        public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
        public Action<double> ScalingChanged { get; set; }

        public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
--- a/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs
+++ b/src/Windows/Avalonia.Win32.Interop/Wpf/WpfTopLevelImpl.cs
@ -44,7 +44,7 @@ namespace Avalonia.Win32.Interop.Wpf
                ((FrameworkElement)PlatformImpl)?.InvalidateMeasure();
            }

-            protected override void HandleResized(Size clientSize)
+            protected override void HandleResized(Size clientSize, PlatformResizeReason reason)
            {
                ClientSize = clientSize;
                LayoutManager.ExecuteLayoutPass();
@ -114,7 +114,7 @@ namespace Avalonia.Win32.Interop.Wpf
            if (_finalSize == _previousSize)
                return finalSize;
            _previousSize = _finalSize;
-            _ttl.Resized?.Invoke(finalSize.ToAvaloniaSize());
+            _ttl.Resized?.Invoke(finalSize.ToAvaloniaSize(), PlatformResizeReason.Unspecified);
            return base.ArrangeOverride(finalSize);
        }

@ -236,7 +236,7 @@ namespace Avalonia.Win32.Interop.Wpf

        Action<RawInputEventArgs> ITopLevelImpl.Input { get; set; } //TODO
        Action<Rect> ITopLevelImpl.Paint { get; set; }
-        Action<Size> ITopLevelImpl.Resized { get; set; }
+        Action<Size, PlatformResizeReason> ITopLevelImpl.Resized { get; set; }
        Action<double> ITopLevelImpl.ScalingChanged { get; set; }

        Action<WindowTransparencyLevel> ITopLevelImpl.TransparencyLevelChanged { get; set; }
--- a/src/Windows/Avalonia.Win32/PopupImpl.cs
+++ b/src/Windows/Avalonia.Win32/PopupImpl.cs
@ -17,7 +17,7 @@ namespace Avalonia.Win32
        [ThreadStatic]
        private static IntPtr s_parentHandle;

-        public override void Show(bool activate)
+        public override void Show(bool activate, bool isDialog)
        {
            // Popups are always shown non-activated.
            UnmanagedMethods.ShowWindow(Handle.Handle, UnmanagedMethods.ShowWindowCommand.ShowNoActivate);
@ -135,7 +135,7 @@ namespace Avalonia.Win32
        private void MoveResize(PixelPoint position, Size size, double scaling)
        {
            Move(position);
-            Resize(size);
+            Resize(size, PlatformResizeReason.Layout);
            //TODO: We ignore the scaling override for now
        }

--- a/src/Windows/Avalonia.Win32/Win32Platform.cs
+++ b/src/Windows/Avalonia.Win32/Win32Platform.cs
@ -6,18 +6,16 @@ using System.IO;
 using System.Reactive.Disposables;
 using System.Runtime.InteropServices;
 using System.Threading;
-using Avalonia.Animation;
 using Avalonia.Controls;
+using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Controls.Platform;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.OpenGL;
-using Avalonia.OpenGL.Egl;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Threading;
 using Avalonia.Utilities;
-using Avalonia.Win32;
 using Avalonia.Win32.Input;
 using Avalonia.Win32.Interop;
 using static Avalonia.Win32.Interop.UnmanagedMethods;
@ -65,7 +63,7 @@ namespace Avalonia

 namespace Avalonia.Win32
 {
-    class Win32Platform : IPlatformThreadingInterface, IPlatformSettings, IWindowingPlatform, IPlatformIconLoader
+    class Win32Platform : IPlatformThreadingInterface, IPlatformSettings, IWindowingPlatform, IPlatformIconLoader, IPlatformLifetimeEventsImpl
    {
        private static readonly Win32Platform s_instance = new Win32Platform();
        private static Thread _uiThread;
@ -122,7 +120,8 @@ namespace Avalonia.Win32
                })
                .Bind<IPlatformIconLoader>().ToConstant(s_instance)
                .Bind<NonPumpingLockHelper.IHelperImpl>().ToConstant(new NonPumpingSyncContext.HelperImpl())
-                .Bind<IMountedVolumeInfoProvider>().ToConstant(new WindowsMountedVolumeInfoProvider());
+                .Bind<IMountedVolumeInfoProvider>().ToConstant(new WindowsMountedVolumeInfoProvider())
+                .Bind<IPlatformLifetimeEventsImpl>().ToConstant(s_instance);

            Win32GlManager.Initialize();

@ -207,6 +206,8 @@ namespace Avalonia.Win32

        public event Action<DispatcherPriority?> Signaled;

+        public event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
+
        [SuppressMessage("Microsoft.StyleCop.CSharp.NamingRules", "SA1305:FieldNamesMustNotUseHungarianNotation", Justification = "Using Win32 naming for consistency.")]
        private IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam)
        {
@ -214,6 +215,22 @@ namespace Avalonia.Win32
            {
                Signaled?.Invoke(null);
            }
+
+            if(msg == (uint)WindowsMessage.WM_QUERYENDSESSION)
+            {
+                if (ShutdownRequested != null)
+                {
+                    var e = new ShutdownRequestedEventArgs();
+
+                    ShutdownRequested(this, e);
+
+                    if(e.Cancel)
+                    {
+                        return IntPtr.Zero;
+                    }
+                }
+            }
+
            return UnmanagedMethods.DefWindowProc(hWnd, msg, wParam, lParam);
        }

@ -253,7 +270,7 @@ namespace Avalonia.Win32
        public IWindowImpl CreateEmbeddableWindow()
        {
            var embedded = new EmbeddedWindowImpl();
-            embedded.Show(true);
+            embedded.Show(true, false);
            return embedded;
        }

--- a/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs
@ -2,9 +2,10 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using Avalonia.Controls;
-using Avalonia.Controls.Platform;
+using Avalonia.Controls.Remote;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
+using Avalonia.Platform;
 using Avalonia.Win32.Input;
 using static Avalonia.Win32.Interop.UnmanagedMethods;

@ -18,7 +19,6 @@ namespace Avalonia.Win32
        {
            const double wheelDelta = 120.0;
            uint timestamp = unchecked((uint)GetMessageTime());
-
            RawInputEventArgs e = null;
            var shouldTakeFocus = false;

@ -94,14 +94,19 @@ namespace Avalonia.Win32
                        var newDisplayRect = Marshal.PtrToStructure<RECT>(lParam);
                        _scaling = dpi / 96.0;
                        ScalingChanged?.Invoke(_scaling);
-                        SetWindowPos(hWnd,
-                            IntPtr.Zero,
-                            newDisplayRect.left,
-                            newDisplayRect.top,
-                            newDisplayRect.right - newDisplayRect.left,
-                            newDisplayRect.bottom - newDisplayRect.top,
-                            SetWindowPosFlags.SWP_NOZORDER |
-                            SetWindowPosFlags.SWP_NOACTIVATE);
+                        
+                        using (SetResizeReason(PlatformResizeReason.DpiChange))
+                        { 
+                            SetWindowPos(hWnd,
+                                IntPtr.Zero,
+                                newDisplayRect.left,
+                                newDisplayRect.top,
+                                newDisplayRect.right - newDisplayRect.left,
+                                newDisplayRect.bottom - newDisplayRect.top,
+                                SetWindowPosFlags.SWP_NOZORDER |
+                                SetWindowPosFlags.SWP_NOACTIVATE);
+                        }
+
                        return IntPtr.Zero;
                    }

@ -364,6 +369,11 @@ namespace Avalonia.Win32
                    return IntPtr.Zero;
                }

+
+                case WindowsMessage.WM_ENTERSIZEMOVE:
+                    _resizeReason = PlatformResizeReason.User;
+                    break;
+
                case WindowsMessage.WM_SIZE:
                    {
                        using(NonPumpingSyncContext.Use())
@ -379,7 +389,7 @@ namespace Avalonia.Win32
                             size == SizeCommand.Maximized))
                        {
                            var clientSize = new Size(ToInt32(lParam) & 0xffff, ToInt32(lParam) >> 16);
-                            Resized(clientSize / RenderScaling);
+                            Resized(clientSize / RenderScaling, _resizeReason);
                        }

                        var windowState = size == SizeCommand.Maximized ?
@ -403,6 +413,10 @@ namespace Avalonia.Win32
                        return IntPtr.Zero;
                    }

+                case WindowsMessage.WM_EXITSIZEMOVE:
+                    _resizeReason = PlatformResizeReason.Unspecified;
+                    break;
+
                case WindowsMessage.WM_MOVE:
                    {
                        PositionChanged?.Invoke(new PixelPoint((short)(ToInt32(lParam) & 0xffff),
--- a/src/Windows/Avalonia.Win32/WindowImpl.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.cs
@ -53,6 +53,7 @@ namespace Avalonia.Win32
        private double _extendTitleBarHint = -1;
        private bool _isUsingComposition;
        private IBlurHost _blurHost;
+        private PlatformResizeReason _resizeReason;

 #if USE_MANAGED_DRAG
        private readonly ManagedWindowResizeDragHelper _managedDrag;
@ -160,7 +161,7 @@ namespace Avalonia.Win32

        public Action<Rect> Paint { get; set; }

-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }

        public Action<double> ScalingChanged { get; set; }

@ -482,7 +483,7 @@ namespace Avalonia.Win32
                : new ImmediateRenderer(root);
        }

-        public void Resize(Size value)
+        public void Resize(Size value, PlatformResizeReason reason)
        {
            int requestedClientWidth = (int)(value.Width * RenderScaling);
            int requestedClientHeight = (int)(value.Height * RenderScaling);
@ -494,6 +495,7 @@ namespace Avalonia.Win32
            {
                GetWindowRect(_hwnd, out var windowRect);

+                using var scope = SetResizeReason(reason);
                SetWindowPos(
                    _hwnd,
                    IntPtr.Zero,
@ -585,7 +587,7 @@ namespace Avalonia.Win32
            _shown = false;
        }

-        public virtual void Show(bool activate)
+        public virtual void Show(bool activate, bool isDialog)
        {
            SetParent(_parent);
            ShowWindow(_showWindowState, activate);
@ -930,7 +932,7 @@ namespace Avalonia.Win32
                _offScreenMargin = new Thickness();
                _extendedMargins = new Thickness();
                
-                Resize(new Size(rcWindow.Width/ RenderScaling, rcWindow.Height / RenderScaling));
+                Resize(new Size(rcWindow.Width/ RenderScaling, rcWindow.Height / RenderScaling), PlatformResizeReason.Layout);
            }

            if(!_isClientAreaExtended || (_extendChromeHints.HasAllFlags(ExtendClientAreaChromeHints.SystemChrome) &&
@ -1135,7 +1137,7 @@ namespace Avalonia.Win32
                        SetParent(null);

                        if (shown)
-                            Show(activated);
+                            Show(activated, false);
                    }
                }
                else
@ -1311,6 +1313,13 @@ namespace Avalonia.Win32
        /// <inheritdoc/>
        public AcrylicPlatformCompensationLevels AcrylicCompensationLevels { get; } = new AcrylicPlatformCompensationLevels(1, 0.8, 0);

+        private ResizeReasonScope SetResizeReason(PlatformResizeReason reason)
+        {
+            var old = _resizeReason;
+            _resizeReason = reason;
+            return new ResizeReasonScope(this, old);
+        }
+
        private struct SavedWindowInfo
        {
            public WindowStyles Style { get; set; }
@ -1325,5 +1334,19 @@ namespace Avalonia.Win32
            public SystemDecorations Decorations;
            public bool IsFullScreen;
        }
+
+        private struct ResizeReasonScope : IDisposable
+        {
+            private readonly WindowImpl _owner;
+            private readonly PlatformResizeReason _restore;
+            
+            public ResizeReasonScope(WindowImpl owner, PlatformResizeReason restore)
+            {
+                _owner = owner;
+                _restore = restore;
+            }
+
+            public void Dispose() => _owner._resizeReason = _restore;
+        }
    }
 }
--- a/src/iOS/Avalonia.iOS/AvaloniaView.cs
+++ b/src/iOS/Avalonia.iOS/AvaloniaView.cs
@ -96,7 +96,7 @@ namespace Avalonia.iOS
            public IEnumerable<object> Surfaces { get; set; }
            public Action<RawInputEventArgs> Input { get; set; }
            public Action<Rect> Paint { get; set; }
-            public Action<Size> Resized { get; set; }
+            public Action<Size, PlatformResizeReason> Resized { get; set; }
            public Action<double> ScalingChanged { get; set; }
            public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }
            public Action Closed { get; set; }
@ -127,7 +127,7 @@ namespace Avalonia.iOS

        public override void LayoutSubviews()
        {
-            _topLevelImpl.Resized?.Invoke(_topLevelImpl.ClientSize);
+            _topLevelImpl.Resized?.Invoke(_topLevelImpl.ClientSize, PlatformResizeReason.Layout);
            base.LayoutSubviews();
        }

--- a/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
@ -230,7 +230,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();
                popupImpl.Setup(x => x.Hide()).Verifiable();

                var window = PreparedWindow();
@ -268,7 +268,7 @@ namespace Avalonia.Controls.UnitTests
                Assert.True(c.IsOpen);

                popupImpl.Verify(x => x.Hide(), Times.Never);
-                popupImpl.Verify(x => x.Show(true), Times.Exactly(1));
+                popupImpl.Verify(x => x.Show(true, false), Times.Exactly(1));
            }
        }

@ -277,7 +277,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();
                popupImpl.Setup(x => x.Hide()).Verifiable();

                var window = PreparedWindow();
@ -306,7 +306,7 @@ namespace Avalonia.Controls.UnitTests

                Assert.False(c.IsOpen);
                popupImpl.Verify(x => x.Hide(), Times.Exactly(1));
-                popupImpl.Verify(x => x.Show(true), Times.Exactly(1));
+                popupImpl.Verify(x => x.Show(true, false), Times.Exactly(1));
            }
        }

@ -315,7 +315,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();
                popupImpl.Setup(x => x.Hide()).Verifiable();

                var sut = new ContextMenu();
@ -336,7 +336,7 @@ namespace Avalonia.Controls.UnitTests
                _mouse.Up(target);

                Assert.False(sut.IsOpen);
-                popupImpl.Verify(x => x.Show(true), Times.Once);
+                popupImpl.Verify(x => x.Show(true, false), Times.Once);
                popupImpl.Verify(x => x.Hide(), Times.Once);
            }
        }
@ -346,7 +346,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();
                popupImpl.Setup(x => x.Hide()).Verifiable();

                var sut = new ContextMenu();
@ -368,7 +368,7 @@ namespace Avalonia.Controls.UnitTests

                Assert.True(sut.IsOpen);
                popupImpl.Verify(x => x.Hide(), Times.Once);
-                popupImpl.Verify(x => x.Show(true), Times.Exactly(2));
+                popupImpl.Verify(x => x.Show(true, false), Times.Exactly(2));
            }
        }
        
@ -413,7 +413,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();

                bool eventCalled = false;
                var sut = new ContextMenu();
@ -429,7 +429,7 @@ namespace Avalonia.Controls.UnitTests

                Assert.True(eventCalled);
                Assert.False(sut.IsOpen);
-                popupImpl.Verify(x => x.Show(true), Times.Never);
+                popupImpl.Verify(x => x.Show(true, false), Times.Never);
            }
        }

@ -533,7 +533,7 @@ namespace Avalonia.Controls.UnitTests
        {
            using (Application())
            {
-                popupImpl.Setup(x => x.Show(true)).Verifiable();
+                popupImpl.Setup(x => x.Show(true, false)).Verifiable();
                popupImpl.Setup(x => x.Hide()).Verifiable();

                bool eventCalled = false;
@ -560,7 +560,7 @@ namespace Avalonia.Controls.UnitTests
                Assert.True(eventCalled);
                Assert.True(sut.IsOpen);

-                popupImpl.Verify(x => x.Show(true), Times.Once());
+                popupImpl.Verify(x => x.Show(true, false), Times.Once());
                popupImpl.Verify(x => x.Hide(), Times.Never);
            }
        }
--- a/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs
@ -232,7 +232,7 @@ namespace Avalonia.Controls.UnitTests
                    ++raised;
                };

-                lifetimeEvents.Raise(x => x.ShutdownRequested += null, new CancelEventArgs());
+                lifetimeEvents.Raise(x => x.ShutdownRequested += null, new ShutdownRequestedEventArgs());

                Assert.Equal(1, raised);
                Assert.Equal(new[] { window }, lifetime.Windows);
--- a/tests/Avalonia.Controls.UnitTests/TopLevelTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TopLevelTests.cs
@ -139,7 +139,7 @@ namespace Avalonia.Controls.UnitTests

                // The user has resized the window, so we can no longer auto-size.
                var target = new TestTopLevel(impl.Object);
-                impl.Object.Resized(new Size(100, 200));
+                impl.Object.Resized(new Size(100, 200), PlatformResizeReason.Unspecified);

                Assert.Equal(100, target.Width);
                Assert.Equal(200, target.Height);
--- a/tests/Avalonia.Controls.UnitTests/WindowBaseTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/WindowBaseTests.cs
@ -137,7 +137,7 @@ namespace Avalonia.Controls.UnitTests
                var target = new TestWindowBase(windowImpl.Object);
                target.IsVisible = true;

-                windowImpl.Verify(x => x.Show(true));
+                windowImpl.Verify(x => x.Show(true, false));
            }
        }

--- a/tests/Avalonia.Controls.UnitTests/WindowTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/WindowTests.cs
@ -663,10 +663,11 @@ namespace Avalonia.Controls.UnitTests
                    var clientSize = new Size(200, 200);
                    var maxClientSize = new Size(480, 480);

-                    windowImpl.Setup(x => x.Resize(It.IsAny<Size>())).Callback<Size>(size =>
+                    windowImpl.Setup(x => x.Resize(It.IsAny<Size>(), It.IsAny<PlatformResizeReason>()))
+                        .Callback<Size, PlatformResizeReason>((size, reason) =>
                    {
                        clientSize = size.Constrain(maxClientSize);
-                        windowImpl.Object.Resized?.Invoke(clientSize);
+                        windowImpl.Object.Resized?.Invoke(clientSize, reason);
                    });

                    windowImpl.Setup(x => x.ClientSize).Returns(() => clientSize);
@ -739,6 +740,36 @@ namespace Avalonia.Controls.UnitTests
                }
            }

+            [Fact]
+            public void SizeToContent_Should_Not_Be_Lost_On_Scaling_Change()
+            {
+                using (UnitTestApplication.Start(TestServices.StyledWindow))
+                {
+                    var child = new Canvas
+                    {
+                        Width = 209,
+                        Height = 117,
+                    };
+
+                    var target = new Window()
+                    {
+                        SizeToContent = SizeToContent.WidthAndHeight,
+                        Content = child
+                    };
+
+                    Show(target);
+
+                    // Size before and after DPI change is a real-world example, with size after DPI
+                    // change coming from Win32 WM_DPICHANGED.
+                    target.PlatformImpl.ScalingChanged(1.5);
+                    target.PlatformImpl.Resized(
+                        new Size(210.66666666666666, 118.66666666666667),
+                        PlatformResizeReason.DpiChange);
+
+                    Assert.Equal(SizeToContent.WidthAndHeight, target.SizeToContent);
+                }
+            }
+
            [Fact]
            public void Width_Height_Should_Be_Updated_When_SizeToContent_Is_WidthAndHeight()
            {
@ -791,8 +822,91 @@ namespace Avalonia.Controls.UnitTests
                    target.LayoutManager.ExecuteLayoutPass();

                    var windowImpl = Mock.Get(target.PlatformImpl);
-                    windowImpl.Verify(x => x.Resize(new Size(410, 800)));
+                    windowImpl.Verify(x => x.Resize(new Size(410, 800), PlatformResizeReason.Application));
+                    Assert.Equal(410, target.Width);
+                }
+            }
+
+
+            [Fact]
+            public void User_Resize_Of_Window_Width_Should_Reset_SizeToContent()
+            {
+                using (UnitTestApplication.Start(TestServices.StyledWindow))
+                {
+                    var target = new Window()
+                    {
+                        SizeToContent = SizeToContent.WidthAndHeight,
+                        Content = new Canvas
+                        {
+                            Width = 400,
+                            Height = 800,
+                        },
+                    };
+
+                    Show(target);
+                    Assert.Equal(400, target.Width);
+                    Assert.Equal(800, target.Height);
+
+                    target.PlatformImpl.Resized(new Size(410, 800), PlatformResizeReason.User);
+
                    Assert.Equal(410, target.Width);
+                    Assert.Equal(800, target.Height);
+                    Assert.Equal(SizeToContent.Height, target.SizeToContent);
+                }
+            }
+
+            [Fact]
+            public void User_Resize_Of_Window_Height_Should_Reset_SizeToContent()
+            {
+                using (UnitTestApplication.Start(TestServices.StyledWindow))
+                {
+                    var target = new Window()
+                    {
+                        SizeToContent = SizeToContent.WidthAndHeight,
+                        Content = new Canvas
+                        {
+                            Width = 400,
+                            Height = 800,
+                        },
+                    };
+
+                    Show(target);
+                    Assert.Equal(400, target.Width);
+                    Assert.Equal(800, target.Height);
+
+                    target.PlatformImpl.Resized(new Size(400, 810), PlatformResizeReason.User);
+
+                    Assert.Equal(400, target.Width);
+                    Assert.Equal(810, target.Height);
+                    Assert.Equal(SizeToContent.Width, target.SizeToContent);
+                }
+            }
+
+            [Fact]
+            public void Window_Resize_Should_Not_Reset_SizeToContent_If_CanResize_False()
+            {
+                using (UnitTestApplication.Start(TestServices.StyledWindow))
+                {
+                    var target = new Window()
+                    {
+                        SizeToContent = SizeToContent.WidthAndHeight,
+                        CanResize = false,
+                        Content = new Canvas
+                        {
+                            Width = 400,
+                            Height = 800,
+                        },
+                    };
+
+                    Show(target);
+                    Assert.Equal(400, target.Width);
+                    Assert.Equal(800, target.Height);
+
+                    target.PlatformImpl.Resized(new Size(410, 810), PlatformResizeReason.Unspecified);
+
+                    Assert.Equal(400, target.Width);
+                    Assert.Equal(800, target.Height);
+                    Assert.Equal(SizeToContent.WidthAndHeight, target.SizeToContent);
                }
            }

--- a/tests/Avalonia.UnitTests/MockWindowingPlatform.cs
+++ b/tests/Avalonia.UnitTests/MockWindowingPlatform.cs
@ -52,13 +52,14 @@ namespace Avalonia.UnitTests
                windowImpl.Object.PositionChanged?.Invoke(x);
            });

-            windowImpl.Setup(x => x.Resize(It.IsAny<Size>())).Callback<Size>(x =>
+            windowImpl.Setup(x => x.Resize(It.IsAny<Size>(), It.IsAny<PlatformResizeReason>()))
+                .Callback<Size, PlatformResizeReason>((x, y) =>
            {
                clientSize = x.Constrain(s_screenSize);
-                windowImpl.Object.Resized?.Invoke(clientSize);
+                windowImpl.Object.Resized?.Invoke(clientSize, y);
            });

-            windowImpl.Setup(x => x.Show(true)).Callback(() =>
+            windowImpl.Setup(x => x.Show(true, It.IsAny<bool>())).Callback(() =>
            {
                windowImpl.Object.Activated?.Invoke();
            });
@ -75,7 +76,7 @@ namespace Avalonia.UnitTests
            {
                clientSize = size.Constrain(s_screenSize);
                popupImpl.Object.PositionChanged?.Invoke(pos);
-                popupImpl.Object.Resized?.Invoke(clientSize);
+                popupImpl.Object.Resized?.Invoke(clientSize, PlatformResizeReason.Unspecified);
            });
            
            var positioner = new ManagedPopupPositioner(positionerHelper);