Add Window closing support

src/Avalonia.Windowing/Bindings/EventNotifier.cs

@@ -9,7 +9,8 @@ namespace Avalonia.Windowing.Bindings
     public delegate void KeyboardEventCallback(WindowId windowId, KeyboardEvent keyboardEvent);
     public delegate void CharacterEventCallback(WindowId windowId, CharacterEvent characterEvent);
     public delegate void AwakenedEventCallback();
-     
+    public delegate byte ShouldExitEventLoopCallback(WindowId windowId);
+
     [StructLayout(LayoutKind.Sequential)]
     public struct EventNotifier
     {
@@ -18,5 +19,6 @@ namespace Avalonia.Windowing.Bindings
         public ResizeEventCallback OnResized;
         public KeyboardEventCallback OnKeyboardEvent;
         public CharacterEventCallback OnCharacterEvent;
+        public ShouldExitEventLoopCallback OnShouldExitEventLoop;
     }
 }

src/Avalonia.Windowing/Bindings/EventsLoop.cs

@@ -18,15 +18,6 @@ namespace Avalonia.Windowing.Bindings
             EventNotifier notifier
         );
 
-        [UnmanagedFunctionPointer(CallingConvention.Cdecl)] 
-        public delegate void TimerDel();
-
-        [DllImport("winit_wrapper")]
-        private static extern void winit_events_loop_timer
-        (
-            TimerDel del2
-        );
-
         public IntPtr Handle { get; private set;  }
         private readonly EventsLoopProxy _eventsLoopProxy;
         private readonly EventNotifier _notifier;
@@ -36,6 +27,7 @@ namespace Avalonia.Windowing.Bindings
         public event MouseEventCallback OnMouseEvent;
         public event AwakenedEventCallback OnAwakened;
         public event ResizeEventCallback OnResized;
+        public event ShouldExitEventLoopCallback OnShouldExitEventLoop;
 
         public EventsLoop()
         {
@@ -47,7 +39,8 @@ namespace Avalonia.Windowing.Bindings
                 OnKeyboardEvent = (windowId, keyboardEvent) => OnKeyboardEvent?.Invoke(windowId, keyboardEvent),
                 OnCharacterEvent = (windowId, characterEvent) => OnCharacterEvent?.Invoke(windowId, characterEvent),
                 OnResized = (windowId, resizeEvent) => OnResized?.Invoke(windowId, resizeEvent),
-                OnAwakened = () => OnAwakened?.Invoke()
+                OnAwakened = () => OnAwakened?.Invoke(),
+                OnShouldExitEventLoop = (windowId) => (byte)OnShouldExitEventLoop?.Invoke(windowId)
             };
         }
 
@@ -59,11 +52,6 @@ namespace Avalonia.Windowing.Bindings
             );
         }
 
-        public void RunTimer(TimerDel del)
-        {
-            winit_events_loop_timer(del);   
-        }
-
         public void Wakeup()
         {
             _eventsLoopProxy.Wakeup();

src/Avalonia.Windowing/Bindings/GlWindow.cs

@@ -71,44 +71,56 @@ namespace Avalonia.Windowing.Bindings
             _handle = winit_gl_window_new(EventsLoop.Handle);
         }
 
+        private bool disposed = false;
         public void Dispose()
         {
-            winit_gl_window_destroy(_handle);
+            if (!disposed)
+            {
+                winit_gl_window_destroy(_handle);
+                disposed = true;
+            }
         }
 
         public void SetTitle(string title)
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_set_title(_handle, title);
         }
 
         public void SetSize(double width, double height) 
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_set_size(_handle, width, height);   
         }
 
         public void SetPosition(double x, double y)
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             var position = new LogicalPosition { X = x, Y = y };
             winit_gl_window_set_position(_handle, position);
         }
 
         public void Present()
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_present(_handle);
         }
 
         public IntPtr GetProcAddress(string symbol)
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             return winit_gl_window_get_proc_addr(_handle, symbol);
         }
 
         public (double, double) GetSize() {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             var size = winit_gl_window_get_size(_handle);
             return (size.Width, size.Height);
         }
 
         public double GetScaleFactor ()
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             return winit_gl_window_get_dpi_scale_factor(_handle);
         }
 
@@ -119,27 +131,32 @@ namespace Avalonia.Windowing.Bindings
 
         public (double, double) GetPosition()
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             var position = winit_gl_window_get_position(_handle);
             return (position.X, position.Y);
         }
 
         public void Show()
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_show(_handle);
         }
 
         public void ResizeContext(double width, double height)
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_resize_context(_handle, width, height);
         }
 
         public void ToggleDecorations(bool visible)
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_set_decorations(_handle, visible ? 1 : 0);
         }
 
         public void Hide()
         {
+            Contract.Requires<InvalidOperationException>(disposed != true);
             winit_gl_window_hide(_handle);
         }
 

src/Avalonia.Windowing/WIndowingPlatform.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Reactive.Disposables;
 using System.Runtime.InteropServices;
 using System.Threading;
@@ -42,9 +43,18 @@ namespace Avalonia.Windowing
             _eventsLoop.OnCharacterEvent += _eventsLoop_OnCharacterEvent;
             _eventsLoop.OnAwakened += _eventsLoop_Awakened;
             _eventsLoop.OnResized += _eventsLoop_Resized;
+            _eventsLoop.OnShouldExitEventLoop += _eventsLoop_OnShouldExitEventLoop;
             _windows = new Dictionary<WindowId, WindowImpl>();
         }
 
+        byte _eventsLoop_OnShouldExitEventLoop(WindowId windowId)
+        {
+            if (_windows.ContainsKey(windowId))
+                _windows.Remove(windowId);
+            
+            return _windows.Any() ? (byte)0 : (byte)1;
+        }
+
         void _eventsLoop_Resized(WindowId windowId, ResizeEvent resizeEvent)
         {
             Dispatcher.UIThread.RunJobs(DispatcherPriority.Layout);
@@ -159,8 +169,6 @@ namespace Avalonia.Windowing
             _eventsLoop.Wakeup();
         }
 
-        private IList<TimerDel> timerTickers = new List<TimerDel>();
-
         public IDisposable StartTimer(DispatcherPriority priority, TimeSpan interval, Action tick)
         {
             // TODO: Need a way to cancel a timer when Dispose is called. 

src/Avalonia.Windowing/WindowImpl.cs

@@ -131,7 +131,7 @@ namespace Avalonia.Windowing
         public Point PointToClient(Point point)
         {
             var position = Position;
-            return new Point(point.X + position.X, point.Y + position.Y);
+            return new Point(point.X - position.X, point.Y - position.Y);
         }
 
         public Point PointToScreen(Point point)