implement Screens api.

src/Avalonia.Windowing/Bindings/EventsLoop.cs

@@ -21,6 +21,13 @@ namespace Avalonia.Windowing.Bindings
             EventNotifier notifier
         );
 
+
+        [DllImport("winit_wrapper")]
+        private static extern UInt32 winit_events_loop_get_monitor_count(IntPtr handle);
+
+        [DllImport("winit_wrapper")]
+        private static extern Monitor winit_monitor_get_monitor(IntPtr handle, UInt32 id);
+
         public IntPtr Handle { get; private set;  }
 
         private readonly EventsLoopProxy _eventsLoopProxy;
@@ -71,9 +78,14 @@ namespace Avalonia.Windowing.Bindings
             winit_events_loop_destroy(Handle);
         }
 
-        public void GetAvailableMonitors() 
+        public UInt32 GetAvailableMonitors() 
+        {
+            return winit_events_loop_get_monitor_count(Handle);
+        }
+
+        public Monitor GetMonitor (UInt32 id)
         {
-            // TODO
+            return winit_monitor_get_monitor(Handle, id);
         }
 
         private class EventsLoopProxy : IDisposable

src/Avalonia.Windowing/Bindings/Monitor.cs

@@ -8,5 +8,6 @@ namespace Avalonia.Windowing.Bindings
     {
         public LogicalSize Size { get; set; }
         public LogicalPosition Position { get; set; }
+        public byte IsPrimary { get; set; }
     }
 }

src/Avalonia.Windowing/Bindings/Monitors.cs

@@ -1,17 +0,0 @@
-using System;
-using Avalonia.Platform;
-
-namespace Avalonia.Windowing.Bindings
-{
-    
-    public class Monitors : IScreenImpl
-    {
-        public int ScreenCount => 1;
-        public Screen[] AllScreens => new Screen[] { new Screen(Rect.Empty, Rect.Empty, true) };
-
-        public Monitors() 
-        {
-            
-        }
-    }
-}

src/Avalonia.Windowing/Bindings/Units.cs

@@ -3,6 +3,13 @@ using System.Runtime.InteropServices;
 
 namespace Avalonia.Windowing.Bindings
 {
+    [StructLayout(LayoutKind.Sequential)]
+    public struct PhysicalSize
+    {
+        public double Width { get; set; }
+        public double Height { get; set; }
+    }
+
     [StructLayout(LayoutKind.Sequential)]
     public struct LogicalPosition
     {

src/Avalonia.Windowing/ScreenImpl.cs

@@ -0,0 +1,44 @@
+using System;
+using Avalonia.Platform;
+using Avalonia.Windowing.Bindings;
+
+namespace Avalonia.Windowing
+{
+    public class ScreenImpl : IScreenImpl
+    {
+        private EventsLoop _loop;
+        private Screen[] _screens;
+
+        public ScreenImpl(EventsLoop loop)
+        {
+            _loop = loop;
+        }
+
+        public int ScreenCount => (int)_loop.GetAvailableMonitors();
+
+        private Screen[] _allScreens;
+        public Screen[] AllScreens
+        {
+            get
+            {
+                if (_allScreens == null  || ScreenCount != _allScreens.Length)
+                {
+                    Screen[] screens = new Screen[ScreenCount];
+
+                    for (UInt32 i = 0; i < ScreenCount; i++)
+                    {
+                        var monitor = _loop.GetMonitor(i);
+
+                        var bounds = new Rect(new Point(monitor.Position.X, monitor.Position.Y), new Size(monitor.Size.Width, monitor.Size.Height));
+
+                        // TODO winit doesnt support the concept of working area. (size minus area used by taskbar.
+
+                        screens[i] = new Screen(bounds, bounds, monitor.IsPrimary == 1);
+                    }
+
+                    _allScreens = screens;
+                }
+                return _allScreens;
+            }
+        }}
+}

src/Avalonia.Windowing/WindowImpl.cs

@@ -75,7 +75,7 @@ namespace Avalonia.Windowing
 
         public Size MaxClientSize => Size.Empty;
 
-        public IScreenImpl Screen => new Monitors();
+        public IScreenImpl Screen => new ScreenImpl(_windowWrapper.EventsLoop);
 
         public Size ClientSize
         {