Add dirty rect parameter to Canvas.OnDraw

Xwt.Gtk/Xwt.GtkBackend/CanvasBackend.cs

@@ -184,7 +184,8 @@ namespace Xwt.GtkBackend
 		protected override bool OnExposeEvent (Gdk.EventExpose evnt)
 		{
 			Toolkit.Invoke (delegate {
-				EventSink.OnDraw (CreateContext ());
+				var a = evnt.Area;
+				EventSink.OnDraw (CreateContext (), new Rectangle (a.X, a.Y, a.Width, a.Height));
 			});
 			return base.OnExposeEvent (evnt);
 		}

Xwt.Mac/Xwt.Mac/CanvasBackend.cs

@@ -111,7 +111,7 @@ namespace Xwt.Mac
 		public override void DrawRect (System.Drawing.RectangleF dirtyRect)
 		{
 			Toolkit.Invoke (delegate {
-				eventSink.OnDraw (new ContextInfo ());
+				eventSink.OnDraw (new ContextInfo (), new Rectangle (dirtyRect.X, dirtyRect.Y, dirtyRect.Width, dirtyRect.Height));
 			});
 		}
 		

Xwt.WPF/Xwt.WPFBackend/CanvasBackend.cs

@@ -166,7 +166,7 @@ namespace Xwt.WPFBackend
 			this.wbitmap.Lock();
 
 			using (Graphics g = Graphics.FromImage (this.bbitmap))
-				CanvasEventSink.OnDraw (new DrawingContext (g));
+				CanvasEventSink.OnDraw (new DrawingContext (g), new Rectangle (0, 0, this.wbitmap.PixelWidth, this.wbitmap.PixelHeight));
 
 			if (this.fullRedraw || this.dirtyRects.Count == 0) {
 				this.wbitmap.AddDirtyRect (new Int32Rect (0, 0, this.wbitmap.PixelWidth, this.wbitmap.PixelHeight));

Xwt/Xwt.Backends/ICanvasBackend.cs

@@ -85,7 +85,7 @@ namespace Xwt.Backends
 		/// <param name='context'>
 		/// Drawing context
 		/// </param>
-		void OnDraw (object context);
+		void OnDraw (object context, Rectangle dirtyRect);
 	}
 }
 

Xwt/Xwt/Canvas.cs

@@ -65,7 +65,7 @@ namespace Xwt
 		
 		protected new class WidgetBackendHost: Widget.WidgetBackendHost, ICanvasEventSink
 		{
-			public void OnDraw (object context)
+			public void OnDraw (object context, Rectangle dirtyRect)
 			{
 				Context ctx = null;
 				try {