Added support for draggable BackgroundWidgets

OpenRA.Game/Widgets/BackgroundWidget.cs

@@ -8,12 +8,15 @@
  */
 #endregion
 
+using System.Drawing;
+
 namespace OpenRA.Widgets
 {
 	public class BackgroundWidget : Widget
 	{
 		public readonly string Background = "dialog";
 		public readonly bool ClickThrough = false;
+		public readonly bool Draggable = false;
 
 		public override void Draw()
 		{
@@ -22,9 +25,33 @@ namespace OpenRA.Widgets
 
 		public BackgroundWidget() : base() { }
 
+		bool moving;
+		int2? prevMouseLocation;
+
 		public override bool HandleMouseInput(MouseInput mi)
 		{
-			return !ClickThrough;
+			if (ClickThrough) return false;
+			if (!Draggable || moving && (!TakeFocus(mi) || mi.Button != MouseButton.Left)) return true;
+			if (prevMouseLocation == null)
+				prevMouseLocation = mi.Location;
+			var vec = mi.Location - (int2)prevMouseLocation;
+			prevMouseLocation = mi.Location;
+			switch (mi.Event)
+			{
+				case MouseInputEvent.Up:
+					moving = false;
+					LoseFocus(mi);
+					break;
+				case MouseInputEvent.Down:
+					moving = true;
+					Bounds = new Rectangle(Bounds.X + vec.X, Bounds.Y + vec.Y, Bounds.Width, Bounds.Height);
+					break;
+				case MouseInputEvent.Move:
+					if (moving)
+						Bounds = new Rectangle(Bounds.X + vec.X, Bounds.Y + vec.Y, Bounds.Width, Bounds.Height);
+					break;
+			}
+			return true;
 		}
 
 		protected BackgroundWidget(BackgroundWidget other)
@@ -32,6 +59,7 @@ namespace OpenRA.Widgets
 		{
 			Background = other.Background;
 			ClickThrough = other.ClickThrough;
+			Draggable = other.Draggable;
 		}
 
 		public override Widget Clone() { return new BackgroundWidget(this); }