Introduce ActorPreviewWidget.

OpenRA.Game/Game.cs

@@ -502,6 +502,10 @@ namespace OpenRA
 
 				using (new PerfSample("render_widgets"))
 				{
+					Game.Renderer.WorldVoxelRenderer.BeginFrame();
+					Ui.PrepareRenderables();
+					Game.Renderer.WorldVoxelRenderer.EndFrame();
+
 					Ui.Draw();
 
 					if (ModData != null && ModData.CursorProvider != null)

OpenRA.Game/Graphics/Renderer.cs

@@ -108,7 +108,11 @@ namespace OpenRA.Graphics
 		public void BeginFrame(int2 scroll, float zoom)
 		{
 			Device.Clear();
+			SetViewportParams(scroll, zoom);
+		}
 
+		public void SetViewportParams(int2 scroll, float zoom)
+		{
 			var resolutionChanged = lastResolution != Resolution;
 			if (resolutionChanged)
 			{

OpenRA.Game/Widgets/Widget.cs

@@ -72,6 +72,8 @@ namespace OpenRA.Widgets
 
 		public static void Tick() { Root.TickOuter(); }
 
+		public static void PrepareRenderables() { Root.PrepareRenderablesOuter(); }
+
 		public static void Draw() { Root.DrawOuter(); }
 
 		public static bool HandleInput(MouseInput mi)
@@ -387,6 +389,18 @@ namespace OpenRA.Widgets
 			return handled;
 		}
 
+		public virtual void PrepareRenderables() { }
+
+		public virtual void PrepareRenderablesOuter()
+		{
+			if (IsVisible())
+			{
+				PrepareRenderables();
+				foreach (var child in Children)
+					child.PrepareRenderablesOuter();
+			}
+		}
+
 		public virtual void Draw() { }
 
 		public virtual void DrawOuter()