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()

OpenRA.Mods.Common/OpenRA.Mods.Common.csproj

@@ -510,6 +510,7 @@
     <Compile Include="SpriteLoaders\TmpRALoader.cs" />
     <Compile Include="SpriteLoaders\TmpTDLoader.cs" />
     <Compile Include="SpriteLoaders\ShpD2Loader.cs" />
+    <Compile Include="Widgets\ActorPreviewWidget.cs" />
     <Compile Include="Widgets\TerrainTemplatePreviewWidget.cs" />
     <Compile Include="LoadScreens\LogoStripeLoadScreen.cs" />
     <Compile Include="LoadScreens\BlankLoadScreen.cs" />

OpenRA.Mods.Common/Widgets/ActorPreviewWidget.cs

@@ -0,0 +1,116 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using OpenRA.Graphics;
+using OpenRA.Mods.Common.Graphics;
+using OpenRA.Mods.Common.Traits;
+using OpenRA.Primitives;
+using OpenRA.Widgets;
+
+namespace OpenRA.Mods.Common.Widgets
+{
+	public class ActorPreviewWidget : Widget
+	{
+		public bool Animate = false;
+		public Func<float> GetScale = () => 1f;
+
+		readonly WorldRenderer worldRenderer;
+
+		IActorPreview[] preview = new IActorPreview[0];
+		public int2 PreviewOffset { get; private set; }
+		public int2 IdealPreviewSize { get; private set; }
+
+		[ObjectCreator.UseCtor]
+		public ActorPreviewWidget(WorldRenderer worldRenderer)
+		{
+			this.worldRenderer = worldRenderer;
+		}
+
+		protected ActorPreviewWidget(ActorPreviewWidget other)
+			: base(other)
+		{
+			preview = other.preview;
+			worldRenderer = other.worldRenderer;
+		}
+
+		public override Widget Clone() { return new ActorPreviewWidget(this); }
+
+		public void SetPreview(ActorInfo actor, Player owner, TypeDictionary td)
+		{
+			var init = new ActorPreviewInitializer(actor, owner, worldRenderer, td);
+			preview = actor.Traits.WithInterface<IRenderActorPreviewInfo>()
+				.SelectMany(rpi => rpi.RenderPreview(init))
+				.ToArray();
+
+			// Calculate the preview bounds
+			PreviewOffset = int2.Zero;
+			IdealPreviewSize = int2.Zero;
+
+			var r = preview
+				.SelectMany(p => p.Render(worldRenderer, WPos.Zero))
+				.OrderBy(WorldRenderer.RenderableScreenZPositionComparisonKey)
+				.Select(rr => rr.PrepareRender(worldRenderer));
+
+			if (r.Any())
+			{
+				var b = r.First().ScreenBounds(worldRenderer);
+				foreach (var rr in r.Skip(1))
+					b = Rectangle.Union(b, rr.ScreenBounds(worldRenderer));
+
+				IdealPreviewSize = new int2(b.Width, b.Height);
+				PreviewOffset = -new int2(b.Left, b.Top) - IdealPreviewSize / 2;
+			}
+		}
+
+		IFinalizedRenderable[] renderables;
+		public override void PrepareRenderables()
+		{
+			renderables = preview
+				.SelectMany(p => p.Render(worldRenderer, WPos.Zero))
+				.OrderBy(WorldRenderer.RenderableScreenZPositionComparisonKey)
+				.Select(r => r.PrepareRender(worldRenderer))
+				.ToArray();
+		}
+
+		public override void Draw()
+		{
+			// HACK: The split between world and UI shaders is a giant PITA because it isn't
+			// feasible to maintain two parallel sets of renderables for the two cases.
+			// Instead, we temporarily hijack the world rendering context and set the position
+			// and zoom values to give the desired screen position and size.
+			var scale = GetScale();
+			var origin = RenderOrigin + new int2(RenderBounds.Size.Width / 2, RenderBounds.Size.Height / 2);
+
+			// The scale affects world -> screen transform, which we don't want when drawing the (fixed) UI.
+			if (scale != 1f)
+				origin = (1f / scale * origin.ToFloat2()).ToInt2();
+
+			Game.Renderer.Flush();
+			Game.Renderer.SetViewportParams(-origin - PreviewOffset, scale);
+
+			foreach (var r in renderables)
+				r.Render(worldRenderer);
+
+			Game.Renderer.Flush();
+			Game.Renderer.SetViewportParams(worldRenderer.Viewport.TopLeft, worldRenderer.Viewport.Zoom);
+		}
+
+		public override void Tick()
+		{
+			if (Animate)
+				foreach (var p in preview)
+					p.Tick();
+		}
+	}
+}