Cleaner attempt at rendering map previews on the fly

OpenRA.FileFormats/Map/MapStub.cs

@@ -45,7 +45,7 @@ namespace OpenRA.FileFormats
 		public int2 BottomRight;
 		public int Width { get { return BottomRight.X - TopLeft.X; } }
 		public int Height { get { return BottomRight.Y - TopLeft.Y; } }
-		public Lazy<Bitmap> Preview;
+		public Map Map { get { return new Map(Package); }}
 	
 		static List<string> Fields = new List<string>() {
 			"Selectable", "Title", "Description", "Author", "PlayerCount", "Tileset", "TopLeft", "BottomRight"
@@ -64,10 +64,6 @@ namespace OpenRA.FileFormats
 				Waypoints.Add(wp.Key, new int2(int.Parse(loc[0]), int.Parse(loc[1])));
 			}
 
-			Preview = Lazy.New(
-				() => new Bitmap(Package.GetContent("preview.png"))
-			);
-
 			Uid = Package.GetContent("map.uid").ReadAllText();
 		}
 		

OpenRA.Game/Graphics/Minimap.cs

@@ -162,5 +162,43 @@ namespace OpenRA.Graphics
 				(int)(bounds.Width * fx + bounds.Left),
 				(int)(bounds.Height * fy + bounds.Top));
 		}
+		
+		
+		static int NextPowerOf2(int v)
+		{
+			--v;
+			v |= v >> 1;
+			v |= v >> 2;
+			v |= v >> 4;
+			v |= v >> 8;
+			++v;
+			return v;
+		}
+		
+		public static Bitmap RenderMapPreview(MapStub stub)
+		{
+			Map map = stub.Map;
+			var tileset = Rules.TileSets[map.Tileset];
+			var size = NextPowerOf2(Math.Max(map.Width, map.Height));
+			Bitmap terrain = new Bitmap(size, size);
+			
+			for (var x = 0; x < map.Width; x++)
+				for (var y = 0; y < map.Height; y++)
+				{
+					var mapX = x + map.TopLeft.X;
+					var mapY = y + map.TopLeft.Y;
+					var type = tileset.GetTerrainType(map.MapTiles[mapX, mapY]);
+					string res = null;
+					if (map.MapResources[mapX, mapY].type != 0)
+						res = Rules.Info["world"].Traits.WithInterface<ResourceTypeInfo>()
+							.Where(t => t.ResourceType == map.MapResources[mapX, mapY].type)
+							.Select(t => t.TerrainType).FirstOrDefault();
+					if (res != null)
+						type = res;
+					
+					terrain.SetPixel(x, y, tileset.Terrain[type].Color);
+				}
+			return terrain;
+		}
 	}
 }

OpenRA.Game/Widgets/MapPreviewWidget.cs

@@ -20,6 +20,8 @@ namespace OpenRA.Widgets
 		
 		public MapPreviewWidget() : base() { }
 
+		static Cache<MapStub,Bitmap> PreviewCache = new Cache<MapStub, Bitmap>(stub => Minimap.RenderMapPreview(stub));
+		
 		protected MapPreviewWidget(MapPreviewWidget other)
 			: base(other)
 		{
@@ -74,10 +76,11 @@ namespace OpenRA.Widgets
 
 			if( mapPreviewDirty )
 			{
-				if( mapChooserSheet == null || mapChooserSheet.Size.Width != map.Width || mapChooserSheet.Size.Height != map.Height )
+				var preview = PreviewCache[map];
-					mapChooserSheet = new Sheet( Game.renderer, new Size( map.Width, map.Height ) );
+				if( mapChooserSheet == null || mapChooserSheet.Size.Width != preview.Width || mapChooserSheet.Size.Height != preview.Height )
+					mapChooserSheet = new Sheet( Game.renderer, new Size( preview.Width, preview.Height ) );
 
-				mapChooserSheet.Texture.SetData( map.Preview.Value );
+				mapChooserSheet.Texture.SetData( preview );
 				mapChooserSprite = new Sprite( mapChooserSheet, new Rectangle( 0, 0, map.Width, map.Height ), TextureChannel.Alpha );
 				mapPreviewDirty = false;
 			}