Rewrite sequence loading logic.

Multiple layers of Lazy<T>ness are replaced with
an explicit two-part loading scheme.

Sequences are parsed immediately, without the need
for the sprite assets, and tell the SpriteCache
which frames they need. Use-cases that want the
actual sprites can then tell the SpriteCache to
load the frames and the sequences to resolve the
sprites.

OpenRA.Game/Graphics/SequenceSet.cs

@@ -0,0 +1,119 @@
+#region Copyright & License Information
+/*
+ * Copyright (c) The OpenRA Developers and Contributors
+ * 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, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using OpenRA.FileSystem;
+using OpenRA.Primitives;
+
+namespace OpenRA.Graphics
+{
+	public interface ISpriteSequence
+	{
+		string Name { get; }
+		int Length { get; }
+		int Facings { get; }
+		int Tick { get; }
+		int ZOffset { get; }
+		int ShadowZOffset { get; }
+		Rectangle Bounds { get; }
+		bool IgnoreWorldTint { get; }
+		float Scale { get; }
+		void ResolveSprites(SpriteCache cache);
+		Sprite GetSprite(int frame);
+		Sprite GetSprite(int frame, WAngle facing);
+		(Sprite, WAngle) GetSpriteWithRotation(int frame, WAngle facing);
+		Sprite GetShadow(int frame, WAngle facing);
+		float GetAlpha(int frame);
+	}
+
+	public interface ISpriteSequenceLoader
+	{
+		int BgraSheetSize { get; }
+		int IndexedSheetSize { get; }
+		IReadOnlyDictionary<string, ISpriteSequence> ParseSequences(ModData modData, string tileSet, SpriteCache cache, MiniYamlNode node);
+	}
+
+	public sealed class SequenceSet : IDisposable
+	{
+		readonly ModData modData;
+		readonly string tileSet;
+		readonly IReadOnlyDictionary<string, IReadOnlyDictionary<string, ISpriteSequence>> images;
+		public SpriteCache SpriteCache { get; }
+
+		public SequenceSet(IReadOnlyFileSystem fileSystem, ModData modData, string tileSet, MiniYaml additionalSequences)
+		{
+			this.modData = modData;
+			this.tileSet = tileSet;
+			SpriteCache = new SpriteCache(fileSystem, modData.SpriteLoaders, modData.SpriteSequenceLoader.BgraSheetSize, modData.SpriteSequenceLoader.IndexedSheetSize);
+			using (new Support.PerfTimer("LoadSequences"))
+				images = Load(fileSystem, additionalSequences);
+		}
+
+		public ISpriteSequence GetSequence(string image, string sequence)
+		{
+			if (!images.TryGetValue(image, out var sequences))
+				throw new InvalidOperationException($"Image `{image}` does not have any sequences defined.");
+
+			if (!sequences.TryGetValue(sequence, out var seq))
+				throw new InvalidOperationException($"Image `{image}` does not have a sequence named `{sequence}`.");
+
+			return seq;
+		}
+
+		public IEnumerable<string> Images => images.Keys;
+
+		public bool HasSequence(string image, string sequence)
+		{
+			if (!images.TryGetValue(image, out var sequences))
+				throw new InvalidOperationException($"Image `{image}` does not have any sequences defined.");
+
+			return sequences.ContainsKey(sequence);
+		}
+
+		public IEnumerable<string> Sequences(string image)
+		{
+			if (!images.TryGetValue(image, out var sequences))
+				throw new InvalidOperationException($"Image `{image}` does not have any sequences defined.");
+
+			return sequences.Keys;
+		}
+
+		IReadOnlyDictionary<string, IReadOnlyDictionary<string, ISpriteSequence>> Load(IReadOnlyFileSystem fileSystem, MiniYaml additionalSequences)
+		{
+			var nodes = MiniYaml.Load(fileSystem, modData.Manifest.Sequences, additionalSequences);
+			var images = new Dictionary<string, IReadOnlyDictionary<string, ISpriteSequence>>();
+			foreach (var node in nodes)
+			{
+				// Nodes starting with ^ are inheritable but never loaded directly
+				if (node.Key.StartsWith(ActorInfo.AbstractActorPrefix, StringComparison.Ordinal))
+					continue;
+
+				images[node.Key] = modData.SpriteSequenceLoader.ParseSequences(modData, tileSet, SpriteCache, node);
+			}
+
+			return images;
+		}
+
+		public void LoadSprites()
+		{
+			SpriteCache.LoadReservations(modData);
+			foreach (var sequences in images.Values)
+				foreach (var sequence in sequences)
+					sequence.Value.ResolveSprites(SpriteCache);
+		}
+
+		public void Dispose()
+		{
+			SpriteCache.Dispose();
+		}
+	}
+}