Decouple the usage of PDT evaluator of chart player.

Assets/Cryville/Crtr/PdtEvaluator.cs

@@ -10,6 +10,15 @@ using UnityEngine;
 
 namespace Cryville.Crtr {
 	public class PdtEvaluator : PdtEvaluatorBase {
+		[ThreadStatic]
+		static PdtEvaluator m_instance;
+		public static PdtEvaluator Instance {
+			get {
+				if (m_instance == null) m_instance = new PdtEvaluator();
+				return m_instance;
+			}
+		}
+
 		readonly Dictionary<PdtOperatorSignature, PdtOperator> _shortops = new Dictionary<PdtOperatorSignature, PdtOperator>();
 		readonly IntKeyedDictionary<PdtOperator> _ctxops = new IntKeyedDictionary<PdtOperator>();
 
@@ -152,6 +161,18 @@ namespace Cryville.Crtr {
 			ContextCascade[--_cascadeHeight].Clear();
 		}
 
+		public void Reset() {
+			_cascadeHeight = 0;
+			ContextCascadeBlocks.Clear();
+			ContextCascadeBlocks.Push(0);
+			ContextEvent = null;
+			ContextJudge = null;
+			ContextSelfValue = null;
+			ContextSkinContainer = null;
+			ContextState = null;
+			ContextTransform = null;
+		}
+
 		public PdtEvaluator() {
 			ContextCascadeBlocks.Push(0);
 			for (int i = 0; i < ContextCascade.Length; i++) ContextCascade[i] = new IntKeyedDictionary<PropSrc>();