add conditional support for MeshUpdateFlags

Runtime/MeshTools/MeshEx.cs

 using UnityEngine;
+using UnityEngine.Rendering;
-public static  class MeshEx
+public static class MeshEx
+#if UNITY_2020_1_OR_NEWER
+	const MeshUpdateFlags UPDATE_FLAGS_SILENT =
+		MeshUpdateFlags.DontNotifyMeshUsers |
+		MeshUpdateFlags.DontRecalculateBounds |
+		MeshUpdateFlags.DontResetBoneBounds;
+#endif
+
+#endif
+	}
+
+	public static void SilentlySetVertices(this Mesh mesh, Vector3[] positions)
+	{
+#if UNITY_2020_1_OR_NEWER
+		mesh.SetVertices(positions, 0, positions.Length, UPDATE_FLAGS_SILENT);
+#else
+		mesh.EnableSilentWrites(true);
+		mesh.SetVertices(positions, 0, positions.Length);
+		mesh.EnableSilentWrites(false);
+#endif
+	}
+
+	public static void SilentlySetNormals(this Mesh mesh, Vector3[] normals)
+	{
+#if UNITY_2020_1_OR_NEWER
+		mesh.SetNormals(normals, 0, normals.Length, UPDATE_FLAGS_SILENT);
+#else
+		mesh.EnableSilentWrites(true);
+		mesh.SetNormals(normals, 0, normals.Length);
+		mesh.EnableSilentWrites(false);
+#endif
+	}
+
+	public static void SilentlyRecalculateTangents(this Mesh mesh)
+	{
+#if UNITY_2020_1_OR_NEWER
+		mesh.RecalculateTangents(UPDATE_FLAGS_SILENT);
+#else
+		mesh.EnableSilentWrites(true);
+		mesh.RecalculateTangents();
+		mesh.EnableSilentWrites(false);
+#endif
+	}
+
+	public static void SilentlyRecalculateNormals(this Mesh mesh)
+	{
+#if UNITY_2020_1_OR_NEWER
+		mesh.RecalculateNormals(UPDATE_FLAGS_SILENT);
+#else
+		mesh.EnableSilentWrites(true);
+		mesh.RecalculateNormals();
+		mesh.EnableSilentWrites(false);
+#endif
+	}
+
+	public static void SilentlyRecalculateBounds(this Mesh mesh)
+	{
+#if UNITY_2020_1_OR_NEWER
+		mesh.RecalculateBounds(UPDATE_FLAGS_SILENT);
+#else
+		mesh.EnableSilentWrites(true);
+		mesh.RecalculateBounds();
+		mesh.EnableSilentWrites(false);
 #endif
 	}
 }

Runtime/SkinAttachment.cs

 			var forceRecalculateAny = forceRecalculateBounds || forceRecalculateNormals || forceRecalculateTangents;
 			if (forceRecalculateAny && meshInstance != null)
 			{
-				meshInstance.EnableSilentWrites(true);
-
-				if (forceRecalculateNormals)
-					meshInstance.RecalculateNormals();
-					meshInstance.RecalculateTangents();
+					meshInstance.SilentlyRecalculateTangents();
+				if (forceRecalculateNormals)
+					meshInstance.SilentlyRecalculateNormals();
-					meshInstance.RecalculateBounds();
-
-				meshInstance.EnableSilentWrites(false);
+					meshInstance.SilentlyRecalculateBounds();
 			}
 		}
 

Runtime/SkinAttachmentTarget.cs

 									break;
 								}
 
-								subject.meshInstance.EnableSilentWrites(true);
-								subject.meshInstance.vertices = stagingData[indexPos];
-								subject.meshInstance.normals = stagingData[indexNrm];
-								subject.meshInstance.EnableSilentWrites(false);
+								subject.meshInstance.SilentlySetVertices(stagingData[indexPos]);
+								subject.meshInstance.SilentlySetNormals(stagingData[indexPos]);
 
 								//Profiler.BeginSample("recalc-bounds");
 								//subject.meshInstance.RecalculateBounds();

Runtime/SkinDeformationRenderer.cs

 				smr.SetPropertyBlock(smrProps);
 			}
 
-			meshInstance.EnableSilentWrites(true);
-			meshInstance.vertices = blendedPositions;
-			meshInstance.normals = blendedNormals;
-			meshInstance.EnableSilentWrites(false);
+			meshInstance.SilentlySetVertices(blendedPositions);
+			meshInstance.SilentlySetNormals(blendedNormals);
-				meshInstance.EnableSilentWrites(true);
-				meshInstance.RecalculateTangents();
-				meshInstance.EnableSilentWrites(false);
+				meshInstance.SilentlyRecalculateTangents();
 			}
 
 			if (renderFittedWeights)