add safety (dry-run with just counts) when rebuilding attachment data + newlines

Editor/SkinAttachmentTargetEditor.cs

 			if (driver.attachData == null)
 			{
 				EditorGUILayout.HelpBox("Must bind SkinAttachmentData asset before use.", MessageType.Error);
+				base.OnInspectorGUI();
 				return;
 			}
 

Runtime/SkinAttachmentDataBuilder.cs

 				BuildDataAttachToVertex(attachData, attachmentIndex, attachmentCount, meshInfo, targetPositions, targetOffsets.val, targetNormals, targetVertices.val, targetCount);
 			}
 		}
+
+		public static unsafe int CountPosesTriangle(in MeshInfo meshInfo, ref Vector3 target, int triangle)
+		{
+			SkinAttachmentPose dummyPose;
+			return BuildPosesTriangle(&dummyPose, meshInfo, ref target, triangle);
+		}
+
+		public static unsafe int CountPosesVertex(in MeshInfo meshInfo, ref Vector3 target, int vertex)
+		{
+			int poseCount = 0;
+			foreach (int triangle in meshInfo.meshAdjacency.vertexTriangles[vertex])
+			{
+				poseCount += CountPosesTriangle(meshInfo, ref target, triangle);
+			}
+			return poseCount;
+		}
+
+		public static unsafe void CountDataAttachToTriangle(ref int poseCount, ref int itemCount, in MeshInfo meshInfo, Vector3* targetPositions, int* targetTriangles, int targetCount)
+		{
+			for (int i = 0; i != targetCount; i++)
+			{
+				poseCount += CountPosesTriangle(meshInfo, ref targetPositions[i], targetTriangles[i]);
+				itemCount += 1;
+			}
+		}
+
+		public static unsafe void CountDataAttachToVertex(ref int poseCount, ref int itemCount, in MeshInfo meshInfo, Vector3* targetPositions, Vector3* targetOffsets, Vector3* targetNormals, int* targetVertices, int targetCount)
+		{
+			for (int i = 0; i != targetCount; i++)
+			{
+				poseCount += CountPosesVertex(meshInfo, ref targetPositions[i], targetVertices[i]);
+				itemCount += 1;
+			}
+		}
+
+		public static unsafe void CountDataAttachToClosestVertex(ref int poseCount, ref int itemCount, in MeshInfo meshInfo, Vector3* targetPositions, Vector3* targetNormals, int targetCount)
+		{
+			using (var targetOffsets = new UnsafeArrayVector3(targetCount))
+			using (var targetVertices = new UnsafeArrayInt(targetCount))
+			{
+				for (int i = 0; i != targetCount; i++)
+				{
+					targetVertices.val[i] = meshInfo.meshVertexBSP.FindNearest(ref targetPositions[i]);
+				}
+				CountDataAttachToVertex(ref poseCount, ref itemCount, meshInfo, targetPositions, targetOffsets.val, targetNormals, targetVertices.val, targetCount);
+			}
+		}
 	}
 }

Runtime/SkinAttachmentTarget.cs

 			{
 				subjects.RemoveAll(p => (p == null));
 
-				// pass 1: build poses
+				// pass 1: dry run
+				int dryRunPoseCount = 0;
+				int dryRunItemCount = 0;
+
-						CommitSubject(ref meshInfo, subjects[i]);
+						CommitSubject(ref meshInfo, subjects[i], dryRun: true, ref dryRunPoseCount, ref dryRunItemCount);
-				// pass 2: reference poses
+				dryRunPoseCount = Mathf.NextPowerOfTwo(dryRunPoseCount);
+				dryRunItemCount = Mathf.NextPowerOfTwo(dryRunItemCount);
+
+				ArrayUtils.ResizeCheckedIfLessThan(ref attachData.pose, dryRunPoseCount);
+				ArrayUtils.ResizeCheckedIfLessThan(ref attachData.item, dryRunItemCount);
+
+				// pass 2: build poses
+				for (int i = 0, n = subjects.Count; i != n; i++)
+				{
+					if (subjects[i].attachmentMode == SkinAttachment.AttachmentMode.BuildPoses)
+					{
+						CommitSubject(ref meshInfo, subjects[i], dryRun: false, ref dryRunPoseCount, ref dryRunPoseCount);
+					}
+				}
+
+				// pass 3: reference poses
 				for (int i = 0, n = subjects.Count; i != n; i++)
 				{
 					switch (subjects[i].attachmentMode)
 			}
 		}
 
-		void CommitSubject(ref MeshInfo meshInfo, SkinAttachment subject)
+		void CommitSubject(ref MeshInfo meshInfo, SkinAttachment subject, bool dryRun, ref int dryRunPoseCount, ref int dryRunItemCount)
 		{
 			Profiler.BeginSample("attach-subj");
 
 						fixed (int* attachmentIndex = &subject.attachmentIndex)
 						fixed (int* attachmentCount = &subject.attachmentCount)
 						{
-							BuildDataAttachToClosestVertex(attachData, attachmentIndex, attachmentCount, meshInfo, &targetPosition, &targetNormal, 1);
+							if (dryRun)
+								CountDataAttachToClosestVertex(ref dryRunPoseCount, ref dryRunItemCount, meshInfo, &targetPosition, &targetNormal, 1);
+							else
+								BuildDataAttachToClosestVertex(attachData, attachmentIndex, attachmentCount, meshInfo, &targetPosition, &targetNormal, 1);
 						}
 					}
 					break;
 							fixed (int* attachmentIndex = &subject.attachmentIndex)
 							fixed (int* attachmentCount = &subject.attachmentCount)
 							{
-								BuildDataAttachToClosestVertex(attachData, attachmentIndex, attachmentCount, meshInfo, targetPositions.val, targetNormals.val, subjectVertexCount);
+								if (dryRun)
+									CountDataAttachToClosestVertex(ref dryRunPoseCount, ref dryRunItemCount, meshInfo, targetPositions.val, targetNormals.val, subjectVertexCount);
+								else
+									BuildDataAttachToClosestVertex(attachData, attachmentIndex, attachmentCount, meshInfo, targetPositions.val, targetNormals.val, subjectVertexCount);
 							}
 						}
 					}
 							fixed (int* attachmentIndex = &subject.attachmentIndex)
 							fixed (int* attachmentCount = &subject.attachmentCount)
 							{
-								BuildDataAttachToVertex(attachData, attachmentIndex, attachmentCount, meshInfo, targetPositions.val, targetOffsets.val, targetNormals.val, targetVertices.val, subjectVertexCount);
+								if (dryRun)
+									CountDataAttachToVertex(ref dryRunPoseCount, ref dryRunItemCount, meshInfo, targetPositions.val, targetOffsets.val, targetNormals.val, targetVertices.val, subjectVertexCount);
+								else
+									BuildDataAttachToVertex(attachData, attachmentIndex, attachmentCount, meshInfo, targetPositions.val, targetOffsets.val, targetNormals.val, targetVertices.val, subjectVertexCount);
 							}
 						}
 					}