support skinning renderers in attachments

Runtime/SkinAttachment.cs

 using System;
 using UnityEngine;
+using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
 using Unity.DemoTeam.Attributes;
 
 namespace Unity.DemoTeam.DigitalHuman
 		[NonSerialized] public MeshAdjacency meshAdjacency;
 		[NonSerialized] public MeshIslands meshIslands;
 
+		[NonSerialized] public Transform skinningBone;
+		[NonSerialized] public Matrix4x4 skinningBoneBindPose;
+		[NonSerialized] public Matrix4x4 skinningBoneBindPoseInverse;
+
+		void DiscoverSkinningBone()
+		{
+			skinningBone = null;
+			skinningBoneBindPose = Matrix4x4.identity;
+			skinningBoneBindPoseInverse = Matrix4x4.identity;
+
+			// search for skinning bone
+			var smr = GetComponent<SkinnedMeshRenderer>();
+			if (smr != null)
+			{
+				int skinningBoneIndex = -1;
+
+				unsafe
+				{
+					var boneWeights = meshAsset.GetAllBoneWeights();
+					var boneWeightPtr = (BoneWeight1*)boneWeights.GetUnsafeReadOnlyPtr();
+
+					for (int i = 0; i != boneWeights.Length; i++)
+					{
+						if (boneWeightPtr[i].weight > 0.0f)
+						{
+							if (skinningBoneIndex == -1)
+								skinningBoneIndex = boneWeightPtr[i].boneIndex;
+
+							if (skinningBoneIndex != boneWeightPtr[i].boneIndex)
+							{
+								skinningBoneIndex = -1;
+								break;
+							}
+						}
+					}
+				}
+
+				if (skinningBoneIndex != -1)
+				{
+					skinningBone = smr.bones[skinningBoneIndex];
+					skinningBoneBindPose = meshInstance.bindposes[skinningBoneIndex];
+					skinningBoneBindPoseInverse = skinningBoneBindPose.inverse;
+					//Debug.Log("discovered skinning bone for " + this.name + " : " + skinningBone.name);
+				}
+			}
+		}
+
 		protected override void OnMeshInstanceCreated()
 		{
 			meshAssetRadius = meshAsset.bounds.extents.magnitude;// conservative
 				meshIslands = new MeshIslands(meshAdjacency);
 			else
 				meshIslands.LoadFrom(meshAdjacency);
+
+			DiscoverSkinningBone();
 		}
 
 		protected override void OnMeshInstanceDeleted()
 				return;
 			}
 
-			Gizmos.matrix = this.transform.localToWorldMatrix;
-
+
+			if (skinningBone != null)
+				Gizmos.matrix = skinningBone.localToWorldMatrix * skinningBoneBindPose;
+			else
+				Gizmos.matrix = this.transform.localToWorldMatrix;
+
 
 			if (attachmentType == AttachmentType.Mesh)
 			{
 				var positions = meshBuffers.vertexPositions;
 
 				var targetPositions = new Vector3[positions.Length];
-				var subjectToTarget = target.transform.worldToLocalMatrix * this.transform.localToWorldMatrix;
-				var targetToSubject = this.transform.worldToLocalMatrix * target.transform.localToWorldMatrix;
+
+				Matrix4x4 targetToWorld = Matrix4x4.TRS(target.transform.position, target.transform.rotation, Vector3.one);
+				Matrix4x4 subjectToTarget;
+				Matrix4x4 targetToSubject;
+				{
+					if (skinningBone != null)
+					{
+						subjectToTarget = target.transform.worldToLocalMatrix * (skinningBone.localToWorldMatrix * skinningBoneBindPose);
+						targetToSubject = (skinningBoneBindPoseInverse * skinningBone.worldToLocalMatrix) * targetToWorld;
+					}
+					else
+					{
+						subjectToTarget = target.transform.worldToLocalMatrix * this.transform.localToWorldMatrix;
+						targetToSubject = this.transform.worldToLocalMatrix * targetToWorld;
+					}
+				}
 
 				for (int i = 0; i != positions.Length; i++)
 				{

Runtime/SkinAttachmentTarget.cs

 		{
 			Profiler.BeginSample("attach-subj");
 
-			var subjectToTarget = this.transform.worldToLocalMatrix * subject.transform.localToWorldMatrix;
+			Matrix4x4 subjectToTarget;
+			{
+				if (subject.skinningBone != null)
+					subjectToTarget = this.transform.worldToLocalMatrix * (subject.skinningBone.localToWorldMatrix * subject.skinningBoneBindPose);
+				else
+					subjectToTarget = this.transform.worldToLocalMatrix * subject.transform.localToWorldMatrix;
+			}
 
 			switch (subject.attachmentType)
 			{
 			Profiler.EndSample();
 		}
 
-		//--------
-		// Attach
-
-		// moved to SkinAttachmentDataBuilder
-
 		//---------
 		// Resolve
 
 						case SkinAttachment.AttachmentType.Mesh:
 						case SkinAttachment.AttachmentType.MeshRoots:
 							{
-								var targetToSubject = subject.transform.worldToLocalMatrix * targetToWorld;
+								Matrix4x4 targetToSubject;
+								{
+									// this used to always read:
+									//   var targetToSubject = subject.transform.worldToLocalMatrix * targetToWorld;
+									//
+									// to support attachments that have skinning renderers, we sometimes have to transform
+									// the vertices into a space that takes into account the subsequently applied skinning:
+									//    var targetToSubject = (subject.skinningBone.localToWorldMatrix * subject.meshInstanceBoneBindPose).inverse * targetToWorld;
+									//
+									// we can reshuffle a bit to get rid of the per-resolve inverse:
+									//    var targetToSubject = (subject.skinningBoneBindPoseInverse * subject.meshInstanceBone.worldToLocalMatrix) * targetToWorld;
+
+									if (subject.skinningBone != null)
+										targetToSubject = (subject.skinningBoneBindPoseInverse * subject.skinningBone.worldToLocalMatrix) * targetToWorld;
+									else
+										targetToSubject = subject.transform.worldToLocalMatrix * targetToWorld;
+								}
+
 								stagingJobs[i] = ScheduleResolve(attachmentIndex, attachmentCount, ref targetToSubject, resolvedPositions, resolvedNormals);
 							}
 							break;