[Bf-blender-cvs] [5f8282b35fb] temp-angavrilov-constraints: Armature: fix bad B-Bone deformation blending with Preserve Volume.

[Alexander Gavrilov]

Commit: 5f8282b35fbfd667eee5a0814f9cb260929964ad
Author: Alexander Gavrilov
Date:   Tue Dec 29 19:55:29 2020 +0300
Branches: temp-angavrilov-constraints
https://developer.blender.org/rB5f8282b35fbfd667eee5a0814f9cb260929964ad

Armature: fix bad B-Bone deformation blending with Preserve Volume.

The double quaternion blending method in addition to the deformation
matrix of each bone requires their rest matrices. For ordinary bones
this literally should use the bone rest matrix without any ambiguity.

However, it was also using the bone rest matrix for all of its
B-Bone segments, which is incorrect and causes strange deformation
in some cases involving extreme non-uniform scale, especially
at boundaries between different B-Bones.

This changes both the Armature modifier and the Armature constraint
to use the actual segment rest matrices. Unlike bones, these can have
scale even in rest pose, so normalization is required.

===================================================================

M	source/blender/blenkernel/intern/armature.c
M	source/blender/blenkernel/intern/constraint.c

===================================================================

diff --git a/source/blender/blenkernel/intern/armature.c b/source/blender/blenkernel/intern/armature.c
index 5d3375cdb5e..8cd58968e04 100644
--- a/source/blender/blenkernel/intern/armature.c
+++ b/source/blender/blenkernel/intern/armature.c
@@ -1582,7 +1582,11 @@ void BKE_pchan_bbone_segments_cache_compute(bPoseChannel *pchan)
                   tmat,
                   b_bone_mats[0].mat);
 
-    mat4_to_dquat(&b_bone_dual_quats[a], bone->arm_mat, b_bone_mats[a + 1].mat);
+    /* Compute the orthonormal object space rest matrix of the segment. */
+    mul_m4_m4m4(tmat, bone->arm_mat, b_bone_rest[a].mat);
+    normalize_m4(tmat);
+
+    mat4_to_dquat(&b_bone_dual_quats[a], tmat, b_bone_mats[a + 1].mat);
   }
 }
 
diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index 9da17282a4f..51ffbf7feb8 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -2592,9 +2592,14 @@ static void armdef_accumulate_matrix(const float obmat[4][4],
 
   /* Accumulate the transformation. */
   if (r_sum_dq != NULL) {
+    float basemat_world[4][4];
     DualQuat tmpdq;
 
-    mat4_to_dquat(&tmpdq, basemat, mat);
+    /* Compute the orthonormal rest matrix in world space. */
+    mul_m4_m4m4(basemat_world, obmat, basemat);
+    orthogonalize_m4_stable(basemat_world, 1, true);
+
+    mat4_to_dquat(&tmpdq, basemat_world, mat);
     add_weighted_dq_dq(r_sum_dq, &tmpdq, weight);
   }
   else {
@@ -2611,7 +2616,7 @@ static void armdef_accumulate_bone(bConstraintTarget *ct,
                                    float r_sum_mat[4][4],
                                    DualQuat *r_sum_dq)
 {
-  float iobmat[4][4], basemat[4][4], co[3];
+  float iobmat[4][4], co[3];
   Bone *bone = pchan->bone;
   float weight = ct->weight;
 
@@ -2625,15 +2630,12 @@ static void armdef_accumulate_bone(bConstraintTarget *ct,
         co, bone->arm_head, bone->arm_tail, bone->rad_head, bone->rad_tail, bone->dist);
   }
 
-  /* Compute the quaternion base matrix. */
-  if (r_sum_dq != NULL) {
-    mul_m4_series(basemat, ct->tar->obmat, bone->arm_mat, iobmat);
-  }
-
   /* Find the correct bone transform matrix in world space. */
   if (bone->segments > 1 && bone->segments == pchan->runtime.bbone_segments) {
     Mat4 *b_bone_mats = pchan->runtime.bbone_deform_mats;
+    Mat4 *b_bone_rest_mats = pchan->runtime.bbone_rest_mats;
     float(*iamat)[4] = b_bone_mats[0].mat;
+    float basemat[4][4];
 
     /* The target is a B-Bone:
      * FIRST: find the segment (see b_bone_deform in armature.c)
@@ -2645,6 +2647,11 @@ static void armdef_accumulate_bone(bConstraintTarget *ct,
     float blend;
     BKE_pchan_bbone_deform_segment_index(pchan, y / bone->length, &index, &blend);
 
+    if (r_sum_dq != NULL) {
+      /* Compute the object space rest matrix of the segment. */
+      mul_m4_m4m4(basemat, bone->arm_mat, b_bone_rest_mats[index].mat);
+    }
+
     armdef_accumulate_matrix(ct->tar->obmat,
                              iobmat,
                              basemat,
@@ -2652,6 +2659,12 @@ static void armdef_accumulate_bone(bConstraintTarget *ct,
                              weight * (1.0f - blend),
                              r_sum_mat,
                              r_sum_dq);
+
+    if (r_sum_dq != NULL) {
+      /* Compute the object space rest matrix of the segment. */
+      mul_m4_m4m4(basemat, bone->arm_mat, b_bone_rest_mats[index + 1].mat);
+    }
+
     armdef_accumulate_matrix(ct->tar->obmat,
                              iobmat,
                              basemat,
@@ -2663,7 +2676,7 @@ static void armdef_accumulate_bone(bConstraintTarget *ct,
   else {
     /* Simple bone. This requires DEG_OPCODE_BONE_DONE dependency due to chan_mat. */
     armdef_accumulate_matrix(
-        ct->tar->obmat, iobmat, basemat, pchan->chan_mat, weight, r_sum_mat, r_sum_dq);
+        ct->tar->obmat, iobmat, bone->arm_mat, pchan->chan_mat, weight, r_sum_mat, r_sum_dq);
   }
 
   /* Accumulate the weight. */