Bugfix #20708: segmented bones don't work well with spline IK

There was a slight discreptancy between the tail values calculated on the spline before the head was displaced for the "chain offset" option and after this operation. However, only the original version got set. 

This small difference resulted in B-Bones thinking that the endpoints of the bones were in places that they were not in, hence causing the curly patterns observed in the report.

2 files changed, 14 insertions, 4 deletions

diff --git a/source/blender/blenkernel/BKE_armature.h b/source/blender/blenkernel/BKE_armature.h
index 242de4d788b..466b5d9a845 100644
--- a/source/blender/blenkernel/BKE_armature.h
+++ b/source/blender/blenkernel/BKE_armature.h
@@ -91,6 +91,7 @@ void where_is_armature_bone(struct Bone *bone, struct Bone *prevbone);
 void armature_rebuild_pose(struct Object *ob, struct bArmature *arm);
 void where_is_pose (struct Scene *scene, struct Object *ob);
 void where_is_pose_bone(struct Scene *scene, struct Object *ob, struct bPoseChannel *pchan, float ctime, int do_extra);
+void where_is_pose_bone_tail(struct bPoseChannel *pchan);
 
 /* get_objectspace_bone_matrix has to be removed still */
 void get_objectspace_bone_matrix (struct Bone* bone, float M_accumulatedMatrix[][4], int root, int posed);
diff --git a/source/blender/blenkernel/intern/armature.c b/source/blender/blenkernel/intern/armature.c
index 0eaef5f250f..029b3c2e141 100644
--- a/source/blender/blenkernel/intern/armature.c
+++ b/source/blender/blenkernel/intern/armature.c
@@ -2018,7 +2018,9 @@ static void splineik_evaluate_bone(tSplineIK_Tree *tree, Scene *scene, Object *o
 	/* finally, store the new transform */
 	copy_m4_m4(pchan->pose_mat, poseMat);
 	VECCOPY(pchan->pose_head, poseHead);
-	VECCOPY(pchan->pose_tail, poseTail);
+	
+	/* recalculate tail, as it's now outdated after the head gets adjusted above! */
+	where_is_pose_bone_tail(pchan);
 	
 	/* done! */
 	pchan->flag |= POSE_DONE;
@@ -2231,6 +2233,15 @@ static void do_strip_modifiers(Scene *scene, Object *armob, Bone *bone, bPoseCha
 	}
 }
 
+/* calculate tail of posechannel */
+void where_is_pose_bone_tail(bPoseChannel *pchan)
+{
+	float vec[3];
+	
+	VECCOPY(vec, pchan->pose_mat[1]);
+	mul_v3_fl(vec, pchan->bone->length);
+	add_v3_v3v3(pchan->pose_tail, pchan->pose_head, vec);
+}
 
 /* The main armature solver, does all constraints excluding IK */
 /* pchan is validated, as having bone and parent pointer
@@ -2364,9 +2375,7 @@ void where_is_pose_bone(Scene *scene, Object *ob, bPoseChannel *pchan, float cti
 	/* calculate head */
 	VECCOPY(pchan->pose_head, pchan->pose_mat[3]);
 	/* calculate tail */
-	VECCOPY(vec, pchan->pose_mat[1]);
-	mul_v3_fl(vec, bone->length);
-	add_v3_v3v3(pchan->pose_tail, pchan->pose_head, vec);
+	where_is_pose_bone_tail(pchan);
 }
 
 /* This only reads anim data from channels, and writes to channels */