Transform: Use parent bone orientation if the bone has not size

As shown in the T68805, non-sized bones (such as the resulting extruded
bone) have no direction or orientation.

This can be bad for operators like `extrude_move` since the user might
want the resulting bone to be aligned with the bone that originated it.

The solution here is to get the parent bone orientation in the
transform operator if the bone has no size.

Differential Revision: https://developer.blender.org/D6486

1 files changed, 13 insertions, 2 deletions

diff --git a/source/blender/editors/armature/armature_utils.c b/source/blender/editors/armature/armature_utils.c
index 2b18fc15f63..451148ed936 100644
--- a/source/blender/editors/armature/armature_utils.c
+++ b/source/blender/editors/armature/armature_utils.c
@@ -232,11 +232,22 @@ EditBone *ED_armature_ebone_find_shared_parent(EditBone *ebone_child[],
 
 void ED_armature_ebone_to_mat3(EditBone *ebone, float mat[3][3])
 {
-  float delta[3];
+  float delta[3], roll;
 
   /* Find the current bone matrix */
   sub_v3_v3v3(delta, ebone->tail, ebone->head);
-  vec_roll_to_mat3(delta, ebone->roll, mat);
+  roll = ebone->roll;
+  if (!normalize_v3(delta)) {
+    /* Use the orientation of the parent bone if any. */
+    const EditBone *ebone_parent = ebone->parent;
+    if (ebone_parent) {
+      sub_v3_v3v3(delta, ebone_parent->tail, ebone_parent->head);
+      normalize_v3(delta);
+      roll = ebone_parent->roll;
+    }
+  }
+
+  vec_roll_to_mat3_normalized(delta, roll, mat);
 }
 
 void ED_armature_ebone_to_mat4(EditBone *ebone, float mat[4][4])