Bones: implement a new Aligned Inherit Scale mode.

Implement one more way of inheriting scale from the parent
bone, as an addition to the choices introduced in D5588.

This new mode inherits parent scale as if the parent and child
were not rotated relative to each other, always applying parent
X scale to child X scale and so forth. It is quite natural for
connected bone chains with coherent roll, like limbs or tentacles,
falling roughly between Average and Fix Shear in how closely
the parent scaling is followed.

Currently this can be achieved by using Inherit Scale: None plus
a Copy Scale with Offset from parent on the child; however, this
is cumbersome, and loses the distinction between true local and
inherited scale in the child's Local space.

This new mode also matches how the Before/After Original mix
modes work in the Copy Transforms constraint.

On the technical side this mode requires adding a right side
scale matrix multiplication into the Local<->Pose conversion,
in addition to the existing two left side matrices used for
location and orientation.

Differential Revision: https://developer.blender.org/D6099

1 files changed, 2 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_armature_types.h b/source/blender/makesdna/DNA_armature_types.h
index 3bad2a04a65..4ead3165715 100644
--- a/source/blender/makesdna/DNA_armature_types.h
+++ b/source/blender/makesdna/DNA_armature_types.h
@@ -267,6 +267,8 @@ typedef enum eBone_InheritScaleMode {
   BONE_INHERIT_SCALE_NONE,
   /* Inherit effects of shear on parent (same as old disabled Inherit Scale). */
   BONE_INHERIT_SCALE_NONE_LEGACY,
+  /* Inherit parent X scale as child X scale etc. */
+  BONE_INHERIT_SCALE_ALIGNED,
 } eBone_InheritScaleMode;
 
 /* bone->bbone_prev_type, bbone_next_type */