[Bf-docboard-svn] bf-manual: [7340] trunk/blender_docs/manual/animation/armatures/bones/properties/relations.rst: Describe use cases for various bone Inherit Scale options.

[Alexander Gavrilov]

Revision: 7340
          https://developer.blender.org/rBM7340
Author:   angavrilov
Date:     2020-11-06 11:12:26 +0100 (Fri, 06 Nov 2020)
Log Message:
-----------
Describe use cases for various bone Inherit Scale options.

The existing descriptions focused on behavior rather than use cases.

Modified Paths:
--------------
    trunk/blender_docs/manual/animation/armatures/bones/properties/relations.rst

Modified: trunk/blender_docs/manual/animation/armatures/bones/properties/relations.rst
===================================================================
--- trunk/blender_docs/manual/animation/armatures/bones/properties/relations.rst	2020-11-05 23:49:02 UTC (rev 7339)
+++ trunk/blender_docs/manual/animation/armatures/bones/properties/relations.rst	2020-11-06 10:12:26 UTC (rev 7340)
@@ -115,9 +115,9 @@
    Full
       The bone inherits all effects of parent scaling and shear.
    Fix Shear
-      Corrects the transformation inherited from the parent to remove shear caused by non-uniform
-      parent scaling and rotation. The process preserves the bone direction, length and volume, and
-      minimally affects roll on average.
+      Full parent effects are applied to the rest state of the child, after which any shear is
+      removed in a way that preserves the bone direction, length and volume, and minimally affects
+      roll on average. The result is combined with the local transformation of the child.
 
       If the inherited scale is non-uniform, this does not prevent shear from reappearing due to
       local rotation of the child bone, or of its children.
@@ -124,13 +124,8 @@
    Aligned
       Parent scaling is inherited as if the child was oriented the same as the parent, always
       applying parent X scale over child X scale, and so on.
-
-      This mode never causes shear and is natural for connected chains like limbs and tentacles.
    Average
       Inherits a uniform scaling factor that is the total change in the volume of the parent.
-
-      This effectively keeps the uniform part of the scaling of the parent, while removing squash
-      and stretch effects. Uniform scaling never causes shear.
    None
       Ignores all scaling and shear of the parent.
    None (Legacy)
@@ -144,6 +139,30 @@
 property in this "family", this will break the scaling propagation,
 i.e. this bone *and all its descendants* will no longer be affected when you scale one of its ancestors.
 
+.. tip::
+   The various *Inherit Scale* options are provided as tools in avoiding shear that is caused
+   by non-uniform scaling combined with parenting and rotation. There is no obvious best way
+   to achieve that, so different options are useful for different situations.
+
+   None
+      Useful for gaining full control over the scaling of the child in order
+      to e.g. manually overwrite it with constraints.
+
+   Average
+      Useful to block squash & stretch propagation between sub-rigs, while
+      allowing uniform changes in the size and volume to pass through.
+
+   Aligned
+      Can be used within bone chains, e.g. tentacles, in order to propagate
+      lengthwise scaling as lengthwise, and sideways as sideways, no matter
+      how the tentacle bends. Similar to using *None* with
+      :doc:`Copy Scale </animation/constraints/transform/copy_scale>` from parent.
+
+   Fix Shear
+      May be useful at the base of an appendage in order to reallocate squash &
+      stretch between axes based on the difference in rest pose orientations of the
+      parent and child. It behaves closest to *Full* while suppressing shear.
+
 .. list-table:: Examples of transforming parented/connected bones with Inherit Rotation disabled.
 
    * - .. figure:: /images/animation_armatures_bones_properties_relations_inherit-rot-disabled.png