Blender Git Loki

Experimental hair shape key control with textures.

Rationale for this feature goes like this:

In meshes the influence of shape keys can be limited to certain vertex
groups. This allows shapes to be applied selectively on parts of the
mesh and possibly even be animated by changing vertex group weights over
time.

With hair shape keys there is no equivalent feature to vertex groups
(defining a vertex group on hair keys would be rather tedious anyway).
It would be possible to use the emitter mesh vgroups to assign a
per-strand blending weight, but since hairs usually are much more dense
than mesh vertices this would sacrifice accuracy.

A better option is to allow textures to influence the hair shape key
blending. For this purpose there is now a new texture influence.
A shape key name needs to be assigned to the MTex in addition to a
factor. It will then act as a multiplier for the shape key weight,
i.e. the base shapekey value still works as an overall control.