Blender Git Loki

New: CrazySpace [tm] correction

When Modifiers are used in Edit Mode to show the deformed result for
editing, all actual coordinates Blender works with are still the ones from
the original Cage. You can notice that with the Transform Widget or
helper lines while transforming.

Even worse, the actual transformations still happened on the original Cage
as well, making it very hard to edit. That caused the feature to be named
"CrazySpace" (baptized by Andy, afaik?).

This commit calculates the deformation transformation per vertex, and
inverse corrects it, so it's more intuitive editing this way.

Unfortunately all the deformation features of Blender don't use matrices
for defining deform, so the existing code cannot be re-used to retrieve
the correct deformation matrix per vertex. The solution I found is based
on calculating per face the transformation based on its first 3 vertices,
and store this transformation averaged in the face's vertices.
The solution can also only work on entire faces, because the full deform
can only be retrieved using 3 vertices. (using 2 vertices will miss edge-
aligned rotation, using 1 vertex can only retrieve translation).

By deriving the deformations per face, small errors will still happen,
especially on very low-poly Meshes with extreme deformations.

The only alternative I know now, is providing each vertex in
a mesh with 2 extreme small tangent vectors, which get deformed using the
existing code as well. That will mess up the existing deformation code too
much though, this solution has the benefit it works with each deform we can
up with later too.

Last note about CrazySpace: it can only be used to tweak Meshes. Do not
even try to add vertices, extrude, or duplicate. Probably we should disable
this... but preventing user errors isn't always power-user-friendly, eh. :)