This makes it so coordinates and normals for CCG are calculated
with mutires displacement taken into account. This solves issues
with multires displacement being lost when entering sculpt mode.
The missing part is averaging of normals along grid boundaries.
But even then sculpting shows decent results.
The plan to solve that would be to introduce function to stitch
grids, which can also be used by Smooth brush which requires
this.
Attempts to substitude CCGDM with an OpenSubdiv based structure
which has less abstraction levels. The missing part in this
substitude is a face pointers which old CCGDM/multires code was
using to stitch faces (averaging boundaries).
Another curial bit missing: "reshaping" of multires CD_MDISPS
to the state of new PBVH grids.
The new code is only available when OpenSubdiv modifier is
enabled (WITH_OPENSUBDIV_MODIFIER=ON) and with debug value of
128. This is so this WIP code is not interfering with current
production machines in the studio.
Reviewers: brecht
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D3685
Nothing really interesting, just starting laying down API which
seems to be a decent substitute to CCGDM, without requiring too
much work be done in sculpting area.
