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Adds a displacement support for OpenSubdiov based subsurf object implemented
as a callback which gives vector displacement in object space. Currently is
implemented to calculate displacement based on myltires displacement grids,
but we can support things in the future if needed.
Submitting to review to see if there is something obviously wrong in the
direction (old multires code was sharing same displacement code to both
calculate final displaced mesh and reshape an existing one, which is rather
confusing and probably can be done more cleanly?).
Reviewers: brecht
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D3604
C-API is way smaller than the rest of the code which uses it.
So better to conditionally compile stub implementation than
to keep adding ifdef everywhere.
Applies to vertices and edges. Biggest annoyance here is that OpenSubdiv's
topology converter expects that there is no loose geometry, otherwise it
is getting confused.
For now solution is to create some sort of mapping from real Mesh vertex
and edge index to a non-loose-index. Now the annoying part is that this
is an extra step to calculate before we can compare topology, meaning FPS
will not be as great as if we knew for sure that topology didn't change.
Loose edges subdivision is different from what it used to be with old
subdivision code, but probably nice feature now is that endpoints of loose
edges are stay at the coarse vertex locations. This allows to have things
like plane with hair strands, without need to duplicate edge vertices at
endpoints.
All this required some re-work of topology refiner creation, which is now
only passing edges and vertices which are adjacent to face. This is how
topology refiner is supposed to be used, and this is how its validator
also works. Vertices which are adjacent to loose edges are marked as
infinite sharp. This seems to be good-enough approximation for now. In the
future we might tweaks things a bit and push such vertices in average
direction of loose edges, to match old subdivision code closer.
The idea is to use this as a replacement of old CCG, now it is
based on OpenSubdiv. The goal is to reduce any possible overhead
which was happening with OpenSubdiv used by CCG.
Currently implemented/supported:
- Creation from mesh, including topology on OpenSubdiv side,
its refinement.
- Evaluation of limit point, first order derivatives, normal,
and face-varying data for individual coarse position.
- Evaluation of whole patches.
Currently not optimized, uses evaluation of individual coarse
positions.
- Creation of Mesh from subdiv, with all geometry being real:
all mvert, medge, mloop, and mpoly.
This includes custom data interpolation, but all faces currently
are getting separated (they are converted to ptex patches, which
we need to weld back together).
Still need to support lighter weights grids and such, but this
is already a required part to have subsurf working in the middle
of modifier stack.
Annoying part is ifdef all over the place, to keep it compilable
when OpenSubdiv is disabled. More cleaner approach would be to
have stub API for OpenSubdiv, so everything gets ifdef-ed in a
much fewer places.
