Blender Git Commits

Moved most of the main cloth solver function out of implicit code core.

Force calculation is disabled, will follow shortly.

Moved init/free functions for solver data out of implicit core.

This also initializes spring matrix indices (off-diagonal 3x3 blocks),
which now uses a new API function.

Moved "set_positions" for cloth out of core implicit solver.

API for the solver now has functions for setting of vertex motion state
and the associated root transform data.

Renamed functions to make them explicitly refer to cloth, and split the
create/free functions for solver data off from the cloth solver.

Moved the cloth solver code into a new subfolder/library inside Blender
code.

The implicit solver itself should remain agnostic to the specifics of
the Blender data (cloth vs. hair). This way we could avoid the bloated
data conversion chain from particles/hair to derived mesh to cloth
modifier to implicit solver data and back. Every step in this chain adds
overhead as well as rounding errors and a possibility for bugs, not to
speak of making the code horribly complicated.

The new subfolder is named "physics" since it should be the start of a
somewhat "unified" physics systems combining all the various solvers in
the same place and managing things like synchronized time steps.

Desperate attempt to get stable collisions: Disable restitution and
handle only one collision contact at a time.

Collision still randomly explodes, even with differing results on the
same file. This could indicate a threading issue, possibly also related
to the dependency graph since multiple objects are involved in
collisions.

Revert "Ignore velocity changes when the cloth solver does not converge."

This reverts commit c52b8ae818844965d56714a71255408873275dc1.

Sadly, at this point solver convergence is an exception rather than the
rule... Individual hairs can "explode" easily and thus disable the whole
simulation, which isn't helpful either.

Ignore velocity changes when the cloth solver does not converge.

This helps keep the simulation stable as long as there are only a few
substeps that become too constrained for the solver.

Eventually we need better feedback about these solver results, so that
artists can tweak situations specifically to resolve bad solver results.
This is somewhat similar to the camera tracker, which also can run into
cases that cannot be resolved and have to be fixed manually.

Moved collision response into the main cloth sim source file and fixed
some coordinate transform issues.

Collision response should be regarded as part of the dynamics system
instead of the basic collision detection.

Correction for inverse constraint matrix rotation.

Transform the constraint matrix and target solver vector z according to
the root frame transforms as well.

This ensures the hair constraints are actually in root space and applied
correctly by the solver.

Use identity transform in the solver data roots to avoid possible errors
when this data is used outside the transform functions.

Option for disabling the root frame transformation altogether, mostly
for testing.

Ported root frame transformation to the old cloth solver.

Switched back to the old solver for the time being.

The Eigen solver is not quite stable currently (possibly due to
incorrect porting of force calculations). It also still lacks threading
support and optimized matrix construction, making it slower in
comparison. Eventually would still like to switch, but fixing these
issues takes time.

Implemented gradient transformation for forces in the root frame (dFdX,
dFdV).

Removed unused variable.

First stage of implementing moving frames of reference for hair/cloth.

This adds transformations for each hair from world to "root space".
Currently positions and velocities are simply transformed for the solver
data and inverse-transformed when copying the results back to the cloth
data. This way the hair movement becomes independent from the movement
of the emitter object. Eventually the "fictitious" forces originating
from emitter movement can be added back in a controlled way.

http://en.wikipedia.org/wiki/Fictitious_force

Ignoring these fictitious forces or scaling their effect is physically
correct, because in the absence of external forces the hair will always
return to rest position in this root frame.

External forces currently are not yet transformed into the root space.

Disable some debugging options in Eigen to make it more usable in Debug
mode.

Eigen can become very slow in debug mode, which is a bit of a problem.
It relies heavily on compiler optimizations to remove function calls
etc. More optimizations may be desirable, possibly putting the implicit
solver into its own little library and enabling optimizations in debug
mode there could help.

Added new data in the cloth modifier for hair root information.

This will allow us to implement moving reference frames for hair and
make "fictitious" forces optional, aiding in creating stable and
controllable hair systems.

Adding data in this place is a nasty hack, but it's too difficult to
encode as a DM data layer and the whole cloth modifier/DM intermediate
data copying for hair should be removed anyway.