Blender Git Loki

Fixed implementation of the Conjugate Gradient method for the cloth
solver that properly supports constraints with some degrees-of-freedom.

The previous solver implementation only used the S matrix (constraint
filter matrix) for pinning vertices, in which case all elements are
zero and the error doesn't show up. With partial constraints (useful for
collision contacts) the matrix has non-zero off-diagonal elements and
the algorithm easily diverges.

There are also initial steps for implementing collision prevention as
described in the Baraff/Witkin paper "Large Steps in Cloth Simulation"
(http://www.cs.cmu.edu/~baraff/papers/sig98.pdf).

Hair collision: Use the S matrix for enforcing contact constraints.

This is a first test, the contacts are very explosive atm because they
basically pin hair vertices globally on collision, which leads to
stretching of the springs which is then suddenly released in the next
frame.

Minor corrections:

* Add some comments to better describe what some numbers mean
* Fix cuddliness and parent position of strips

Preparation for collision code fixing.

Instead of handling contact tests and collision response in the same
function in collision.c, first generate contact points and return them
as a list, then free at the end of the stepping function. This way the
contact response can be integrated into the conjugate gradient method
properly instead of using the hackish and unstable double evaluation
that is currently used.

Cleanup: added some comments to the members of Implicit_Data.

Merge branch 'master' into terrible_consequencer

Cleanup: No point in passing all the implicit solver arguments
individually.

Cleanup: removed the unused olddV vectors from implicit solver data.

Revert "Gooseberry feature request, allow select left-right strips
operator to select all"

This change has been in master all the time after all, exposed the
operation better in master.

This reverts commit 799f974668004b3d2b7873f51951eb22b5fcf2f3.

Some more debug elements for hair collisions.

Extended line/face collision near-check, to allow for distance margins.

The original BLI method for line/triangle intersection returns false
in case the line does not actually intersect, but in order to generate
repulsion forces we need to also handle contacts inside the margin.

Gooseberry feature request, allow select left-right strips operator to
select all strips independently of channel of the active strip.

Fix crash when setting parent.

Merge branch 'master' into terrible_consequencer

Fix bounce/repulse calculation.

Hair debugging: use "categories" (strings) for grouping debug elements
and support clearing for categories.

Fix for hair collision detection: need to use the second point of the
timestep segment.

This ensures the distance for a collision pair is the one of the current
point position, and the response gets calculated accordingly.

Use repulsion forces in combination with the one-time penalty forces
in collision.

Fix for crash when going into particle edit mode with baked hair
simulation.

Note that this currently generates an extreme amount of points, by
making a edit pathcache curve for each hair in every frame! But at least
doesn't simply crash now.

Clear debug_data pointer in local cloth modifier data of the particle
systems on blend file load.