Blender Git Loki

New edit mode for hair.

Moved code for the hair edit data structures to blenkernel.

This makes it work more like editmesh, and avoid the awkward and
basically bad-level approach in particles, where the edit data is an
anonymous pointer in particle systems together with a callback for
freeing.

Store hair edit data in particle systems and manage it in the operator
for entering/exiting the edit mode.

Reconstruct most basic particle data when applying the hair edit, so
particle hairs remain visible.

Note that currently the hair root location (num/num_dmcache, fuv, foffset)
is not stored from edit data, so all hairs end up in a default location.

Skeleton code for sampling meshes.

Usable random distribution algorithm.

Does not include area weighting yet.

Eval function to get a location and normal vector from mesh samples.

Added a basic RNA definition for the mesh sampling system.

Added a bool return to the eval function to give feedback on invalid
samples.

Normalize the normal vector after sample eval to account for
interpolation.

Changed mesh sample definition to use 3 vertex weights instead of a
face index. This is easier to sample uniformly and avoids the need for
tesselation for evaluating.

Added generalized method for creating an array of mesh samples with
arbitrary stride.

Shifted the dispatch from the algorithm side to the storage side of the
sampling system to keep the code simple.

Now there is a MSurfaceSampleStorage struct that encodes the storage
details, which the algorithms don't have to care about.

Minor syntax fix.

New editor library for hair edit mode.

Fix for invalid access to undefined hair data in edge-only cloth meshes.

Cloth data is used both for hair and actual cloth, which makes things
really difficult. The face number was used for distinguishing the two
types (no faces == hair mesh), but the extra hair data necessary for
hair sim is generated by particles and not available for edge-only cloth
meshes. This really needs to be sanitized ...

Presets for hair dynamics.

This is necessary because the hair dynamics settings are not part of the
ParticleSettings datablock, but part of the convoluted cloth modifier
inside the particle system struct. In the future this will be recoded
properly, but in the meantime presets provide a simple an unobtrusive
way to have reusable dynamics settings for hair.

Merge branch 'master' into gooseberry

Radical simplification of the wind effect on hair, since the previous
approach does not work very well.

Using a cross section estimate still causes large oscillations due to
varying hair force based on angles. It also requires a sensible hair
thickness value (particle radius) which is difficult to control and
visualize at this point.

The new model is based purely on per-vertex forces, which seems to be
much more stable. It's also somewhat justified by the fact that each
hair vertex represents a certain mass.

Improved force field effects on hair strands.

The previous calculation was modulated with the angle between the wind
direction and the segments, which leads to very oscillating behavior.

Now the formula includes an estimate for the geometric cross section
of a hair segment based on the incident angle and the hair thickness
(currently just the particle size). This gives a more stable behavior
and more realistic response to wind.