Blender Git Loki

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.

Conflicts:
release/scripts/startup/bl_ui/properties_particle.py

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.

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp

Fix for wind force function call.

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.

Conflicts:
source/blender/blenkernel/intern/particle_system.c
source/blender/physics/intern/BPH_mass_spring.cpp

New python submodule `mathutils.interpolate` for various mesh interpolation and weighting methods.

This module will contain mirrored functions for calculating and applying
weights for points on a mesh. This includes barycentric and UV weighting
and possibly more advanced global weighting such as harmonic weights.

The naming should follow this scheme:
<type>_{2d,3d}_{calc,apply}

e.g.
poly_2d_calc
poly_2d_apply
uv_3d_calc
...

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D939

Fix for missing library linking in blenderplayer.

Another fix for particle instance child lookups, was not subtracting
parent amount.

Fix for invalid particle pointer access in mixed particle/child loop.

Better update function for particle settings affecting nested cloth
modifier.

Fix for applying the bending randomness factor.

A stupid hack is needed here, changing the way the factor is applied to
angular bending springs. In cloth sim the bending factor of individual
springs is applied as a mix value between the bending stiffness and a
max value, but this max value isn't even used in hair sim so that
approach becomes useless.

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp

Randomness factor for hair bending stiffness.

This helps to create some variation in a hair system, which can
otherwise become very uniform and boring. It's yet another confusing
setting in a system that should have been nodified, but only option for
now (broken windows ...)

Conflicts:
source/blender/blenkernel/intern/particle_system.c
source/blender/physics/intern/BPH_mass_spring.cpp

Fix for particle instance initial frames.

These were not orthonormal and tended to flip with changing hair
direction, now use the particle hair matrix which is stable wrt. the
mesh surface.

Fix for particle instance modifier: use a stable parallel-transport
framing method instead of the Frenet frame.

The Frenet frame is very succeptible to sudden twists along straight
sections of a curve where the second derivative (curvature) becomes 0.

Nicer hashing functionality for sim debugging using a variadic macro
to support multiple hash identifiers.

Using explicit hashing functions for every sim debug call defeats the
purpose of having a quick feedback system. Now this can be done simply
by passing an arbitrary number of hash inputs (integers) at the end of
the function calls, which are then combined by a system of variadic
macros (based on the ELEM feature). Up to 8 identifiers are supported
currently, but more could be added easily if needed.

Conflicts:
source/blender/blenkernel/intern/particle_system.c
source/blender/physics/intern/BPH_mass_spring.cpp

Some tweaking of value ranges for hair target density and removed
density factor (already included in grid velocity).

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp

Inverted effect of target density was unstable, the divergence term
needs to be substracted instead.

Use dedicated debug values in cloth settings instead of abusing unused
other values.

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp

Fixed wrong stride values used for offsetting the index of Eigen values.

The Eigen solver for hair grids uses an extra margin of 1, which means
greater stride values.

Hair grid code was using an invalid hair segment at each hair end with
zero vectors, leading to bad density values.

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp

A bunch of debug drawing changes.

Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp