Blender Git Loki

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

Corrected the divergence and gradient calculation for the hair grid
solver input and output.

This uses the central difference method (instead of combined forward/
backward difference), which makes it easier to correctly account for
grid borders.

Fallback method for defining density in the hair grid using discrete
samples.

This is just an intermediate method to make sure the density is valid.
Eventually the closest-point method should be used, but for testing
the poisson solver this is easier to debug.

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

Added a margin to the number of cells used in the poisson grid solver,
to ensure we always have one layer of empty cells around the fluid.

Fix for merge errors and leftover unused code lines.

Implementation of a target density feature for the hair simulation.

This allows setting a target density which the fluid simulation will
take into account as an additional term in the pressure Poisson
equation. Based on two papers
"Detail Preserving Continuum Simulation of Straight Hair" (McAdams et al. 2009)
and
"Two-way Coupled SPH and Particle Level Set Fluid Simulation" (Losasso et al. 2008)

Currently the target pressure is specified directly, but it will be
a lot more convenient to define this in terms of a geometric value such
as "number of hairs per area" (combined with hair "thickness").

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

Another fix for off-by-one hair grid resolution errors.

Rewriting the grid rasterization function for hair segments.

Draw actual hair keys when the "Guide Hair" setting is enabled.

Without this certain debug tasks become very hard to visualize.

Fix for grid drawing in 3D view, was using one less grid cell.

Merge branch 'hair_immediate_fixes' into gooseberry

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

Implemented PIC and FLIP methods for combining the fluid grid simulation
with the Lagrangian hair model.

Main solver step for generating a divergence-free hair velocity field
on the grid.

This uses the Eigen conjugate-gradient solver to solve the implicit
Poisson equation for the pressure Laplacian:

div(grad(p)) = div(v)

As described in "Detail Preserving Continuum Simulation of Straight Hair"
(McAdams, Selle, 2009).

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