Blender Git Commits

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

Pampering the stupid MSVC compiler again, it fails to build valid C code.

Added new header for Eigen utility classes.

These make passing data between Eigen vector and matrix types and plain
C arrays more convenient.

Updated a few comments.

Compile hair volumetrics code as C++, so we can use Eigen easier.

Minor debug code fix.

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

Use a fixed, uniform cell size for hair continuum grids.

This is a bit more awkward for artists to use, but necessary for
a stable solution of the hair continuum calculation. The grid size is
defined by the user, the extent of the grid is then calculated based on
the hair geometry. A hard upper limit prevents bad memory allocation
in case too small values are entered.

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

Removed unused voxel_filter_size DNA property.

This is an artifact of earlier attempts to implement velocity smoothing,
but doesn't work anyway.

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

Renamed HairVertexGrid to HairGrid, since it's not actually storing
hair vertex data.

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