Blender Git Loki

IK solver for hair strands that provides a better solution for keeping
consistent segment lengths when transforming vertices.

Warning: The implementation is not correct yet, but all the steps should
be there.

The main idea is to treat strands as a sequence of joints that are
displaced out of their original locations by a transform or other tool.
The solver then tries to find a global per-strand solution that keeps
the segment lengths unmodified, with a minimum change in angles from
the original starting shape. Such a solution is much more usable and
efficient than the current O(n^2) attempt of "spreading the error"
across the strand.

The inverse kinematics method is very flexible. It can also include
stretching, which would be very welcome for features like the length
tool. Different parts of the strand could be weighted separately using
scaling factors for the angle/stretch parameters.

Conflicts:
source/blender/physics/intern/implicit.h

Primitive transform operator support for strand vertices.

This does not yet prevent root transforms and/or length changes.

Ported over the relaxation method for hair vertices from particle edit
mode.

This method is simple, but not really very usable. It works by
successively relaxing segments that are too long or too short, moving
both vertices along the edge between them. This is repeated N^2 times
(N: number of vertices on the strand).

A true IK solver could give a lot better results, as well as providing
many opportunities to apply weighting for targets (e.g. preferring to
move non-selected over selected vertices). Many different methods for
simple IK solvers exist, so there should be one that works well for
large number of simple strands. See e.g.
http://www.math.ucsd.edu/~sbuss/ResearchWeb/ikmethods/iksurvey.pdf

Use a simple low-pass filter to generate a smoother, more stable
direction vector for the hair stroke tool.

This is necessary for directional tools such as combing, where the
stroke direction can lead to unwanted results if it changes too
abruptly.

Support for sim_debug drawing in hair edit mode (dev feature).

Improved hair combing tool, adjusting edge directions instead of
vertex positions.

This works a lot better with strokes perpendicular to the general hair
strand direction. With the previous comb tool such strokes would only
make a small dent in the hair curve and then vertices would slip out
of the tool circle. The edge combing affects the local direction of
strands, which acts as a kind of grabbing functionality by moving
further vertices in front of the tool circle. The result is that
drawing a curvy hair shape with the comb becomes much easier.

In addition, the new tool also uses edge filtering and weighting rather
than vertices. This means that small brushes also work well, instead
of having no effect when hitting the edge segments between vertices.

Further improvement could be achieved later by using a global strand
solver, which adjusts vertex positions based on an error metric along
the whole of the strand.

Renamed the edithair files in BKE to editstrands.

The rationale behind this is that the BKE code could be used for
modeling hair and fur as well as a number of other features such as
grass. The primary addition to BMesh is the limitation to strand-like
topology (simple vertex chains, optionally rooted on a mesh surface).

The editor code OTOH is quite hair specific, since the result should
be suitable for hair simulation, and the workflow should mimick actual
hair grooming intuitively. Eventually the hair edit mode could become
a generalized strand edit mode with slightly different tool sets for
various purposes, but for now it is quite specifically built for hair.

Conflicts:
source/blender/blenkernel/CMakeLists.txt
source/blender/blenkernel/intern/particle.c

Sanity check for strand root/tip checks, now supports single vertices.

MSVC compiler cannot handle standard C code.

Conflicts:
source/blender/editors/physics/particle_edit.c

Fix for hair-to-particle export: need to set weight=1.0 for hair roots,
since the particle system uses this for pinning them to the mesh.

Fix scons build files for new hair edit code parts.

Fixed lib-linking for hair edit settings brush and object pointers.

Basic Add tool for creating new strands in hair edit mode.

New simple storage method for single sample values.

Fix for uninitialized return value.

New mesh sample evaluation function for shape key data.

Generic raycast method for generating mesh surface samples.

Conflicts:
source/blender/blenkernel/intern/mesh_sample.c

Better feedback about valid sample from mesh sampling methods.

Conflicts:
source/blender/editors/object/object_shapekey.c

Support for common operators, keymap entries and radial controls for
hair brush settings.

Fix for OpenlGL state restoration after strand drawing, disable color
material option.