Hair and Particle Systems - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 128

to puff out toward the ends instead. The shape
value determines how far up the hairs start to
clump.

Length Determines how long the child particles
grow as a proportion of the parent particle
length. The threshold value below this setting
allows some particles to reach the full length,
while others are cut down to the shorter value
specified by the Length setting.

Figure 9-6: Different kink settings applied to the children of a
single parent particle. Left to right: No Kink (but with Clump
turned on so that the strands come to a point), Curl, Radial,
Wave, and Braid.

Parting Controls These options only appear if
Virtual Parents is set to 0. Turning up the part-
ing (cap) amount forces child particles to pick
a side when interpolating between parents that
point in different directions. As you might imag-
ine, this is useful for parting hair (though as we
will see later, there are other ways). The min and
max values determine the range of angles or dis-
tances between parent hairs that child particles
will part over.

Vertex Groups
In this panel, you can assign various vertex groups
to control the settings over the surface of a mesh.
This panel is where we apply the vertex groups we
created earlier in order to control the density and
length of our initial parent hairs before combing
and cutting them (see Figure 9-7).

Roughness You can apply three kinds of rough-
ness to the child hairs. The Uniform Rough
setting roughens up the hair depending on
location, affecting all hairs in a local area in
the same way. The size value determines the
scale of these perturbations. The Endpoint
Rough setting randomizes the endpoints of
the hairs, pushing them farther apart (much
like the opposite of the Clump setting). The
Random Rough setting roughens the hairs inde-
pendently, with the size value determining the
scale of perturbations and the threshold value
determining what proportion of hairs are left
unaffected by this roughening. (Random rough-
ness is good for adding stray hairs or for making
hair look frizzy.)

Figure 9-7: Using vertex groups to control hair length and den-
sity. You can add vertex groups for the other properties later
on, but this is all we need for now.

Kink (Nothing/Curl/Radial/Wave/Braid) These
options (shown in Figure 9-6) add secondary
patterns to the way the child hairs follow the
parents. Curl causes the hair to form curls,
Radial makes the hairs move periodically
closer and farther apart, Wave adds waves to
the hair, and Braid makes them form a three-
stranded braid. The settings below these choices
determine the amplitude and frequency of this
secondary pattern, as well as how it is affected by
clumping and distributed along the hairs using
the shape value. The flatness value causes the
hairs to flatten together when taking on these
secondary shapes.

Using vertex groups to control particle systems
affects both the initial generation of parent par-
ticles and the later distribution of child particles.
However, once you start editing the parent particles
in Particle mode, you can add or remove particles
and edit them independently of the properties
defined by vertex groups using the Particle mode
brushes, as discussed in the next section.