Hair and Particle Systems - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 124

Current weight paint brush

Brush settings

Brush tool

Red = fully assigned

Brush curve

Blue = not assigned

Weight Tools operators

Figure 9-4: Weight Paint mode. Red areas represent vertices fully assigned to the current group, and blue areas represent verti-
ces that are not assigned to the current group.

Hair Density To completely remove part of a mesh from a ver-

tex group, you can use the Subtract brush in Weight
Paint mode, but it's easier to do this precisely in
Edit mode. To do so, use the Object Data tab of the
Properties editor to edit vertex groups and manu-
ally add or remove vertices by selecting them in
Edit mode and pressing the Assign or Remove but-
tons. For example, for the Bat Creature, I manually
selected the wings and removed them from the den-
sity (and length) vertex group to be sure the wings
wouldn't grow hair.

To control where the Bat Creature's hair will grow, I
needed to paint a vertex group that defined where
I wanted hair and where I didn't. I began by adding
a new vertex group that I'll call hair density . Then in
Weight Paint mode ( ctrl - tab ), I began assigning
areas I wanted to be furry to the group using a Mix
type brush. I could remove areas using the Subtract
brush and smooth the transition between hairy and
hairless areas with the Blur brush. (Because I am
editing only the hair density for now, the boundar-
ies of the vertex group will still have long hairs. To
make the hairy regions fade out into shorter hairs, I
will create a second vertex group in a minute to con-
trol the hair length.)
Figure 9-4 shows my hair-density group: Areas
on the upper body and upper legs are fully assigned
to the group, areas like the arms and lower legs are
only partially assigned, and areas like the wings and
face that are to remain hairless are not assigned at all.

Hair Length
The hair-length vertex group (see Figure 9-5) con-
trols the length of the hair by defining how long the
hair created by our particle system will grow, relative
to the maximum length we choose in the Particle
System settings. This group is similar to the hair-
density group, except that I assigned the chest and
pelvis much more than other areas, giving them the