8

688 Chapter 8: Modifiers
linked to the Advanced Springs rollout > Shape
Str. and Shape Sway settings.
The differences between Stretch and Stiffness
are subtle, and understanding them is further
complicated by the fact the two affect each other.
In addition, how they work depends on object
topology. For example, say you create a box, add a
Flex modifier, apply Create Simple Soft Body, and
then set a high St retch value and a low Stiffness
value. If you use the box in a Flex-based dynamics
simulation,suchasdroppingitontoasurface
(deflector) with gravity, you might expect the box
to fall over and flatten out. But instead, because
of the b ox’s topology, which causes Create Simple
Soft Bo dy to apply a relatively small number of
shape springs, you’d actually get b etter results
with a low Stretch value and a high Stiffness value.
However, if you use a sphere of eight segments
instead, you’ll get the collapsing behavior w ith
the default Stretch and Stiffness settings, and as
expected, increasing rig idity with h igher Stiffness
settings.
In soft-body simulations, such as the above-cited
example of dropping an object onto a surface,
particularly with dense meshes, you might get
betterresultsbyapplyingthemeshtoanFFD
space warp that’s bound to the object. If the
object’s shape isn’t suitable for use with the space
warp, you might have to instead use t he
Advanced
Springs (page 1–691)
rollout settings to apply
springs manually. In such cases, you should create
shape springs between opposite vertices rather
than adjacent ones.
Cloth-like animation usually works b est with a
high Stretch s etting and a low Stiffness setting. For
soft bodies, you would usually use high settings
for both Stretch and Stiffness, depending on how
"squishy" you want the object to be.
Weights and Painting rollout
When you first apply Flex to an object, the
modifier automatically sets vertex weig hts based
on distance from the modifier’s center . The
higher a vertex weight, the less prone it is to being
affected by Flex effects. The modifier applies the
highest weights to vert ices closest to its center,
and the lowest weights to vertices farthest from
the center. So, for example, with a cylinder w hose
pivot point is at the base, you’ll get the greatest
amount of flexing at the top. But with a sphere, all
of whose vertices are equidistant from the pivot
point (center), all ver tices h ave, by default, equal
weight values.
The Paint Weights controls let you use a spherical
brush with adjustable radius and falloff to change
vertex weights in the viewports, thus controlling
the amount of lag. The Ver tex Weights controls let
you apply absolute or relative weighting to single
vertices or groups of vertices.
Paint Weights group
Pai n t —At any sub-object level, click Paint,
and then drag the curs or over t he mesh in the
view por ts to "paint" vertex weights using the
cur rent Strength and Feather settings. Vertex
colors changes to reflect the new vertex weight.