Wind and Dynamics

In real life, fur and grass move. Without natural swaying and motion, fur can look fake, like it's made from stiff wire. Sasquatch adds motion to fur based on both dynamics, caused by the object motion, and from wind.

Wind

Wind is a "global" effect, which means it's applied to all of the fur in your scene. While individual objects can have controllable sensitivity to wind, most of the definition of wind is done for all fur in the scene in the pixel plugin of Sasquatch.

Wind is a lot of fun to play with. It's easy to apply, and if you keep your scene simple enough to render quickly, you can see the results in just a few minutes. For fun, feel free to use strong wind, but for realism it's usually best to keep the effect very small and subtle. If the wind is so strong that it's easy to notice immediately, you're probably using too much!

Wind pushes fibers in the direction it's moving. Wind Speed controls the strength of the wind. Values of about 1~m/s are about right to get realistic effects. Wind speed can be animated with the "A" button next to the control. Stronger wind will bend the Sasquatch fibers more.

Wind pushing fibers

Wind direction is very configurable. By default, wind travels in the +X direction, but you can use the item picker to the right of the Wind Speed control to select an item (usually a null) to define the direction. The wind will move in the +X direction of the controller item, and can be animated over time.

You can use multiple wind direction controls to make wind curve and bend, very much like multiple bias control combing. You might arrange them to cause the wind to turn sharply around the corner of a building, or flow through a curving cave. You can make a vortex by arranging several controllers in a circle, each pointing along the curve.

Wind alone will cause Sasquatch fur fibers to bend, but doesn't add any turbulent, animated, effects unless you use Gusts, described later in this chapter.

Blowers

Wind controllers make air that flows over your entire scene. Sasquatch allows you to add "Blowers" to make a local effect that sprays air at a specific area. They act like small sources of air, like from a fan or blow dryer. In practice, they're very useful to make local effects like the rush of wind from a car passing by or the downblast of a landing helicopter.

"Blower" pushing fibers

The strength of the blower effect is set by Blower Speed. Like Wind Speed, it's measured in meters per second. Blowers tend to use much higher values than wind (10~m/s is reasonable) since the effects are localized. You can pick the item (or items!) that act like a blower using the item picker to the right. It's common to use Null objects for this. The blowers can be animated over time.

Blowers have an inherent size to them as well. Blower Size controls, roughly, what range the blower has. You might use a value of 0.1 meters to make a blower that lets you ruffle a small patch of fur on a gorilla, but 10 meters to push the grass under a landing helicopter.

Blowers are useful for other effects. Since Sasquatch fur ignores collisions with other objects, it can be awkward to make an object push fur around. You can use a blower to do it for you as a kind of a manual method. This actually works pretty well to do things like flatten grass under a foot or press down fur on an animal when you pet it.

Gusts

Both Wind and Blowers are boring by themselves, because all they do is push the fur. Gusts make the wind strength ragged and animated, making the fibers wave and wiggle. These gusts can affect Wind and Blowers independently.

Wind Gusts and Blower Gusts control the strength of the randomizing effect. It's common for them to have a similar speed as the Wind or Blower Speeds.

When wind is blowing across a field of grass, you can see the different gust patches travel across the grass. The scale of these patches may be large (for a landscape) or small (perhaps from a fan blowing across fur.) Gust Patch Size determines how large the random patches of gust effects are. The field of grass might use 100~meters, but a window fan would use only 1~meter or less. If this value is too large, all of your fur will tend to sway at the same time. If it's too low, the fur's motion will be chaotic and patternless, with neighboring fibers reacting completely differently.

The Gust Timing controls how quickly the gusts change their pattern. A small preview lets you judge the timing interactively. The preview also shows Gust Turbulence which controls how chaotic and disorganized the gusts are. A field of grass often moves smoothly like ocean waves, and has low Turbulence. Most other fur motion looks best with high Turbulence of perhaps 80%.

Object Sensitivity

You can control the sensitivity of an individual object to wind (and blowers) in its Sasquatch displacement panel. The Root Wind and Tip Wind settings determine how much that instance of fur reacts to wind and blowers. A little like Droop, you can control the bending of the fibers at the root and tip independently.

This gives you independent control over wind in every instance of fur in your scene, so you can reduce the effect on just one surface if you wish. This is handy, since you can make global, scene-wide adjustments in the pixel panel, but per-surface adjustments in the individual displacement panels.

Surface Subdivision can have an effect on the quality of wind on a surface, especially when you're using strong gusts or blowers. If the wind effects look like they don't have enough detail on one surface, you may want to increase Surface Subdivision to see if that fixes the problem.

Dynamics

Dynamics make fur fibers shake, sway, and shift as your object accelerates or spins. Most real fur has surprisingly little motion even when shaken violently, but Sasquatch lets you add realistic subtle motion (or cartoon-like wild reactions!) Like Wind, it's tempting to use strong dynamics on everything because it's fun and easy, but the best results come from subtlety, not wild bouncing.

Dynamics are easy to apply, controlled by Root Flop and Tip Flop in the main Sasquatch panel. Higher values make the fibers react more to acceleration. Like Droop and wind sensitivity, you have independent control over the reaction by both the root and tip of the fibers.

Restoration Force sets the speed of the fur's reaction; is it heavy, loose fur, which takes a long time to react to motions? Or is it springy wire, which will bounce back and forth quickly? Low Restoration values make the fur react slowly, and high values make it springy and bouncy. Restoration Force does not control the amount of reaction (that's Tip and Root Flop), it controls the speed of the reaction.

Damping determines how long fur reacts after it's been jostled. Large values will make any motion quickly die out. Low values let the fur swing back and forth for a longer time after it's been pushed.

The dynamic fur motion only reacts to object and bone motion. It does not react to motion from morphing or displacements.

Fur dynamics do not require any precomputation, ``baking'' or pre-computation. You can render any frame of the animation in any order.

Long Hair Dyanmics and ClothFX

Long hair dynamics can be very difficult. Sasquatch's use of guides allows you to sculpt complex hairstyles, but that versatility makes it difficult to simulate the motion of those shapes!

All long hair motion and dynamics is based on manipulating the hair guides themselves. If they bounce and sway realistically, so will the Sasquatch hair. This means you can use manual animation methods such as bones, morphing, Messiah, and Morph Gizmo to control hair motion. The WhirleyPoints plugin in our Taft collection is especially effective for this.

The most powerful solution is to use LightWave built in dynamics simulation tool, ClothFX. It's a very, very powerful system for simulating realistic motion of hair and cloth, and it works extremely well with Sasquatch long hair guides. It takes some patience and study to learn to use this new LightWave feature, but it pays off well.

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