Fur and Surface Fibers

You can just apply Sasquatch to an object to render fur, but you'll rarely want to keep the default settings for length and density. This chapter covers these basic (but essential) topics.

Surface and Part Selection

By default, Sasquatch applies fur to your entire object. Often, though, you'll want to restrict the fur to appear just on part of your object. There are several ways to do this.

The simplest is by surface name In the top center of the Sasquatch panel, you can choose the option Apply fur only to named area. When you select this option, you can type the name of the surface in the Surface(s) control and fur will be added only to that surface. You can also choose to render fur on all but the named surfaces.

The "Surfaces(s)" entry allows you to specify multiple surface namesby separating each name with commas. Capitalization matters. You can also use the "*" wildcard to match entire groups of names. Don't use spaces to separate the names.

For example, "S*,Dup*" will match surfaces named Super, Sugar, Sam, Duper, Duplicate and DupDup, but not Aardvark, zebra, sam, Dummy or Dusty. The number of selected surfaces is shown with the total number of surfaces as two numbers, like "2/5" if two surfaces are selected from an object with five surfaces.

Instead of using surfaces, you can also use LightWave Parts by clicking on the "Surface(s)" button to toggle it to show "Part(s)" instead.Parts are object polygon groups defined in Modeler. Sasquatch's interface lets you toggle between surface and part selection. Using parts to "segment" your object for fur, you can keep control of your surfaces for normal LightWave texturing. This is especially useful when you're updating or modifying a model, since you can change fur areas without breaking your surfaces. Part support has all of the features that surface support has, including multiple selection, creeping, and soft transitions.

You can use a second copy of Sasquatch (added into LightWave's second displacement map slot) to add fur to a second part, surface, or group of parts or surfaces. This gives you independent control over the fur on each surface. You can even add a second copy of Sasquatch to the same surface or part. In this case, the layers of fur are layered on top of one another. This is quite useful for some types of fur; for example, real wolf fur has a mix of short, coarse fibers with a winter coat of longer, finer fibers. You can use two (or more!) copies of Sasquatch to create exactly this kind of mix.

When you're using multiple instances of Sasquatch on a single object, it's useful to use the "Optional Comment" control to give each instance its own name. This is ignored by Sasquatch but the name is displayed in LightWave's panel, allowing you to distinguish the different instances more easily. For example, you might have a cat object, with one instance applying body fur and another making whiskers. Labelling the instances "body" and "whisker" will help prevent you from picking the wrong instance to edit later.

Transition Softness

Using surfaces or parts to define the fur application area is convenient, but sometimes the transition from one region to another is too abrupt, stopping the fur suddenly at the edge. (It can look sort of like a piece of cut carpeting.) You can soften the transition edge of the applied area by using the Transition Softness control. This will make the fiber density smoothly decrease across the surface edge. The density will begin to lower inside the surface, and will start to extend slightly past the surface. This makes it ideal to crossfade two Sasquatch fur patches. If you use the same Transition Softness settings for both copies of Sasquatch, you'll get a smooth cross-fade between them.

This transition only occurs at surface boundaries, not object boundaries. You won't start losing fur at the tip of an ear or end of a nose if you use the transition. It only affects where two surfaces directly join.

Creep

You can also "creep" the fur across the surface edges with the Creep over Boundary control. This makes the fur expand beyond its original surface. This is useful because often your object surfaces are used for normal LightWave surface texturing, and it's annoying to set up a special surface just for fur. For example, you might be making a wolf's legs. You want the bottom half of the legs covered with white fur. You could add Sasquatch to the wolf's feet, and increase Creep over Boundary to make the fur grow halfway up the legs.

You can also use a negative value for Creep to make the fur withdraw from the boundary, filling only the central part of the surface.

Like Transition Softness, Creep controls the blend between two adjoining surfaces. If you use a positive Creep of (for example) 10% on one surface, and a corresponding Creep of -10% on the other surface, the transition between the two will match. It's sort of like one surface has an army which has crossed over the border and invaded another country.

Both Creep and Transition Softness are percentages roughly based on the size of your object. You may need small values for the transition of a small area (like nose fur transitioning into the face fur) but a larger value for bigger areas (like head fur transitioning into body fur.) You can use values greater than 100% (or less than -100%) but it's not usually necessary.

Fur Density

Density controls the number of fibers used to make fur. The density is a percentage (which you can overdrive past 100% in the rare occasions you need to.)

Density is adjusted to match the the scale of your object. Sasquatch will produce the same number of fibers on a 1000 meter sphere as a 1 meter sphere. This makes it easier to cut and paste settings between objects.

The density value is also "nonlinear", which means that if you double the density, you'll get more than twice the number of fibers. This is a useful feature since some landscape objects have extremely sparse grass, but some animal fur is extremely dense. This nonlinear behavior makes it easy to keep the density settings within a reasonable range of 0 to 100%, even for these two extreme cases. This does mean that the Density control is sensitive, so small changes in the Density setting will make large changes in the number of fibers. (Mathematically, if you double the Density setting, you'll get 4 times as many fibers.)

Notice that Density controls fiber density, not the absolute number of fibers. A single object with both a small and a large surface with the same density will have more fibers on the large surface. This is a convenient advantage especially when cross-fading two fur patches, since the density settings are the same for both surfaces even though one surface is larger.

A Density value of 0% will produce no fibers on a surface. This is actually very useful when using S panels, since you can define the fur application areas using an image map, as described in the next sect

Density and S Panels

It's very common to use the S~panel texturing option to control Density. (See the S Panel chapter for more details about using S panels.) This gives you an alternative way to control where fur appears on your object instead of using surfaces.

Using S~panels, you can use a LightWave weight map or image map (or fractal noise, or the other S~panel controls) to specify the density of the fur over the object. This method is easiest when you don't want to worry about surfaces and just want to paint an image map to specify where the fur is or isn't. This gives precise control over complex objects, since you can paint shades of grey to accurately control the areas you want fur to appear. With surface selection, you'd have to specifically isolate groups of polygons and apply multiple copies of Sasquatch to them.

If you're using S~panels to control density, you may want to increase the Surface Subdivision control if the applied density looks "blurred" or incorrect. This is a subtle but important point discussed on page~\pageref{subdivision}.

You can combine both methods and restrict Sasquatch to a surface but also paint a density map. Fibers will only appear where both methods intersect. This can be useful when you want to paint a detailed map but some features are too small or detailed to specify. For example, you might make a painted image to control the density of fur on a wolf's head, but use the surface selection to make sure no fur appears on the wolf's lips or inside of its nose. It's hard to paint the inside of a nose, but by naming the surface you can mak

Length and Coarsness

The Length control is used only for fur, and (obviously) controls the length of each fiber. Like Density, Length is nonlinear, so it doesn't have to be changed much to make a large effect. Also like Density, you can overdrive the value past 100%, though it's rarely necessary. And, like Density again, the length is relative to your object's size, which is very convenient since you don't have to deal with tiny numbers for a bee with 1 millimeter fuzz or huge numbers for bamboo with 10 meter stalks.

Sometimes your fur looks boring if every fiber is the same length. You can randomize the length of each fiber by using the Length Vary control. A Length Vary of 0% will make all fibers have the same length. Length Vary of 20% will make every fiber randomly choose a length from 80% to 120% of the normal length. A Length Vary of 90% will make the fibers range from 10% to 190% of the normal length.

When used with Clumps, Length Vary affects the length of the entire clump. In that case, the Fiber Length Vary clump setting controls the random length of the fibers within the clump.

Sasquatch's Hair mode does not use Length (fibers are defined by the guide chains) but Length Vary is still active. See the LongHair section

Coarseness

When fur fibers get longer, they also get thicker. You can control how thick a fiber is (compared to its length) by using the Coarseness control. Coarseness is linear, so if you double this value, each fiber will be twice as thick.

Coarseness is very important when defining the "feel" of fur (and hair). Smaller values of coarseness will make thinner, soft feeling fibers. However, thin fibers are less visible, so you'll often have to increase Density to visibly cover a surface with fibers. Coarseness doesn't change rendering time significantly, but Density does, so you can make fur render much faster by using less Density and more Coarseness to compensate. Of course very coarse fibers look more like yarn or ropes, which may not be the appearance you want.

You can make each fiber get thinner near its tip with the Tip Narrowing control. A value of 100\% will make each fiber narrow into a conical, needle point. Real hair and fur fibers don't narrow along their length at all, but many plants and grasses do. But the effect of thinner tips often looks good on hair and fur anyway! In practice, you don't normally view fibers so closely that you see this effect directly. Instead you notice that the edges of furry objects become softer and less dense. This is often desirable, so you may want to experiment with Tip Narrowing if you want a softer edge but don't want to reduce the overall coarseness.

Object Scale Dependence

As Sasquatch was developed, we've experimented with several different rules for setting length and density. We found that it's awkward to allow you to enter in an absolute density like "100 fibers per square centimeter" or length like "14 centimeters." This didn't work for two reasons. First, the absolute density of fibers ranges over a huge scale; you may have 100,000 fibers per square centimeter in a thick otter fur, which is 1,000,000,000 per square meter! And some insects may have even higher densities. But you may have a desolate landscape which has less than one strand of grass per square meter.

Absolute measurements also make it difficult to cut-and-paste settings from one object to another. It's very nice to be able to take a good looking fur setting and simply copy it to another object and have it work properly. When length and density are based on the object size, you can do this easily, even if you're copying bumblebee fuzz to a dragon.

Of course, this scale independence can cause problems. The most common one is if you have good looking fur, but then you remodel the object. This changes the scale of the object, and the fur will react! This is annoying and often surprising (since it's easy to forget about.) But after a lot of debate, we've concluded that the relative density and length settings work best.

Sasquatch includes an extra control, titled Object Size, to allow you to override and control the "scale size" Sasquatch uses to compute the length and density. Normally this control is set to "Auto" which tells Sasquatch to base the length and density on the object size.

If you want to lock the length and density scale Sasquatch uses, you can set the effective scale manually by turning off "Auto" and entering a size explicitly. If you hold "shift" while pressing the Auto button, the Automatic size will be copied into the manual override size.

For a practical example, let's say you were modeling a wolf head. You've set up beautiful fur on the object, but you decide to make the nose a little longer. This increases the object size, so all fur renders a little longer and a little more sparsely. If you want to keep your old fur, you can first shift-click the "Auto" Object Size button to lock the size before you model. After this, you can remodel the head any way you like, but the fur lengths and densities will be left unchanged.

The manual Object Size is also good for landscapes, where you want to use the same length grass on two objects. If you use the same Object Size for both, it's easy to share other settings without having to worry about the grass on each object having different lengths.

Next Section