hairSystemShape
 
 
 

These are descriptions of the attributes in the hairSystemShape node (also hairSystem node). When modifying these attributes they affect the entire hair system.

Related topics

Clump and Hair Shape

This section contains attributes to control the hair clumps and overall hair shape.

Hairs Per Clump

This is the number of hairs rendered for each Current Position hair curve.

Baldness Map

Reduces the hair density using a texture. The texture used must be a 2D texture.

Sub Segments

This determines the number of smoothly interpolated segments at render time. The hermite interpolation smooths the shape of the line, in addition to providing more detail for curls and fine features. The added segments affect the rendered look only and do not affect the dynamic simulation.

Thinning

This controls the proportion of shorter length hairs.

Clump Twist

This is the rotation of the clump group about the primary hair axis.

Bend Follow

This determines how much the rotation of the overall clump follows the primary hair axis. Short straight hair may work better with this value near zero, as the end of wide clumps will blend better when they twist. With this value at 1.0 the cross section of the hair clump will always be perpendicular to the tube direction, which can work well for long relatively thin clumps. When this value is zero the cross section is always perpendicular to the surface normal at the start of the hair clump.

Clump Width

This is the base or maximum width for the dynamic hair groups.

Hair Width

This is the global width for hairs.

Clump Width Scale

Using a ramp (graph) you can define a varied width for hair clumps. Clump Width Scale affects the width from root to tip of the hair clump. The left of the graph is the root and the right is the tip. You might want the hairs within the clump to come to a tip at the end of the clump, in which case the right value should be smaller than the left. This attribute multiplies the Clump Width parameter value, so a value of 1.0 will leave the Clump Width unchanged. If the Clump Width attribute is zero then this parameter will have no effect.

Hair Width Scale

Using a ramp (graph) you can define a varied width for the overall hair shape. Hair Width Scale affects the width from root to tip of the hairs. The left of the graph is the root and the right is the tip. This attribute multiplies the Hair Width parameter value, so a value of 1.0 will leave the Hair Width unchanged, but if the Hair Width attribute is zero then this parameter will have no effect.

Clump Curl

Using a ramp (graph) you can define a varied curl for hair clumps. Clump Curl controls the rate of curling about the primary axis of each hair clump. The left of the graph is the root and the right is the tip. The mid value of the ramp (0.5) represents no twist while values greater than that will result in positive twisting and smaller values will cause twisting in the reverse direction.

Clump Flatness

Using a ramp (graph) you can define a varied flatness for hair clumps. Clump Flatness affects the flatness of the clump group from root to tip. The left of the graph is the root and the right is the tip.

Clump Interpolation

This value specifies the amount of interpolation between the hair clumps of your current hair system. For each hair clump, Clump Interpolation evaluates its three closest neighbors and does the following:

The higher the Clump Interpolation value, the more distributed the hairs in your hair clumps appear. This is useful when you want to create a smooth continuous head of hair with less obvious clumping.

This attribute has an overall effect on all the hair clumps of your current hair system. The effects of this attribute are more apparent with higher Clump Widths than with lower Clump Widths. Clump Interpolation is 0.0 by default.

WarningWhen Clump Interpolation in greater than 0.0, the hairs in your hair clumps may not lie within their clump boundaries.

This can cause undesirable hair collisions as collisions only occur within the original hair clump boundaries, not in the regions of clump interpolation.

Interpolation Range

This value determines how far apart clumps can be and still interpolate with each other. Interpolation Range is multiplied by your current hair system’s Clump Width to define the maximum distance hair clumps are allowed to lie from each other for them to be included in the clump interpolation.

For example, an Interpolation Range of 8 specifies that the hair solution will look for clumps that are within a distance of 8 times the Clump Width value. All hair clumps that lie outside this range are not included in the clump interpolation.

This is useful when you want to vary the widths of your hair clumps to make your hair follicles look more natural. Interpolation Range is 8.0 by default.

Dynamics

This section contains attributes to control the dynamics of the hair curves.

Solve

Iterations

This controls the number of iterations per time step of the hair solver. This affects hair Stiffness and Length Flex, as well as the accuracy of collisions. Large values are required for very high stiffness. A large value will also increase the time required by the solver.

Length Flex

The amount the hair can stretch along its length.

No Stretch

When on, the lengths of your output hair curves are fixed at the lengths of your start hair curves. No Stretch keeps the lengths of your output hair curves constant and it prevents them from stretching. This lets you create realistic, flexible, non-stretchy hair without having to increase the number of Iterations for your hair solver.

When using No Stretch, your hair curves should always be constrained at their follicle bases. No Stretch is off by default.

Note

If you want your hair to collide with geometry and not stretch, then do not turn on No Stretch. Instead, set a high number of Iterations and a low level of Stiffness for your hair system.

Evaluation Order

Specifies how the hair object's curves are evaluated.

Sequential

Output hair curves are evaluated cumulatively from the first to the last curve in the hair system. This setting can reduce the amount of stretch in output curves particularly in hair systems that hat have high numbers of hair curves.

Parallel

Output hair curves are evaluated independent of their order.

Start Frame

This is the frame after which the simulation will run. Nothing will play back for this object prior to Start Frame.

Current Time

This is the current time used for the hair solution. By default, it is given an incoming connection from the main time node. This can be replaced with some other connection (such as, from an expression or param curve) and then the solving is done based on that time value. There must be some incoming connection in order for the Hair System object to play back.

Stiffness

The amount the hair can flex with regard to the rest position.

Stiffness Scale

Stiffness Scale affects the stiffness from root to tip of the hair. The left of the graph is the root and the right is the tip. Typically the root of a hair is thicker and therefore stiffer than the tip. This attribute multiplies the Stiffness parameter value, so a value of 1.0 will leave the Stiffness unchanged, but if the Stiffness attribute is zero then this parameter will have no effect.

Forces

Drag

This simulates friction with the air, in addition to helping to stabilize the simulation. When the Drag value is 1.0 the hair behaves as if it has no inertial motion or follow through. It will move as if it is in thick fluid.

Motion Drag

This damps the movement of your hair curves relative to the movement of their follicles. The Motion Drag value determines how much your hair curves move with their follicles and to what extent the shape of your hair can be influenced by other forces. This lets you damp your hair’s excess movement, such as bobbing and wiggling, without having to increase Iterations.

For example, if you set Motion Drag to 1.0, then your hair will move with its follicles, appearing to drag the surrounding air with it.

You can also influence the effects of Motion Drag with the Stiffness Scale attribute. For example, you can use the Stiffness Scale ramp drop-off to create more Motion Drag at the roots of your hair than the ends. Motion Drag is 0.0 by default.

Note

Motion Drag does not interfere with hair collisions.

Damp

This dampens the motion of the hair with respect to itself. When this value is high the hair tends to move with the parent object, but will not inherit much of the momentum due to this motion. This can help both stabilize the simulation and reduce dynamic behavior due to motion of the base surface. This is critical when you have curved Rest Positions in moderately stiff hair. This can also be adjusted per follicle for problem hairs, such as ones that develop oscillations that won’t relax; see Damp in the follicleShape node section.

Friction

This simulates friction on contact with other surfaces.

Mass

Controls the simulated mass of the hair CVs and only shows an effect if you apply external fields that consider mass, such as Drag.

Gravity

A built-in downward force in the y-direction simulating gravity.

Dynamics Weight

This is the scale factor for the effect of attached dynamic fields on the hair motion.

Start Curve Attract

Start Curve Attract

Determines the amount of attraction of the current hair position to the start position. This attribute is useful, for example, where you want to have stiff hair, or hair that moves with a character. Also, if you put keyframed animation on your start curves, you can use the Start Curve Attract attribute to blend between the simulation and the start curve animation.

Normally you would leave the Start Curve Attract value at zero for long flowing hair. However, for short hair it can be difficult to make hair stiff enough. Use a value greater than zero when the hair needs to be very stiff, yet at the same time have some dynamic properties. At a value of 1.0 the hair position will be the start curve position (relative to the transformed follicle position); only collisions and forces will still deflect the hair. Without Start Curve Attract this scenario could otherwise require a very high iteration count and damp value, especially if there are many CVs per hair.

When Start Curve Attract is set to a value of 1.0, there is 100% attraction to the start curve position. You can control which parts of the curve are attracted to the start curve by using the Stiffness Scale attribute. If you have animated start curves then this would produce behavior that is similar to when the Simulation Method is set to Static. However, dynamic fields are still added on top of the solve.

TipUsing the Start Curve Attract attribute for hair stiffness, you may not need to create rest curves in many cases.

For colliding hair, this attribute may dampen out excess hair motion without requiring the Damp attribute, and with an Iteration value of as little as 1.

Drag fields with Inherit Velocity set to 1 (see Fields > Drag) can be parented to a head and applied to the hair. At high Drag values, the hair will move exactly with the head. In many respects the effect of this is superior to the Start Curve Attract attribute, although it depends on the exact effect you are after.

Attraction Damp

Damps the effect of Start Curve Attract, decreasing the velocity of hair as it moves towards its start curves’ positions. This is useful when you want to lessen the springiness (caused by higher Start Curve Attract values) of hair, or when you want to apply dynamic fields on top of animated hair. When Attraction Damp is 1, the motion of hair moving towards its start curves is fully damped, leaving only its Start Positions and field forces to dynamically influence its motion.

Attraction Scale

The Attraction Scale ramp attenuates the Start Curve Attract attribute value along the length of the hair clumps in your hair system.

You can use the ramp graph to define a varied stiffness from root to tip for the hair clumps in your hair system. The leftside of the ramp graph represents the roots of the hair clumps in your hair system and the rightside represents the tips. For example, if you want the roots of your hair clumps to be less stiff than their tips, then the value on the rightside of the ramp graph should be smaller than the value on the leftside.

The Attraction Scale ramp values are multipliers of the Start Curve Attract attribute value on the hair system. So an Attraction Scale of 1.0 does not affect the Start Curve Attract, and a Start Curve Attract of 0.0 is not effected by Attraction Scale.

Selected Position

This is the position along the hair clumps of the current hair system for the point selected on the Attraction Scale graph. This is also represented by the position of the point on the X-axis.

Selected Value

This is the scale value associated with the Selected Position on the Attraction Scale graph for the hair clumps in the current hair system. This is also represented by the position of the point on the Y-axis.

Interpolation

Defines the mathematical method used to smooth the values of the current hair system’s hair curves. Ramp Interpolation controls the way the intermediate values are calculated.

None

No interpolation is done; the different colors just show up as different bands in the final texture.

Linear

The values are interpolated linearly in RGB color space.

Smooth

The values are interpolated along a bell curve, so that each color on the ramp dominates the region around it, then blends quickly to the next color.

Spline

The values are interpolated with a spline curve, taking neighboring indices into account for greater smoothness.

Collisions

This section contains attributes to control the collision properties of the hair system. For information on how to set up hair collisions, see Make hair collide.

Collide

If turned on then the hair system collides with the connected objects.

Collide Over Sample

Use this to adjust the quality collision sampling. Larger values will help keep hairs from pushing through surfaces.

Collide Width Offset

This value is added to Clump Width before determining collisions. The amount is relative to the clump width. It can be used to handle situations where there is some interpenetration, or where you have passive hairs that are outside the boundaries of active clumps. In cases where the hairs collide too far off an object, you can use negative values to allow a little interpenetration of clumps.

Self Collide

If this is turned on then the hair system simulates hair to hair interaction.

Repulsion

When Self Collide is turned on, this controls how much or how little the hairs repel each other.

Static Cling

When Self Collide is turned on, this controls how much or how little the hairs stick together.

Num Collide Neighbors

When Self Collide is turned on, this controls the number of hairs each hair collides with.

Collide Ground

If this is turned on then the hair system collides with an infinite plane at the ground height. This collision does not impact the speed of the solution, unlike geometry collisions.

Ground Height

When Collide Ground is turned on, this determines the height of the ground plane.

Draw Collide Width

If this is turned on then circles are drawn around each line representing its width used for collision.

Width Draw Skip

Use this to adjust the quality of the tube collide width drawing. A value of zero will cause a circle to be drawn for every segment of the tube, which may clutter the display for a tube with many segments.

Turbulence

This section contains attributes to control the turbulence properties of the hair system.

Intensity

Increasing this will increase the amount of force applied by the turbulence.

Frequency

Lowering this will make the turbulence vortices larger. This is a spacial scale factor on the turbulence function and has no effect if the turbulence strength is zero.

Speed

The rate at which turbulence pattern changes over time.

Shading

This section contains attributes to control the hair shading or color.

Hair Color

The base color for hairs. The final color used is determined after the Hair Color Scale and randomization parameters are applied. Also individual hair clumps may override the Hair Color.

Use the Hair Color map button next to this attribute to map a texture to the hair color to create different hair shading looks. The following image uses a black and white checker texture mapped to the Hair Color attribute.

Hair Color Scale

Hair Color defines the global color of the hairs from root to tip. The left of the graph is the root and the right is the tip.

Advanced ramp features exist. For more information, see the following topics in the Shading guide:

Displacements

This section contains attributes to control the displacement properties of the hair.

Curl

This is the amount of curl displacement applied to each hair. The amount of displacement is relative to the hair width. The Clump Curl creates large scale curls about the clump center, while this attribute creates curls about the direction of individual hairs.

Curl Frequency

This is the rate of curl. Larger values result in more curls. The amount of displacement is relative to the hair width.

Noise Method

Random is good for fuzzy, kinky hair, while the other, smoother noise methods can provide natural shaping and substructure to hair clumps.

Random

Defines the noise as a wiggle for each hair with no relation to neighboring hairs.

Surface UV

Defines the noise displacement volumetrically and is relative to the UV distribution of the hairs across the surface. The noise is a 3D volume with a scale in U and V across the surface with the third dimension (W) mapped down the length of the hairs.

Clump UV

Defines the noise relative to the clump, and while neighboring clumps have completely independent noises, the frequency of the noise is not affected by the surface parametric density.

Noise

This is the amount of perlin noise displacement of the hair. The amount of displacement is relative to the hair width. This can create a knotted, kinky look to the hair.

Detail Noise

The amount of secondary high frequency noise added when the smooth (Surface UV, Clump UV) Noise Methods are used. It can add subtle detail on top of smooth undulations from the base noise. If non-zero, a second noise offset calculation is performed, so this can make evaluation of the hair slightly slower than the smooth noise with no detail noise.

Noise Frequency

This is the spacial scale of the noise offset along hair. Increasing this value results in finer kinks in the hairs.

Noise Frequency U

When the smooth (Surface UV, Clump UV) Noise Methods are used, this attribute scales the noise frequency in the U parameter direction relative to the surface the hair is attached to.

Noise Frequency V

When the smooth (Surface UV, Clump UV) Noise Methods are used, this attribute scales the noise frequency in the V parameter direction relative to the surface the hair is attached to.

Noise Frequency W

When the smooth (Surface UV, Clump UV) Noise Methods are used, this attribute scales the noise frequency along the length of the hair.

Sub Clump Method

Determines how sub-clumps are defined in UV.

Surface UV

The sub-clumps are laid out relative to the overall surface UV space. Some follicles may therefore share a clump with a neighboring follicle. The density of sub-clumps will be affected by the parametric density of the surface the hair system is attached to. The total number of clumps across a surface will be the Num UClumps multiplied by the Num VClumps.

Clump UV

The number of sub-clumps for each clump will be the Num UClumps multiplied by the Num VClumps. All follicles, regardless of clump width, will have the same number of sub-clumps and the width of the sub-clumps will be related to the clump width. With Surface UV the smaller clumps will have fewer sub-clumps and the clump width will be relative to the parametric density of the surface.

Sub Clumping

The amount that secondary clumps pull together. Sub Clumping is useful for a wet look. The clumps are defined in a grid relative to the UV space of the surface the hair is attached to.

Sub Clump Rand

Randomizes the sub-clumps with a noise function. The clumps will get smeared into irregular shapes with higher values.

Num UClumps

The number of sub-clumps in the U dimension of the surface the hair system is attached to.

Num VClumps

The number of sub-clumps in the V dimension of the surface the hair system is attached to.

Displacement Scale

Using a ramp (graph) you can vary the amount of displacement applied from root to tip of the hair clump, affecting Curl, Noise and Sub Clumping.

The left of the graph is the root and the right is the tip. If the left side is zero then the effect will be added gradually—the root position of the hair will not be changed.

Multi Streaks

This section contains attributes to control the Multi Streaks shading for Paint Effects strokes. These attributes only apply if your hair output includes Paint Effects (see Create your own hair on surfaces).

Multi Streaks

Multi Streaks is the number of added sub hairs for each hair in a clump. These hairs will share the same shape and shading as the base hair they are derived from. They are created at render time and are simple duplicates, and therefore do not take up any shape computation. This allows you to have a great number of (Paint Effects) tubes and yet render them in a reasonable amount of time.

Multi Streak Spread1

The maximum offset for added hairs relative to the clump width.

Multi Streak Spread2

The maximum offset for added tubes relative to the clump width at the tube tip.

Light Each Hair

Render times can be much faster if you share the same illumination for each hair in a Multi Streak. If the Multi Streak spread is relatively large or self shadowing between hairs within a Multi Streak group is desired then Light Each Hair should be turned on. Also turning this on could avoid popping artifacts in situations with moving hard-edged shadows.

Render Stats

This section contains attributes that control how Hair is reflected and refracted in other objects. They apply only to the mental ray renderer.

Receive Shadows (mental ray)

Turns on the shadow-catching ability of the fur. Works only when using the mental ray for Maya renderer.

Visible in Reflections (mental ray)

When on, the fur reflects in reflective surfaces. Works only when using the mental ray for Maya renderer.

Visible in Refractions (mental ray)

When on, the fur refracts through transparent surfaces. Works only when using the mental ray for Maya renderer.