Houdini 20.0 Nodes Geometry nodes

Guide Process

Modifies guide or hair using one or more operations.

Since 16.0

This node modifies guide curves using one or more of the following operations:

All operations can be masked with paintable skin attributes and textures. Operations can also affect parts of a guide curve with varying intensity.

Parameters

General

Group Type

The type of input group.

Group

A group to use for masking. Any operations will only be applied to the primitives or points within this group.

Curve Per Skin Point

Assume that there’s a curve primitive for every point on the skin geometry, with the primitive number of each curve corresponding to the number of the skin point at its root.

This allows the operator to get skin attribute values directly from those points, rather than interpolating values using skinprim and skinprimuv.

When the id attribute is present on the curves, the skin point number corresponding to the id of each primitive is used, and the curve and skin point counts don’t have to match.

Random Seed

Use this seed for all random operations. This causes random operations like Set Length (with Randomize enabled) to have a different effect on each curve.

Visualize Masks

Visualize the effect of Skin Mask, Curve Mask, and Noise Mask by coloring curves in the viewport.

Input Mask

Blend

Blends the overall effect of the operation.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Curve Mask

Use Curve Mask

Controls the effect of operations along the length of each curve.

Enables the curve mask. All other parameters are hidden when this is disabled.

Range In Absolute Length

When enabled the range parameters below operate in world units.

Range Min

The position along the curve where the effect of the ramp starts. Curve points before this position use the first value of the ramp.

Range Max

The position along the curve where the effect of the ramp ends. Curve points after this position use the last value of the ramp.

Note

The parameters below quickly change the overall shape of the curve to achieve often needed effects, like affecting only roots or tips. Changing any of them modifies the ramp and replaces any manual edits on it.

Effect Position

Sets the position where the curve is affected most. The root is at 0 and the tip at 1.

Falloff

High values result in wide, bell-shaped ramp. Low values in a pointy shape.

Influence Width

Scales the falloff handles around the effect position for additional control.

Curve Mask Ramp

Controls the curve mask directly.

Source Mode

Groom Object

Load the groom from a groom object.

Groom File

Load the groom from a file.

Groom Object

Load the groom data from this source object.

Groom File

Load the groom data from this file.

Noise Mask

Use Noise Mask

When enabled masks the effect of any operation using a noise function.

Amount

Blends the effect of the noise mask.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Noise Mask Frequency

The frequency of the noise.

Gain

High values result in more contrasted noise and fewer areas with medium values.

Bias

Biases the noise towards low or high values.

Operations

You can apply multiple operations using a single instance of this node.

Common Parameters

The following parameters apply to all operations.

Active

Controls whether this operation is applied.

Solo

If any operations have the 'Solo' enabled only those operations are applied.

Operation

The operation to apply.

Set Direction

Rotate curves towards a direction.

Set Lift

Lift curves off the skin or flatten curves against the skin.

Set Length

Lengthen or shorten curves.

Displace

Push curve points along the skin normal.

Wave

Displaces using a wave pattern.

Smooth

Average neighboring curves.

Frizz

Offset curve points using noise.

Bend

Bend curves.

Set Simulation Attributes

Sets attributes that are used by hair simulation.

Note

The following parameters are specific to each operation. They are only displayed when the corresponding operation is chosen from the Operation dropdown menu.

Set Direction

Blend

Blends the overall effect of the operation.

Uniform Direction

A uniform direction to rotate towards.

Direction Attribute

A direction to rotate towards.

Direction Amount

Amount to rotate towards a direction around the skin normal. This only changes direction in the skin plane without changing how far the curve lifts off the skin.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Lift Amount

Lift curves off the skin or flatten curves against the skin to match the given direction. This only rotates away from or towards the skin but doesn’t change the orientation around the skin normal.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Mode

Rigidly Rotate

Rotates the entire curve around it’s root.

Rotate Each Segment

Rotates each segment, allowing individual segments to rotate by different amounts when using a Curve Mask.

Lift

Blend

Blends the overall effect of the operation.

Randomize

Randomizes the effect per curve.

Lift

The global lift value to blend towards.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Min Lift

When Randomize is enabled, this is the lowest lift value used.

Max Lift

When Randomize is enabled, this is the highest lift value used.

Follow Skin Contour

Causes flattened curves to follow the contour of the skin, rather than just pointing straight in the direction of the skin tangent.

Results in a more natural effect but is a bit slower to compute.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Set Length

Mode

Set

Set curve length to an absolute value.

Add

Lengthen curves by the specified amount.

Subtract

Shorten curves by the specified amount.

Multiply

Scale curves by the specified amount.

Method

Scale

Uniformly scale curves around the root point.

Cut Or Extend

Cut or extend curves at the tip.

Blend

Blends the overall effect of the operation.

Randomize

Randomizes the operation’s effect.

Length

The length to change curves to. In Add or Subtract mode, this is the amount to change length by.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

This doesn’t apply to Multiply mode.

Min Length

The smallest length to use when Randomize is enabled.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

This doesn’t apply to Multiply mode.

Max Length

The greatest length to use when Randomize is enabled.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

This doesn’t apply to Multiply mode.

Scale Factor

Scale curve length by this factor.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

This only applies to Multiply mode.

Min Scale Factor

The lowest scale factor used when Randomize is enabled.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

This only applies to Multiply mode.

Max Scale Factor

The highest scale factor used when Randomize is enabled.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Note

Only applies to Multiply mode.

Cull Threshold

After changing curve lengths, cull any curves that are shorter than this value.

Displace

Amount

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Make Wavy

Frequency X

The frequency of waves tangential to the skin.

Amplitude X

The amplitude of waves tangential to the skin.

Frequency Y

The frequency of waves in the normal direction of the skin.

Amplitude Y

The amplitude of waves in the normal direction of the skin.

Straighten

Tangent Straightness

Straightens curves in the skin plane.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Normal Straightness

Straightens curves in the skin normal’s direction.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Smooth

Blend

Blends the overall effect of the operation.

Smoothing Mode

Object Space

Average the shape and orientation of neighboring curves.

Skin Space

Average the shape of neighboring curves while preserving their orientation relative to the underlying skin.

Search Radius

Search for neighbors within this radius. The search is performed on curve roots, so this specifies distance between roots.

Num Neighbors

The maximum number of neighbors to take into account. The actual number may may be lower when fewer neighbors are found within the Search Radius.

Frizz

Frequency

The frequency of the noise function.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Random Frequency

Add a random value to Frequency. The random value is generated between the negated and positive value of this parameter.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Limit Frequency To Representable Values

Clip the frequency to a range that can be represented using the number of points per unit length found on each curve. Without this, high values can result in random values instead of predictable noise.

Amplitude

The maximum distance to offset curve points.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Random Amplitude

Add a random value to Amplitude. The random value is generated between the negated and positive value of this parameter.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Bend

Blend

Blends the overall effect of the operation.

Bend Axis Mode

Bend in Root Direction

Bend in the direction the root points in, relative to the skin.

Uniform Axis

Specify a uniform, global axis around which to rotate all guides.

Curve Attribute

Use an attribute on each curve as its bend axis.

Skin Attribute

Use a skin attribute as the bend axis.

Bend Axis

The bend axis to use when Bend Axis Mode is set to Uniform Axis.

Axis Curve Attribute

A vector attribute on the curves to use as the bend axis.

Axis Skin Attribute

A vector attribute on the skin geometry to use as the bend axis.

Angle

Bend curves by this angle. This is the angle across the entire length of the curve.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Random Angle

Add a random value to Angle. The random value is generated between the negated and positive value of this parameter.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Randomness Bias

Biases the Random Angle towards the bottom or top end of the range.

This parameter can be overridden using an attribute or texture. To do this, select an option from the drop-down menu next to the parameter.

Set Simulation Attributes

Simulation Attributes

The list of attributes to set or modify.

Active

Enable this attribute.

Attribute

The attribute to set. The dropdown provides a list of all attributes used by the Wire Solver.

See the Wire Object help for details on how these attributes influence wire behavior.

Class

This attribute class to create.

This parameter is disabled for some attributes, since they must be of a specific class.

Please see the Wire Object help for details.

Scalar Attribute Parameters

Mode

Controls how scalar values are combined with any existing attribute values.

Set

Set the attribute, disregarding existing attribute values.

Add

Set the attribute to the sum of the parameter value and the existing attribute value.

Minimum

Set the attribute to the minimum of the parameter value and the existing attribute’s value.

Maximum

Set the attribute to the maximum of the parameter value and the existing attribute’s value.

Multiply

Set the attribute to the product of the parameter value and the existing attribute’s value.

Value

The value to use for scalar attributes. Note that this may be modified by the VEXpression below and combined with existing attributes, as specified by the Mode parameter.

VEXpression

The output of this VEX expression is evaluated and combined with existing attribute values as specified by the Mode parameter.

The variable value represents the Value parameter.

See VEX snippets for information on special syntax in the snippet parameter. See the VEX chapter for information on the VEX language.

Toggle Attribute Parameters

Mode

Controls how toggle values are combined with existing attribute values.

Set

Sets the attribute to the parameter value, disregarding any existing attribute values.

Minimum

Set the attribute to the minimum of the parameter value and the existing attribute’s value.

Maximum

Set the attribute to the maximum of the parameter value and the existing attribute’s value.

Toggle

Toggles the existing attribute value.

Value

The value to use for toggle attributes. Note that this may be modified by the VEXpression below and combined with existing attributes, as specified by the Mode parameter.

VEXpression

The output of this VEX expression is evaluated and combined with existing attribute values as specified by the Mode parameter.

The variable value represents the Value parameter.

See VEX snippets for information on special syntax in the snippet parameter. See the VEX chapter for information on the VEX language.

See also

Geometry nodes