Interpolate Hair Curves

The Interpolate Hair Curves node generates new hair curves by interpolating existing guide curves on a surface mesh. It allows for efficient grooming workflows where a small number of guide curves define the overall shape, and the node fills in additional interpolated curves to create a dense, detailed hair system.

For simpler duplication-based setups, the Duplicate Hair Curves node provides a lighter-weight alternative that may perform faster.

Note

This node or modifier requires valid Surface geometry or object inputs, along with a Surface UV Map, to function properly.

Inputs

Geometry

The input geometry containing the guide hair curves to interpolate.

Surface Input Type

Determines how the surface data is provided for interpolation.

Object:

Use an object reference to provide the surface.

Geometry:

Use a geometry input directly connected to the surface mesh.

Surface

The surface object used as the attachment base for the interpolated curves. Its transforms must match those of the modifier object.

Surface UV Map

The UV map used to find attachment locations for the interpolated curves on the surface.

Surface Rest Position

When enabled, sets the surface mesh to its rest position before attaching curves. This ensures consistent root positions when deformation is applied afterward.

Tip

When combining this node with Deform Curves on Surface, enable Surface Rest Position if the deformation node follows this one, so that pre-deformed coordinates are used for consistent interpolation.

Follow Surface Normal

When enabled, aligns the interpolated curves with the surface normal at their root attachment point.

Part by Mesh Islands

When enabled, treats separate mesh islands on the surface as independent regions for interpolation, preventing cross-blending of guides between disconnected areas.

Interpolation Guides

The number of nearest guide curves used to interpolate the shape of each new curve. Higher values result in smoother transitions but may slightly reduce performance.

Distance to Guides

The maximum distance from a guide curve within which interpolation occurs. Curves outside this range will not influence the result.

Distribution

Distribution Method

Determines how root points for interpolated curves are distributed across the surface.

Random:

Distributes roots randomly across the surface.

Poisson Disk:

Uses Poisson disk sampling to maintain a minimum distance between root points, producing an even and natural distribution.

Density

The number of interpolated hair curves generated per unit of surface area. Higher values increase the total hair density.

Density Mask

A scalar factor used to locally scale the curve density across the surface.

Mask Texture

Uses an image texture to control which areas of the surface generate hair. The image is sampled using the Surface UV Map input.

Tip

Texture sampling occurs after root points are generated, so accuracy is not limited by mesh resolution. The Density Mask input is typically faster; using both together can balance quality and performance.

Viewport Amount

A factor used to reduce curve density in the viewport for performance optimization. This does not affect the final render density.

Seed

Sets the random seed for the interpolation and distribution processes. Changing this value generates a different random distribution while maintaining the same parameters.

Outputs

Geometry

The resulting geometry containing the interpolated hair curves.

Guide Index

An integer attribute storing the index of the main guide curve used to generate each interpolated curve.

Surface Normal

The surface normal direction at each curve’s root attachment point.