Houdini 20.0 Nodes Geometry nodes

Spline Curve Clay geometry node

Deforms a spline surface by reshaping a curve on the surface.

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The Curve Clay op is similar to the Clay SOP in that you deform a spline surface not by modifying the CVs but by directly manipulating the surface. However, instead of using a point on the surface, you use one or more faces to deform that surface. Also, Curve Clay does not yet support polygonal meshes.

The combination of inputs will determine the modes of transformation. For any combination of inputs, the following parameters modify the following behaviors of the op.

The combination of inputs determines the way the op deforms the surface. There are three valid combination types: 1 input, 2 inputs, and 3 inputs.

One input

When only the surface is specified, it must contain at least one profile in order for Curveclay to work. In this case, you must specify how the surface should be deformed in the region near the profile (whether to deform the profile along a vector \[X, Y, Z or User Defined], or along the surface normal). You must also specify how far out the surface should be pulled, using the Distance parameter.

When one or more profiles form a closed loop, you have the option to displace the inside of the loop, by enabling the option Deform Inside of Loop. Another option allows you to form a closed loop by using several open profiles. The algorithm is the same as the one used in the Trim SOP when not treating curves individually. This might be useful for putting a regular dent into a surface (e.g. A circle, or a font).

Two inputs

When the surface and a set of deforming faces is specified (the deformed faces are the third input) the profiles on the surface will be snapped to the deforming faces. This option has no additional inputs. This might be useful when you want to snap any profile to any free floating curve.

Three inputs

When all three inputs are specified, the Rest faces will first be projected to the surface. The projection is done in two ways: along a specific vector (X, Y, Z, or User Defined) or along the Minimum Distance to the surface. Each point on the curve will first be projected to the surface. Then this curve will not be snapped to the deforming face. Rather, the curve will be deformed by the difference between the rest face and the deforming face. This option provides flexibility on all inputs. For example, this would be ideal for creating random mountain ranges.

When using CurveClay on a wrapped surface, here are some points to remember:


Face Group

Subset of faces (NURBS,Bezier,polygons) to project, or subset of profiles to deform, depending on how many inputs are connected.

Examples include 0.5 1.2-3.9 5.*

This group can even take surfaces (possibly intermixed with profile curves) when the 2nd input is not present, indicating that all the surface’s profiles must be used. Then, the example above becomes: 0.5 1.2-3.9 5

Surface Group

Subset of spline surfaces to be deformed when all three inputs are connected.

Divisions on Face

Segments on the face(s) or profiles.


How tightly to pull the surface around the face.


Amount of surface refinement.



Controls curve projection. Enabled if all 3 inputs exist.

Projection Axis

Choice of several projection axes:


Project curve points to their closest places on surface.

X, Y, Z

X, Y or Z axis.

User Defined

Enter the vector into the field below /projdir.



How to deform surface. Enabled if only 1 input exists.

Projection Axis

Choice of several projection axes:


The profiles will be deformed along the surface normal.

X, Y, Z

X, Y or Z axis.

User Defined

Enter the vector into the field below /deformdir.


Distance deformed along the vector.

Deform Inside

Check if the inside of closed loops should be deformed.


Check if multiple curves form a closed loop.


CurveClayBasic Example for Spline Curve Clay geometry node

This is a demonstration of how the CurveClay SOP can create an embossed effect on nurbs or bezier geometry.

Two different methods of using the CurveClay SOP to imprint font onto a sphere are shown.

The first method uses a single projected profile, the second method uses two profiles.

UltraSharpFont Example for Spline Curve Clay geometry node

This example demonstrates how to refine a curveclay geometry.

A letter “t” is projected onto a grid. The CurveClay SOP understands profile information and uses it to deform the surface geometry.

To get sharp edges on a curveclay, play with the Sharpness and Refinement parameters.

See also

Geometry nodes