Houdini 20.5 Nodes VOP nodes

Curl Noise 2D VOP node

Creates divergence-free 2D noise using a curl function.

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Since 10.0

This operator generates divergence-free 2D noise, computed using a curl function on standard Perlin Noise. The operator can handle intervening geometry, allowing the noise field to “flow” around the given object.

The inputs of the Curl Noise operator have the same effect as their counterparts in the Turbulent Noise operator. The four new inputs are Step Size (h), Surface Effect Radius (d), Distance to Surface (dist), and Surface Normal (normal).

Inputs

The data type of the position (pos) input is controlled by the Signature parameter.

Outputs

noise

The output of the noise function. The data type of this output is controlled by the Signature parameter.

Parameters

Noise type

The type of noise to generate. Different algorithms give noise with different characteristics.

Fast

The default. A faster and more interesting variant of Perlin noise.

Frequency is scaled by 1.25.

Sparse Convolution

Sparse Convolution noise is similar to Worley noise. Does not have artifacts at grid points.

Frequency is scaled by 1.25.

Alligator

Produces a bumpy output. Named for its alleged resemblance to alligator skin.

Frequency is scaled by 1.64.

Perlin

A noise where the visual details are the same size. Wikipedia article

Perlin Flow

A noise that’s stable over time, like a rotated Perlin noise, useful to create noise that seems to swirl and flow smoothly across time. Use the Flow rotation parameter below to control the rotation.

Simplex

A noise similar to Perlin but the noise lattice is on a tetrahedral mesh rather than a grid. This can avoid the grid patterns often visible in Perlin noise.

Worley Cellular F1

Produces cellular features similar to plant cells, ocean waves, honeycombs, cratered landscapes, and so on. Wikipedia article

Worley Cellular F2-F1

A variant of Worley noise that produces blunted and cornered features.

Manhattan Cellular F1

A variant of Worley F1 noise that uses Manhattan distance calculation. Useful when you want unusual-looking noise.

Manhattan Cellular F2-F1

A variant of Worley F2-F1 noise that uses Manhattan distance calculation. Useful when you want unusual-looking noise.

Chebyshev Cellular F1

A variant of Worley F1 noise that uses Chebyshev distance calculation. Useful when you want unusual-looking noise.

Chebyshev Cellular F2-F1

A variant of Worley F2-F1 noise that uses Chebyshev distance calculation. Useful when you want unusual-looking noise.

Frequency

The frequency of the noise. Higher values give smaller scaled details in the noise.

Offset

The offset of the input into the noise function. If you visualize the noise as a 2D graph or 3D height field, this has the effect of “panning” across the space of possible noise outputs. If you have the general noise effect you want but just want to get a different set of values for a different look, try changing the offset.

Amplitude

Controls the noise’s minimum and maximum values. When you think of noise as a curve, the parameter controls the height of the peaks and valleys.

Roughness

The scale increment between iterations of fractal noise added to the basic output. The higher the value the larger the “jaggies” added to the output. You can use a negative value for roughness.

Attenuation

Flattens the noise to prevent extreme spikes by damping the values. Higher values create a smoother look.

Turbulence

Controls the degree of noise. Higher values create a more chaotic and less smooth look, with more peaks and valleys.

Step Size

Controls the resolution of the curl function used to generate the noise. A lower value will lead to tighter spirals in the noise.

Surface Effect Radius

Determines the magnitude of the effect that intervening geometry has on the created noise field. A higher value causes greater disturbances resulting from intervening geometry.

Distance to Surface

The signed distance value indicating the distance from the current position to the closest surface of intervening geometry. Piping in the result of a signed distance field with respect to a piece of geometry will allow the generated noise to react appropriately to that surface geometry.

Surface Normal

The normal of the surface closest to the current position. Piping in a volume gradient is one way of passing in the desired normal values, and the result is a noise field that “flows” along the given surface. For best results, Distance to Surface and Surface Normal should be informed by the same surface for each position that the Curl Noise operator is performed on.

Collision SDF

The file to load a collision field from. This will override the normal and distance values, instead, those values will be computed directly from the first volume primitive in the file. This allows the distances to vary within the noise computation, producing more accurate boundaries than if only a single sample is provided. Note the file does not have to be a disk file, it can also be an op: reference to a node or an opinput: reference to an input.

Enable Bouncing SDF

Whhen the sample point is inside the surface, the parameter will reflect the noise value in the normal direction so it is pointing outwards. This helps ensure any particles that end up inside the surface are pushed outwards by the noise field.

See also

VOP nodes