Houdini 20.5 Nodes Geometry nodes

Cloud Billowy Noise geometry node

Applies a billowy cloud like displacement noise to a fog volume.

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Since 20.0

Overview

Adds a noise displacement pattern to a volume field in order to create a billowy cloud like appearance. Various noise shaping options are available as well as masking controls. This is ideal for modeling large cumulus clouds, while the Cloud Wispy Noise is used to add wispy details to the cloud.

Parameters

General

Mask

When this checkbox turned on, use the blend between the original input volume (given by Density Volume) and to modified volume by this node. Setting this value to 0 means that this node will not have an effect on the input volume. Optionally, you can provide a mask volume (given by Mask Volume) to mask specific regions in the volume field.

Invert Mask

Negates the fog volume mask from the second input, if any.

Iterations

Controls the number of displacement iterations. Using a single iteration is generally not enough to create pleasing billowy details. However, doing more than one iteration will slow down the cooking process. When this is turned on, use the Attenuation tab to vary the billowy properties for each iteration for a more visually pleasing results.

Override Look

Cloud Visualization

When the checkbox is on, overwrites the visualization for the volume.

Shading

Controls how to shade the volume. When generating cloud patterns, use Occlusion to see all the finer details and Reversed Occlusion to display clouds in a more realistic manner.

Ambient Occlusion

Uses ambient shadowing to display the volume.

Reversed Occlusion

Reverses the ambient shadowing for volumes which can be used to give a more realistic cloud look with internal scattering.

Density Scale

Fixed multiplier on the density field to control how opaque the volume is. If you are using a larger scene scale, you may need a smaller density scale.

Note

Fog density is density per unit length, and is independent of the resolution. So the same sized box, at 100 or 10 divisions, should be the same opacity. This means very small boxes will become transparent, especially if HDR rendering isn’t on. You can enable HDR rendering on the Scene tab of the Display Options dialog.

Setting the HDR Textures format to at least 16-bit for 3D textures can also help resolve low-density volumes. These settings can be found under the Texture tab of the Display Options.

Ambient Shadow Scale

Determines the intensity of self shadows from ambient light sources. The final amount of self-shadowing from these lights is controlled by the product of Density Scale, Shadow Scale, and Ambient Shadow Scale. The video demonstrates the value increasing from 0 to 1.

Note

Turning off this checkbox does not disable ambient shadowing. Instead, it keeps this property of the geometry unchanged. If no Ambient Shadow Scale is set, Ambient Occlusion on the Geometry tab of the Display Options controls the default amount of self-shadowing from ambient lights.

Note

The default headlight is treated as an ambient source by fog volumes.

Exposed Color

Color of smoke that’s receiving direct light from an ambient light source. The default white setting indicates that areas exposed to external lights are bright. You can set this darker than Occluded Color to achieve a more cloud-like look, where areas deeper within the cloud experience more light scattering and thus appear brighter. Set Ambient Colors must be enabled to control this parameter.

Occluded Color

Color of smoke that’s not receiving any light from an ambient light source. The default black setting indicates that areas occluded from light are dark. You can set this brighter than Exposed Color to achieve a more cloud-like appearance, where areas deeper within the cloud (that is, those occluded from outside light) are more luminous due to a greater degree of internal scattering. Set Ambient Colors must be enabled to control this parameter.

Billowy Noise

These parameters control the global billowy noise pattern. When Iterations is turned on, these values will only apply on the first iteration, while the Attenuation tab controls the rate of change in the values for each iteration.

Noise

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.

Perlin Cloud

Generates perlin noise based cloud pattern influenced by the Distortion parameter.

Perlin noise with Distortion set to -1 (left) and +1 (right):

Simplex Cloud

Generates simplex noise based cloud pattern influenced by the Distortion parameter. Simplex 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.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Fast Simplex Cloud

Generates fast simplex noise based cloud pattern influenced by the Distortion parameter. This simplex noise function uses a different lattice structure and a cheaper accumulation method.

Simplex noise with Distortion set to -1 (left) and +1 (right):

Amplitude

Controls the effect of the distortion. Large values will create larger billowy details in the pattern, but might create unrealistic looking cloud patterns.

Element Size

Uniform scale of elements in the distortion noise. This scale is relative to Element Size, which controls the overall pattern size.

Offset

Offset within the evaluated noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

Worley Details

Add Worley Details

When turned on, a worley noise is combined with the noise pattern (specified by Noise Type) to give puffy cloud noise. Enabling this, will largely diminish the distortion effect (specified by Distortion).

Noise pattern with added worley noise:

Blend

Controls the amount of mixing between the noise pattern (specified by Noise Type) and the worley noise. A value of 0 means no worley noise is applied to the noise pattern.

Erosion

Controls how fast the edges of the noise pattern turn to zero. The larger the value, the more the edges are eroded creating smaller and smaller cloud patches.

Element Size Scale

Multiplier on the Element Size parameter that effects the worley noise pattern.

Value Correction

Bias

This value controls how much the medium grey (noise values around 0.5) is pulled towards zero (if Bias is less than 1) or pulled towards one (if Bias is greater than 1). A value of 0.5 leaves the noise values unaffected.

Gain

Controls how much the medium greys (noise values around 0.5) are pulled together, while values around 0 and 1 are pulled apart. The value of 0.5 leaves the noise values unaffected.

Gamma

Controls the overall gamma of the generated noise. Values less than 1 will darken the noise, increasing the range of values in originally bright areas. Conversely, values greater than 1 will stretch out the range of values for originally dark areas, which will increase the overall brightness of the noise.

Contrast

This value expands or shrinks the overall range of tonal values. Particularly, each noise value is pushed towards (if Contrast is less than 1) or away from (if Contrast is greater than 1) medium grey (noise values at 0.5).

Value Offset

Shifts the internal noise pattern range (roughly 0-1) to displace the volume in the opposite direction of the surface normal as well. A value of 0.25 will shift this range to -0.25-0.75.

Clamp Below Zero

When the Value Offset is larger than zero, this will set any negative noise value back to zero. Use this to create a displacement pattern that has areas without any displacement.

Complement

Inverts the generated noise pattern.

Fractal

The fractal controls let you add additional fractal noise on top of the output of the basic noise type.

Fractal Type

None

Does not add any additional noise on top of the basic noise.

Standard

Adds pseudo-random noise on top of the basic output.

Terrain

Adds noise like “Standard” but dampens the noise in the valleys, which can be useful for generating mountainous terrain.

Hybrid

Like terrain, but with more sharpness in the valleys.

The following parameters are available when Fractal type is anything except None.

Max octaves

The number of iterations of distortion to add to the output of the basic noise. The more iterations you add, the more “detailed” the output. Note that the output may have fewer octaves than this parameter (that is, increasing the parameter will eventually stop adding detail), because the node eventually stops when there’s no more room to add more detail in the output.

Lacunarity

The frequency increment between iterations of fractal noise added to the basic output. Note that you can use a negative value.

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.

Warping

Distortion

Controls how much the noise is distorted in the direction of decreasing noise values if Distortion is greater than 1, and in the direction of increasing noise values if Distortion is less than 1. When worley details are added to the noise pattern, the effect of distortion are largely diminished.

Distortion with a value of 1:

Distortion with a value of -1:

Stretch

How much to stretch the noise in each direction. The advantage of using this instead of Element Size is that it preserves some details unstretched, making the stretched noise pattern more natural looking.

Comparing Element Scale of 3 (left) to Stretch value of 3 (right) along the X-axis:

Droop

Warps the generated noise such that the noise pattern is bending or hanging towards the given droop direction.

Noise pattern without (left) and with droop applied (right):

Droop Direction

The direction in which the noise is warped.

Advection

Advect Noise

Advect Noise

Applies additional noise offset to the main noise to create finer details.

Amplitude Scale

Controls the effect of the advection, large values will advect the noise more. This is a multiplier on the noise amplitude (given by Amplitude).

Element Size Scale

Uniform scale of elements in the noise. This is a multiplier on the noise element size (given by Element Size).

Offset

Offset within the evaluated advection noise field (added to each axis). If you have the general noise effect you want, but want to get a different set of values for a different look, try changing the offset.

Fractal

Max Octaves

The number of iterations of distortion to add to the output of the basic noise. The more iterations you add, the more “detailed” the output. Note that the output may have fewer octaves than this parameter (that is, increasing the parameter will eventually stop adding detail), because the node eventually stops when there’s no more room to add more detail in the output.

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.

Processing

Noise Generation

Number of Noises

These many numbers of noise patterns are generated in one iteration; each with different noise offset. Increasing this value will generate somewhat more filled and larger displacement noise.

Rest Position Bias

Controls how the internal billowy noise is sampled based on position, greatly effecting the look of the displacement. The value of 1 means that the noise is sampled according to the closest point on the surface defined by the signed distance field of the incoming volume. Just as with displacing a geometry along its normal, the generated peaks have no detail along the axis of displacement. This visual drawback can be eliminated by enabling multiple billowy noise iterations (given by Iterations). A value of 0 means that the noise is sampled using the world position of each voxel. While this method applies displacement in all directions, by increasing the noise amplitude (given by Amplitude), this method can very easily lead to numerous isolated fog pieces around the main cloud.

Up Vector Bias

When turned on, the displacement will decrease based on the surface normal direction and the up vector.

Up Vector

User specified up vector for noise falloff.

Deepen Valleys

When this is turned on and multiple iterations are set (given by Iterations), this will use the accumulated noise pattern in each iteration as a scalar on noise amplitude of the next iteration.

Volume Operations

Expand Distance Scale

To apply noise displacement to the incoming volume, the active area must be expanded. The expansion amount is automatically calculated based on the given settings, and this value is a multiplier on top of that value. If you notice artifacts in the generated volume, the displacement amount is probably larger than expansion distance, in which case increase this number to create a larger active region.

Voxel Size Scale

When this is turned on, it resamples the incoming volume in each iteration. This parameter is useful when multiple iterations are set (given by Iterations) to increase the number of voxels in the volume with each iteration (given by the Voxel Size Scale parameter on the Attenuation tab). It is rather common first to use a low-resolution incoming volume for testing. However, when you switch the input volume for a higher resolution version, the displacement features might look visually different. To preserve the features, leave the incoming resolution the same while this parameter and multiple iterations are enabled.

Resample SDF

To find the normals of the incoming volume, the volume has to be converted to a signed distance field volume. When this is turned on, a lower resolution volume is used than generated the SDF field, speeding up the conversion process. Increased values will generate lower resolution SDF field.

Fog Isovalue

The crossing point of this value in the volume will be converted to the iso surface. For example, 0 for signed distance fields or 0.5 for fog volumes.

Attenuation

When Iterations are turned on, these parameters control the rate of change in the corresponding parameter values for each iteration.

Billowy Noise
Noise

Amplitude

When Iterations and this parameter are turned on, this controls the amplitude reduction for each iteration.

When Amplitude is set to 1 and this parameter is 0.35, the table shows the final amplitude value for each iteration:

Iteration #1

Iteration #2

Iteration #3

1

0.35

0.1225

Element Size

When Iterations and this parameter are turned on, this controls the element size reduction for each iteration.

Number of Noises

When Iterations and this parameter are turned on, this controls the reduction in the number of noises for each iteration.

Worley Details

Blend

When Iterations and this parameter are turned on, this controls the worley blend reduction for each iteration.

Erosion

When Iterations and this parameter are turned on, this controls the worley erosion reduction for each iteration.

Value Correction

Bias

When Iterations and this parameter are turned on, this controls the bias reduction for each iteration.

Gain

When Iterations and this parameter are turned on, this controls the gain reduction for each iteration.

Gamma

When Iterations and this parameter are turned on, this controls the gamma reduction for each iteration.

Contrast

When Iterations and this parameter are turned on, this controls the contrast reduction for each iteration.

Fractal

Max Octaves

When Iterations and this parameter are turned on, this controls the number of octave reductions for each iteration.

Roughness

When Iterations and this parameter are turned on, this controls the roughness reductions for each iteration.

Distortion

When Iterations and this parameter are turned on, this controls the distortion reductions for each iteration.

Droop

When Iterations and this parameter are turned on, this controls the droop reductions for each iteration.

Stretch

When Iterations and this parameter are turned on, this controls the stretch reductions for each iteration.

Processing

Rest Position Bias

When Iterations and this parameter are turned on, this controls the rest position bias reductions for each iteration.

Up Vector Bias

When Iterations and this parameter are turned on, this controls the up vector bias reductions for each iteration.

Voxel Size Scale

When Iterations and this parameter are turned on, this controls the voxel size reductions for each iteration.

Bindings

Bindings

Density Volume

The name of the volume to be used as density for generating the billowy noise. Usually you should leave it as density.

Mask Volume

The name of the volume to be used as mask generating the billowy noise. Usually you should leave it as mask.

Examples

simple_clouds Example for Cloud Billowy Noise geometry node

This example demonstrates the use of a collection of cloud tools to generate a variety of clouds.

See also

Geometry nodes