Houdini 20.5 Nodes VOP nodes

Sky Box VOP node

Creates a sky noise pattern with volumetric clouds.

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Since 20.0

Overview

This tool will generate procedural clouds inside the given bounds. This is a low-level tool, and it is recommended to use the Sky Box SOP that provides more control and supports sky fields.

Parameters

Skybox

Altitude

The position on the Y-axis where the bottom of the cloud sits. Increase the number to position to cloud higher up in the atmosphere. Make sure this altitude falls into the bounding box given by Size and Center.

Thickness

The vertical extent of the cloud. Smaller wispy clouds might require a thin layer, while large billowy clouds usually need a larger thickness. Make sure this altitude falls into the bounding box given by Size and Center.

Seed

Controls random selection for variation. Change the value if the current variation is undesirable.

Weather

Coverage

Controls how much of the sky is obscured by clouds. Lower values will create smaller cloud patches with lesser density separated by larger spaces, while large values will create one continuous denser, large cloud volume.

Precipitation

Additional control over how much of the sky is obscured by clouds.

Anvil

Controls how much the cloud spreads out at the top of the cloud.

Cloud Layer

Bounds

Size

Controls the overall size of the sky region that is filled with clouds.

Center

Controls the overall position of the sky region that is filled with clouds.

Erode Boundary

The generated sky region is always clipped according to the given bounds. When the skybox is large enough, this clipping might not be visible. However, when only a small patch of clouds is needed, turn on this control to create a much more natural boundary based on a spacial noise. The boundary is always eroded in an oval shape.

Erosion

Controls how much cloud area erodes away from the boundary. Larger values will leave a smaller sky region with clouds, but their boundary will be more broken up.

Sharpness

Controls the smoothness of the eroded boundary. A lower value makes the boundary softer, which can be used for wispy clouds, while larger value could be used for denser billowy clouds.

Element Size

Uniform scale of elements in the spacial noise that is used for erosion.

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.

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).

Curve Sky

Curve Sky

Allows vertical deformation of the generated sky to create a sky dome. This is useful in shifting distant clouds to meet horizon lines.

Horizon Offset

Controls the center position of the sky dome. Use this control when the sky dome is not located at the origin.

Horizon Altitude

Sets the position on the Y-axis where the bottom of the sky dome sits.

Horizon Distance

The radius of the sky dome. Increase this value to create a larger sky dome.

Curvature Ramp

This ramps controls the curvature of the sky dome based on the distance from the center of the sky dome.

Vertical Profile

Vertical Profile

Controls the density of the cloud across the height, relative to the thickness of the cloud (given by Thickness). The first two components control the relative heights at which the density rises from 0 (no cloud) to 1 (dense cloud). While the second two components control the relative heights at with the density falls from 1 (dense cloud) to 0. For example, values such as (0, 0.1, 0.9, 1) will create a cloud that has very little fading in and out across the altitude rise, and most of the cloud is a filled dense cloud. Values such as (0, 0.4, 0.6, 1) will create a cloud that has a much smaller dense layer.

Vertical Extrusion

Raises the vertical thickness of the cloud relative to its given thickness (given by Thickness). If the thickness is set to 100 and this parameter is 1, the overall vertical thickness of the cloud will be 200.

Flatten Top

Controls how flat the top of the clouds should appear.

Flatten Bottom

Controls how flat the bottom of the clouds should appear.

Billowy Noise

The default noise generated inside the sky box to create billowy cumulus cloud like shapes.

Billowy Noise

Noise Type

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

Perlin Cloud

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

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

Simplex Cloud

Generates a simplex noise-based cloud pattern influenced by the Distortion parameter. Simple noise is 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 a 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):

Element Size

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

Element Scale

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

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.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

Offset

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

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

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).

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.

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.

Alligator Noise

Applies additional alligator noise to the default billowy noise generated inside the sky box to create billowy cumulus cloud like shapes.

Alligator Noise

Add Alligator Noise

Generates an additional alligator noise that is combined with the default billowy noise. Use the Vertical Profile Mask in the Mask folder to control the vertical blending of this noise.

Amplitude Scale

Controls how much the alligator noise will affect the default billowy noise.

Element Size Scale

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

Element Scale

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

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.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

Offset

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

Value Correction

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).

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.

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.

Masking

Vertical Profile Mask

This ramp lets you control the strength of the alligator noise function across the vertical profile of the skybox. The horizontal axis represents the vertical height (minimum on the left, maximum on the right). The vertical axis represents the strength of output when the noise function generates that point within the range.

Wispy Noise

Generates wispy noise inside the sky box to create more broken-up cloud shapes.

Wispy Noise

Add Wispy Noise

Generates a fine, feather like wispy noise that can be combined or overwritten by the default billowy noise. Use the controls inside the Mask folder to change the blending with the billowy noise.

Amplitude

Controls the strength of the wispy noise. Larger values create finer and more broken up shapes, while lower values create smoother wispy details.

When Attribute Type is Vector, click the Per Component button for separate amplitudes along each axis.

Amplitude Scale

When Attribute Type is Vector and you turn on the Per Component button, this lets you scale the Amplitude separately across each axis.

Element Size Scale

Uniform scale of elements in the noise.

Click the Per Component button for separate scales along each axis.

Element Scale

When you turn on the Per Component button, this lets you scale the Element Size separately across each axis.

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.

You can animate the noise using an expression such as $T * 0.25 here. This is faster to compute than Animate Noise, but gives the visual effect of “panning” across the noise field, which may or may not be acceptable.

Click the Per Component button for separate additional offsets along each axis.

Offset

When you turn on the Per Component button, this lets you add the a separate offset along each axis.

Turbulence Noise

Add Turbulence

When enabled, a turbulence noise is generated to displace the default wispy noise to create additional finer wispy details.

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 strength of the turbulent noise. Larger values create finer and more broken up shapes, while lower values create smoother wispy details.

When Attribute Type is Vector, click the Per Component button for separate amplitudes along each axis.

Amplitude Scale

When Attribute Type is Vector and you turn on the Per Component button, this lets you scale the Amplitude separately across each axis.

Attenuation

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

Value Correction

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).

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.

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.

Masking

Mask Center

Masks the wispy noise based on the density of the default billowy noise using a threshold range. Mask Center and Mask Width control the masking range. By default, where the billowy noise density is at the minimum and maximum of this range, the wispy strength multiplier is 1 and 0, respectively. Wispy noise is reduced in areas where the mask value is smaller. Set this value to 1 and Mask Width to 0 to fill the skybox with wispy noise.

Mask Width

Controls the range of values used for masking the wispy noise in conjunction with Mask Center. The effective range of mask values is from Mask Center - Mask Width * 0.5 to Mask Center + Mask Width * 0.5.

Vertical Profile Mask

This ramp lets you control the strength of the wispy noise function across the vertical profile of the skybox. The horizontal axis represents the vertical height (minimum on the left, maximum on the right). The vertical axis represents the strength of output when the noise function generates that point within the range.

Animation

Animation

Pulse Duration

Vary the generated noise with time. This controls the rate of change of the noise pattern.

Enable Directional Offset

When turned on, offsets the evaluated noise patterns that gives the visual effect of “panning” across the noise field simulating a wind like effect.

Speed

Controls how fast the noise pattern movies in the direction given by Direction.

Direction

The direction that is used to offset the noise pattern.

Upward Bias

When turned on, this controls how much the direction (given by Direction) will blend towards the Y-axis. Use this control to add a small amount of upwards motion to the direction.

Cloud Top Offset

Controls the offset difference between the bottom and the top of the skybox.

Density

Density Scale

Normalize Density

With reduced coverage values (given by Coverage) the density output by the skybox is also reduced. When this is turned on, the density range will more closely match the 0 to 1 range.

Maximum Density

When the checkbox is on, clamp density values so they are never greater than this value.

Billowy Scale

Multiplies the density using this value in the regions where billowy noise is generated.

Wispy Scale

Multiplies the density using this value in the regions where the wispy noise is generated. Generally, wispy noise is more opaque than a filled billowy cloud.

Enable Remap Ramp

Turn this on to shape the output of the density with a ramp.

Density Remap Ramp

When Enable Remap Ramp is on, this ramp lets you control the density output. The horizontal axis represents the input density range (minimum on the left, maximum on the right). The vertical axis represents the number to output when the density value is at that point within the range.

Scale Along Vertical Profile

Turn this on to shape the output of the density along the vertical profile of the skybox.

Vertical Density Ramp

This ramp lets you control the output density across the vertical profile of the skybox. The horizontal axis represents the vertical height (minimum on the left, maximum on the right). The vertical axis represents the density scale to output when the noise function generates that point within the range.

See also

VOP nodes