Houdini 20.0 Nodes Geometry nodes

Volume Noise Fog geometry node

Adds or generates noise in volume/VDB primitives.

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Since 19

Overview

The Volume Noise Fog SOP provides a simple interface for quickly adding coherent noise to voxel values, reducing the need to create VOP networks or write VEX code. All of the models provided by the Unified Noise VOP and Cloud Noise VOP can be used with this node.

Parameters

General

Mask

When this checkbox enabled, use the blend between the original input volume (given by Fot Volume Name) and to modified volume by this node.

Invert Mask

Reverses the the mask that blend between the original input volume (given by Fot Volume Name) and to modified volume by this node.

Mask Volume Name

The name of the fog volume to mask this node’s effect.

Fog Volume Name

The name of the volume primitive to modify with noise.

Noise Value

Operation

Specifies how to combine the generated adjustment value with the incoming volume. If the target primitive does not exist on the input geometry, all operations will have the same effect.

Set

Use this operation if you want to overwrite any existing value with the generated adjustment value.

Add

The generated adjustment value will be added to the existing volume primitive.

Subtract

The generated adjustment value will be subtracted from the existing volume primitive.

Multiply

The existing volume primitive value will be multiplied by the generated adjustment value.

Minimum

Output will be minimum of the existing volume primitive value and the adjustment value.

Maximum

Output will be maximum of the existing volume primitive value and the adjustment value.

Range Values

The adjustment value will be generated in the selected range. This parameter governs how this range is specified.

Positive

From 0 to the Amplitude value.

Negative

From negative Amplitude to 0 value.

Zero Centered

From negative Amplitude to positive Amplitude.

Min/Max

The range contains all values between Min Value and Max Value.

Min Value

Max Value

Custom Range

0

1

0 to 1

5

10

5 to 10

-5

7

-5 to 7

Min + Range Length

The range contains all values between Min Value and Min Value + Range Length. For instance, if Min Value is 2 and Range Length is 5, the minimum and maximum limits of the range will be 2 and 7, respectively.

Min Value

Range Length

Custom Range

0

1

0 to 1

5

10

5 to 15

-5

7

-5 to 2

Middle ± Range Length

The range contains all values between Middle Value - Range Length / 2 and Middle Value + Range Length / 2. For instance, if Middle Value is 8 and Range Length is 4, the minimum and maximum limits of the range will be 6 and 10, respectively.

Middle Value

Range Length

Custom Range

0

1

-0.5 to 0.5

5

10

0 to 10

-5

7

-8.5 to 1.5

Amplitude

When Range Values is Positive, the generated noise is from 0 to this value. When Range Values is Negative, the generated noise is from the negative of this value to 0. When Range Values is Zero Centered, the generated noise is from the negative of this value to the positive this value.

Min Value

When Range Values is Min/Max or Min + Range Length, this is the minimum value of the generated noise.

Max Value

When Range Values is Min/Max, this is the maximum value of the generated noise.

Middle Value

When Range Values is Middle ± Range Length, this is the middle value of the custom range.

Range Length

When Range Values is Min + Range Length or Middle ± Range Length, this is the length of the custom range.

Output Raw Value

When this is on, the distribution of values is non-uniform, being more likely to fall near the center of the range than the edges. When this is off, values have a more uniform distribution across the range.

Enable Remap Ramp

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

Remap Ramp

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

The default ramp (diagonal from bottom-left to top-right) outputs each number “as itself”.

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).

Minimum

If this checkbox is turned on, the generated noise values are clamped to the specified Minimum.

Maximum

If this checkbox is turned on, the generated noise values are clamped to the specified Maximum.

Scale Value

Scales the adjustment value. A value of 1 will output the adjusted value, ignoring the initial value, while 0 means that no adjustment takes place. Scaling can be done either by uniform value Constant or by value of the Blend Volume (when the menu on the right of this parameter is set to Use Volume).

Scale Volume Name

Specifies the volume primitive to use as the scale volume for the adjusted value.

Fold

Complement

Computes the complement of the noise by subtracting the generated noise from 1.

Noise Pattern

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.

Sparse Convolution

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

Alligator

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

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):

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.

Shift Offset from Center

Shifts the Offset to avoid the ugly noise pattern at the center of the noise function.

Use VEXpression

Turn this checkbox on to use a VEXpression to override parameters based on arbitrary attribute values.

Animation

Animate Noise

Vary the generated noise with time. Some noise types do not support this feature.

Applying animation this way on geometries with millions of element count is slower to compute than using expressions such as $T * 0.25 in the Offset parameter to “pan” across the noise field.

Pulse Duration

When Animated Noise is on, this controls the rate of change of the 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

Lattice Warp and Gradient Warp are two methods for adding “fractal-ness” to the basic noises by warping the noise space.

Lattice Warp

Adds “stringiness” or “wiriness” to standard noise.

Lattice Warp Size

Controls base feature size of the generated noise. The value applies to each axis.

Gradient Warp

Widens the peaks or valleys of the noise output.

Accumulate Lattice Warp

Accumulates the warp for each iteration (octave) of added fractal noise. This can add interesting smudgy effects when used in images, and interesting landmarks when used for terrain.

Accumulate Gradient Warp

Accumulates the warp for each iteration (octave) of added fractal noise.

Flow Rotation

When Noise type is “Flow”, this controls the rotation of the “swirl”, from 0 to 1. Because this parameter is fractional, you can’t just use $F to animate it, since all integral values will look the same, representing a complete revolution. Instead, try something like $FF / 100.

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.

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.

Post-Process

Minimum

If this checkbox is turned on, the final output values are clamped to the specified Minimum.

Maximum

If this checkbox is turned on, the final output values are clamped to the specified Maximum.

See also

Geometry nodes