Houdini 21.0 Nodes Geometry nodes

Pyro Thruster Exhaust geometry node

Creates volumes and particles to simulate thruster exhausts without the need of simulation.

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Overview

The Pyro Thruster Exhaust node uses a single primitive with a normal to generate a volume to be used as a thruster exhaust effect. The volume is always pointing towards the direction of the input normal, and the shape of the exhaust is controlled by the input primitive’s shape when provided.

This node can also output particles flowing in the direction of the thruster. These particles can be used for adding sparks using Particle Trail, or adding a 2D heat haze effect.

Tip

To visualize the particles turn on the Show Guide checkbox on the Particles tab.

The advantage of this node is that it doesn’t require expensive pyro simulations to create simple thruster effects. To add more complexity to the look, use multiple of these nodes with various settings. For an example of this workflow, see the Thruster Exhaust shelf tool.

Warning

The input of this node must be a single primitive. Alternatively, you can use the Group parameter to select exactly one element that is used to generate the thruster.

Parameters

Group

The primitive number to use for generating the thruster.

General

Shape

Voxel Size

The size of a voxel for the exhaust volume. Cutting your voxel size in half will require eight times the memory and time, so adjust this value sparingly.

Uniform Scale

Scales the incoming primitive to make the radius of the exhaust volume bigger or smaller.

Local Translate

The amount of translation based on the orientation of the incoming primitive. Use the Z-axis of this parameter to position the exhaust volume forward or backward along the facing direction.

Thickness

Whether the exhaust volume shape should be hollowed. When this parameter is 1, the volume is generated on the whole surface of the incoming primitive. Lowering this value erodes the volume from the center, eventually leaving a thin layer of exhaust volume at the edge of the incoming primitive.

Length

Controls the length of the exhaust volume. Increase this value if you want a thruster to emit longer and more visible volume.

Jitter Length

When turned on, the exhaust volume’s length is reduced over time in a random varying fashion. This helps to create the illusion that the thruster is more chaotic with constantly changing length.

Min Length

The relative minimum length that the exhaust volume is allowed to be scaled with. The default 0.75 means a reduction of 25% in length. For example, if Length is 10, the volume will vary between the length of 7.5 and 10.

Speed

Controls how fast the length of the exhaust volume is changing. Keep this value high to create a more chaotic thruster animation.

Scale Across Length Ramp

Controls the thickness of the exhaust volume along its length. The horizontal axis represents the length of the volume (given by Length). The left side of the ramp represents where the thruster base is at the incoming primitive.

Exhaust

Add Noise

Creates a noise that moves along the length to create the illusion of a fast moving exhaust volume from the thruster. To control the speed of the noise over time, use the Speed parameter under Animation simple folder.

Noise

Noise Type

Controls the type of the noise that is applied to the exhaust volume.

Fast

A faster and more interesting variant of Perlin noise.

Alligator

Produces a bumpy output. This is named for its alleged resemblance to alligator skin.

Strength

Controls the effect of the noise. Lower this value to make the noise less prominent. The value of 0 turns off the noise.

Element Size

Uniform scale of elements in the noise across all axes.

Axis Size Scale

An additional scale along the Z-axis that faces the direction of the thruster exhaust. The smaller the volume, the more the noise will stretch along the length of the exhaust volume, creating the illusion of a fast-moving exhaust.

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.

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).

Bend

When turned on, increase the value of this parameter to slowly bend the noise towards the center. This helps to create the illusion that the exhaust is pulled towards the center.

Cutoff

When turned on, increase the value of this parameter to slowly erode the exhaust volume, leaving only patches of bursts instead.

Distort Density

Creates a noise that distorts the exhaust volume creating a more chaotic effect. To control the speed of the noise over time, use the Speed parameter in the Animation section.

Distortion

Strength

Controls the effect of the noise. Lower this value to make the noise less prominent. The value of 0 turns off the noise.

Element Size

Uniform scale of elements in the noise across all axes.

Axis Size Scale

An additional scale along the Z-axis that faces the direction of the thruster exhaust. The smaller the volume, the more the noise will stretch along the length of the exhaust volume, creating the illusion of a fast-moving exhaust.

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.

Expand Voxels

Expands the active area by at least this number of voxels. Increase this value when distortion (given by Strength) is too large, and the exhaust volume appears clipped at the boundaries.

Animation

Time

By default, this is the current Houdini time that is used to animation the exhaust noises.

Time Offset

Offsets the time given by the Time parameter. Use this to shift the animation in time.

Speed

Controls the speed by which the noise is moving along the exhaust volume. Increasing values create the illusion of a more powerful thruster.

Pulse Duration

This controls the rate of change of the noise pattern.

Temperature

Temperature Scale

Intensity of the emission component of the exhaust volume.

Scale Along Length

When turned on, the intensity of the emission component of the exhaust volume is scaled along the length by Intensity Ramp.

Intensity Ramp

Controls the intensity of the emission component for the exhaust volume along its length. The horizontal axis represents the length of the thruster (given by Length). The left side of the ramp represents where the thruster base is at the incoming primitive.

Color Ramp

Controls the color of the emission component for the exhaust volume based on the intensity of the volume.

Assign Material

Creates a shop_materialpath primitive attribute that will point to a specified material, ensuring that it is used for renders. Turn this off if you do not want to assign a material at the SOP level.

Assign Material

Assign Material

The path to the shader that is assigned to the exhaust volume.

Particles

Scatter

Point Count

The number of particles to generate coming out from the thruster.

Prune Threshold

When turned on, this helps to randomize the number of particles visible given by Point Count. Higher values towards 1 mean that fewer and fewer particles are visible at a given moment.

Length

Controls how far the particle can travel from the input primitive in the direction of the thruster. By default, this is the same length as the exhaust volume.

Seed

The integer type attribute to use for random selection of particle distribution.

Particle Noise

When turned on, a noise is added to the path of the particles.

Noise

Amplitude

The strength of the noise to apply to the particle path.

Element Size

Uniform scale of elements in the noise.

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.

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.

Animation

Speed

Controls the speed by which the particles are moved along the path.

Attributes

Velocity Scale

Controls the scale of the velocity point attribute on the particles.

Normalized Age

The point attribute storing a zero to one value which start to increase from 0 when the burst component is created until 1 when the burst component is killed.

See also

Geometry nodes