Houdini 20.0 Nodes Geometry nodes

Debris Source geometry node

Generates point emission sources for debris, pyro, or particle sources from separating fractured rigid body objects.

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Since 19.0

Overview

This SOP scatters points along the surfaces of fractured geometry to represent debris emission sources. This allows you to detect points near regions where the fractured pieces have recently separated. The points that are separated can be used to emit small debris, particles, or you can rasterize them into a pyro volume source.

Parameters

General

Reset Simulation

Resets the simulation.

Interior Group

Specifies the primitives to scatter points on. Typically, this group should contain only the interior polygons created by the fracturing process so that the original surface is not affected.

Rest Frame

Frame used when initializing the state of each debris emission point.

Cache Memory (MB)

Specifies how much memory in megabytes can be consumed by the cache for this simulation. Once this limit is exceeded, old cache entries are either deleted or saved to disk to make more room, depending on the value of the Allow Caching To Disk parameter value above.

Scatter

Density Scale

Value or multiplier indicating the density of points to generate.

When scattering By Density without a Density Attribute, this is the expected number of points per length unit for curves, per area unit for surfaces, and per volume unit for volumes and tetrahedra. When scattering In Texture Space without a Density Texture, this is the expected number of points in the full unit square. When using a Density Attribute or Density Texture, this is multiplied by those to determine the actual density in physical or texture space, respectively.

This is disabled if Force Total Count is enabled or if Generate is Count per Primitive.

Density Attribute

An attribute specifying the density of points to generate, when Generate is By Density. The attribute can be a point, vertex, primitive, or detail attribute, and in the case of point and vertex attributes, the density will be linearly interpolated over the area of the primitive. This is ideal for use with the Paint node. When Force Total Count is enabled, this specifies relative distribution of point density, not actual density.

Max Point Limit

This is an optional strict limit on the number of points to generate, to avoid fatal accidents. If the number of points that would have been generated exceeds this, a warning will be generated indicating the number of points that would have been generated, and a number of points less than or equal to this limit will be generated, in a roughly similar distribution.

When Generate is In Texture Space, this is a limit on the number of points scattered in the texture space unit square. Barring any repeats in the texture mapping, the number of generated points should be less than or equal to this limit.

Seed

When Generate is By Density, this random seed is used for determining the number of points to be generated on each primitive and for generating the points on each primitive, as well as randomizing the order. When Generate is In Texture Space, this is used for determining the number of points scattered in the texture space unit square, generating the points in texture space, and randomizing the order.

Release

Distance Threshold

The distance points have to separate to be considered released.

Click the randomization button on the right side of this parameter to randomize the value per incoming element. This will create/select a corresponding attribute adjust node to give you greater control over the parameter’s value.

Attributes

Point Number Attribute

For each generated point, the node will store the original point number in this attribute.

Released Attribute

The attribute to store whenever a point is separated beyond the Distance Threshold.

Distance Attribute

The attribute to store the separation distance for each point.

Volume Attribute

The attribute to store the volume of the fractured pieces the point was scattered on. Use this attribute to make the source points disperse on smaller fractured pieces, or emit less smoke from them.

Depth Attribute

Stores how far away each point is from the closest primitive that is not in the Interior Group, when an Interior Group is provided. Using this attribute, you can separate points scattered just around the edge of the Interior Group.

Rest Position

The attribute to store the position of each point given by Rest Frame.

Age Attribute

The point attribute storing a value which starts to increase from zero when the point is released. Use this in combination with Life Span, Remove Unreleased, and Remove at Life End to output only a few selected points to use as the debris source for further rigid body simulation.

Life Span

The length of time each point will remain active after release. Enable Remove at Life End to delete points that are released, but not active anymore.

Click the randomization button on the right side of this parameter to randomize the value per incoming element. This will create/select a corresponding attribute adjust node to give you greater control over the parameter’s value.

Density Attribute

The point attribute storing a value which starts to decrease from 1 to zero when the point is released using Life Span. Use this in combination with Life Span, Remove Unreleased, and Remove at Life End to output only a few selected points to use as a rasterized pyro volume source for debris dust simulation.

Remap Density Over Normalized Age

When Density Attribute is enabled, use this to control the density values over the life of the points.

Density Ramp

Controls how the density values change over the life of each point.

Color Over Normalized Age

When Age Attribute and Life Span both enabled, use this to color points based on their life. Use this for visualization purposes.

Color Ramp

Controls the color over the life of each point.

Post-Process

Speed Threshold

If your incoming geometry or template points have a velocity attribute, use this to keep only a few selected points based on speed. This is useful if you only want to emit from fast moving debris.

Volume Threshold

This will remove any point that is scattered on debris, which has less volume than the given threshold. Use this to avoid emitting from very tiny fragments.

Depth Threshold

Removes any point that is more than this threshold away from the primitives given by the Interior Group. Use this to avoid emitting right from the edge of the debris.

Remove Unreleased

Deletes points that are not yet separated beyond the Distance Threshold.

Remove at Life End

Deletes points that are separated and points where their age attribute value is higher than their life attribute.

Geometry nodes