Houdini 20.0 Nodes Dynamics nodes

POP Wind Shadow dynamics node

Applies a wind shadow to particles

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This node applies a wind shadow to particles based on Source Geometry. Particles within the wind shadow have their velocity mixed with the velocity of the geometry that is creating the wind shadow. This gives the effect that the geometry is blocking the wind from affecting the particle.

This node should be applied after any POP Wind nodes since it will updated the targetv attribute to take into account the wind shadow. The blocking geometry’s v attribute is used to replace the wind velocity in areas in shadow.



Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.


This is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.


Only affect a group of points (created with, for example, a Group POP or Collision Detection POP) out of all the points in the current stream.


Ray Direction

The direction in which to perform the raycast.


In the opposite direction of the wind attribute.


In the same direction as the particle is moving.


In the opposite direction of the relative wind velocity.

Geometry Source

Specifies the geometry to use.


Use the SOP specified in the SOP Path parameter.

DOP Objects

Use the named DOP object in this DOP network.

First Context Geometry

Use the SOP connected to the DOP network’s first input.

Second Context Geometry

Use the SOP connected to the DOP network’s second input.

Third Context Geometry

Use the SOP connected to the DOP network’s third input.

Fourth Context Geometry

Use the SOP connected to the DOP network’s fourth input.

SOP Path

Path to the SOP (when Geometry Source is set to SOP).

DOP Objects

Name of the DOP objects (when Geometry Source is set to DOP Object).

External Shadow

Scale for how much shadow to apply when the external geometry is hit.

Self Shadow

Scale for how much shadow to apply when the geometry itself is hit.

Max Distance

The maximum distance to check for occlusions.

Ray Bias

The distance to offset the ray from the particle. This is used to avoid self intersections if the node is used for self wind shadow.

Shadow Angle

The spread to send shadow rays. A value of 90 will sample the full hemisphere, and a value of 180 will send rays in all directions.

Shadow Samples

Number of samples to send randomly within the cone angle. If the cone angle is zero, only one sample will be taken.

Distance Falloff

This ramp maps the distance of the particle to the to the output value of the mask.

Blur Wind Shadow

Apply blurring to the wind shadow mask and wind shadow velocity.

Blurring Iterations

The number of times the input geometry is blurred. The higher the number, the more blurring.

Blur Influence Type

Blurring relies on each point being able to see what its neighbors' attributes are. This parameter determines how points see their neighbors.


Neighbors are determined by mesh connectivity. Each point mixes its attribute value with the value of its neighbors to achieve blurring.


Neighbors are determined by proximity. Each point has a maximum number of neighbors given by the Max Neighbors parameter, where each neighbor must be within a certain distance away given by the Proximity Radius parameter.

Blur Proximity Radius

Determines how far points influence each other when Influence Type is set to proximity.

Blur Max Neighbors

Determines the maximum number of neighbors each point is permitted to have. Large numbers of neighbors may reduce performance.

Update Wind Velocity

Update the targetv according to the computed windshadow_mask and windshadow_v.



Wind Velocity



Shadow Mask

Shadowed Air Velocity

Shadow Hit Distance


WindBlock Example for POP Wind Shadow dynamics node

This example explores the different ways to set up wind shadow in vellum simulations.

See also

Dynamics nodes