Houdini 20.0 Nodes Dynamics nodes

POP Mask from Shadow dynamics node

A POP node that creates a mask based on whether particles are occluded by geometry.

This node sets a mask attribute based on whether a particle is occluded from geometry. To do this, it performs a raycast from each particle in specified direction attribute. If there is a hit within the distance specified by Max Distance, then the mask is set according to Distance Falloff evaluated at the hit distance.



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.


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).

Shadow Mask

This attribute is set to the ray hit distance from the particle, after mapping through the Distance Falloff ramp.

In wind shadowing, this value is typically 1, indicating that the particle is fully occluded from the wind, with the value falling off towards 0 as it gets farther from the geometry blocking the wind.

Shadowed Velocity

If the ray hits, this attribute is set to the velocity of the point on the object that was hit. Otherwise, this is unchanged.

This is used in wind shadowing to determine the velocity the particle should have when it is in shadow.

Shadow Hit Distance

This attribute is set to the distance that the ray hit on the Collision Geometry.

Affect Existing Mask

How to combine the new mask with any existing wind shadow mask.


The old mask is cleared out and replaced by the new one.


The distance attribute is used to keep the mask and velocity value of whichever is closest.

Ray Direction

The direction in which to perform the raycast.


In the opposite direction of the backward direction attribute.


In the same direction as forward direction attribute.


The forward direction attribute has the backward attribute subtracted from it, and that is the ray cast direction.

Backwards Direction

The ray is sent in the opposite direction of this attribute.

Forward Direction

The ray is sent in the direction of this attribute.

Mask Amount

Scale the final mask value by this. A value of zero disables the update.

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.



The name of the simulation data to apply the POP node to. This is commonly Geometry, but POP Networks can be designed to apply to different geometry.

See also

Dynamics nodes