Wind shadow lets you use collision geometry to block wind from affecting the vellum geometry (External Shadow) and vellum geometry to block wind from affecting other parts of the vellum geometry (Self Shadow). External shadow is useful when simulating something like a character walking somewhere windy, then ducking behind a tree. Everything else in the scene will continue to be affected by wind, but the area behind the tree is blocked from the wind. This is also useful when there is no wind but you have local movement, such as a cape on a moving character. Their body will block the air from affecting the cape, resulting in a much more realistic simulation. Self shadow is useful when simulating something like a skirt, where the front side blocks wind from affecting the back side.

You can apply wind shadow in DOPs using POP Mask from Shadow, POP Attribute Blur, and POP Wind Shadow.


This is designed to run after you've setup your wind velocities. A series of POP Wind nodes will composite together a weighted average wind direction and air resistance, and that is then used for updating the shadow direction. Since the object’s own motion is used, you also get shadowing effects in still air once the object starts to move.

Alternatively, you can do all of this in SOPs in the Wind Shadowing section of the Forces tab of the Vellum Solver SOP.


The windshadow_mask attribute allows you to visualize what is being affected by wind.

How to

To...Do this

Change the direction and intensity of the wind

Use the Built-in Wind parameter on the Forces tab of the Vellum Solver SOP.

Visualize what is being affected by wind

  1. Put down a Color SOP and connect it to the first output of the Vellum Solver SOP.

  2. Type windshadow_mask in the Attribute field.

Fix the problem of an object not blocking the wind

Increase the Max Distance parameter on the Vellum Solver SOP. This will extend the area of obstruction.

For example, if Max Distance is set to 10, the object will look back 10 units to see if there is anything that could be blocking the wind. Increasing this to 20 will look back 20 units, so objects that are further away can still block the wind.

For a moving object, make sure whatever is blocking the wind has a velocity attribute on it. In order for this to work, the cloth needs to look at the blocking object and know the speed it’s moving at.

Soften hard edges

Increase the Shadow Angle parameter on the Vellum Solver SOP and turn on Blur Iterations to smooth out the noise. This creates a more realistic look by suggesting wind is going around the blocking geometry.

Have nearby objects affected

Set the Blur Influence Type to Proximity. This will cause the blur to look across any gaps in connectivity, so objects that are not directly blocked will still be affected based on proximity.


These examples are based on Vellum cloth, but wind shadow can also be used for grains, particles, and hair.