Houdini 18.5 Nodes Dynamics nodes

RBD Guide dynamics node

Guide Bullet Packed Primitives.

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Since 18.5

Overview

This DOP node is used in conjunction with the RBD Guide Setup SOP node. It uses input geometry to guide the bullet simulation, acting as a virtual constraint system. It modifies the velocity and angular velocity attributes to match the guided pieces' position and rotation to their guide geometry counterpart. It also handles unguiding, or breaking pieces free from the guiding process, when certain thresholds are met.

This node should be added as a pre-solve process since it affects the RBD’s velocity or target velocity. The solver integrates it as it handles collisions. While unguiding (breaking free from the guides) can be performed in the pre-solve, it is generally better to do it post-solve right after the integration step.

Parameters

Guiding

Enable

Enables the guiding of the RBD Bullet primitives.

Method

Choose between a direct velocity (v) and angular velocity (w) update or a target velocity (targetv) and target angular velocity (targetw) update method to use when guiding.

Velocity

Updates v and w directly. This is the most precise way of guiding, however it can lead to jittering when collisions get in the way.

Target Velocity

Updates targetv and targetw attributes, used in combination with the Air Resistance and Drag parameters, to compute a force that will move the object towards the desired velocity and a torque that will move the object towards the desired angular velocity. This is more forgiving that the direct v and w updates and helps eliminate jittering as pieces are allowed to deviate further from their guided positions and orientations. The solver’s implicit drag option needs to be on for this to work properly.

Air Resistance

Specifies how important it is to match the target velocity (targetv) and target angular velocity (targetw).

Drag

This attribute is used to further scale the drag amount, when an object is dragged by the targetv and airresist attributes.

Blend

Blend amount to lerp guided velocity and angular velocity with natural velocity and angular velocity. Lowering this value results in a soft dampened spring-like constraint and can help reduce some jittering that may occur when guided velocities and angular velocities struggle with collisions.

Time Scale

Needs to match the bullet simulation time scale in order for the correct velocity and angular velocity to be applied.

Un-Guiding

Enable

Enables the un-guiding of guided pieces, allowing them to break free from the guides.

Instantaneous

Linear Threshold

When the distance between the computed guided position and the resulting post-solve position is greater than the linear threshold multiplied by guide strength, the piece will become unguided.

Angular Threshold

When the angle (in degrees) between the computed guided orientation and the resulting post-solve orientation is greater than the angular threshold multiplied by guide strength, the piece will become unguided.

Distance Threshold

When the difference between the distance of the guide piece to the bullet primitive and their distance at rest increases beyond the distance threshold multiplied by guide strength, the piece will become unguided.

Accumulated

Linear Threshold

When the accumulated distance between the computed guide position and the resulting post-solve position is greater than the distance threshold multiplied by guide strength, the piece will become unguided.

Angular Threshold

When the accumulated angle (in degrees) between the computed guide orientation and the resulting post-solve orientation is greater than the angular threshold multiplied by guide strength, the piece will become unguided.

Distance Threshold

When the accumulated difference between the distance of the guide piece to the bullet primitive and their distance at rest increases beyond the distance threshold multiplied by guide strength, the piece will become unguided.

Guided Neighbors

Use Neighbors

Enables un-guiding pieces whose neighbors within a guided cluster have all become unguided.

Inputs

Guide Source

Specifies the source of the guide geometry.

SOP Path

The SOP geometry to use as guide.

Geometry Source

Specifies the source of the RBD geometry.

SOP Path

When unguiding, point this parameter to the SOP geometry that has been previously through the RBD Guide Setup in order to allow the RBD piece’s attributes to be animated and updated during the course of the simulation (strength for example).

See also

Dynamics nodes