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Constraint networks

The RBD Material Fracture tool not only fractures your geometry, but it also creates constraints for you between those pieces. If you want to create more constraints, there are 3 SOPs that allow you to do so, separate from the fracturing process. They follow the same 3 input/3 output RBD workflow, and give you a lot of control for building constraints. This is useful when you're fracturing two different types of materials, and want to create boundary constraints between them.

RBD Constraints From Lines

This tool is a very interactive way to build constraints, as you can simply click and draw constraints between the pieces you want to be connected in the viewport. Once the constraint is drawn, you can choose the Connection Type to determine how the constraints are set up. For more information, see the RBD Constraints From Lines help page.

RBD Constraints From Curves

This tool lets you draw a curve in the viewport, and will create constraints between points on the geometry of nearby pieces within a specified search radius. RBD Constraints from Curves also gives you the option to provide a curve in the 4th input, so that you can use it procedurally. For more information, see the RBD Constraints From Curves help page.

RBD Constraints From Rules

This tool is a procedural node for creating constraints based on a set of rules and conditions. For example, you can constrain pieces based on groups and then only constrain the pieces that are within a certain bounding region.

All three constraint nodes will create simple primitives with a rest length attribute. The RBD Constraint Properties SOP node can be used afterward to create constraint groups and set up constraint types (such as glue or soft constraints). The help for the Constraint Network DOP has more background information about constraint networks (Constraint Network is the low-level DOP node responsible for converting SOP constraint geometry into the equivalent DOP constraints).

Types of connections

All three constraint nodes (RBD Constraints From Lines, RBD Constraints From Curves, and RBD Constraints From Rules) will let you choose between the following types of connections.

The default connection that’s created is Hinges. These create a hinge-like constraint between pieces, which you can visualize by the white dot on the constraint line.

Drawing Surface Points constraints will create anchor points where you clicked the mouse on the piece to place the constraint.

Center of Mass constraints will calculate the center of mass for the constrained pieces and create constraints between their centroids.

RBD Convert Constraints

The RBD Convert Constraints SOP allows you to easily take your existing constraints and convert them into a different type of constraint. The Constraint Type dropdown menu lets you decide if you want your constraints to be from the Center of Mass, Surface Points, or Faces.

Tip

Use the RBD Exploded View SOP to better visualize how your constraints are connected between the pieces.

Center of Mass

Surface Points

Faces

For more information, see the RBD Convert Constraints SOP help page.

Controlling constraint behavior

The RBD Bullet Solver node has parameters on the Constraints tab that let you control the behavior of constraints. The Breaking Thresholds subtab allows you to determine when to break constraints apart. For example, you can use the Distance Threshold to set the distance between anchor points beyond which a constraint will break, or the Force Threshold to set the force beyond which a constraint will break.

Note

Turning on the constraint color visualizations can help determine which breaking threshold to use, and also help with debugging.

The RBD Constraint Properties node provides functionality similar to the parameters on the RBD Material Fracture node’s Constraints tab. You can use this as a convenient interface to edit values in the constraint network if you want to do more complex custom constraints. There are parameters to control plasticity in terms of stretching as well as the angle between the two objects in degrees where plasticity starts to take effect. This is useful for bending and breaking effects, where you want things to bend and hold their shape. For more information, see Bending and breaking.

Destruction

RBD Material Fracturing

Next steps

Guided Tutorial: Introduction to Material Based Destruction

  • Getting Started

    Loading the source scene and exploring it.

  • Tutorial

    Step by step introduction to material based destruction.