Houdini 18.5 Destruction

Using custom cutters

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The high-level tool for pre-fracturing geometry is the RBD Material Fracture SOP, which allows you to accurately fracture geometry based on a specific type of material. Custom material types are more advanced than the preset concrete, glass, and wood types. It’s a way of bridging the gap between doing your own fracturing and using the presets. This option lets you use your own cutting planes, but still take advantage of all the controls the RBD Material Fracture SOP node has to offer, such as edge detail, interior detail, constraint creation, and rewiring. It also exposes the boolean "treat as" parameter for solid or surface cuts which can be useful for metal fracturing.

Note

Fracture per Piece is useful to target specific custom cutters to specific pieces. If a name primitive attribute is found on the cutting geo, only the cutting geo with a matching name will be used to cut the pieces being fractured.

To...Do this

Visualize the guides for the cutter geometry

Choose Custom from the Material Type dropdown menu on the RBD Material Fracture SOP node.

Control how many cutting planes are created

Increase or decrease the Scatter Points parameter to add or remove the number of default cutting planes that are created. By default the RBD Material Fracture SOP node will scatter a few cutting planes.

Add more noise to the cuts

Turn on Edge Detail.

Use your own cutting plane

Turn off the Scatter Cutting Geo checkbox, wire in your own geometry to the 4th input of the node, and turn on the Input Cutting Geo checkbox.

Note

You can wire in multiple cutting planes to the 4th input.

Draw exactly where the fracture will be

Use the Draw Curve tool and extrude it to turn it into geometry, since this node requires geometry to be used as the input for the cutting plane.

Understanding Chipping parameters

The chipping parameters can give you a lot of control over the look of the chipped pieces.

To...Do this

Control how many pieces get chipping applied

Increase or decrease the Chipping Ratio parameter. A value of 1 will give you chipping on every piece.

Determine how many of the corners get chipping applied

Adjust the Corner Ratio. A value of 1 will give you chipping on every corner.

Regulate how big the chips are

Modify the Corner Depth parameter to control how big the chips will be relative to the center of the piece. Increasing this parameter will make the chips bigger.

Provide variation in cutting planes

Use the Directional Noise parameter. A value of 0 positions the cuts straight on to the corner. Increasing the noise will cause them to be offset in different directions, which will make them look less regular.

Control how strongly the chipped pieces stick to the main fracture piece.

Modify the Chipping Glue Strength on the Constraints tab.

Example: Using geometry as a custom cutter

  1. Create a Box at the origin using the tool on the Create shelf.

  2. Dive down to the geometry level and increase the Size in the Y direction to 4.

  3. Move it up so that it’s sitting flush on the ground plane by increasing the Y value of the Center parameter to 2.

  4. Append an RBD Material Fracture SOP to the first input of the box.

    The default Material Type is Concrete (voronoi fracture). In this example, we’ll be using a bunch of spheres to cut up the geometry.

  5. Create an ISO Offset SOP and wire the box into its first input. This will create a volume for copying the spheres.

  6. Set the Uniform Sampling Divs to 100.

  7. Append a Scatter SOP after the ISO Offset node and change the Force Total Count to 25 to scatter a few points inside the geometry.

  8. Append an Attribute Randomize SOP after the Scatter node.

  9. Set the Attribute Name to pscale, change the Dimensions to a value of 1, set the Min Value to 0.5 and the Max Value to 2. This will randomize the pscale attribute, which controls the scale of the spheres that will be copied onto the points. They will vary between a size of 0.5 and 2.

  10. Create a Sphere SOP, change the Primitive Type to Polygon, set the Frequency to 8, and reduce the Uniform Scale to 0.5.

  11. Create a Copy to Points SOP and wire the sphere into the first input and the attribute randomize node into the second input.

  12. Wire the output of the copy to points node to the last input of the RBD Material Fracture node. This will allow the spheres to be used as the cutting geometry for the box.

  13. On the RBD Material Fracture SOP, change the Material Type to Custom, set the Guide Geometry to Cutter Geometry, turn off the Scatter Cutting Geo checkbox, and turn on the Input Cutting Geo checkbox. You should see the spherical guide cuts in your geometry.

  14. On the Constraints tab, set the Primary Strength to 200.

  15. Append an RBD Bullet Solver SOP to the RBD Material Fracture SOP.

  16. On the Ground tab, change the Add Ground Plane dropdown from None to Ground Plane.

  17. Press in the playbar to play the simulation.

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.