Bounds Fracture operator

The Bounds Fracture operator allows you to slice particle meshes across the longest axis of their oriented bounding box.

This operator is ideal for slicing long, thin particles up along their longest local bounding box axis.

Bounds Fracture Rollout

Bounding Box Orientation

  • Particle TM: the fracture bounding box will be oriented to the particle’s transform.

  • Particle shape: the fracture bounding box will be oriented along the primary axes of the particle’s shape mesh.

Particle shape mode uses an oriented-bounding-box algorithm to compute a closest-fit bounding box around the arbitrary mesh of a particle shape. This bounding box may not be aligned to the particle’s transform.

  • Center bounds: computes the center of the bounding box as the average of all input mesh vertices. Disable this setting to use the particle position as the bounding box center.

Slice Axis

  • Longest axis: slices will occur along the longest axis of the bounding box.

  • X/Y/Z axis: slices will occur along the specified axis of the bounding box.

  • Random axis: slices will occur along a random axis of the bounding box.

  • Length ratio threshold: the minimum ratio between the length of the longest local bounding box axis, and the second longest bounding box axis, in order for a particle to qualify for longest-axis bounds slicing.

A long, thin particle is a particle with a local bounding box axis that is considerably longer than its other two bounding box axes. For example, a particle with local bounding box dimensions of [10, 1, 0.5] will be long and thin because its bounding box X-axis is at least 10 times longer than both its Y and Z-axes (this ratio is what is measured by the length ratio threshold). In that example, if you set the “length ratio threshold” setting to 5, the particle will qualify for slicing because 10 is greater than 5. However, if you set the length ratio threshold to 15, the particle will not qualify for slicing because 10 is less than 15.

Slice Count
  • Absolute: the number of slices for qualifying particles will be absolute (the same).

  • Relative: the number of slices for qualifying particles will be relative to the ratio between the length of their longest and second longest local bounding box axes.

When “relative” slice count mode is enabled, the number of slices set by the “count” setting will be multiplied by the length ratio, described above.

  • Count: the base number of slices, per qualifying particle.

  • Variation %: the per-particle percentage of variation to apply.
  • Max slices: the maximum number of slices that will be generated along the bounds for any given particle.

  • Bounds radius thresh: particles will only be sliced if the radius of their oriented-bounding-box exceeds this value. This value prevents tiny particles from being sliced. The bounding box radius is half of the length of the longest axis of the particle’s oriented bounding box.

  • Slice plane divergence: the maximum angle that any given slice plane normal will diverge from the direction of the longest bounding box axis.

  • Slice offset variation %: the amount of offset variation to apply to the slice plane’s position along the longest bounding box axis, relative to the distance between each slice.


  • Seed: the seed value for all varied parameters.
  • Center pivots: controls whether the pivots of resulting fracture particles will be centered on their mesh.

Slices Rollout


  • Cap holes: controls whether slices will be capped with new faces.
  • Override cap MatID: controls whether cap faces will be given a material ID override.

  • ID: the cap face material ID value.

  • Generate cap UVs: controls whether UVW coordinates will be generated on new cap faces.

  • Normalize: controls whether cap UVW coordinates will be normalized.

  • Size: the size of the cap face UVW coordinates.

  • Select cap faces: controls whether new cap faces will be flagged for selection.


  • Optimize slice borders: controls whether slice borders will be optimized, removing things like extraneous vertices along parallel edges.