The Fracture input rollout has parameters which allow you to tune how input meshes are pre-processed, prior to fracturing. Certain parameters are only visible when using the Multifracture operator, over the tyMultifracture modifier, and vice-versa.
World-space scale: when enabled, various coordinate-relative parameters (ex: noise strength) will be adjusted to match the input mesh’s scale.
Convert coordinates: when enabled, the input mesh’s transform will be reset, converting all of its points to world-space coordinates in the process.
Process open surfaces: when enabled in combination with a subtract operation (instead of a slice operation), open surfaces (which normally cause problems for the subtraction operation) will be treated as thin shells, alleviating those problems in the process.
Open surfaces treated as thin shells will not maintain their volume after the subtract operation is completed.
Perturb vertices: when enabled, the vertices of operand meshes will be perturbed by a random amount prior to the fracture operation.
Use face selection: when enabled, only the selected faces/elements of a mesh will be fractured.
Due to the way the multifracture algorithm processes meshes and their faces, if you enable “use face selection”, the selected faces will be detached from the mesh for the fracture operation and converted into a separate mesh element prior to being fractured. If your face selection consists of full mesh elements only, the detachment process will have no detrimental effect on the resulting mesh. However, if your face selection consists of only partial mesh elements, the detachment process will disconnect the selected faces from the rest of the mesh and those faces will remain disconnected after the fracture operation is complete.
Per-element fracture: when enabled, input meshes elements will be split apart and fractured individually, rather than as a single mesh.
Randomize seeds: when enabled, various fracture seeds will be randomized on a per-element basis.
Relative to surface area: when enabled, various fracture point counts will be multiplied by the ratio between an individual element’s surface area relative to the specified threshold values.
Min/max threshold: these values determine the threshold range of the ratio multipliers. For example, if you set the “max threshold” value to a surface area of 100, and an element has a surface area of 200, its fracture point count will be multiplied by 2 (prior to being clamped by the “min/max mult” values.
Min/max mult: these values clamp the threshold multipliers. For example, if you set the “max threshold” value to a surface area of 100, and an element has a surface area of 1000, its base fracture point count multiplier will be 10 - but if you set the “max mult” value to 5, the multiplier will be clamped to 5.
Adjusting the “relative surface area” parameters can give you fairly fine-tuned control over how many fractures an element will undergo, relative to its size. This prevents scenarios where fracture settings which apply to very large elements will also apply equally to very tiny elements, and vice versa. For example, you may want to fracture a large element 1000 times, but fracture tiny elements only once or twice. By tuning the “relative surface area” parameters, you can exert this level of fracture control over elements in a single modifier/operator.
Raycast: when selected, a raycast-based face classification method will run during the operation, to classify faces as either inside or outside of operands. For closed meshes, this is very accurate. For open meshes, this method can produce artifacts.
Fast winding number: when selected, a fast winding number face classification method will run during the operation, to classify faces as either inside or outside of operands. This offers more accuracy than the raycast method when meshes contain holes and open edges (at the cost of some performance). This method does not track nested elements, and is not suitable for situations where meshes are meant to have interior, nested cavities.
Randomize seeds by ID: when enabled, fracture seeds will be randomized on a per-particle basis.
Randomize seeds by time: when enabled, fracture seeds will be randomized depending on the frame the fracture takes place.
Relative to property: when enabled, various fracture point counts will be multiplied by the ratio between an individual particle’s property relative to the specified property and threshold values.
Min/max threshold: these values determine the threshold range of the ratio multipliers. For example, if you set the “max threshold” value to a surface area of 100, and a particle has a surface area of 200, its fracture point count will be multiplied by 2 (prior to being clamped by the “min/max mult” values.
Min/max mult: these values clamp the threshold multipliers. For example, if you set the “max threshold” value to a surface area of 100, and a particle has a surface area of 1000, its base fracture point count multiplier will be 10 - but if you set the “max mult” value to 5, the multiplier will be clamped to 5.
Adjusting the “relative property” parameters can give you fairly fine-tuned control over how many fractures a particle will undergo, relative to its size. This prevents scenarios where fracture settings which apply to very large particles will also apply equally to very tiny particles, and vice versa. For example, you may want to fracture a large particle 1000 times, but fracture tiny particles only once or twice. By tuning the “relative property” parameters, you can exert this level of fracture control over particles in a single operator with limited filters.
Limited recursion: when enabled, you can limited how many times a particle can be successive re-fractured by the operator.
Max depth: controls how many times a particle can be refractured by the operator, before it will simply be ignored by the operator.
Channel: the custom float channel where the fracture depth for a given particle (and its children) will be stored.
By enabling “limited recursion”, you can have a Multifracture operator’s timing set to something other than ‘on entry’, without re-fracting the same particles over and over, leading to an exponential explosion of particles. For example, you may want to ensure a particle is only refractured once (so it will be fractured, and then it’s children will be fractured, but its children’s children won’t be fractured) by setting the “max depth” to 2.