Masks¶

Masks produce a 0 to 1 influence from space, particle state, random values, or timeline position. They can limit emitter birth, effect influence, Logic conditions, and the Mask source used by Data Mapping fields.

A value of 0 excludes the particle, 1 applies full influence, and intermediate values provide a soft transition where the connected control supports one. Check the mask on its own before troubleshooting the effect or mapping it controls.

On Effects, Masks affect the Particles domain. Enabling Cloth, Soft Body, or Strands on the same effect does not apply its particle Mask to those objects. See Common effect settings.

Lists workflow¶

1. Open the Masks section of an Emitter, Effect, Logic condition, or mapped property.
2. Use Add Mask... to create a definition or reuse an existing scene-wide Mask.
3. Configure its spatial source or particle range.
4. Use Influence to scale that mask's own 0 to 1 output.
5. Add more masks and set each later mask's Blend Mode relative to the accumulated result.
6. Use Invert Output when only that definition should be reversed.
7. Test masks one at a time before enabling a complex stack.

When one Mask definition is used in multiple locations, the UI shows its usage count. Editing it updates every use. Make Unique copies the definition for only the current stack so subsequent edits do not affect its other uses.

Nodes workflow¶

Nodes provides one dedicated node per Mask type. A Mask node can connect directly to an Emitter or Effect Mask input, a Logic Condition Mask input, or the Mask Source of a Float or Vector Field.

Use Mask Blend to combine masks. Connect single or composed Mask expressions to Accumulated and Mask, then choose Multiply, Add, Subtract, Maximum, or Minimum. Both inputs accept further Mask Blend outputs; nested combinations preserve their grouping. The same expressions can drive emission, effect influence, Logic conditions, Data Mapping, Material Change and Sleep/Wake inputs.

In Nodes:

• Float and Vector Fields with Source: Mask also offer a local Add Mask... list when Mask Source is unconnected. Connecting an expression uses that expression and preserves the local list for later reuse.
• Connect one Mask output to several compatible inputs to share it.
• Mask Blend supports the same combinations as Lists, including Screen, Overlay, Divide and Difference. Maximum and Minimum are equivalent to Lighten and Darken.
• Reverse a Nodes mask with that node's Invert Output. A standalone Invert entry requires list-stack context and is not a valid graph expression by itself.

Combining masks¶

The first evaluated mask establishes the value. Each later mask combines with that accumulated result.

The Lists-only Invert entry reverses the accumulated result at its position. If evaluated before any ordinary mask, it reverses the next mask instead. Prefer Invert Output when the intention is simply to reverse one definition.

Spatial masks¶

Box and Sphere¶

Box Empty or Sphere Empty defines the region through the Empty's transform. Falloff softens the influence inside the boundary: zero creates a hard edge, while larger values start the transition farther toward the center. Use Invert Output to affect the exterior instead.

Linear and Plane¶

Linear projects particle position from Start Empty to End Empty. Influence is 0 at and before Start, 1 at and after End, with a linear gradient between them.

Plane Empty defines a plane from its position and local normal. Thickness creates a centered slab with hard inclusion inside half the thickness.

Curve¶

Curve measures distance to one Curve object or every Curve in a Collection. Thickness is the full-influence inner radius; Soft Edge is the additional distance over which influence falls to zero.

Control Points samples only authored points. Evaluated samples curve segments and uses Sample Count; the direct Curve object's Preview Resolution is also available. Higher sampling resolves curved shapes more accurately and costs more to prepare. Curve masks track static geometry, rigid transforms, and deformation.

Object¶

Object uses one mesh or a Collection of meshes.

• Volume returns influence inside the mesh. Small openings and minor surface defects are repaired automatically. Flat or unrepairable volumes produce an error.
• Surface returns influence outside the mesh and falls from the surface to zero across Soft Edge.

Object masks track static geometry, rigid transforms, and deformation. A Collection expands the source set; use a direct Object when one mesh is sufficient.

Axis Position¶

Select world X, Y, or Z. Min maps to 0 and Max maps to 1, with a linear gradient between them. Reversing Min and Max reverses the gradient.

Particle-state masks¶

These masks evaluate existing particle properties and are unavailable on Emitters: Velocity, Age, Mass, Group, and Particle Proximity. A Nodes connection of one of these masks to an Emitter reports an error.

• Velocity is a hard speed interval. Particles between Min and Max receive full influence; particles outside receive zero. The order of Min and Max is normalized automatically.
• Age uses normalized lifetime, 0 at birth and 1 at death. Min maps to 0 and Max maps to 1, so this is a gradient rather than a hard interval. Reverse the values or use Invert Output for the opposite progression.
• Mass maps particle mass linearly from Min = 0 influence to Max = full influence. Reversing the range reverses the gradient.
• Group returns full Influence only for the selected named Group and zero for all others.
• Particle Proximity uses the strongest nearby-particle contribution inside Distance. Falloff shapes the distance response. Filter by Group restricts which neighboring particles count, not which evaluated particles receive the mask. Larger search distances and dense particle sets cost more.

Emitter source speed¶

Source Speed is available only on a particle Emitter, in Lists or Nodes. Cloth, Soft Body, and Strands do not use rate-based particle emission. The mask measures how fast the sampled source position moved since the previous frame, including mesh deformation. Min Speed maps to zero birth probability and Max Speed maps to full probability, with a linear transition. Influence, Invert Output, and mask blending apply as for other birth masks. It measures source motion even when Inherit Velocity is zero; launch velocity does not affect the mask.

At a stationary source, the default range of 0 to 10 blocks emission. Set Invert Output to emit while stationary. On the first simulation frame or after a timeline jump that resets source history, source speed is zero because there is no earlier sampled position. Grid and Hexagonal sources fill only once, so their Source Speed is also zero. When Source Speed is combined with spatial masks, each birth samples one source position, so intermediate mask values reduce the number of births rather than being retried at other positions.

Procedural masks¶

Noise¶

Noise evaluates a spatial, animated 0 to 1 pattern.

• Strength scales its maximum output.
• Scale is feature size. Higher values create larger features.
• Speed evolves the pattern over time; zero keeps it static.
• Pivot shifts values toward black below 0.5 or white above 0.5. A value of 0.5 is neutral.
• Contrast is neutral at 1. Higher values increase separation; lower values flatten it.
• Seed selects a deterministic variation.
• Octaves, Lacunarity, and Persistence control fractal detail count, frequency spacing, and retained fine-detail amplitude.

Random¶

Random is deterministic per particle for a given Seed. Choose Float (0 to 1) for a stable random value that varies effect strength. Integer (0 or 1) compares the random value with Threshold and produces a hard selection.

Time mask¶

Time creates a global timeline window in Frames or Seconds. It does not use per-particle age.

• Start begins the active interval.
• Fade In rises from zero after Start.
• End is the point at which the window reaches zero.
• Fade Out begins before End and falls toward zero.

If Fade In and Fade Out together exceed the window duration, both are proportionally shortened to fit. Use Time for a scene-wide emission or effect window and Age when each particle should progress according to its own lifetime.

Examples¶

Random particles inside a region¶

In Lists, add a Box mask first and a Random mask second with Multiply. In Nodes, connect Box to Mask Blend Accumulated, Random to Mask, and select Multiply. The Box supplies the spatial boundary and Random selects a stable subset only inside it.

Effect that grows with particle age¶

Use an Age mask with Min at the point where the transition should begin and Max where it should reach full strength. Connect or assign it to the effect Mask. This differs from a Logic age threshold because the mask supplies a continuous factor.

Timeline window restricted to one group¶

Combine Time and Group with Multiply. Time controls the global activation interval, while Group prevents particles in other named groups from receiving the influence.

Troubleshooting¶

• A reused mask changes several systems: It is a shared Lists definition. Use Make Unique to edit only the current use.
• A Nodes combination is invalid: Both Mask Blend inputs accept single or composed expressions. Check that each required source is connected and configured. Use Invert Output on a Mask to reverse its definition.
• An Object Volume mask leaks: Check transforms, intersecting surfaces and deformation. Small source openings are repaired automatically; large missing sections exceed automatic preparation limits.
• A Curve mask misses bends: Use Evaluated sampling and raise Sample Count.
• An Age mask looks like a fade instead of a selection: Age maps Min to Max continuously. Use a Logic condition for a hard threshold, or compress the mask range.
• Particle Proximity is expensive: Reduce Distance, restrict the neighboring population with Filter by Group, or use a simpler spatial mask when possible.
• Nothing is affected: Check the connected control, Influence, Invert Output, blend order and required source objects. Confirm that the particle values enter the configured range.