Physics Event Nodes¶

Use Physics Event nodes to react to particle, fluid and deformable events. Filter or combine their Event Streams, control when they trigger, then connect them to an action.

Where to find it¶

Use Shift+A > Events. Source, processing and action nodes share this category; the socket type distinguishes Particle Streams, Event Streams and final Simulation actions.

Where to start¶

Connect exactly one compatible particle/deformable branch to an On … Event source. Process the Events stream as required, connect it to an Event Action, then connect the action's Action output to Simulation Output / Outputs.

The complete event behavior and Lists workflow are documented in Physics Events.

Event source nodes¶

On Deformable Event¶

Input: Deformable (Particle Stream)
Output: Events

Watches one Cloth, Soft Body or Strands branch. Available event types are Tear, Constraint Break, High Strain, High Stress, High Damage, Collision and Contact. Tear requires Cloth; Constraint Break requires Cloth or Strands; the other deformable metrics/contact types support the compatible deformable families described on the Physics Events page.

High Strain/Stress/Damage expose their threshold, while Collision/Contact expose Minimum Strength. Limit caps accepted events per frame.

On Particle Event¶

Input: Particles
Output: Events

Watches ordinary particles. Event types are Birth, Death, Collision Begin, Enter Volume and Leave Volume. A named Source Group can narrow the source population. Collision/Volume events can also target one Collision effect. Collision Begin exposes Minimum Speed.

On Fluid Event¶

Input: Fluid Particles
Output: Events

Watches FLIP Impact or MPM Impact from an ordinary particle stream used by the selected fluid solver. It supports Source Group, target Collision and Minimum Speed filtering. MPM Impact can additionally restrict the source to one MPM material.

Event processing nodes¶

Filter Events¶

Input / Output: Events

Accepts only records that match enabled filters:

• event strength range;
• world-space position box;
• source speed range;
• movement-direction cone;
• contact-normal cone where that event supplies a contact normal;
• source Weight Map range, using Emitter Vertex Weight for particle/fluid sources or Deformable Pin Weight for deformables.

A filter shows an error if its source cannot supply the requested data or its range is empty or invalid.

Merge Events¶

Inputs: First, Second
Output: Events

Combines two Event Streams so one downstream action can react to both. Duplicate incoming event branches are retained only once. Limits and stateful processors remain branch-local after a merge.

Accumulate Events¶

Adds event strengths across frames and releases an event when the accumulated strength reaches Trigger At. Only one Accumulate stage is allowed on each event branch.

Debounce Events¶

After one accepted event, ignores repeated events on that branch for Cooldown Frames. Only one Debounce stage is allowed per branch.

Limit Events¶

Caps Max Per Frame for each source branch. When used after Merge Events, each incoming branch keeps its own budget.

Rate Limit Events¶

Allows Max Events during a rolling/configured Over Frames window for each branch. Only one Rate Limit stage is allowed per branch.

Delay Events¶

Queues Spawn Particles or Emit Pyro actions for Delay Frames. Delay is the final stateful processing stage; source-changing actions cannot be delayed because they operate on the current source state.

Processing order¶

For one event branch, use stateful processors in this order:

Filter → Accumulate → Debounce → Limit → Rate Limit → Delay

Merge Events can combine source branches before the final action, but each branch must still obey the valid stage order. Graph Diagnostics reports an out-of-order chain.

Event action nodes¶

Spawn Particles on Event¶

Input: Events
Output: Action (Simulation)

Creates particles at accepted events. The node exposes Count, Radius, Speed and optional Use Event Strength / Full Strength At scaling. Detailed inherited/new group, color and particle-property behavior is documented in Physics Events.

Emit Pyro on Event¶

Input: Events
Output: Action

Injects Pyro at accepted event locations. The node exposes Radius, Density, Temperature and optional Event Strength scaling. A usable active Pyro Domain → Dynamics branch is required.

Modify Data on Event¶

Input: Events
Output: Action

Changes the source particle directly on the current frame. Independently enable:

• Velocity and set a Speed Multiplier;
• Radius and set a Radius Multiplier;
• Color and set the replacement color.

This action also works with Fluid Impact events. It cannot follow Delay Events.

Change Group on Event¶

Moves the source particle into the selected Target Group on the current frame. Later effects can immediately use that group selection. It cannot follow Delay Events.

Break Constraint on Event¶

For a compatible Deformable event, breaks nearby Cloth or Strand links around the event vertex. This supports local rupture after Strain, Stress, Damage, Collision or Contact triggers and may break several neighboring links. It cannot follow Delay Events.

Event strength and recursion¶

When Use Event Strength is enabled on Spawn Particles or Emit Pyro, the event's measured strength scales the action until Full Strength At produces the configured full response. Birth, Death, Enter/Leave Volume, Tear and Constraint Break use fixed strength 1; impact and threshold events supply measured values.

Particles spawned by a Physics Event do not recursively fire another Birth Event. Event count and particle budgets remain enforced even when Event Streams are merged or processed.

Troubleshooting¶

• An Event source reports incompatible scope: feed it exactly one compatible emitter branch, using Emitter Branch if necessary.
• Filter Events reports unavailable data: disable the filter that the current event type cannot supply, such as contact normal on a non-contact event.
• A processor reports invalid order: reorder the Event Stream chain to Filter → Accumulate → Debounce → Limit → Rate Limit → Delay.
• A source-changing action after Delay is rejected: remove Delay or use Spawn Particles / Emit Pyro as the delayed action.
• Emit Pyro does nothing: confirm that the scene has a valid active Pyro Domain → Dynamics branch and that the event action reaches Simulation Output / Outputs.