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In response to a trigger, the Crowd Transition DOP switches the agent to a new state, and also switches the agent from playing the clip associated with the old state to playing the clip for the new state.

The Crowd Transition node has simple controls for blending between the animation clips of the “before” and “after” states. If you need more control (for example, waiting for a certain frame to start the transition, or transitioning through intermediate clips between the start and end clips), you can set up a transition graph.

A transition graph stores detailed information about how to transition between different clips. For example, the graph may specify:

  • Start the idlewalk clip transition at frame 16.

  • First transition from idle to idle_to_walk.

  • Then transition from idle_to_walk to walk.

Transition graphs are more work to set up, but give you much more control over transitions. If the default blended transitions look good enough at your level of detail, it may not be necessary to use transition graphs.

How to set up a transition graph

  1. After you load/generate the agent primitive in SOPs, append an Agent Clip Transition Graph SOP to the agent. Set up the different transitions in the parameters.

  2. On the Crowd Object DOP in the crowd simulation network, set the Clip Transition Graph parameter to point to the Agent Clip Transition Graph SOP.

  3. On any Crowd Transition DOPs for the state changes that should use the graph, turn on Use Clip Transition Graph.

Tips and notes

The Agent Clip Transition Graph SOP stores the relationship graph as geometry, where points represent clips and polylines represent transitions, with data stored in attributes. This allows the possibility of creating your own custom tools to generate or edit the graph.

See also

Crowd simulations

Getting started

  • Basics

    An overview of Houdini crowd simulation concepts.

  • Setup

    How to set up and edit a crowd simulation.

The moving parts

  • Agents

    About agents, the moving actors that make up a crowd simulation.

  • States

    About agent states, the virtual mood of each agent that controls the agent’s animation and the behaviors it runs.

  • Triggers

    How to specify conditions that cause agents to change from one state to another.

  • Caches

    Tips for efficiently caching and loading crowd sims.

SOP crowds



  • Diversity

    How to create a more realistic crowd by making agents look and act differently.

  • Attaching cloth

    You can add and constrain vellum cloth as part of agent shape geometry, and then simulate the cloth based on agent movements.


  • Foot planting

    How to set up agents to adapt their animation to terrain and prevent skating.

  • Terrain

    How to specify terrain geometry for agents to walk across.

  • Obstacles

    How to set up obstacles for agents to avoid.