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In response to some trigger, the Crowd Transition DOP switches the agent to new state, and 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 clip), you can set up a transition graph.

A transition graph stores detailed information about how to transition between different clips. For example, the graph might specify that the idlewalk clip transition should start at frame 16 and transition from the idle clip to the idle_to_walk clip, then to the walk clip.

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, you don’t need to bother with 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. In the crowd simulation network, on the Crowd Object DOP, set the Transition graph parameter to point to the Agent Clip Transition Graph SOP.

  3. On any Crowd Transition DOPs for a 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

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 which controls the agent’s animation and which behaviors it runs.

  • Clips

    How to associate animation with agents in certain states.

  • Triggers

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

Next steps

  • Foot planting

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

  • Transition graphs

  • Attributes

    Useful attributes for reading in triggers, or that you can set to affect behavior.

  • Sensors

    How to make agents behave differently based on their virtual senses.

  • Diversity

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

  • Weights

    How the Houdini crowd solver decides which behaviors to apply to an agent at each time step.

  • Terrain

    How to specify terrain geometry for agents to walk across.

  • Obstacles

    How to set up obstacles for agents to avoid.

  • Dynamics interaction

    Tips on setting up interaction between agents and other types of dynamics.

  • Ragdoll simulation

  • Adding direction

    How to assert manual control over different aspects of the crowd simulation.

  • Fuzzy Logic

  • Caches

    Tips for efficiently caching and loading crowd sims.