BUILD A SELL-OUT STADIUM CROWD

Mario Leone takes to the stage with a step-by-step guide to creating an arena full of cheering people in Houdini

- Mario Leone

With so few online resources readily available for creating crowds, the ability to do just that in Houdini 20 was exciting for me.

A crowd system is made up of characters that have a set of rules to define their appearance, animations and interactions. Such crowds are essentially animated characters attached to particles, with the movement of those characters, commonly called agents, in a crowd simulation based on an underlying particle simulation in DOPs.

In a crowd simulation, the agents are in a particular state at any given time, such as standing, walking or running. Events can happen in a crowd simulation that change the state of the agent, for example from walking to running. These events are called triggers.

Crowd simulations require both a geometry (SOP) network and simulation (DOP) network. The geometry network is used to create and define the agents and their positions from existing models such as terrain, or in this case our stadium. A simulation network holds the logic that controls the movement of each particle, and in turn the agent attached to it. Within the DOP network, agents can interact with other dynamic elements.

It’s important to remember that when we talk about a crowd, it doesn’t only mean humans. It could be a shoal of fish or a herd of buffalo running in a field, as long as they all follow similar rules and behaviours.

This is a beginner-friendly tutorial, so there’s no prior crowd simulation experience required, but some familiarity with Houdini would be helpful.

We’ll cover the basics of crowds, how to create one, and the logic behind them. We’ll also be working procedurally so we can start with a few agents to keep our performance under control, before increasing the number in the final stages.