You can control particle behavior in many different ways, but the most common ways include controlling the particle's motion and the way in which it interacts with object surfaces.
There are several particle compounds that let you control the particle's behavior. These compounds are fairly complex and complete within themselves, but you can also use them in conjunction with State systems as part of a larger effect. Within a State system, you can choose one of these compounds to create the effect that happens when trigger compound's value is reached: example, new particles can be spawned when they collide with an obstacle.
Most of these behavioral compounds are described in this section, but there are a few others that are described elsewhere:
Collision (surface interaction) compounds — see About ICE Particle Collisions below for a list.
You can use particles as rigid bodies in collisions — see ICE Rigid Bodies for information.
Attracting particles to goals and other objects — see ICE Particle Goals and Surface Force
Moving particles along a curve — see ICE Particles Flowing Along a Curve
Moving particles around an obstacle, which is especially useful for crowds and flocking simulations — see ICE Particles Flowing Around an Object
Making particles orbit around an object — see ICE Particles Orbiting Around an Object
Coagulating and clumping particles together to create liquid or swarming effects — see Coagulate Force and Neighboring Particles Force
You can create different types of particle collisions depending on what type of behavior you want to happen upon impact. Collisions are often used to change the particle's behavior in a State system, but you can create collisions without using State compounds.
When particles collide with an obstacle's geometry, the collision geometry type that is used for the obstacles is its actual shape. As well, the particle's size is taken into account upon collision. However, if you're using instanced shapes as the particle geometry, an approximated bounding sphere is created around it: its actual shape is not used.
One thing you may notice when particles collide with objects is that their rotation doesn't change after a collision. That is, if a rotated particle collides with an object, it doesn't change its rotation as might happen in real life (such as with faster rotation or changed rotational direction upon impact).
These are the types of behavior you can make the particles have upon collision with obstacles:
The different collision compounds are based on the Basic Collide node. If you want to create your own collision compounds, you can use this all-purpose node to serve as a base.
Particle Surface Interaction Attributes
There are several particle attributes that are used to define particle surface interactions with obstacles and particles moving toward goals. These attributes are used in several compounds that are described in this section, but you can also use them on their own in an ICE tree by specifying them in the Get Data and Set Data nodes, as described in Using ICE Particle Attributes.
For more information on attributes in general, see ICE Attributes.