A particle state system is based on two types of compounds: a State Machine compound and one or more State compounds that are plugged into it.
The State Machine compound is the central processor for all the State compounds that define particle behavior. At every frame, this compound executes the values from all the States compounds that are plugged into it. The states are executed in the order in which they’re plugged in to the State Machine, from top to bottom.
You can define the number of iterations per frame that the State compounds are evaluated per frame. Keep this value low to reduce processing times, but you may need to set this higher for particles that move quickly from frame to frame.
Each State compound lets you define a particle behavior that is used with the State Machine compound. Each behavior is a combination of a “trigger” compound and an “effect” compound, such as particles spawning new particles when they collide with an obstacle. You can have effect compounds be evaluated only once upon entering the state, or have them evaluated every frame for a continuous effect.
You can have multiple State compounds all linked together consecutively, working as part of a larger effect. The particles can transition from one state to the next as you specify with its unique State ID. Particles stay in one state until a trigger is “pulled” and a new state is used.
Each State compound contains its own Simulate Particles node, so you can unplug or delete the Simulate Particles node that is usually plugged into the ICETree node. It probably won’t interfere with the state execution, but it isn’t necessary.
Setting Up the Particle State System Base
To create the base for a particle state system
1. Create a particle emission—see Creating ICE Particle Emissions for information.
2. In the ICE tree’s preset manager, click the Task tab and select Particles.
3. Drag the State Machine compound from the States group into the ICE view.
4. Plug this compound’s Execute output into a Port on the ICETree node.
5. Drag one or more State compounds from the States group into the ICE view.
Create a State compound for each particle behavior set that you want to create.
6. Plug each State compound into an Execute State port of the State Machine compound in the order in which you want them evaluated (top to bottom).
7. Unplug (or delete) the Simulate Particles node from the ICE Tree node.
Now you need to define each State compound’s ID and color to uniquely identify it:
8. Open each State compound’s property editor and give each state a State ID number to uniquely identify it.
If you want to have the particles transition to another state upon the trigger being pulled, select that state’s ID in the Change State on Trigger list.
For more information, see below in Setting the Particle’s State ID.
9. In the State property editor, select a State Color to identify the particles when they’re in this state as you’re working. This color is used just for working/viewing, so you can change it when you’re ready to do your final effect—see below, Setting the State Color.
10. Select the trigger, as described in Selecting the Trigger.
11. Set up the effect, as described in Defining the Effect.
12. Using the process outlined here, you can keep adding State compounds and setting up trigger and effects compounds to make more complex effects.
Setting the Particle’s State ID
You can set the initial state in the particle’s Emit compound, which determines its state when it is born. State 0 is default initial state ID into which particles are born. And unless you use a State compound to define State 0 to be something else, this is what is set for the particle for the duration of its lifetime. Particles always stay in a certain state unless you switch them to another state using a State compound.
To put the particles into another state, you must define a new state using the State compound and give it a new ID (set the State_ID attribute). Then you can select that state in another State compound’s Change State on Trigger list. That makes the particles switch states and use the properties of the new state. For example, in the property editor for the State 0 compound, you could select State 1 in this list as the state to which the particles will transition when the Trigger value is reached.
It’s important that you give each state its own unique state ID as soon as you create it, otherwise it may not get evaluated. If there are two states that have the same ID in the same state system, only the state that is plugged in higher up on the State Machine gets evaluated.
For each State compound, you should select a State Color to identify the particles when they’re in this state as you’re working. This color is used just for working/viewing, so you can change it when you’re ready to do your final effect.
Select the Set Particle Color to State Color option if you want to see this color on the particles in the viewport. If this option is off, you’ll just see the color defined in the State compound, but not on the particles.
You can use the State Color as you’re working with setting up the states, then turn off the Set Particle Color to State Color option when you’re finished setting up the states so that all particles are displayed with the same color.
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