Creating an Initial State for Particles
When you’re working with particle simulations, you often need to have a certain state of the simulation be the first frame of the simulation. Instead of computing a pre-roll simulation to arrive at the correct state for the beginning, you can select any frame in an existing simulation and use that as the initial state. The initial state includes the number of particles that are already emitted at the start of simulation along with their properties.
To create an initial state, you must first create a particle cloud and set up the simulation to your liking. Then you can capture any frame of the resulting simulation to be the initial state.
When you set an initial state, a particle cloud and initial state property is created as a child of the existing simulation’s particle cloud, but without a simulation operator. As well, the particle types associated with the existing particle cloud are copied to the initial state. Then at the first frame of simulation, the simulation operator copies this initial state data to the simulated cloud and continues the simulation from that state onward.
Once you set the initial state, you can modify it to your liking, such as using deform operators to manipulate the particles.
To set an initial state for a particle cloud
1. Create a particle cloud and set up the simulation as you like.
2. Run the simulation in Standard Caching mode (see Choosing the Way Particle Simulations Are Played Back) so that you can move back and forth among the generated PTP files.
3. Go to the frame that you want to set as the initial state. This will be the first frame of the simulation that is played.
4. Select the particle cloud and choose Modify > Particles > Set Initial State from the Simulate toolbar.
An initial state property is created and connected to the particle cloud’s simulation operator (the initial state has no simulation operator of its own). It is a child of the selected particle cloud. The cloud is hidden and has render visibility off by default.
You can repeat these steps to replace the initial state using different frames.
5. Play the simulation and see that the first frame of the simulation is the initial state that you set and the rest of the simulation continues as it did from that point onward.
6. If you like, you can delete the original particle cloud’s emitter to keep only the initial state of the particles.
To edit the initial state’s properties
1. Open the Initial State property editor by doing one of the following:
- Select the original or initial state cloud and choose Modify > Particles > Edit Initial State Prop.
or
- Click the Initial State Property icon in the explorer.
2. Select these options as you like:
- Select Mute to temporarily deactivate the initial state.
- Select Transfer Velocity to transfer the velocity of particles from the selected particle cloud to the initial state cloud. Deselect this to have static particles.
- Select Live Forever to make the particles in the initial state stay in the scene for many, many seconds. This option is useful for creating static clouds, especially when used in deformations (see Deforming Particle Clusters).
Disconnecting and Reconnecting Initial States
To disconnect initial states
• Select a particle cloud with an initial state and choose Modify > Particles > Disconnect Initial State. This does not delete the initial state.
To connect or reconnect initial states
• Select a particle cloud and choose Modify > Particles > Connect Initial State. This connects an unconnected initial state to its parent particle cloud’s simulation operator.
Creating a New Particle Cloud Based on the Initial State
You can create a new particle cloud based on the original particle cloud that has the initial state. This lets you keep the original particle cloud’s simulation and disconnect its initial state. This is useful, for example, to create a simulation from sketched particles (see Sketching Particles).
To create a new particle cloud based on the initial state
• Select the original particle cloud with the initial state and choose
Create > Particles > From Initial State.
This creates a new particle cloud and adds a simulation operator. The emitter and particle type are used from the original particle cloud, but is not copied to the new cloud so you cannot change these properties.
Autodesk Softimage v.7.5