Creating an Initial State for ICE Simulations
When you’re working with ICE simulations (particles, rigid bodies, or deformed objects), you often need to have a certain state of the simulation be the first frame of the simulation, such as a candle already burning or rigid bodies already in a settled state. 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. For particles, 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 simulation and set it up to your liking. Then you can go to any frame of the simulation and capture it to be the initial state of that simulation. That state is stored and used as the beginning of the simulation the next time you play it. The rest of the simulation continues from that point as it did in the original simulation time frame.
To set an initial state for a simulation
1. Create an ICE particle, rigid body, or deformation simulation as you like.
2. Go to the frame that you want to set as the initial state. This will be the frame that is played before the first frame of the resulting simulation when played back.
3. Select the particles or deformed objects and choose ICE > Edit > Set Initial State from the Simulate toolbar.
The Set Initial State command sets the initial state of a simulation by disconnecting the Simulated ICETree node so that it is not a part of the construction stack anymore, freezing the stack (which deletes all operators in the stack), and then reconnecting the Simulated ICETree node back into the Simulation region in the stack, all without you seeing anything.
You can repeat these steps to change the initial state using different frames.
4. Play the simulation. The frame that you set as the initial state is not used as the first frame of the resulting simulation, but is actually the frame before the first frame.
For example, let’s say that you create a simulation starting at frame 1, then stop it at frame 50 and set that frame as the initial state. Then when you play back the simulation (using the initial state) and go to frame 1, you will see a little simulation step between the frame you set as the initial state (frame 50) and frame 1. Frame 1, in this case, is the frame that is one step after the initial state frame you set.
You can reset the initial state for a particle simulation by creating an unsimulated ICETree operator for the point cloud, deleting all points of the point cloud, and then freezing its modeling stack. Using a point cloud with no points is the same as setting no initial state.
To reset the initial state
1. Go to the first frame of the particle simulation.
2. In the ICE Tree view, choose Create > ICE Tree to create a non-simulated ICETree node.
3. Drag this ICETree operator into the Modeling region of the operation stack.
4. From the preset manager, click the Tool tab and get a Point Cloud > Delete Point node and connect it to the ICETree node.
5. Open this node’s property editor and select the Deleted checkbox to delete all the points.
6. Click the Freeze M (Freeze Modeling) button at the bottom of the MCP panel to freeze the Modeling region of the operation stack. The ICETree operator in that region is deleted, but the ICETree operator in the Simulation region remains intact.
7. Play the simulation and see that your original (pre-initial state) simulation has returned.
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