Deforming Particle Simulations
You can apply almost any of the standard deformation tools (such as lattices, cages, Push, Twist, or Taper) to particle, fluid, or explosion simulations. This is a powerful way of making complex particle systems, especially when combined with natural forces. For example, you could make a whirling tornado by containing a particle system within a twisted and tapered lattice and then applying a vortex force; or have a school of fish deform along a curve.
You apply deformations to particle clouds or clusters. Particle clouds are just like any other geometry meaning that you can apply standard object-based deformations to them. You also create clusters of particles in the same way as you do for standard points and then use any cluster-based deformations on them, such as shape animation or envelopes.
For information on deformations in general, refer to Deformations [ Modeling and Deformation Basics ].
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If you’re using natural forces on the particle cloud you want to deform, you should apply the forces first and then do the deformations. This is so that the deform operator sits “on top” of the cloud and uses all the simulation information that it contains. |
You can apply all object-based deformations to a particle cloud. All particle types associated to the cloud are affected by the deformer.
To deform a particle cloud
1. Select the particle cloud you want to deform.
2. Choose any of the deformations from the Deform menu (in the Model, Animate, or Simulate toolbar).
In this example, Deform > by Curve is used.
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When particle streams are deformed by a curve, the direction of the particles themselves is not tangent to the curve. This is because a deformer is unaware of what particles represent: it only moves the particles as if they were points in a geometry. As well, the deformer acts after the simulator, so the simulator doesn’t know about it. |
To deform a particle cloud using a lattice
1. Select the particle cloud.
2. Create a lattice by choosing Get > Primitive > Lattice. Set up the lattice to have the subdivisions and size you want.
When you choose this command, the lattice is automatically applied to the particle cloud because the cloud was selected.
3. Deform the lattice in any way, such as simply transforming its points or by using any of the standard Deform operators on it.
Example: Deforming Particles by Surface
You can create a cool effect of having particles “crawl” over the surface of an object by deforming the particle cloud on a sphere’s surface.
1. Choose Create > Particles > From Primitive > From Grid to create a basic particle system.
2. On the Emission page, set the Spread to 90 and the Speed to 0.5.
3. Create a default surface sphere on which you will deform the particles.
4. Select the particle cloud and choose Modify > Deform > by Surface. In the Surface Deform property editor, set the Scaling to X:1; Y:0; Z:1.
This spreads the particles over the surface of the sphere and makes them crawl instead of flying away.
To have finer control over deformations, you can deform particle clusters. This allows you to deform particles based on their particle type, not just the whole cloud, because particle clusters are defined per particle type.
You can do any of the following deformations on a particle cluster:
• Scale, rotate, and translate them, especially using proportional modeling.
• Create shape keys from them for shape animation.
• Use them as envelopes.
• Apply standard deform operators, such as Twist, Bend, and Surface.
• Use particles as cage deformers for other objects.
To deform particle clusters
1. In Point mode, select the particles you want to use for a cluster and click the Cluster button on the Edit panel.
Do this step for each cluster of particles you want to create.
2. Select the cluster you want to deform and use any deformation on it, as listed above.
Deforming Clusters in a Static Cloud
Although particles are points, there are some issues that make particle points different than standard points. The main issue to consider is that with a simulation, particles are born and die over the length of the simulation. This means that the same particles don’t necessarily stay for the duration. Particles are assigned into clusters based on their index in the particle cloud. An index is only recycled when a particle dies, and new particles are only appended at the end.
Because of these restrictions, the best way to use particle clusters for deformations is use them on a static cloud. To do this, you make an initial state of the simulation and have the particles live forever (see Creating an Initial State for Particles). This way, all the particles needed for the deformation are available by frame 1 and the number of particle clusters in the cloud are constant throughout the simulation.
If the cloud is not static (meaning that new particles are being generated during simulation and other ones are dying), the particle clusters do not stay coherent during the simulation, which means that the deformations on them do not stay coherent either.
For example, when you set shape keys, you set them on a cluster of a defined number of points. If this number changes, the shape keys don’t produce the same results.
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