ICE Particles Sliding on Obstacles
Using the Slide on Surface compound, you can make particles cling to and slide on an obstacle’s surface. Obstacles can be deform-animated and the particles will follow the shape of the changing surface. You also have several controls to help create the correct conditions in which the particles will drip off the obstacle. This is useful for creating sweat, water condensation, or other liquid drops sliding down a surface and then dripping off.
You can choose to use the Slide on Surface compound on its own or as part of a more extensive effect via a State system.
Making Particles Slide on an Obstacle
To make particles slide on and drip off of an obstacle
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 Slide on Surface compound from the Surface Interaction group into the ICE view.
4. Plug this compound’s Execute output into a Port on the ICETree node.
5. Create one or more objects that you want to use as obstacles for the particles. These objects need to have geometric surfaces, such as polygon meshes or NURBS surface objects. Make sure that the particles will reach these obstacles at some point in the simulation.
6. Drag each obstacle’s name into the ICE Tree view to create a node for it.
7. Plug each obstacle’s Value output into a Surface port of the Slide on Surface compound.
8. In the Slide on Surface property editor, you can set the Slide parameters. These parameters determine how the particles slide off the obstacle.
You can set the proximity method (particles slide according to closest surface, vertex/knot or smooth surface), offset method (particle size or a distance that you set), the cutoff distance (how close the particles have to be to the obstacle to slide), surface friction (how much speed is lost per frame), and rolling particles (uses the Roll Particles compound, as discussed in Rolling Particles).
For more information on the parameters, click the ? icon in the property editor or see Slide on Surface.
9. To make particles drip, see Making Particles Drip Off the Obstacle.
To use the Slide on Surface compound with a state system
1. Create a particle emission—see Creating ICE Particle Emissions for information.
2. In the ICE Tree, set up a State Machine and State compounds as you like, as described in Workflow Overview of Creating a Particle State.
3. Plug the Slide on Surface compound’s Execute output into an Execute Every Frame port of a State compound.
4. Continue with creating the effect you want with the State compound.
Making Particles Drip Off the Obstacle
In the Slide on Surface property editor, you can set the Drip parameters which create the conditions for particles to drip. With sliding particles, you usually want to control the timing in when they drip off the obstacle.
To make particles drip off of an obstacle
1. Set up the particles to slide on an obstacle as described in the previous section, Making Particles Slide on an Obstacle.
2. Open the Slide on Surface property editor and set the Drip parameters:
- Set the Angle Threshold, which is the angle at which the object needs to be before particles will drip off it. This is based on the obstacle’s surface normals and gravity or other forces in the scene. At a low angle, the particles will not drip off easily, whereas at a high angle, they drip off quickly.
- Set the Force Threshold, which is the maximum force required to make the particles drip. This is used mostly when the obstacle is moving and you want the particles to slide off the surface based on the obstacle’s velocity. A high threshold makes it more difficult for the particles to drip off, whereas a low threshold makes it easy for them to slide off.
- Set the Minimum Number of Neighboring Particles that need to be together so that the particles will drip. This is useful for effects such as dripping water, where a certain amount of water drops must collect before they have enough mass to drip.
- Set the Cutoff Distance to Neighboring Particles, which is the distance (in Softimage units) in which the particles must be from each other before they can drip.
Autodesk Softimage v.7.5