ICE Particles Sticking to Obstacles
Using the Stick to Surface compound, you can make particles stick to an obstacle’s surface upon collision and remain there for the duration of their lifetime (such as paint being sprayed onto a surface) unless you set up some condition that makes them fall off the obstacle (unstick).
Obstacles can be deform-animated and the particles will follow the shape of the changing surface. This is useful for creating wet snow or mud hitting a surface.
You can choose to use the Stick to Surface compound on its own or as part of a more extensive effect via a State system.
Making Particles Stick to Obstacles
To make particles stick to 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 Stick to Surface compound from the Surface Interaction group into the ICE view.
You can also use the Stick to Location compound and later define the location for where the particles will stick: Collision Location, Emit Location, Slide Location, Goal Location, or Input Location (use any object plugged into the Input Location port as the location). For more information, see Stick to Location.
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 Stick to Surface compound.
8. In the Stick to Surface property editor, you can set the collision method (for deformed objects or static), use the particle size or create an offset from the obstacle, and align the particles to the obstacle’s surface normals.
For more information on the parameters, click the ? icon in the property editor or see Stick to Surface.
9. To unstick the particles from the surface, see Detaching (Unsticking) Particles from Obstacles.
To use this 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 Stick to 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.
Detaching (Unsticking) Particles from Obstacles
If particles are stuck to an obstacle using the Stick to Surface compound, you can detach (unstick) them from obstacle’s surface by either setting parameters in the Stick to Surface property editor, or you can use the Unstick from Surface compound in a State system.
To release stuck particles from the object
In the Stick to Surface property editor, you can set up the conditions that release the particle from the surface.
1. Set up the particles to stick to an object as described in the previous section, Making Particles Stick to Obstacles.
2. Open the Stick to Surface property editor and set these parameters:
- Select the Allow Unstick parameter. This allows the particles to be released from the surface of the object if the Angle and Force Thresholds are at appropriate values.
- Set the Angle Threshold, which is the angle at which the object needs to be before particles will fall off it (unstick). 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 unstick easily, whereas at a high angle, they will.
- Set the Force Threshold, which is the maximum force required to make the particles fall off the obstacle (unstick). This is used mostly when the obstacle is moving and you want the particles to release from the surface based on the obstacle’s velocity. A high threshold makes it more difficult for the particles to unstick, whereas a low threshold makes it easy.
To release stuck particles 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 Stick to Surface compound’s Execute output into an Execute Every Frame port of a State compound.
4. Drag the Unstick from Surface compound from the Surface Interaction group into the ICE view.
5. Plug its Execute output into the Execute Once on Enter State port of the State compound.
6. Continue with creating the effect you want with the State compound.
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