About Syflex Collisions

As part of a typical Syflex cloth or curve simulation, you need to set up how the cloth or curve reacts to collisions. Collisions can be with other objects, or they can be self-collisions, such as preventing a cloth from intersecting itself when it folds up or flaps in the wind. A collision object (also called an obstacle) obstructs the points of the simulated object, causing the points to interact with and move around it in some way.

Although they aren't collision object properties, velocity and mass also play a large role in how a cloth object reacts in a collision:

A cloth object moving at a high velocity is going to deform more than one moving at a low velocity.
A cloth object with a high mass value is going to deform less than one with a low mass value, but it will have greater momentum.

NoteEnergy and momentum cannot be transferred from the cloth to a collisions object or vice versa.

Types of Collisions

There are several types of collisions that you can create for cloth or curve simulations, using these Syflex ICE compounds:

Syflex Collide Capsule or Sphere or Plane create shaped bounding boxes around a null for the collision object - see Creating Collisions with Bounding Box Objects.
Syflex Collide Mesh uses polygon meshes for collision objects - see Creating Collisions with Polygon Mesh Objects.
Syflex Collide Self allows the cloth object to collide with itself - see Creating Self Collisions.

As a rule of thumb, you should use the bounding shapes (capsule, sphere, and plane) for collision objects if possible. Collision calculations with these shapes are faster than with polygon mesh collision objects, which use the actual shape. However, you will need to use polygon mesh objects when you need to have the exact shape of the collision object for the interaction with the cloth, such as for a shirt colliding with a character's arms, armpits, and upper body.

Evaluation Order of Collide Nodes

In ICE, the evaluations of a node start from its top port and go down, so the order in which nodes are plugged in usually matters.

This is the case for the Collide nodes: the order in which you plug in any of the Syflex Collide node outputs into the Syflex Cloth or Syflex Curve nodes' Force ports can make a difference in the resulting simulation. For example, if you are using several Collide nodes to have multiple collisions happening in the same area of the cloth, you need to plug in the Collide nodes in the order that you want them evaluated.

Forces, such as gravity or wind, are always computed before collisions, so the order of the Force nodes doesn't matter.

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