physicsGroup

The group this shape belongs to, used to treat a set of shapes on one body as a single object when reporting contact and trigger begin and end events. Grouping marks the shape's contact and trigger begin/end events with whether they are the first or last event between the two groups involved. A shape starts with no group and can be assigned a group once only; the group then cannot be changed for the lifetime of the shape. Every shape given the same group must belong to the same body, otherwise the first and last marking of their events is unreliable.

public PhysicsWorld.PhysicsGroup physicsGroup { get; set; }