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soft_body_attachments

A particle can also be attached directly to a rigid-body (SoftBody::attach_particle), which is the simplest way of combining the two kinds of bodies: a rope tied to a swinging ball, a flag attached to its pole, etc. Unlike pinning, an attachment is a two-way point-to-point constraint: the rigid-body holds the particle, and the particle pulls the rigid-body back. The anchor is the position the particle has when the attachment is created, expressed in the local frame of the rigid-body. Note that a particle attached twice keeps both of its attachments, and that an attachment is undone with SoftBody::detach_particle:

// Attach the last particle of a rope to a rigid box, at the particle's position.
let rope = SoftBodyBuilder::rope(Vector::new(8.0, 9.0), Vector::new(12.0, 9.0), 25)
    .pinned_particles([0])
    .softness(SpringCoefficients::new(40.0, 1.0));
let rope_handle = world.insert_soft_body(rope);
let last_position = world.soft_bodies[rope_handle].particle_position(24);
let (weight, _) = world.insert(
    RigidBodyBuilder::dynamic().translation(last_position - Vector::new(0.0, 0.4)),
    ColliderBuilder::cuboid(0.3, 0.3).density(2.0),
);
world.soft_bodies[rope_handle].attach_particle(24, weight, &world.bodies);