This constraint prevents particles from moving outside of one or more polygons. If a particle ventures outside it will be moved back to its closest point inside the specified polygon(s) and have its velocity set to zero.
The following parameters defines the training of the constraint and can be
passed along a call to impose()
polygon : A two column matrix giving the polygon, or a list of matrices
to use multiple polygons. Overlapping polygons will be subtracted from each
other so it is possible to define polygons with holes.
Other constraints:
dominator_constraint,
infinity_constraint,
path_constraint,
velocity_constraint,
x_constraint,
y_constraint