=head1 NAME

Box2D::b2Joint - Base joint class.

=head1 SYNOPSIS

  # Don't use this class directly, use a subclass.

=head1 DESCRIPTION

The base joint class. Joints are used to constraint two bodies together
in various fashions. Some joints also feature limits and motors.

=head1 METHODS

=head2 GetAnchorA()

Get the anchor point on bodyA in world coordinates. Implemented in
C<Box2D::b2DistanceJoint>, C<Box2D::b2FrictionJoint>,
C<Box2D::b2GearJoint>, C<Box2D::b2LineJoint>, C<Box2D::b2MouseJoint>,
C<Box2D::b2PrismaticJoint>, C<Box2D::b2PulleyJoint>,
C<Box2D::b2RevoluteJoint>, and C<Box2D::b2WeldJoint>.

Returns a C<Box2D::b2Vec2>

=head2 GetAnchorB()

Get the anchor point on bodyB in world coordinates. Implemented in
C<Box2D::b2DistanceJoint>, C<Box2D::b2FrictionJoint>,
C<Box2D::b2GearJoint>, C<Box2D::b2LineJoint>, C<Box2D::b2MouseJoint>,
C<Box2D::b2PrismaticJoint>, C<Box2D::b2PulleyJoint>,
C<Box2D::b2RevoluteJoint>, and C<Box2D::b2WeldJoint>.

Returns a C<Box2D::b2Vec2>

=head2 GetBodyA()

Get the first body attached to this joint.

Returns a C<Box2D::b2Body>

=head2 GetBodyB()

Get the second body attached to this joint.

Returns a C<Box2D::b2Body>

=head2 GetNext()

Get the next joint the world joint list.

Returns a C<Box2D::b2Joint>

=head2 GetReactionForce( $inv_dt )

Get the reaction force on body2 at the joint anchor in Newtons.
Implemented in C<Box2D::b2DistanceJoint>, C<Box2D::b2FrictionJoint>,
C<Box2D::b2GearJoint>, C<Box2D::b2LineJoint>, C<Box2D::b2MouseJoint>,
C<Box2D::b2PrismaticJoint>, C<Box2D::b2PulleyJoint>,
C<Box2D::b2RevoluteJoint>, and C<Box2D::b2WeldJoint>.

Parameters:

=over 4

=item * C<float32> C<$inv_dt>

=back

Returns a C<Box2D::b2Vec2>

=head2 GetReactionTorque( $inv_dt )

Get the reaction torque on body2 in N*m. Implemented in
C<Box2D::b2DistanceJoint>, C<Box2D::b2FrictionJoint>,
C<Box2D::b2GearJoint>, C<Box2D::b2LineJoint>, C<Box2D::b2MouseJoint>,
C<Box2D::b2PrismaticJoint>, C<Box2D::b2PulleyJoint>,
C<Box2D::b2RevoluteJoint>, and C<Box2D::b2WeldJoint>.

Parameters:

=over 4

=item * C<float32> C<$inv_dt>

=back

Returns a C<float32>

=head2 GetType()

Get the type of the concrete joint.

Returns a C<Box2D::b2JointType>

=head2 GetUserData()

Get the user data pointer.

=head2 IsActive()

Short-cut function to determine if either body is inactive.

Returns a C<bool>

=head2 SetUserData( $data )

Set the user data pointer.

Parameters:

=over 4

=item * C<scalar> C<$data>

=back

=head1 SEE ALSO

=over 4

=item * L<Box2D>

=item * L<Box2D::b2JointDef>

=item * L<Box2D::b2DistanceJoint>

=item * L<Box2D::b2FrictionJoint>

=item * L<Box2D::b2GearJoint>

=item * L<Box2D::b2LineJoint>

=item * L<Box2D::b2MouseJoint>

=item * L<Box2D::b2PrismaticJoint>

=item * L<Box2D::b2PulleyJoint>

=item * L<Box2D::b2RevoluteJoint>

=item * L<Box2D::b2WeldJoint>

=back

=head1 BUGS

See L<Box2D/BUGS>

=head1 AUTHORS

See L<Box2D/AUTHORS>

=head1 COPYRIGHT & LICENSE

See L<Box2D/"COPYRIGHT & LICENSE">

=cut