=head1 NAME

Box2D::b2GearJoint - Connects two joints together.

=head1 SYNOPSIS

  my $joint = $world->CreateJoint( $joint_def );
  $joint->SetRatio( $ratio );

=head1 DESCRIPTION

A gear joint is used to connect two joints together. Either joint can
be a revolute or prismatic joint. You specify a gear ratio to bind the
motions together: coordinate1 + ratio * coordinate2 = constant The
ratio can be negative or positive. If one joint is a revolute joint and
the other joint is a prismatic joint, then the ratio will have units of
length or units of 1/length.

Warning: The revolute and prismatic joints must be attached to fixed
bodies (which must be body1 on those joints).

=head1 METHODS

=head2 GetAnchorA()

Get the anchor point on bodyA in world coordinates. Implements
C<Box2D::b2Joint>.

Returns a C<Box2D::b2Vec2>

=head2 GetAnchorB()

Get the anchor point on bodyB in world coordinates. Implements
C<Box2D::b2Joint>.

Returns a C<Box2D::b2Vec2>

=head2 GetRatio()

Returns a C<float32>

=head2 GetReactionForce( $inv_dt )

Get the reaction force on body2 at the joint anchor in Newtons.
Implements C<Box2D::b2Joint>.

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. Implements C<Box2D::b2Joint>.

Parameters:

=over 4

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

=back

Returns a C<float32>

=head2 SetRatio( $ratio )

Set/Get the gear ratio.

Parameters:

=over 4

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

=back

=head1 SEE ALSO

=over 4

=item * L<Box2D>

=item * L<Box2D::b2GearJointDef>

=item * L<Box2D::b2Joint>

=item * L<Box2D::b2World>

=back

=head1 BUGS

See L<Box2D/BUGS>

=head1 AUTHORS

See L<Box2D/AUTHORS>

=head1 COPYRIGHT & LICENSE

See L<Box2D/"COPYRIGHT & LICENSE">

=cut