function Turret.rotateTo( dir, dt )
{
	dir = dir.normalized;
	
	// do not let it rotate too quickly
	axis = vec3_cross( dir, this.direction ).normalized;
	angle = acos( min( 1, vec3_dot( dir, this.direction ) ) );
	maxmove = dt;
	if( angle > maxmove )
		dir = mat3().rotate_axis_angle_v3( axis, maxmove ).transform( this.direction ).normalized;
	
	// limit rotation
	axis = vec3_cross( dir, this.orig_direction ).normalized;
	angle = acos( min( 1, vec3_dot( dir, this.orig_direction ) ) );
	if( angle > this.maxangle )
		angle = this.maxangle;
	
	// rotate
	this.rotation = this.orig_rotation.normalized.rotate_axis_angle_v3( axis, angle ).normalized;
	this.direction = this.rotation.transform( vec3( 1, 0, 0 ) );
	this.mesh_inst.matrix = mat4().scale_v3( this.scale ).rotate_quat( this.rotation ).translate_v3( this.position );
	this.body.orientation = this.rotation.invert();
	
	lt = this.light;
	lt.direction = this.direction;
	lt.position = this.position + this.direction;
	lt.updir = this.rotation.transform( vec3(0,0,1) );
	lt.genSpotLightMatrices();
}