func (r Ray) String() string {
	return fmt.Sprintf("(o:%v,v:%v)", r.o, r.v)
}
func (r Ray) String() string {
	return fmt.Sprintf("(o:%v,v:%v)", r.o, r.v)
}
func ( r Ray ) String ( ) string { return fmt . Sprintf ( " " , r . o , r . v ) }
// String returns a string representation of r like with (o:Vec,v:Vec).
String returns a string representation of r like with ( o : Vec v : Vec ) .