    # File lib/rubygame/ftor.rb, line 344
            def rotate!(angle)
    #               case(angle)
    #               when HALF_PI, -THREE_HALF_PI
    #                       self.set!(@y,-@x)
    #               when THREE_HALF_PI, -HALF_PI
    #                       self.set!(-@y,@x)
    #               when PI, -PI
    #                       self.set!(@y,-@x)
    #               when 0, TWO_PI, -TWO_PI
    #                       self.set!(@y,-@x)
    #               else
                            self.a += angle
    #               end
                    return self
            end