# 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