code: def scroll(self, delta_x, delta_y):
          
          if delta_x < 0:
              shift_x = 0
              xend = self.width + delta_x
              dt_x = 1
          else:
              shift_x = self.width - 1
              xend = delta_x - 1
              dt_x = -1
          if delta_y < 0:
              y = 0
              yend = self.height + delta_y
              dt_y = 1
          else:
              y = self.height - 1
              yend = delta_y - 1
              dt_y = -1
          while y != yend:
              x = shift_x
              while x != xend:
                  self.format.set_pixel(
                      self, x, y, self.format.get_pixel(self, x - delta_x, y - delta_y))
                  x += dt_x
              y += dt_y
docs: shifts framebuf in x and y direction