code: def blend_rect(self, x0, y0, x1, y1, dx, dy, destination, alpha=0xff):
          
          x0, y0, x1, y1 = self.rect_helper(x0, y0, x1, y1)
          for x in range(x0, x1 + 1):
              for y in range(y0, y1 + 1):
                  o = self._offset(x, y)
                  rgba = self.canvas[o:o + 4]
                  rgba[3] = alpha
                  destination.point(dx + x - x0, dy + y - y0, rgba)
docs: Blend a rectangle onto the image