def blit(self, surface, pos=(0, 0)):
        """
        Blits a surface on this surface at pos

        :param surface: Surface to blit
        :param pos: Top left point to start blitting
        :type surface: Surface
        :type pos: tuple
        """
        for x in range(surface.width):
            for y in range(surface.height):
                px = x + pos[0]
                py = y + pos[1]
                if 0 < px < self.width and 0 < py < self.height:
                    self.matrix[px][py] = surface.matrix[x][y]