<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def blit(self, surface, pos=(0, 0)):
 """ Blits a surface on the screen at pos :param surface: Surface to blit :param pos: Top left corner to start blitting :type surface: Surface :type pos: tuple """

        for x in range(surface.width):
            for y in range(surface.height):
                point = (x + pos[0], y + pos[1])
                if self.point_on_screen(point):
                    self.matrix[point[0]][point[1]] = surface.matrix[x][y]