实施＆＃34; gravity＆＃34;影响

Question

目前我正在尝试用一匹跳过障碍的马来制作游戏，而我正在制作马动画。我可以让马跳起来，但我仍然未能实施＆＃34; gravity＆＃34;并使马在跳跃后重新回到地面。

这是我目前的代码：

import pyglet
import time

# background_sound = pyglet.media.load(
#          'Documents/Leave The Night On.mp3',
#          streaming=False)


class horse(pyglet.sprite.Sprite):
    def __init__(self, batch):
        self._img_main = pyglet.image.load("sihorseav.png")

        self.img_right1 = pyglet.image.load("sihorseav.png")
        self.img_right2 = pyglet.image.load("sihorseav.png")
        self.anim_right = pyglet.image.Animation.from_image_sequence([self.img_right1, self.img_right2], 0.5, True)
        pyglet.sprite.Sprite.__init__(self, self._img_main)        
        self.time = 0

    def forward_movement(self, flag=True):
        if keymap[pyglet.window.key.UP]:
            self.horse.time = time.time()
            self.horse.jump()

    def jump(self):
        print time.time()-self.time
        self.y -= -200 +20**(time.time()-self.time+.2)


class Window(pyglet.window.Window):
    def __init__(self, *args, **kwargs):
        super(Window, self).__init__(*args, **kwargs)
        self.batch = pyglet.graphics.Batch()
        self.label = pyglet.text.Label(text="Score: 0", x=850, y=650, batch=self.batch)
        image = pyglet.resource.image('sibackground.jpg')
        self.background = pyglet.sprite.Sprite(image, batch=self.batch)
        self.player = horse(batch = self.batch)
        self.keys_held = []

    def on_key_press(self, symbol, modifiers):
        self.keys_held.append(symbol)
        if symbol == pyglet.window.key.UP:
            self.player.time=time.time()
            self.player.jump()
    def on_draw(self):
        self.clear()
        self.batch.draw()       
        self.player.draw()
        self.label.draw()


def main():
    window = Window(width=960, height=700, caption='Pyglet')
    pyglet.app.run()

if __name__ == '__main__':
    main()