<p>我通常使用<code>clock.tick(fps)</code>返回的delta time(自上次<code>tick</code>起经过的时间)并将其传递给sprite的<code>update</code>方法来增加或减少计时器变量。当计时器低于0时,我创建一个<code>Bullet</code>类的实例,将其添加到sprite组并重置计时器。在</p>
<pre><code>import pygame as pg
from pygame.math import Vector2
pg.init()
ALIEN_IMAGE = pg.Surface((20, 15))
ALIEN_IMAGE.fill((40, 200, 90))
BULLET_IMAGE = pg.Surface((5, 5))
BULLET_IMAGE.fill((240, 120, 0))
class Alien(pg.sprite.Sprite):
def __init__(self, pos, all_sprites, bullets):
super().__init__()
self.image = ALIEN_IMAGE
self.rect = self.image.get_rect(center=pos)
self.vel = Vector2(1, 0)
self.pos = Vector2(pos)
self.bullet_timer = 1 # 1 second.
self.all_sprites = all_sprites
self.bullets = bullets
def update(self, dt):
self.pos += self.vel
self.rect.center = self.pos
# Decrease the countdown timer.
self.bullet_timer -= dt
if self.bullet_timer < 0: # Time is up so create a bullet.
bullet = Bullet(self.rect.center, Vector2(0, 5))
# Add the bullet to the sprite groups.
self.all_sprites.add(bullet)
self.bullets.add(bullet)
self.bullet_timer = 1 # Reset timer after firing.
class Bullet(pg.sprite.Sprite):
def __init__(self, pos, velocity):
super().__init__()
self.image = BULLET_IMAGE
self.rect = self.image.get_rect(center=pos)
self.vel = velocity
self.pos = Vector2(pos)
def update(self, dt):
self.pos += self.vel
self.rect.center = self.pos
def main():
screen = pg.display.set_mode((640, 480))
clock = pg.time.Clock()
all_sprites = pg.sprite.Group()
bullets = pg.sprite.Group()
alien = Alien((0, 30), all_sprites, bullets)
alien2 = Alien((60, 30), all_sprites, bullets)
all_sprites.add(alien, alien2)
done = False
while not done:
# dt = delta time (passed time since last clock.tick call).
dt = clock.tick(30) / 1000 # / 1000 to convert to seconds.
for event in pg.event.get():
if event.type == pg.QUIT:
done = True
all_sprites.update(dt)
screen.fill((30, 30, 30))
all_sprites.draw(screen)
pg.display.flip()
if __name__ == '__main__':
main()
pg.quit()
</code></pre>