Vertical Scrolling Background in Pygame

Question

I am trying to make my background image list to reposition themselves as soon as they hit the bottom of my screen....

I have a Camera Object which updates its self.state to the position of my moving ball.

Here's my Background Class:

class Background(pygame.sprite.Sprite):
def __init__(self, x, y):
    pygame.sprite.Sprite.__init__(self)
    self.image = pygame.image.load('images/clouds.jpg').convert()
    self.x = x
    self.y = y
    self.rect = self.image.get_rect()
    self.rect.left, self.rect.top = self.x, self.y   

def update(self,cam):
    self.rect.left = self.x + (0.2*cam.state.left)
    self.rect.top = self.y + (0.2*cam.state.top)

The 0.2* is to make it move slower than my actual camera shift.

Here's how I build the bg images before my big main loop:

all_backgrounds = pygame.sprite.Group()
#building bg images
for i in xrange((WIDTH+BG_WIDTH)/BG_WIDTH):
    for j in xrange((HEIGHT+BG_HEIGHT)/BG_HEIGHT):
        all_backgrounds.add(Background(BG_WIDTH*i,BG_HEIGHT*j))

Then in my main loop:

......
all_backgrounds.update(cam)
......
all_backgrounds.draw(screen)

I am looking for good suggestions on how to make it work smoothly. I tried using if statements in my Background.update() but it makes it laggy and issues with tear & overlap lines because of Int, float conversions.

Answer 1

You could try out: PyParallax looks like it does what you want plus more.