iphone - Infinite scrolling on a sprite(Parallax) -

i newbie world of cocos2d developing first tutorial , facing 1 problem problem have image (1024 x 320) , orientation landscape need move image continuously right left purpose have used space shooter tutorial ray(thanks him) image doesn't seem appearing again , again. code is..

-(id) init {     if( (self=[super init])) {         cgsize screensize = [ccdirector shareddirector].winsize;          // 1) create ccparallaxnode         backgroundnode = [ccparallaxnode node];         [self addchild:backgroundnode z:-1];          // 2) create sprites we'll add ccparallaxnode         = [ccsprite spritewithfile:@"bg_front_spacedust.png"];         //back.position=ccp(screensize.width/2, screensize.height/2);         back.rotation = -90;         back1 = [ccsprite spritewithfile:@"bg_front_spacedust.png"];         back1.rotation = -90;          // 3) determine relative movement speeds space dust , background         cgpoint dustspeed = ccp(0.1, 0.1);          // 4) add children ccparallaxnode         [backgroundnode addchild:back z:0 parallaxratio:dustspeed positionoffset:ccp(screensize.width/2, screensize.height/2)];         nslog(@"back.content width is...%f",back.contentsize.width);         [backgroundnode addchild:back1 z:1 parallaxratio:dustspeed positionoffset:ccp(screensize.width/2, screensize.height*2)];          // 5) enable updates         [self scheduleupdate];  }     return self; }   - (void)update:(cctime)dt {      // 1) update background position     cgpoint backgroundscrollvel = ccp(0,-1000);     backgroundnode.position = ccpadd(backgroundnode.position, ccpmult(backgroundscrollvel, dt));      // 2) check background elements moving offscreen     nsarray *spacedusts = [nsarray arraywithobjects:back, back1, nil];     (ccsprite *spacedust in spacedusts) {         if ([backgroundnode converttoworldspace:spacedust.position].x < -spacedust.contentsize.width) {             [backgroundnode incrementoffset:ccp(2*spacedust.contentsize.width,0) forchild:spacedust];         }     } } 

please me out of this
in advance.

try one

if (backgroundnode.position.y <-screensize.height*2)             backgroundnode.position = ccp(0,0);  

as init method called once approach doing done 1 time need again set position of backgroundnode 0 in update method. here multiple may vary