在cocos2d背景的连续滚动(Continuous Scrolling of background

我的代码对于连续滚动......

NSArray *spaceDusts = [NSArray arrayWithObjects:_spacedust1, _spacedust2, nil];
for (CCSprite *spaceDust in spaceDusts) {
if ([_backgroundNode convertToWorldSpace:spaceDust.position].x < -   spaceDust.contentSize.width) {
    [_backgroundNode incrementOffset:ccp(2*spaceDust.contentSize.width,0)   forChild:spaceDust];
}
}

背景图像大小为1024 * 384

当正确符文到这个模拟器的工作，但是当我在设备使用（iphone）
其设置背景到中心，并采取一些加载图像

提前致谢.....

我对在cocos2d游戏背景滚动代码：

#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
 #define MM_BG_SPEED_DUR       ( IS_IPAD ? (6.0f) : (2.0f) )

-(void)onEnter
{
    [super onEnter];
    [self initBackground];

    [self schedule: @selector(tick:)];
}

-(void)initBackground
{
   NSString *tex = @"BG/Background.png";//[self getThemeBG];

    mBG1 = [CCSprite spriteWithFile:tex];
    mBG1.position = ccp(s.width*0.5f,s.height*0.5f);
    [self addChild:mBG1 z:LAYER_BACKGROUND];

    mBG2 = [CCSprite spriteWithFile:tex];
    mBG2.position = ccp(s.width+s.width*0.5f,s.height*0.5f);

    mBG2.flipX = true;
    [self addChild:mBG2 z:LAYER_BACKGROUND];

}


-(void)scrollBackground:(ccTime)dt
{
    CGSize s = [[CCDirector sharedDirector] winSize];

    CGPoint pos1 = mBG1.position;
    CGPoint pos2 = mBG2.position;

    pos1.x -= MM_BG_SPEED_DUR;
    pos2.x -= MM_BG_SPEED_DUR;


    if(pos1.x <=-(s.width*0.5f) )
    {
        pos1.x = pos2.x + s.width;
    }

    if(pos2.x <=-(s.width*0.5f) )
    {
        pos2.x = pos1.x + s.width;
    }

    mBG1.position = pos1;
    mBG2.position = pos2;

}

-(void)tick:(ccTime)dt
{
    [self scrollBackground:dt];
}