Vertically scrolling background - Sprite Kit - ios

Question

I'm working on a game that is in portrait mode and can't seem to get this background to scroll smoothly on the y-axis. It doesn't properly add a second background so there is always a gap between the 2 backgrounds.
Heres the code:
static const float BG_VELOCITY = 100.0;
static inline CGPoint CGPointAdd(const CGPoint a, const CGPoint b)
{
return CGPointMake(a.x + b.x, a.y + b.y);
}
static inline CGPoint CGPointMultiplyScalar(const CGPoint a, const CGFloat b)
{
return CGPointMake(a.x * b, a.y * b);
}
Methods:
-(void)initalizingScrollingBackground
{
for (int i = 0; i < 2; i++) {
SKSpriteNode *bg = [SKSpriteNode spriteNodeWithImageNamed:#"bg"];
bg.zRotation = M_PI_2;
bg.position = CGPointMake(320, self.frame.origin.y);
bg.anchorPoint = CGPointZero;
bg.name = #"bg";
[self addChild:bg];
}
}
- (void)moveBg
{
[self enumerateChildNodesWithName:#"bg" usingBlock: ^(SKNode *node, BOOL *stop)
{
SKSpriteNode * bg = (SKSpriteNode *) node;
CGPoint bgVelocity = CGPointMake(0, -BG_VELOCITY);
CGPoint amtToMove = CGPointMultiplyScalar(bgVelocity,_dt);
bg.position = CGPointAdd(bg.position, amtToMove);
//Checks if bg node is completely scrolled of the screen, if yes then put it at the end of the other node
if (bg.position.y <= -bg.size.height)
{
bg.position = CGPointMake(bg.position.x,
bg.position.y + bg.size.height*2);
}
}];
}
What am I doing wrong that it has a gap in between the two backgrounds. Note: Background size is 568 x 320 if that is necessary info.
Thanks.

Answer 1

There a few problems. The biggest is the fact that your image is made in landscape mode. Simply edit the image in photoshop or preview to rotate it 90 degrees, then take out the zRotation. This will work for your height dilemma. Then change bg.position = CGPointMake(320,... etc to bg.position = CGPointMake (0, i * bg.size.height);
Also change your if statement to:
if (bg.position.y <= -bg.size.height)
{
bg.position = CGPointMake(0, bg.position.y + bg.size.height*2);
}
And your code will work.