How to make a background continuously scroll vertically with spritekit - ios

Question

I have my background set and it is scrolling horizontally, here is my code:
-(void)initalizingScrollingBackground
{
for (int i = 0; i < 2; i++)
{
SKSpriteNode *bg = [SKSpriteNode spriteNodeWithImageNamed:#"background"];
bottomScrollerHeight = bg.size.height;
bg.position = CGPointMake(i * bg.size.width, 0);
bg.anchorPoint = CGPointZero;
bg.name = #"background";
[self addChild:bg];
}
}
and also this code:
- (void)moveBottomScroller
{
[self enumerateChildNodesWithName:#"background" usingBlock: ^(SKNode *node, BOOL *stop)
{
SKSpriteNode * bg = (SKSpriteNode *) node;
CGPoint bgVelocity = CGPointMake(-BG_VELOCITY, 0);
CGPoint amtToMove = CGPointMultiplyScalar(bgVelocity,_dt);
bg.position = CGPointAdd(bg.position, amtToMove);
//Checks if bg node is completely scrolled off the screen, if yes then put it at the end of the other node
if (bg.position.x <= -bg.size.width)
{
bg.position = CGPointMake(bg.position.x + bg.size.width*2,
bg.position.y);
}
[bg removeFromParent];
[self addChild:bg]; //Ordering is not possible. so this is a hack
}];
}
The second part makes the background scroll. Without it, the background is still.
Also, without the movebottomscroller, my sprite appears on top of the background. With the movebottomscroller, he appears behind the scrolling background. Is there any command to bring him to the front, above any other backgrounds?
Thank you!

Answer 1

Try the approach below, hope that works for you.
#interface GameScene()
#property (nonatomic) NSTimeInterval lastTimeSceneRefreshed;
#end
#implementation GameScene
- (instancetype)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
[self buildBackground];
[self startScrolling];
}
return self;
}
// This method will add 3 background nodes
- (void)buildBackground {
float centerX = CGRectGetMidX(self.frame);
SKSpriteNode *firstBackgroundNode = [SKSpriteNode spriteNodeWithImageNamed:#"background"];
firstBackgroundNode.name = #"background";
firstBackgroundNode.position = CGPointMake(centerX,
firstBackgroundNode.size.height*firstBackgroundNode.anchorPoint.y);
[self addChild:firstBackgroundNode];
float previousYPosition = firstBackgroundNode.position.y;
for (int i = 0; i < 2; i++) {
SKSpriteNode *backgroundNode = [SKSpriteNode spriteNodeWithImageNamed:#"background"];
backgroundNode.position = CGPointMake(centerX,
previousYPosition + backgroundNode.frame.size.height);
previousYPosition = backgroundNode.position.y;
backgroundNode.name = #"background";
[self addChild:backgroundNode];
}
}
- (void)update:(CFTimeInterval)currentTime {
// Updating background nodes
// We don't want to update backgrounds each frame (60 times per second)
// Once per second is enough. This will reduce CPU usage
if (currentTime - self.lastTimeSceneRefreshed > 1) {
[self backgroundNodesRepositioning];
self.lastTimeSceneRefreshed = currentTime;
}
}
- (void)backgroundNodesRepositioning {
[self enumerateChildNodesWithName:#"background" usingBlock: ^(SKNode *node, BOOL *stop)
{
SKSpriteNode *backgroundNode = (SKSpriteNode *)node;
if (backgroundNode.position.y + backgroundNode.size.height < 0) {
// The node is out of screen, move it up
backgroundNode.position = CGPointMake(backgroundNode.position.x, backgroundNode.position.y + backgroundNode.size.height * 3);
}
}];
}
- (void)startScrolling {
SKAction *moveAction = [SKAction moveByX:0 y:-200 duration:1];
[self enumerateChildNodesWithName:#"background" usingBlock: ^(SKNode *node, BOOL *stop)
{
[node runAction:[SKAction repeatActionForever:moveAction] withKey:#"movement"];
}];
}

Answer 2

I don't fully understand your approach here, but I can answer your question so I'll just go ahead and do that - I hope I haven't misunderstood.
SKNode has a method insertChild:atIndex: that would allow you to put the background nodes at the back, or put the sprite at the front.
SKNode Class Reference