vertical scroll for SpriteKit

vertical scroll for SpriteKit

#import "MyScene.h"

@interface MyScene()

@property (nonatomic, strong) SKSpriteNode *currentBackground;
@property (nonatomic, assign) CFTimeInterval lastUpdateTimeInterval;

@end

static NSString* const BACK_GROUND = @"background";

@implementation MyScene

-(id)initWithSize:(CGSize)size
{
    if (self = [super initWithSize:size])
    {
        self.currentBackground = [self createBackground];
        [self addChild:self.currentBackground];
    }
    
    return self;
}


-(void)update:(CFTimeInterval)currentTime
{
    CFTimeInterval timeSinceLast = currentTime - self.lastUpdateTimeInterval;
    
    self.lastUpdateTimeInterval = currentTime;
    
    if (timeSinceLast > 1)
    {
        timeSinceLast = 1.0 / 60.0;
        self.lastUpdateTimeInterval = currentTime;
    }
    
    [self enumerateChildNodesWithName:BACK_GROUND usingBlock:^(SKNode *node, BOOL *stop) {
        
        node.position = CGPointMake(node.position.x, node.position.y- 200 * timeSinceLast);
        
        if (node.position.y < -(node.frame.size.height + 100))
        {
            [node removeFromParent];
        }
    }];
    
    if (self.currentBackground.position.y < -(self.size.height - 100))
    {
        SKSpriteNode *temp = [self createBackground];
        temp.position = CGPointMake(0, self.currentBackground.position.y + self.currentBackground.frame.size.height);
        [self addChild:temp];
        self.currentBackground = temp;
    }
}

- (SKSpriteNode *)createBackground
{
    SKSpriteNode *background = [SKSpriteNode spriteNodeWithImageNamed:@"background.png"];
    background.anchorPoint = CGPointMake(0, 0);
    background.position = CGPointMake(0, 0);
    background.name = BACK_GROUND;
    background.zPosition = -1;
    
    return background;
}

@end