Spritekit scene anchorpoint affecting child node positioning - ios

Question

I have created my SKScene subclass which sets the anchorpoint and then adds one SKSpriteNode for the world, the world has multiple SKSpriteNodes for the obstacles, player etc. I am also centering on the
The problem I am having is that as I have set the anchorpoint of the scene to (0.5, 0.5), the position of any child node that I add to the world starts at the center of the world. How do I fix the postion of the nodes so that position = (0,0) will be at the bottom left of the world node and any child nodes added to it, instead of the center?
#implementation LevelScene
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
NSLog(#"width:%f height:%f", self.view.bounds.size.width, self.view.bounds.size.height);
// set the physics body
self.physicsWorld.gravity = CGVectorMake(0,-5);
self.physicsWorld.contactDelegate = self;
self.anchorPoint = CGPointMake(0.5, 0.5);
NSMutableDictionary *plistDict = [[NSMutableDictionary alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"LevelScene" ofType:#"plist"]];
NSString *backgroundImage = [plistDict objectForKey:#"background"];
// add a node that holds the background
background = [SKSpriteNode spriteNodeWithTexture:[SKTexture textureWithImageNamed:backgroundImage] size:CGSizeMake(1024, 768)];
background.position = CGPointMake(0, 0);
[self addChild:background];
world = [SKSpriteNode spriteNodeWithColor:[SKColor brownColor] size:CGSizeMake(1024, 768)];
world.position = CGPointMake(0, 0); // this should be bottom-left
world.size = CGSizeMake(1024, 768);
world.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:world.frame];
world.physicsBody.categoryBitMask = worldCategory;
[self addChild:world];
// load in the game tiles (these are non-dynamic tiles the player can use)
[self loadInTiles];
// add in game object to the world skspritenode - this just creates a subclass of skspritenode and sets position to 0,0
[self addGameObject:CGPointMake(0, 0)];
...
}
// ...setup functions, input handling, etc
-(void)didSimulatePhysics {
// setup the player to move depending on their direction
[player updatePosition];
[self centreOnNode:player];
}
-(void)centreOnNode: (SKSpriteNode *)node {
CGPoint cameraPositionInScene = [node.scene convertPoint:node.position fromNode:node.parent];
CGFloat x = node.parent.position.x - cameraPositionInScene.x;
CGFloat y = node.parent.position.y - cameraPositionInScene.y;
NSLog(#"camera x:%f y:%f", x, y);
NSLog(#"world frame origin x:%f y:%f", world.frame.origin.x, world.frame.origin.y);
node.parent.position = CGPointMake(x, y);
}

Answer 1

If you want to set the world sprite's origin to the bottom left side, just set it's anchor point.
world.anchorPoint = CGPointMake(0,0);
With this, the world sprite's coordinate system will be just like that of the scene's default.
Make sure to remove the line:
self.anchorPoint = CGPointMake(0.5, 0.5);

Answer 2

Replace this row:
world.position = CGPointMake(0, 0);
by this:
world.position = CGPointMake(-CGRectGetMidX(self.frame), -CGRectGetMidY(self.frame));
(0,0) is the center of the scene, since you set anchor point of the SKScene to (0.5,0.5)