cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   jonathan0382
   Member

   Hi all,

   I'm trying to understand z-order, which I would have expected to be simple, except things are not working as I'd planned. I assumed z-order was basically just depth, and children with higher z-orders are drawn more towards the viewer, so on top of children with lower z-orders.

   My question is this: is z-order absolute across a layer with all of its children?

   Reason I ask is because I have a scene with the following children and z-orders: in my notation '-->' means is a child of...

   treeSprites (z:4) --> backGroundSprite (z:1) --> parallaxNode (z:0) --> gameLayer (z:0) --> gameScene

   characterSprite (z:3) --> CharacterSpriteManager (z:0) --> gameLayer (z:0) the same gameLayer as above.

   So I would expect that because the trees z:4, and the character is z:3, the character should be drawn under the trees. This is not the case. The character is always on top, and this I don't get.

   Can someone please explain this to me?

   Thanks,

   Jonathan0382

   -------
   Shape Reactor..... a shameless plug. Anyone want a free download?

   Posted 2 years ago #
2. 

   Steve Oldmeadow
   Administrator

   You are misunderstanding how z order works. Just look at the code for CocosNode in particular the visit and insertChild methods. There is no magic.

   Posted 2 years ago #
3. 

   jonathan0382
   Member

   Ok, I looked at the visit and insertChild methods, and understand that there is a NSMutableArray that stores the children of a CocosNode at index = z order, and the children are visited in order of increasing index. (right?)

   I also read this http://en.wikipedia.org/wiki/Z-order and my understanding of z order in general is good.

   So, am I correct in thinking therefore that z order is branching, instead of absolute? What I mean is if you have a layer with multiple children, and these have multiple children, the 'draw' will iterate through the array of the first child of the layer (by first I mean with the lowest z order), and then through this child's children before moving onto the second child (by z order) of the layer etc? This is hard to explain, though I could draw it in a second. Basically, does it work along a whole branch, with all of its sub-branches, before moving on to the next branch?

   If this is the case then how exactly would I be able to have some trees be drawn above the character and some below. It is important that the trees are attached to parallaxNode, and that the character isn't.

   (If I'm still misunderstanding please forgive my stupidity)

   Thanks for the help!

   Posted 2 years ago #
4. 

   PhilM
   Member

   Thats how I'd imagine z order is handled, although I have no idea of its correct.

   If the foreground trees are always in front of the char, then could you not add a 2nd parallax node, above the char sprite layer? Depending on your layer structure, you might need to manually update the position of this 2nd parallax node based on the background one.

   If the trees can go both in front, and behind, I'm not sure of an easy way without swapping the sprites between layers manually. There was a discussion about a similar issue on here recently when using the tile map I believe.

   Posted 2 years ago #
5. 

   Clain
   Member

   Basically, does it work along a whole branch, with all of its sub-branches, before moving on to the next branch?

   Yes, like in Flash or Photoshop.

   If this is the case then how exactly would I be able to have some trees be drawn above the character and some below

   I'd use another parallax node, as PhilM suggested,

   Posted 2 years ago #
6. 

   jonathan0382
   Member

   @PhilM: 2nd paragraph: I need to update the z-order of the sprites at runtime depending upon the position of the game character. The character needs to be able to run behind the trees if its position.y is larger, and in front if the position.y is less.
   @Philm 3rd paragraph & @Clain: I had thought of swapping the sprites between layers, but I don't really want to do this... still, it seems like a good enough way, so I'll give it a go.

   Thanks all!

   Posted 2 years ago #

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