Cocos2d adding a background image to a layer?

Question

I just finished reading some of the cocos2d documentation, and as far as I understand to add a background image to a layer you have to do something like:

Sprite * bg = [Sprite spriteWithFile:@"Background.png"];
[layer addChild:bg z:0];

Allthough as far as my testing goes you can just directly add the sprite to the scene like this:

@implementation IntroScene
- (id) init {
self = [super init];
if (self != nil) {
    Sprite * bg = [Sprite spriteWithFile:@"Background.png"];
    [bg setPosition:ccp(240, 160)];
    [self addChild:bg z:0];
    [self addChild:[MenuLayer node] z:1];
}
return self;

}

What is the difference between this 2 options, and what is the better way to set a background for a layer?. Any help will be greatly appreciated.

Answer 1

You do not need to have a layer, but they are handy. Think of the layers as a way of grouping sprites (both visually and organizationally). You may want your background images grouped as a layer and all the enemies in a game as another layer. This allows you to deal with each set more cleanly. e.g. You can remove a specific layer instead of finding all of the enemies and removing them.

If it helps, play with layers in Photoshop or a graphics editing program. Layers in cocos2d work similarly.

For a simple scene, adding the background to a layer or to a scene won't make much difference. But it doesn't take long before the benefits of layering kicks in.

Answer 2

Also layers control drawing order (over and above any inter-layer z ordering).

In geoSpark, for example, I have a background layer, a spark layer, a UI layer, etc. (Simplified). But this allows me to make sure my UI stuff is always above any game stuff (the spark layer) and all that is above the background.

If your game does only additive rendering, draw order won't matter much. :)

-- David

Answer 3

scene is a blackboard, layer is a page... news is wrote on page, but, if you want you can write on the board. If you want erase all new.

Answer 4

In cocos2d we can add any node on any node. But it depends on level of hierarchy.

You can add Layers on Scenes. If you want same property or look for all layers that you add on a CCScene you can add those in CCScene (as in your second case). but if you want to have different feature on each layer add those to CCLayer.

CCLayer is meant for grouping a set of nodes/sprites for some purpose. For example you can add a layer which includes options after pausing a game, or HUD layer for displaying som kind always on screen along with some scrolling layer (liken in some scrolling platform games).

Finally you can even CCNode on a CCScene, a layer on another layer, and even a CCNode on a CCSprite. But the order of drawing in graphics context in cocos2d differs.

Hope you got the difference.

Good luck!