Scene vs. Layer « cocos2d for iPhone

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Scene vs. Layer

(23 posts) (11 voices)

Started 2 years ago by eshirt
Latest reply from marciokoko

Tags:

eshirt
Member

First, thanks to this board and thanks to all the contributors to the cocos2d framework! I'm loving it and I think I'm starting to wrap my head around most of the concepts.

I've got one major thing that's been unclear... What's the difference between a Scene and a Layer, practically speaking? I know from reading that a Scene is composed of Layers, which gets called and displayed by the Director.

But in all the examples I've seen (the MenuTest example is one example) all the game classes created are just subclassing Layer. I'll set up an example of how I think I understand it with an abstract game example:

A MenuScene loads its first MainMenuLayer which presents the user the usual options. When a user taps "Settings", the SettingsLayer gets pushed into the MenuScene, similar for the ScoresLayer, RulesLayer, etc.

But when the user taps "New Game", the Director would call a new GameScene, which would start the game.

Is that how it's supposed to work? Or is it one scene per project, and layers for every "screen"?

Sorry if it's a stupid question, I just couldn't find a clear explanation.

Posted 2 years ago #
micah
Member

I'm actually just starting to wrap my head around cocos2d also, working on my first small test game before I start a real project, and I have this exact same question right now.

Specifically, I'm trying to make a simple instructions page that has some text and a Sprite for a back button to go back to the main menu. I made and Instructions scene (inheriting from Scene), but then I found that Scenes don't accept touch events, layers do. So do I need to make Instructions inherit from Layer instead so that it can accept touch events?

Posted 2 years ago #
natanavra
Member

Ok so here's how I perceive this:
Scenes and Layers both subclasses of CocosNode.
Scenes are windows, they define what can the player see, they help you order you project.
Layers are user interfaces, they are the touch handlers and everything that has to do with interaction and display.

Scenes are containers for your layers, and you can manage you layers through Scenes.

To sum up:
Scenes are flow managers; what will be on top, what comes next, etc. etc.
Layers are everything that has to do with interaction and graphic display.

Ahhh this is pretty messy, as I myself understand how this works, but it's hard to explain (especially for a 16 y/o dude from ISR).
Anyways, I hope this helped you wrap your heads around the main idea of Scenes and Layers, I also suggest reading some tuts, like Monocole's white paper (it's terrific)!!

~ Natanavra.

Posted 2 years ago #
eshirt
Member

natanavra - thanks for your reply. I guess I understand the concepts of Scenes and Layers and how they interact.

So, when building a game with a main menu, settings screen, scores, new game, and continue game options, would you use just one Scene and push in and out different layers? Or would each of those screens get a Scene, then each one have their own interaction layers?

Posted 2 years ago #
natanavra
Member

Nah...
If your Layers are connected then yes, let's say you have a GameScene and you have a LevelLayer inside and a win/lose Layer inside.
So every time you finish a level, you add a win/lose Layer to your GameScenes.

Only if the layers need some sort of interacting between them, or they have some general similar idea, then manage them inside a Scene.
But for different things use different Scenes.
You can have:
OptionsScene
GameScene
MenuScene
HelpScene
AboutScene
etc. etc.

and inside every Scene, you need/can have a an in-Scene interaction manager, the Layer.

Sorry if I didn't explain the concept too well, and got you confused. I think it's better you read somewhat more professional explanations (see the Wiki, a ton of goodies!).

~ Natanavra.

Posted 2 years ago #
Mitch Lindgren
Member

Natanavra's explanation is pretty good, I think.

My rule of thumb is that whenever I'm going to have a transition, I use a new scene. Practically speaking, this means I have two scenes - a menu scene and a game scene. Within the menu scene, I switch layers in and out for different menu pages - I do this because the menu has an animated background which I want to be continuous between different menu pages. The game scene is basically just a scene on which I added a game layer - I have three different subclasses of game layer for different modes.

Posted 2 years ago #
crmagicxxx
Member

Let me try to explain :)

Do anybody of you use Spaces on their Macs? (Expose and Spaces in System Preferences) I have to tell you I started using it 5 days ago and I am stunned. I am pretty new to Mac world so it was revelation for me :)

If so, then think of a scene as "space" (1, 2, 3, 4, ...) and layer as everything you have on that "space" like "windows" could be sprites, labels, etc... With one limitation, you can't just move content of one Scene to another like you can move windows from spaces to spaces... (you can of course have references between scenes, but that's next step, having in mind understanding scenes and layers are basics)

Hope that helped :)

Posted 2 years ago #
Osiris
Member

@natanavra - I took you as much older, maybe your youth is what gives you the ability to respond as well as you do to all the newcomers and what seems like repetitive questions. kudos, dude.

Posted 2 years ago #
natanavra
Member

@Osiris, Thanks man, I try to do my best... How come you thought of me as an older one, my profile pic gives me away lol...

~ Natanavra.

Posted 2 years ago #
eshirt
Member

Natanavra & lindgrenM - Thanks, that clears everything up. I had pretty much assumed that my basic game would contain a MenuScene and a GameScene, but then I went a got myself all confused. :) All clear now! Thanks again!

Posted 2 years ago #
eshirt
Member

Sorry in advance for the long post, let me see if I've wrapped my head around this. If I were to create a soccer game, would this be an acceptable class list? Is there a better way to accomplish this? Thanks everyone for their input - it's been very helpful!

> MenuScene
>> MenuLayer (shows buttons and menu options, pushes new layers on button press)
>> SettingsLayer (replaces MenuLayer when related button is pressed)
>> RecordLayer (shows win/loss record)
>> RulesLayer (shows instructions)

> GameScene
>> GameLayer (loads when user taps "New Game", shows field bg)
>> HomeTeamLayer (an overlay showing above the field that lets you choose your team)
>> VisitingTeamLayer (an overlay that replaces the HomeTeamLayer)
>> ConfirmLayer (replaces VisitingTeamLayer to confirm team selection)
>> ScoreLayer (shows on the field after team selection is done, tracks score and timer)
>> PlayerLayer (manages actual gameplay interaction and collision for players)
>> MessageLayer (manages on-screen messages like "GOAL!")

> PenaltyKickScene
>> PenaltyKickLayer (facilitates penalty kick mini-game)
>> ResultLayer (displays "goal" or "no goal" message)

> EndGameScene
>> EndGameLayer (displays appropriate message if user wins/loses)

Posted 2 years ago #
natanavra
Member

Hmmm... This is pretty Acceptable I guess...
Here's how I'd do this:

(Require some experience with cocos)

> MenuScene (Use a menu class inside (special input recieve class, doesn't involve layer))

> SettingsScene (When a menuItem is pressed)... Display a Menu inside.
> ScoresScene
> InstructionsScene

This basically how I'd do it...
Basic concept: Keep different groups of screens (views) in different Scenes; Use Layers for in Scene Displays and User complex input (Game Input).

I suggest you go through the examples, to see basic functionalty and what is used when... The HelloClasses are a really good place to start, and this site's wiki is a good source as well!

When you'll start experimenting, you'll get a better grasp of Scene vs. Layer.

~ Natanavra.

Posted 2 years ago #
eshirt
Member

Natanavra, that makes sense too - although lindgrenM suggested something more along the lines of what I outlined, I think.

One Scene per "screen" certainly makes sense, but all the examples that I've seen (the HelloClasses and MenuTest for example) do everything in one Scene with multiple layers.

I think your way makes the most sense though, so I'll try and work with that. Any guidance on using the Menu class? From the examples, it uses MenuItem, MenuItemSprite, etc. I'm pretty sure I can figure it out from that, but if there's a good resource somewhere on the web, I'm sure it'll help.

Thanks!

Posted 2 years ago #
astropaul
Member

I'm also trying to get my head around this. When transitioning between two Scenes, do you run dealloc in both the Layer and Scene you are leaving? I have the following:

@interface FrontPageScene : Scene {}
@end

@interface FrontPageLayer : Layer {}
@end

All the Scene does is add the layer. In this FrontPage scene a user can click a button to start the game. This runs the following:

GameScene *gs = [GameScene node];
[[Director sharedDirector] replaceScene:[FadeTRTransition transitionWithDuration:1.0 scene:gs]];

The new scene is shown, but the transition is jerky. It gets to like 50% then skips
straight to the next Scene. I am wondering is this because when calling replaceScene it runs dealloc on the scene you are leaving? I have the following in my FrontPage Scene and Layer implementations:

@implementation FrontPageScene
-(id)init
{
if( (self=[super init] ))
{
FrontPageLayer *layer = [FrontPageLayer node];
[self addChild:layer];
}
return self;
}

-(void)dealloc
{
NSLog(@"FrontPageScene dealloc ");
[super dealloc];
}
@end

And the FrontPage Layer implementation, also has a dealloc:

@implementation FrontPageLayer
-(id) init
{
NSLog(@"FrontPage Layer init");
// always call "super" init
// Apple recommends to re-assign "self" with the "super" return value
if( (self=[super init] ))
{
// Set background
Sprite *bg = [Sprite spriteWithFile:@"test-frontpage.png"];
[bg setPosition:ccp(160, 240)];
[self addChild:bg z:0];
}
}

-(void)dealloc
{
// don't forget to call "super dealloc"
[super dealloc];
}

Is this the correct way to do it?

Posted 2 years ago #
astropaul
Member

I'm also trying to get my head around this. When transitioning between two Scenes, do you run dealloc in both the Layer and Scene you are leaving? I have the following:

@interface FrontPageScene : Scene {}
@end

@interface FrontPageLayer : Layer {}
@end

All the Scene does is add the layer. In this FrontPage scene a user can click a button to start the game. This runs the following:

GameScene *gs = [GameScene node];
[[Director sharedDirector] replaceScene:[FadeTRTransition transitionWithDuration:1.0 scene:gs]];

The new scene is shown, but the transition is jerky. It gets to like 50% then skips
straight to the next Scene. I am wondering is this because when calling replaceScene it runs dealloc on the scene you are leaving? I have the following in my FrontPage Scene and Layer implementations:

@implementation FrontPageScene
-(id)init
{
if( (self=[super init] ))
{
FrontPageLayer *layer = [FrontPageLayer node];
[self addChild:layer];
}
return self;
}

-(void)dealloc
{
NSLog(@"FrontPageScene dealloc ");
[super dealloc];
}
@end

And the FrontPage Layer implementation, also has a dealloc:

@implementation FrontPageLayer
-(id) init
{
NSLog(@"FrontPage Layer init");
// always call "super" init
// Apple recommends to re-assign "self" with the "super" return value
if( (self=[super init] ))
{
// Set background
Sprite *bg = [Sprite spriteWithFile:@"test-frontpage.png"];
[bg setPosition:ccp(160, 240)];
[self addChild:bg z:0];
}
}

-(void)dealloc
{
// don't forget to call "super dealloc"
[super dealloc];
}

Is this the correct way to do it?

Posted 2 years ago #
eshirt
Member

astropaul has a good question, too. Unfortunately, I don't have an answer :) I hope someone else can help him. But looking at his code compared to the example HelloWorld code brings up another question for me.

HelloWorld (the default for the project template) seems to use a HelloWorld Layer with a class method

+(id) scene;

to create a scene from within the Layer. Is this the preferred way to handle this, or would a real-life project look more like astropaul's example, where a Scene is a separate class?

Posted 2 years ago #
pabloruiz55
Member

hi, yes doing a replace scene will dealloc the current scene, which will dealloc the layers it contains also, (unless something is retaining them...)

The problem you mention in the transition i think it has been discussed before, it may be because of what the scene is loading... I think the solution wa to load assets onEnter instead onInit of the layer. (i am not sure about this though)

For me i have an scene and layer for each "screen" of my game.
splash, main menu, each option, my game,etc. Mostly beacuse i want transitions between them.

Some scenes contain a couple of layers instead, for example in my main menu when the play wants to start a new game i want to ask if he wishes to continue a previous game, here i create a new layer at runtime which on init load a colorlayer and a menu.
Of course i could have create a new scene for this.

Posted 2 years ago #
astropaul
Member

Hi pabloruiz55,

Yes, that explains it. I now load all my sprites in the

-(void)onEnterTransitionDidFinish {}

method. However I am still not clear on dealloc.
Should I have a dealloc in both Layer object and Scene object?
Or just one or the other?

Posted 2 years ago #
pabloruiz55
Member

Yes you should, at least in may case i forgot to put the dealloc function in my scene and that caused the layer's dealloc not to be called.

Posted 2 years ago #
aimacworx
Member

dealloc method is optional and is not required.
the rule of the thumb is, if you have objects allocated and needs to be released at exit of scene or layer, you must use dealloc method because this method guarantees to be executed when you leave a scene or layer by the iPhone button or through transitions.

What is the difference between scenes and layers?
Adding to the above explanations, my rule of thumb is, if your going to use menuItem to manage buttons for transitions, use scenes. but, when displaying animations and labels, etc. use layers. Using multiple Scenes lets you build the application in modular way, where each scene can be totally independent to each other where objects are created and deallocated within separate scenes. Object and variables created locally within scenes do not mix-up with other object in other scenes.

hope this helps...
erwin

Posted 1 year ago #
marciokoko
Member

Im so confused. I have a game idea where first you are on a ship and shoot enemies. Then you switch to a car and shoot targets. Then you're on a horse and jump obstacles...etc. Does that mean I need a scene for the mainmenu, then one for the ship action, then another one for the car action and another one for the horse action and a final one for the gameover action?

Another way to look at it; angry birds, is each level a scene?

Posted 7 months ago #
skyhawk
Member

No, each level in angry birds is not its own scene. that would be bad programming. Your scenario doesn't even compare to theirs.

Anyways, if you truly want, you could have your entire game in 1 scene.

Only you can decide how you want to program given the tools given to you.

Posted 7 months ago #
marciokoko
Member

Well, thats where Im confused then, because how would I have the one HelloWorldLayer Class call a player X, target X and logic X, and then discard all those sprites and load a player Y, target Y and logic Y and discard all that again and so on? So this means in the same HelloWorldLayer Class I would have:

addPlayerX method
addTargetX method
gameLogicX method

addPlayerY method
addTargetY method
gameLogicY method

etc?

Posted 7 months ago #

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