cocos2d for iPhone

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

1. 

   mikey_allen
   Member

   Hi, this is my first post. My name is Michael, I work for a small games development firm in Belfast. Partially for the challenge partially for fun I want to try porting over a few 2d projects I've worked on during university (they were mostly XNA games) to iPhone. The only thing I'm unsure of is lighting and blending, can cocos2d-iPhone support multiple blending options out of the box or would I need to write this stuff in?

   For example, in XNA I would take a paper texture and apply a custom per pixel multiplication (based on Photoshops Multiply algorithms). This gave my scenes a very interesting texture, which could be animated for even more depth.

   Also in xna by using the correct blending functions I would take a partially white partially transparent texture and use this as a lighting source, can cocos2d do this?

   Posted 2 years ago #
2. 

   riq
   Key Master

   Yes, each sprite can have it's own blending function (in v0.8):

   [sprite setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE }];  // example of additive blending

   Posted 2 years ago #
3. 

   Osiris
   Member

   Are there any examples of OpenGL Blending? - especially on how to create lighting EFX like lens flares and blooms?

   Posted 2 years ago #
4. 

   Osiris
   Member

   Do I just ask the wrong questions? or is there a big "L" on my avatar?

   Posted 2 years ago #
5. 

   Lam
   Member

   By custom per-pixel operations I'm assuming you mean shaders?

   If that's what you mean than the fixed function pipeline blending example that Ricardo showed is probably not what you wanted but... uh it hasn't been implemented yet.

   But you can rewrite EAGLView for opengles2.0
   I would love to see additions to allow for both opengles versions :)

   Posted 2 years ago #
6. 

   Osiris
   Member

   I didnt say anything about custom-per-pixel anything. I'm just looking from something that would let one make optical blooms and flares - like you see between levels in "geo Defense"

   Posted 2 years ago #
7. 

   pabloruiz55
   Member

   @osiris:
   To make a glow effect (aacording to this article: http://www.humus.name/index.php?page=3D&ID=32) you would have to create a blur effect on a copy of your image and then render it on top with a transparent blending mode...

   To do the gaussian blur programaticlly you would need to use pixel shaders... (at least from what i found: http://www.gamedev.net/community/forums/topic.asp?topic_id=316402)

   A simpler way would be to create the "glowing" sprite in photoshop and just draw it on top of your sprite, i think...

   Posted 2 years ago #
8. 

   Lam
   Member

   @osiris:
   Sorry I was replying to mikey_allen's thread but I'm new to this and did not use the @ sign.

   Your effect is actually doable with Ricardo's example. With a blend of src=GL_SRC_ALPHA, dst=GL_ONE, you have an additive blend and if you layer multiple sprites, glows for example, you'll get that bloom effect.

   It works well when you use a couple of sprites to create the glow effect.

   Posted 2 years ago #
9. 

   Osiris
   Member

   sweet! I'll look into it. Thanks!

   Posted 2 years ago #
10. 

    Osiris
    Member

    Of course, I say that, but I have no idea how to incorporate GL Code into cocos2d. I barely know how to code cocos2d into cocos2D. I learned some stuff about scenes and layers today that I'm going to have to redo in my game to make things "right".

    Posted 2 years ago #
11. 

    Steve Oldmeadow
    Administrator

    @Osiris - you don't have to incorporate OpenGL code. The blending just determines how the pixels of your image are combined with whatever is in the frame buffer. Additive just means the alphas are combined so you get an increase in brightness. A lot of the example particle systems rely on additive blending for their effect. Riq has already given you the code to use additive blending for a sprite. Now all you need is the right images, something like stars.png or fire.png that are included with cocos2d. If you want an effect like geoDefense try drawing stars.png with additive blending and create an action that scales it from some really large size down to nothing. Make sure that you are drawing it over something that has lots of alpha too though, notice how geoDefense has lots of alpha for the border glows. Also a black background will look best, as per geoDefense.

    Posted 2 years ago #
12. 

    Osiris
    Member

    @Steve - Thank You! Starting to experiment now!

    Posted 2 years ago #
13. 

    Osiris
    Member

    is there a way to make it work for Atlas Sprites?

    Posted 2 years ago #
14. 

    Osiris
    Member

    it also set my sprites pseudo-transparent, like opacity was set to 70% or so. Is that normal?

    Posted 2 years ago #
15. 

    pabloruiz55
    Member

    @osiris: i think the only way to apply it to an AtlasSprite is to apply it on the whole manager. So you would need to gather all the sprites you would blend into another manager...

    Posted 2 years ago #
16. 

    Osiris
    Member

    @pablo - thats cool. The only problem I have right now is that my backgrounds are not alpha so, im not seeing much of a change.

    Is there an example picture anywhere of what this effect should look like?

    Posted 2 years ago #
17. 

    Steve Oldmeadow
    Administrator

    ^ geoDefense is a good example. I also think the Galaxy particle system example is a nice example of additive blending. Maybe try what Lam suggested, i.e. use a couple of sprites then they will work off of each other. For example use two stars.png sprites and rotate them at different speeds.

    Posted 2 years ago #
18. 

    Osiris
    Member

    yep - I intend to do that this weekend -- after I figure out how to asynchronously load these backgrounds.

    Posted 2 years ago #
19. 

    nsxdavid
    Member

    Yeah... that's how geoDefense does it.... but, what I don't get is... the blend function mentioned here isn't what I use to do that at all. I use GL_ONE, GL_ONE. I mean you want to add all the colors (source and dest).

    -- David (geoDefense Author)

    ps. geoDefense does not use cocos2d but lot of my new stuff does.

    Posted 2 years ago #
20. 

    Osiris
    Member

    I'll try that too! I generally shoot in the dark until something bounces back and hits me in the head.

    Thanks David, I have geoDefense and love it. That game was one of my inspirations for getting into this!

    Posted 2 years ago #
21. 

    Osiris
    Member

    I just checked

    [bullet1 setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE }];

    vs

    [bullet1 setBlendFunc: (ccBlendFunc) { GL_ONE, GL_ONE }];

    and I can't visually tell the difference. Am I missing something?

    Posted 2 years ago #
22. 

    onedayitwillmake
    Member

    It's interesting that it uses GL_ONE, GL_ONE - normally when I read online everything uses GL_ONE, and srcminusalpha or color combination.

    Osirus, I would say it might be hard to notice because it depends on the assets themselves, and how their colors mix.
    Sometimes I had a hard time noticing the difference depending on the asset.

    Posted 2 years ago #
23. 

    Osiris
    Member

    true. I use it for bullets and its nothing but a glowing plasma ball that is a PNG that fades to alpha. created on Photoshop

    Posted 2 years ago #
24. 

    nsxdavid
    Member

    GL_ONE , GL_ONE means that everything is additive. The colors from the sprites are added to what is already there on the surface. That's additive blending. You don't use the alpha channel at all, because black is 0 right? And anything plus 0 is no change.

    -- David

    Posted 2 years ago #
25. 

    Scoobadood
    Member

    I'm looking for a similar solution but have dynamic textures so it's not possible for me to pre-render the blur into a separate texture.

    I've been playing with RenderTextures as an FBO and get pretty ordinary results by rendering to a lower rez texture with linear filtering and then scaling up.

    I think what I need to be able to do is to apply a decent (Gaussian) filter or reasonable approximation to the texture to blur it. Sadly all the references I've found suggest that I need pixel shaders to do this properly (or performantly).

    Does anyone know of a sensible way to get a reasonable approximation (i.e. better thatn the GL linear interpolation) blur effect?

    If I *do* have to process each pixel separately, how would I do that? In particular, how would I get hold of each pixel without using readPixel which from some research sounds painfully slow?

    Posted 2 years ago #
26. 

    Matt Rix
    Member

    Hey Scoobadood, I experimented with a similar thing to you: "I've been playing with RenderTextures as an FBO and get pretty ordinary results by rendering to a lower rez texture with linear filtering and then scaling up.".

    Just wondering how far you got? I was able to do it, but it didn't look right, so I couldn't achieve the kind of blurry motion trails that I wanted.

    Posted 2 years ago #
27. 

    nsxdavid
    Member

    This sort of thing can work, but you probably drop your frame rate in half doing the render to texture.

    Posted 2 years ago #

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