cocos2d for iPhone

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

1. 

   RedshirtRich
   Member

   Hey!

   I have a simple top-down action game I'm working on, but have never used any kind of physics library. I've tried to browse the forums on both Chipmunk and Box2d integration in Cocos, but I am admittedly in way over my head.

   I have created a collision map for my level, which pulls in the black/alpha mask and gives me an array of 1's and 0s for my pixel locations.

   (further info on this here: http://www.cocos2d-iphone.org/forum/topic/1188 )

   I had initially hoped to get away with my collisions WITHOUT a physics library, but I have had a few issues.

   Right now, the collision map works... sort of. I am just calling to the position of my player to see if it has collided with any walls/buildings (black pixels in the mask). But this call only gets the center pixel of my player, so it only registers when the player is already half-way onto the buildings. Plus, my movement looks jittery, as I am forcing the player to "back out" on contact, otherwise that single point would be eternally stuck.

   I would like to get my collision for the player to check over the whole sprite, or at least a point at the 'front' and 'back' of the player, so that if the front hits a building (and gets 'stuck') I could back out of it.

   I know that a CGRect call for collision looks fairly easy, but as I am rotating my player around, that CGRect is relative. I had thought about calling to the 'front' or 'back' of the player by just giving an offset to the CGPoint position of the player, but again, I think that call would just go 'up' or 'down' on the screen from the center point and not take the rotation orientation into account.

   I can definitely see the NEED for a physics engine for even simple collision calls like this, but I'm not sure which to use or where to start.

   Posted 2 years ago #
2. 

   PhilM
   Member

   I'm in the same process. Moving away from a collision image to a physics engine, partly because of the more detailed collision detection, and partly because I'm feeling the need for more physics calculations that I don't really want to do myself.

   With the collision image, I used a point at the center bottom of the sprite (rather than very center), and this worked fine for walking on uneven surfaces, although you'd get a slight overlap with walls or steep floors unless an extra collision check was added at the front of the sprite. This was ok for the game I'm working on, but might not be for other games.

   For physics, chipmunks been integrated with cocos2d for much longer than box2d, so you'll find lots more info about it on the forums (& old google groups). Having said that, more people seem to be heading in the box2d direction, and I'm trying to get my head around it myself.

   Theres a thread on here that has a sample project showing usage of chipmunk for collision only, which might be of interest (sorry, can't remember which one, but a bit of searching should pull it up).

   I'd have a play with some of the demos & see what works best for you.

   Posted 2 years ago #
3. 

   RedshirtRich
   Member

   A point at the center bottom of your image works when you never rotate the image, but won't work in my case.

   I know that most simple collision can be called with the CGRect , but would that pose a problem when I have my image spun to 45 degrees and basically have a diamond?

   There is a CGRectContainsPoint in the CGGeometry of the Core Graphics framework. It seems like there might be a way to use that, provided it would keep track or your rotation.

   I'll look for the chipmunk collision...

   Posted 2 years ago #
4. 

   RedshirtRich
   Member

   Okay, I checked out the demo from your suggested topic:

   ( http://www.cocos2d-iphone.org/forum/topic/577 )

   and that looks awesome. But would it possible work with the collision map image? Or would I have to split my whole world into separate sprites?

   I have a number of odd shaped buildings, which couldn't get PERFECT collision with the sprite boxes, and I was hoping to leave my 'world' as just a collection of huge background images.

   Posted 2 years ago #
5. 

   Game Smith
   Member

   I haven't used chipmunk or box2d, so this may not be applicable at all. But it sounds like you need some kind of polygon based collision. You might look and see if either lib provides this.

   Posted 2 years ago #

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