My Cocos2d / Chipmunk paradox. « cocos2d for iPhone

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My Cocos2d / Chipmunk paradox.

(7 posts) (2 voices)

Started 2 years ago by Kahless
Latest reply from Kahless

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Kahless
Member

Hi everyone,

I am relativley new to all this and i am having trouble with the whole getting chipmunk bodies to follow my sprites thing.

More specifically i am using this piece of code to make my sprites follow the chipmunk controlled bodies.

static void
eachShape(void *ptr, void* unused)
{
cpShape *shape = (cpShape*) ptr;
Sprite *sprite = shape->data;
if( sprite )
{
cpBody *body = shape->body;
[sprite setPosition: cpv( body->p.x, body->p.y)];
[sprite setRotation: (float) CC_RADIANS_TO_DEGREES( -body->a )];
}
}

This works fine for that, but what i also want to do is have some chipmunk bodies following sprites around that are controlled by varous actions using a similar piece of code like this.

static void
eachShape(void *ptr, void* unused)
{
cpShape *shape = (cpShape*) ptr;
Sprite *sprite = shape->data;
if( sprite )
{
cpBody *body = shape->body;
body->p = sprite.position;
[sprite setRotation: (float) CC_RADIANS_TO_DEGREES( -body->a )];
}
}

My problem is i can only seem to have one or the other running in my game layer, as i said i am new to all this and cannot seem to come up with a solution to having both chipmunk and action controlled sprites with bodies that sync.

Any help or advice would be greatly appreciated!

Posted 2 years ago #
patrickC
Member

First sections seems ok, and you say it works so that's good.
In the second bit, you're manually setting the "p" of the chipmunk body, this is not a widely accepted thing to do and, if you're doing this on active bodies, will screw up the simulation itself.
For the bodies that follow sprites, do they still need to be simulated by chipmunk?
If so, you should try and find a way for them to follow by using forces.
If, during the movement, they don't need to be simulated, you should be able to remove the body (not the shape), from the chipmunk space and move it around, while keeping collision with the shape active too.
Personally speaking, I'd try and use only forces if I need to move chipmunk bodies.
If you explain more what you're trying to do, maybe there's a better approach to it?

Posted 2 years ago #
Kahless
Member

Ok thx patrickC

I am trying to get a simple top down shooter off the ground, i want the player and enemy projectiles to be controlled by chipmunk but i want the ship sprite to have actions associated with them putting them through various set movement sequences. I want chipmunk for collision detection and movement on the projectiles as it seems to fit nicely for it. I only need chipmunk for collision detection on enemy and player ships, but i just cant seem to get the body/shape to follow them around.

Posted 2 years ago #
patrickC
Member

Ok, you could try this.
When creating the body and shape for the ship, add the ship shape as static (not active), then create a body for it and associate it to the shape.
Then, add the shape but NOT the body to the chipmunk space.
This will give you a shape that generates collision, movable through it's body, but not simulated in the chipmunk space.
If you then move the body like you were doing before that should get you going.
body->p=sprite.position;
I'm doing this in my current game and it works fine.
Hope that helps

Posted 2 years ago #
Kahless
Member

I see what you are saying with not adding the body to the chipmunk space, but i'm not sure if that is going to address my issue of

[sprite setPosition: cpv( body->p.x, body->p.y)];

and

body->p = sprite.position;

interfering with each other, they are globally trying set each others values and they seem mutually exclusive.
Is there a way i can use one line of code for one class of sprite like ships and the other for another class of sprite like projectiles so they do not interfere? Right now they just try to set each other for all sprites and cause some crazy loop.

Thx for your help so far patrickC it's all good input for me!

Posted 2 years ago #
patrickC
Member
Ah I see.
Well the problem there is that you're iterating over your shapes with that chipmunk function.
That's something you want to avoid doing, or at least that's what the chipmunk developer says.
You should keep lists of your ships/enemies/whatever in separate arrays.
If you're only going to have one player ship, then just have a constant reference to it:
```
Sprite *playerShipSprite;
cpShape *playerShipShape;
```
Similarly, for the enemies, you could create a wrapper class for whatever you need them to have (sprite, chipmunk shape/body, other stuff), and add them to an array when you create them.
Then, in you game step, you iterate over all the enemies and treat them as so, do stuff to your player ship, and whatever else you need to do.
This is generally what most people do I think.
For example, in my game I have lots of people going about, and cars too.
Obviously, the people need to behave very differently from the cars :)
So, I subclassed and NSObject, made it so that it has references to a sprite and chipmunk shape (among other stuff for gameplay), then add the object to an NSArray at creation time.
During the game loop, I can manipulate the array and add/remove people and so forth.
Hope that helps
Patrick
Posted 2 years ago #
Kahless
Member

Ok i created a wrapper class and an array for my enemy sprites and adjust the body position with a method and it works along side the chipmunk stuff now, awsome thanks for the advice patrick, that has been eating my brain for a few days now.

Thx again :)

Posted 2 years ago #

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