Cannot get physics shape?

[trojanfoe]

I have the following planet prefab:

and when I load a level containing this planet, I want to determine its radius, so I can place objects on the surface. The prefab has a custom class and I have provided the following method to get the radius:

- (CGFloat)radius
{
    ChipmunkBody *body = [[self physicsBody] body];
    NSArray *shapes = [body shapes];
    NSAssert([shapes count] == 1, @"Expected exactly one shape");
    cpShape *shape = [[shapes firstObject] shape];
    return cpCircleShapeGetRadius(shape);
}

However that assertion is firing as there are 0 objects in shapes. The body object is not nil.

Can anyone tell me what I am doing wrong please?

[adamgeo]

I had a similar issues with shapes but I have changed things and I dont need it anymore.

This is how I went about it. Not sure if its a good or bad way to do it.

// add to CCPhysics+ObjectiveChipmunk.h and import where needed
@property(nonatomic, readonly) CCPhysicsShape *shapeList;

// add to CCPhysicsBody.m
- (CCPhysicsShape*) shapeList {
    return _shapeList;
}

// usage for class where CCPhysics+ObjectiveChipmunk.h is imported
CCPhysicsShape* shapeList = node.physicsBody.shapeList;
for(CCPhysicsShape *shape = shapeList; shape; shape=shape.next) {
    hello shape!
}

There might some other imports needed, I cant remember. Its not hard to find what xcode is asking for though

[trojanfoe]

Hey thanks for the reply. I looked into the CCPhysicsBody and the associated ChipmunkObject a bit more and the CCPhysicsBody has a valid _shapeList:

but the ChipmunkObject does not:

and [CCPhysicsBody shapes] uses the ChipmunkBody to build the returned array:

- (NSArray *)shapes
{
	NSMutableArray *arr = [NSMutableArray array];
	cpBodyEachShape(&_body, (cpBodyShapeIteratorFunc)PushShape, arr);
	
	return arr;
}

Which brings up the questions:

1. Why are there two lists?
2. Why are they out-of-sync with each other?
3. Why not just return _shapeList instead of building a new list?

Looks like a bug of some sort to me. @slembcke, I could really use your help here.

[trojanfoe]

OK I found a workaround for this. It's a classic timing issue.

I was doing the above processing from within the didLoadCCB method of the scene, however if I move it to the onEnter method, the ChipmunkObject is valid.

I can live with that and I've learnt something and thanks to @adamgeo for the prod in the right direction; I would rather not make drastic changes to the vanilla Cocos2d source code, however.

[adamgeo]

I would rather not make drastic changes to the vanilla Cocos2d source code, however.

Yeah it's a pain in the arse. Every update requires remembering what I did. Wish I was more organised.

I was scaling the shapes when the sprite was scaled but either @slembcke or @birkemose piped up as while ago with a reason why that wasn't happening by default. I think it was something along the lines playing god with physics?? Not sure. I can't remember what it was but I don't need it now anyway.

[trojanfoe]

One thing you can do is take a recursive diff of your changes to a vanilla version and then apply the diff using patch to any new versions that come along.

Better still, fork the Cocos2d github repo and merge v1.4 into your branch periodically. You can then use your version of Cocos2d as a git submodule of your project.