Question

I’m trying to create a squishy ball with Cocos2d and Chipmunk (via SpaceManager) using a bunch of rects all chained together then joined with springs to a central body.

Something like these examples

But in order to do this, i think I need to store all the cpShapes in an array after I’ve created them so I can then loop through the array to link them all together with constraints.

However, when i try to put cpShapes in an array, I get an error telling me it’s an “incompatible pointer type”. So… I either need to use something other than an array (I’ve tried a set, that didn’t work either) or I need to do something to the shape to make it compatible… but what? OR I need another aproach.

Any ideas?

Here’s the code so far should it be relevant…

- (id) init
{

    if ( (self = [super init]) ) {

        SpaceManager * spaceMgr = [[SpaceManager alloc] init];
        [spaceMgr addWindowContainmentWithFriction:1.0 elasticity:1.0 inset:cpv(5, 5)];

            // This is a layer that draws all the chipmunk shapes
        ChipmunkDrawingLayer *debug = [[ChipmunkDrawingLayer node] initWithSpace:spaceMgr.space];
        [self addChild:debug];

        int ballPeices = 10; // the number of peices I want my ball to be composed of
        int ballRadius = 100;
        float circum = M_PI * (ballRadius * 2);

        float peiceSize = circum / ballPeices;
        float angleIncrement = 360 / ballPeices;

        CGPoint origin = ccp(240, 160);
        float currentAngleIncrement = 0;

            NSMutableArray *peiceArray = [NSMutableArray arrayWithCapacity:ballPeices];

        for (int i = 0; i < ballPeices; i++) {

            float angleIncrementInRadians = CC_DEGREES_TO_RADIANS(currentAngleIncrement);

            float xp = origin.x + ballRadius * cos(angleIncrementInRadians);
            float yp = origin.y + ballRadius * sin(angleIncrementInRadians);

                    // This is wrong, I need to figure out what's going on here.
            float peiceRotation = atan2( origin.y - yp, origin.x - xp);

            cpShape *currentPeice = [spaceMgr addRectAt:ccp(xp, yp) mass:1 width:peiceSize height:10 rotation:peiceRotation];

            currentAngleIncrement += angleIncrement;

                    [peiceArray addObject:currentPeice]; //!! incompatible pointer type

        }



        spaceMgr.constantDt = 0.9/55.0;
        spaceMgr.gravity = ccp(0,-980);
        spaceMgr.damping = 1.0;

    }

    return self;

}

Answer 1

The incompatible pointer type is easy to explain 🙂

[NSMutableArray addObject] is defined as such:

- (void)addObject:(id)anObject

So what is an id then? Great question! Remember, Objective-C is still C at it’s core. According to the Objective-C Programming Guide

typedef struct objc_object {
    Class isa;
} *id;

That’s great, now we know about *id but what about id itself? That’s what is referenced in the method signature. For that, we have to look at objc.h

typedef id (*IMP)(id, SEL, ...);

Clearly, cpSpace* doesn’t fit that, so you’ll be getting incompatible pointer type if you try to put those into NSMutableArray using that message.