Using blocks with Chipmunk callbacks

gistfile1.c

// Define this function somewhere
static void CallArbiterBlock(cpBody *body, cpArbiter *arbiter, void (^block)(cpArbiter *arbiter)){block(arbiter);}

// Then you can do this:
// __block makes the variable writable from within a block, otherwise they are read only.
__block cpVect impulseSum = cpvzero;
cpBodyEachArbiter(scaleStaticBody, (cpBodyArbiterIteratorFunc)CallArbiterBlock, ^(cpArbiter *arb){
	impulseSum = cpvadd(impulseSum, cpArbiterTotalImpulse(arb));
});

// Convenient because the callback is in the same place as the code where the rest of your data probably is.
// You don't need to make one time use context structs. The compiler does it for you instead.


// *************************
// The alternative using function callbacks looks like this:

// If I had wanted to pass more than one value to the callback, it would have been annoying.
static void
ScaleIterator(cpBody *body, cpArbiter *arb, cpVect *sum)
{
	(*sum) = cpvadd(*sum, cpArbiterTotalImpulse(arb));
}


cpVect impulseSum = cpvzero;
cpBodyEachArbiter(scaleStaticBody, (cpBodyArbiterIteratorFunc)ScaleIterator, &impulseSum);