Check if a physicsbody is touching another without waiting for didBeginContact - objective-c

Question

I know you can detect contact collisions using SKPhysicsContactDelegate, but can you check if a physicsbody is currently touching another physicsbody?
I need this for checking which area in the scene is still available to put an item (eg. pick a random spot, and if there's something in the way, pick another random spot).
There's this function:
/* Returns an array of all SKPhysicsBodies currently in contact with this one */
- (NSArray *)allContactedBodies;
But it doesn't appear to return anything useful until after the next update of creating the node.

Answer 1

You can write a function to iterate manually through all the nodes and check if the two circles intersect a point.
Since you said that the radius of the circles will differ each time, you have to keep track of it. One method is to use the user data of the node.
[node.userData setObject:[NSNumber numberWithFloat:10.0] forKey:#"radius"];
Then you can find if there are intersecting circles in the following way.
-(BOOL)checkPointForNode:(CGPoint)point withRadius:(CGFloat)nodeRadius
{
for (SKNode* child in [self children])
{
NSNumber *childRadius = child.userData[#"radius"];
if (childRadius != nil)
{
CGFloat diffX = point.x - child.position.x;
CGFloat diffY = point.y - child.position.y;
CGFloat distance = sqrtf(diffX * diffX + diffY * diffY);
CGFloat sumRadius = nodeRadius + childRadius.floatValue;
if (distance <= sumRadius)
{
return YES;
}
}
}
return NO;
}
The function returns YES if there is a circle within the boundary of the circle you are going to add. This means you cannot add a new node without touching another node. Otherwise it returns NO. This means you can add a new node without touching any other nodes.