SpriteKit/Objective-C: Applying SKPhysicsBody to parent node so it treats child nodes as one

Question

I have an SKNode that is has two child SKShapeNodes.

+(instancetype)skeetWithRandomColorsAtPosition:(CGPoint)position WithSize:(CGFloat)size {

InnerSkeetNode *inner = [InnerSkeetNode innerSkeetWithHue:PurpleHue AtPosition:position WithSize:size];
OuterSkeetNode *outer = [OuterSkeetNode outerSkeetWithHue:BlueHue AtPosition:position WithSize:size];

SkeetNode *skeetnode = [SkeetNode node];
[skeetnode addChild:outer];
[skeetnode addChild:inner];

[skeetnode setUpPhysicsBody];

return skeetnode;
}

...so basically the parent node is made up of two shapes -- inner and outer -- of different colours.

Now I want to apply a physics body to skeetnode:

-(void)setUpPhysicsBody {
self.physicsBody = [SKPhysicsBody    
bodyWithRectangleOfSize:self.frame.size];
self.physicsBody.affectedByGravity = YES;
}

…but the problem is that it remains unaffected by the game's physics world.

However, the two child nodes will be affected if I set up physics bodies on them separately. The problem is, they act as two bodies. For collision purposes, I want to treat them as a single node -- hence adding them to the parent.

There's SKPhysicsJointFixed. But, after trying it out (and according to the documentation) I can only add the joint to a scene, not to a discrete node.

Is it possible to add to children to an SKNode and treat them as one physics body? Any help would be appreciated!

It's because you are using self when creating a physics body and this case self is the SKNode which has no shape by itself. Try using SKShapeNode and adding a child to it. — sangony

user3574603 user3574603 · Accepted Answer · 2015-03-04T19:43:25

Thanks, sangony. I double checked and found skeetnode.physicsBody was nil.

So I inherited SKSkeetNode from SKSpriteNode and created an instance this way:

SkeetNode *skeetnode = [SkeetNode spriteNodeWithTexture:nil size:CGSizeMake(size, size)];

Now it works perfectly.

SpriteKit/Objective-C: Applying SKPhysicsBody to parent node so it treats child nodes as one

1 Answers