Physics Bodies are being offset from their node upon creation - objective-c

Question

I have been working on a puzzle game that uses a customizable grid with levels that are preset and created when the scene inits. They are comprised of static blocks scattered around the grid and a movable player controlled block. The gravity of the world is controllable and the block falls in that direction (up, down, left, right). I am using SKContactDelegate to track when the player block touches a block or the edge of the grid and stops it in place.
The problems I am having involve the physics bodies of the blocks and grid edge.
I am using bodyWithRectOfSize for the blocks and bodyWithEdgeLoopFromRect for the grid border.
The physics bodies of 1x1 blocks placed in the grid and the player 1x1 block have normal physics bodies (as they should be). However, larger blocks ex: 1x5, the bodies are shifted down on the y axis for no reason. Also depending on the grid size, the grid edge would be offset by a random number. Note: the bodies are offset and the nodes themselves are in the right place.
This is the code for creating the blocks; this one works fine
(cellsize is the size of each grid space)
Basic 1x1 block
-(SKShapeNode *)basic {
CGRect blockRect = CGRectMake(10, 10, self.cellSize, self.cellSize);
UIBezierPath *blockPath = [UIBezierPath bezierPathWithRoundedRect:blockRect cornerRadius:8];
SKShapeNode *blockNode = [SKShapeNode node];
blockNode.path = blockPath.CGPath;
blockNode.fillColor =[UIColor blackColor];
blockNode.lineWidth = 0;
blockNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:blockRect.size];
blockNode.physicsBody.categoryBitMask = blockCategory;
blockNode.physicsBody.dynamic = NO;
return blockNode;
}
and custom blocks (offset down on the y axis)
-(SKShapeNode *)basicWithWidth:(int)width WithHeight:(int)height {
CGRect blockRect = CGRectMake(10, 10, self.cellSize * width, self.cellSize * height);
UIBezierPath *blockPath = [UIBezierPath bezierPathWithRoundedRect:blockRect cornerRadius:8];
SKShapeNode *blockNode = [self basic];
blockNode.path = blockPath.CGPath;
blockNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:blockRect.size];
blockNode.physicsBody.categoryBitMask = blockCategory;
blockNode.physicsBody.dynamic = NO;
return blockNode;
}
And here is the grid edge
SKShapeNode *edge = [SKShapeNode node];
CGRect edgeRect = CGRectMake(10, 10, 260, 260);
UIBezierPath *edgeShape = [UIBezierPath bezierPathWithRoundedRect:edgeRect cornerRadius:8];
edge.path = edgeShape.CGPath;
edge.lineWidth = 0;
edge.fillColor = [UIColor grayColor];
edge.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:edgeRect];
edge.physicsBody.categoryBitMask = boardCategory;
[self addChild:edge];
Note: The edge and blocks are children to a "board" node that is a child of the game scene
Thank you for reading this.

Answer 1

When you use SKPhysicsBody's bodyWithRectangleOfSize:, it is centered on its node's origin. What you want to do in your case is center them on the center of the rect that defines your node. To do that, use bodyWithRectangleOfSize:center: instead.
For example, you define your block with the rect:
CGRect blockRect = CGRectMake(10, 10, self.cellSize, self.cellSize);
So, you'll want your physicsBody centered on the center of that rect. You easily get the center of a CGRect with:
CGPoint center = CGPointMake(CGRectGetMidX(blockRect), CGRectGetMidY(blockRect));
To create the physicsBody centered there, use:
blockNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:blockRect.size center:center];
Note: bodyWithRectangleOfSize:center: is only available in iOS 7.1 and later
iOS 7.0 method
For iOS 7.0, you can use bodyWithPolygonFromPath: instead, it just takes an additional line of code:
CGPathRef blockPath = CGPathCreateWithRect(blockRect, nil);
blockNode.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath: blockPath];