SpriteKit中的这两个语句有什么区别？

Question

this part is a SKShapeNode

var rect = CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: 30, height: 30)) 

self.path = CGPathCreateWithRect(rect, nil)

AND

let rect = SKShapeNode(rectOfSize: CGSize(width: 30, height: 30))

They seems to be acting differently in the simulator and I'm wondering if these are different in any way.

Answer 1

The origin, (0, 0) point, of a SKShapeNode is the center of the node and its path is drawn relative to that point. Therefore, a shape node created with the following CGRect

CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: 30, height: 30))

will be drawn with its bottom-left corner in the center of the shape node.

The convenience method SKShapeNode(rectOfSize...) centers the rect in the shape node by offsetting the origin argument of the CGRect by half of the rectangle's width and height. In this case, the rect's origin is (-15, -15).

You can create a CGRect that is centered in an SKShapeNode by offsetting its origin:

let height = CGFloat(30)
let width = CGFloat(30)
let anchorPoint = CGPoint(x:0.5, y:0.5)

CGRect(origin: CGPoint(x: -width*anchorPoint.x, y: -height*anchorPoint.y), size: CGSize(width: width, height: height))

where anchorPoint defines the relative "point in the sprite that corresponds to the node's position."

You can also use SKShapeNode(path:path, centered:true) which will center the path using its bounding box.