CODEWITHSUNDEEP
swiftsprite-kit
Brejuro
Brejuro

Reputation: 3541

How to rotate an SKShapeNode line around its bottom point

I'm confused on how to rotate a line (SKShapeNode) around it's bottom point (begin point, here), think of a clock here.

I have the following, but it doesn't seem to be rotating as expected.

    public let line = SKShapeNode()
    private let linePath = CGMutablePath()

    init(begin: CGPoint, end: CGPoint) {
        self.begin = begin
        self.end = end


        linePath.move(to: begin)
        linePath.addLine(to: end)

        line.path = linePath
        line.strokeColor = UIColor.black
        line.lineWidth = 3
        SceneCoordinator.shared.gameScene.addChild(line)
    }


    public func rotate(angle: Double) {
         var transform = CGAffineTransform(rotationAngle: CGFloat(angle))
         line.path = linePath.mutableCopy(using: &transform)

    }

Upvotes: 0

Views: 409

Answers (1)

Martin R
Martin R

Reputation: 540145

Your function rotates the path around the shapes position (which is (0, 0) by default) and not around the starting point of the line as intended.

To solve the problem, create the shape with a position equal to the starting point of the line, and with a line relative to that point:

linePath.move(to: CGPoint.zero)
linePath.addLine(to: CGPoint(x: end.x - begin.x, y: end.y - begin.y))
line.path = linePath
line.position = begin
// ...
SceneCoordinator.shared.gameScene.addChild(line)

Note that instead of transforming the path you can rotate the node:

line.zRotation = angle

or with animation:

line.run(SKAction.rotate(toAngle: angle, duration: 0.2))

You can compute the position of the endpoint in the scene's coordinate system with

let endPos = line.convert(CGPoint(x: end.x - begin.x, y: end.y - begin.y), to: line.scene!)

Upvotes: 1

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