How to keep a 30˚ distance between two lines anchored at a point

Question

I am trying to create two lines that are anchored at a certain point (sprite) and rotate to form a 30 degree angle between them. Below is an image what I want to achieve.

This is what I've done so far:

extension Int {
  var degreesToRadians: Double { return Double(self) * .pi / 180 }
}
extension FloatingPoint {
  var degreesToRadians: Self { return self * .pi / 180 }
  var radiansToDegrees: Self { return self * 180 / .pi }
}

class GameScene: SKScene, SKPhysicsContactDelegate {

var anchorSprite = SKSpriteNode(imageNamed: "anchorSprite")
var armLeft = SKSpriteNode(imageNamed: "lineSprite")
var armRight = SKSpriteNode(imageNamed: "lineSprite")

override func didMove(to view: SKView) {

    self.physicsWorld.gravity = CGVector(dx: 0, dy: -1.8)
    self.physicsWorld.contactDelegate = self

    var tealBg = SKSpriteNode(imageNamed: "tealBg")
    tealBg.position = CGPoint(x: frame.midX, y: frame.midY)
    tealBg.zPosition = 10
    addChild(tealBg)

    anchorSprite.position = CGPoint(x: frame.midX, y: frame.midY + frame.midY/2)
    anchorSprite.zPosition = 20

    anchorSprite.physicsBody = SKPhysicsBody(rectangleOf: anchorSprite.frame.size)
    anchorSprite.physicsBody?.categoryBitMask = pinCategory
    anchorSprite.physicsBody?.isDynamic = false

    addChild(anchorSprite)

    armRight.anchorPoint = CGPoint(x: 0.5, y: 1)
    armRight.position = anchorSprite.position
    armRight.zPosition = 20
    armRight.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
    armRight.zRotation = CGFloat(Double(15).degreesToRadians)//CGFloat(Double.pi/6)
    armRight.physicsBody!.isDynamic = true
    addChild(armRight)

    armLeft.anchorPoint = CGPoint(x: 0.5, y: 1)
    armLeft.position = anchorSprite.position
    armLeft.zPosition = 20
    armLeft.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
    armLeft.zRotation = CGFloat(Double(-15).degreesToRadians)//CGFloat(-Double.pi/6)
    armLeft.physicsBody!.isDynamic = true
    addChild(armLeft)

    //Pin joints
    var pinAndRightArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armRight.frame.maxY))
    self.physicsWorld.add(pinAndRightArmJoint)

    var pinAndLeftArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armLeft.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armLeft.frame.maxY))
    self.physicsWorld.add(pinAndLeftArmJoint)

}

Below is an image from running the above code (they are close together).

How can I make sure the lines are always 30˚ apart and maintain 30˚ apart even when rotated?

have you tried `armLeft.zRotation = CGFloat(Double(345).degreesToRadians)`? — Jože Ws, May 27 '17 at 22:11

Robert · Accepted Answer · 2017-05-28T06:17:41.113

2

To keep your two lines separated by exactly 30°, you can use an SKPhysicsJointFixed, which is just what it sounds like: it pins two physicsBodies together in a fixed position. Since you already have them positioned the way you want, just add this code where you have the other SKPhysicsJoints to hold them that way:

let fixArms = SKPhysicsJointFixed.joint(withBodyA: armLeft.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint.zero)
self.physicsWorld.add(fixArms)

Result:

edited May 28 '17 at 06:17

answered May 27 '17 at 22:08

Robert

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This is working, but my only issue is the physics bodies make contact/collision unrealistic – iGetIt May 28 '17 at 05:23
@iGetIt Sorry, using physics bodies was a bad way to go about this. There's a much simpler approach using a Joint to keep them fixed instead. See my updated answer. – Robert May 28 '17 at 06:19
@Robert please check out my question. I would be very grateful if you could help https://stackoverflow.com/questions/44294768/how-to-rotate-sprites-around-a-joint – Containment May 31 '17 at 21:20

score 0 · Answer 2 · answered May 28 '17 at 13:47

If you make the line nodes children of the anchor sprite (instead of the scene), rotating the anchor sprite node will rotate all the lines along with it without doing anything special with physics. You just need to mind the anchor points so that they align properly (i.e. line's anchor at its extremity rather than center)

How to keep a 30˚ distance between two lines anchored at a point

2 Answers2