模拟两个Sprite Kit节点的万有引力 [英] Simulate universal gravitation for two Sprite Kit nodes

问题描述

我在Sprite Kit中有两个节点，我正在用Swift编写。

I have two nodes in Sprite Kit, and I'm writing in Swift.

如何通过重力使节点相互吸引？另外，我如何使用他们的群众？如果一个物体有很大的质量，它应该更多地吸引。

How would I make the nodes attracted to each other by the force of gravity? Also, how would I use their masses? If an object has a big mass, it should gravitate more.

推荐答案

你可以遍历所有节点并计算所有节点的冲动其他节点使用适当比例的万有引力方程。我刚刚写了一个快速的例子来说明这是如何完成的。您可以制作自己的自定义质量因子，但我只是使用Sprite Kit。我还增加了一个强度因子来放大冲动。我还假设固定时间步长为1/60秒。

You can loop through all nodes and calculate the impulse to all other nodes using the appropriate ratios of the universal gravitation equation. I just wrote a quick example showing how this is done. You can make your own custom "mass" factor, however I'm simply using Sprite Kit's. I also added a strength factor to amplify the impulse. I'm also assuming fixed time step of 1/60 seconds.

class GameScene: SKScene {
    var nodes: [SKShapeNode] = []
    let dt: CGFloat = 1.0/60.0 //Delta time.
    let radiusLowerBound: CGFloat = 1.0 //Minimum radius between nodes check.
    let strength: CGFloat = 10000 //Make gravity less weak and more fun!
    override func didMoveToView(view: SKView) {
        self.physicsWorld.gravity = CGVector()
        for i in 1 ... 50 { //Create 50 random nodes.
            let rndRadius = 15 + CGFloat(arc4random_uniform(20))
            let rndPosition = CGPoint(x: CGFloat(arc4random_uniform(UInt32(self.size.width))), y: CGFloat(arc4random_uniform(UInt32(self.size.height))))
            let node = SKShapeNode(circleOfRadius: rndRadius)
            node.position = rndPosition
            node.physicsBody = SKPhysicsBody(circleOfRadius: rndRadius)
            self.addChild(node)
            nodes.append(node)
        }
    }
    override func update(currentTime: NSTimeInterval) {
        for node1 in nodes {
            for node2 in nodes {
                let m1 = node1.physicsBody!.mass*strength
                let m2 = node2.physicsBody!.mass*strength
                let disp = CGVector(dx: node2.position.x-node1.position.x, dy: node2.position.y-node1.position.y)
                let radius = sqrt(disp.dx*disp.dx+disp.dy*disp.dy)
                if radius < radiusLowerBound { //Radius lower-bound.
                    continue
                }
                let force = (m1*m2)/(radius*radius);
                let normal = CGVector(dx: disp.dx/radius, dy: disp.dy/radius)
                let impulse = CGVector(dx: normal.dx*force*dt, dy: normal.dy*force*dt)

                node1.physicsBody!.velocity = CGVector(dx: node1.physicsBody!.velocity.dx + impulse.dx, dy: node1.physicsBody!.velocity.dy + impulse.dy)
            }
        }
    }
}

而不是执行计算手动你也可以添加字段节点到物理机构模拟效果。虽然被警告，但某些版本的Sprite Kit中的字段节点已损坏。

Instead of performing the calculation manually you could also add field nodes to your physics bodies to simulate the effect. Although be warned, field nodes are broken in certain versions of Sprite Kit.

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