ios - 如何使物体 swift 从边缘反弹

Question

我正在努力让我的“敌人”跳出所有界限。例如，当 Enemy 与屏幕的左、右、上、下碰撞时，它应该改变方向。

这是我当前的代码:

import SpriteKit
import GameplayKit

struct Physics {
    static let Enemy: UInt32 = 0x1 << 1
    let BorderCategory : UInt32 = 0x1 << 2
    let BottomCategory : UInt32 = 0x1 << 3
    let BallCategory   : UInt32 = 0x1 << 4

}

class GameScene: SKScene {

    var Enemy = SKSpriteNode()
    var gameStarted = Bool()
    var gameState = "running"
    var destX : CGFloat = 0.0
    var destY : CGFloat = 0.0
    var score = 0

    override func didMove(to view: SKView) {
        let borderBody = SKPhysicsBody(edgeLoopFrom: self.frame)
        borderBody.friction = 0
        self.physicsBody = borderBody
        let screenSize: CGRect = UIScreen.main().bounds     // get the screen size
        let screenWidth = screenSize.width                  //get the width
        let screenHeight = screenSize.height                //get the height


        Enemy = SKSpriteNode(imageNamed: "red2")
        Enemy.size = CGSize(width: 60, height: 70)
        Enemy.position = (CGPoint(x: self.frame.width / 6 - Enemy.frame.width, y: self.frame.height / 10))

        Enemy.physicsBody = SKPhysicsBody(circleOfRadius: Enemy.frame.height / 2)
        Enemy.physicsBody?.categoryBitMask = Physics.Enemy
        //Enemy.physicsBody?.categoryBitMask = Physics.Ground | Physics.wall
        //Enemy.physicsBody?.contactTestBitMask = Physics.Ground | Physics.wall
        Enemy.physicsBody?.affectedByGravity = false
        Enemy.physicsBody?.isDynamic = true


        self.addChild(Enemy)
        Enemy.physicsBody?.velocity = CGVector(dx: 50, dy: 50)

        if (Enemy.position.x == screenWidth) {
            Enemy.physicsBody?.velocity = CGVector(dx: -50, dy: 0)      // change direction at edge DOESN'T WORK
        }

        if(Enemy.position.y == screenHeight){
            Enemy.physicsBody?.velocity = CGVector(dx: 0, dy: -50)      //change direction at edge  DOESN'T WORK
        }
    }

Answer 1

好的，根据您的代码，我编写了一个有效的弹跳 Sprite 。它使用物理引擎来实现这一点，而不是手动改变方向(我猜你应该如何去做)。

override func didMove(to view: SKView) {
    let borderBody = SKPhysicsBody(edgeLoopFrom: frame)
    borderBody.friction = 0
    borderBody.categoryBitMask = Physics.wall
    physicsBody = borderBody
    let enemy = enemySprite(size: CGSize(width: 60, height: 70), position: CGPoint(x: frame.size.width/2, y: frame.size.height/2))
    addChild(enemy)
    let force = SKAction.applyForce(CGVector(dx: 300, dy: 300) , duration: 0.1)
    enemy.run(force)
}

func enemySprite(size: CGSize, position: CGPoint) -> SKSpriteNode {
    let enemy = SKSpriteNode(color: SKColor.red(), size: CGSize(width: 60, height: 80))
    enemy.position = CGPoint(x: frame.width/2, y: frame.height/2)
    enemy.physicsBody = SKPhysicsBody(circleOfRadius: enemy.frame.height / 2) // A bit silly with circle, but you seem to have an image for this use
    enemy.physicsBody?.categoryBitMask = Physics.enemy
    enemy.physicsBody?.restitution = 1
    enemy.physicsBody?.friction = 0
    enemy.physicsBody?.collisionBitMask = Physics.wall
    enemy.physicsBody?.affectedByGravity = false
    enemy.physicsBody?.angularDamping = 0
    enemy.physicsBody?.linearDamping = 0
    return enemy
}

另外一个要考虑的问题是你如何设置场景？场景大小是否与 View 大小相同？否则场景的 physicsBody 不会使球在您期望的位置反弹...