swift - 使用 enumerateBodies 沿RayStart 反弹光线
问题描述
我想追踪子弹在我的 SpriteKit GameScene 中移动的路径。我正在使用“enumerateBodies(alongRayStart”),我可以轻松计算与物理体的第一次碰撞。
给定接触点和接触法线,我不知道如何计算反射角。
我想计算路径,超过 5 次反射/反弹,所以首先我:
- 投射一条射线,获取与它相交的所有物体,并获取最近的物体。
- 然后我使用该接触点作为我下一次反射/反弹的开始......但我正在努力解决应该设置的终点......
我认为我应该做的是获得接触点和接触法线之间的角度,然后计算一个与之相反的新点......
var points: [CGPoint] = []
var start: CGPoint = renderComponent.node.position
var end: CGPoint = crossHairComponent.node.position
points.append(start)
var closestNormal: CGVector = .zero
for i in 0...5 {
closestNormal = .zero
var closestLength: CGFloat? = nil
var closestContact: CGPoint!
// Get the closest contact point.
self.physicsWorld.enumerateBodies(alongRayStart: start, end: end) { (physicsBody, contactPoint, contactNormal, stop) in
let len = start.distance(point: contactPoint)
if closestContact == nil {
closestNormal = contactNormal
closestLength = len
closestContact = contactPoint
} else {
if len <= closestLength! {
closestLength = len
closestNormal = contactNormal
closestContact = contactPoint
}
}
}
// This is where the code is just plain wrong and my math fails me.
if closestContact != nil {
// Calculate intersection angle...doesn't seem right?
let v1: CGVector = (end - start).normalized().toCGVector()
let v2: CGVector = closestNormal.normalized()
var angle = acos(v1.dot(v2)) * (180 / .pi)
let v1perp = CGVector(dx: -v1.dy, dy: v1.dx)
if(v2.dot(v1perp) > 0) {
angle = 360.0 - angle
}
angle = angle.degreesToRadians
// Set the new start point
start = closestContact
// Calculate a new end point somewhere in the distance to cast a ray to, so we can repeat the process again
let x = closestContact.x + cos(angle)*100
let y = closestContact.y + sin(-angle)*100
end = CGPoint(x: x, y: y)
// Add points to array to draw them on the screen
points.append(closestContact)
points.append(end)
}
}
解决方案
我猜你正在寻找这样的东西,对吧?
1.工作代码
首先让我发布完整的工作代码。只需创建一个基于 SpriteKit 的新 Xcode 项目,然后
在 GameViewController.swift 中设置
scene.scaleMode = .resizeFill
删除您在其中找到的常用标签
GameScene.sks
替换
Scene.swift
为以下代码
>
import SpriteKit
class GameScene: SKScene {
override func didMove(to view: SKView) {
self.physicsBody = SKPhysicsBody(edgeLoopFrom: frame)
}
var angle: CGFloat = 0
override func update(_ currentTime: TimeInterval) {
removeAllChildren()
drawRayCasting(angle: angle)
angle += 0.001
}
private func drawRayCasting(angle: CGFloat) {
let colors: [UIColor] = [.red, .green, .blue, .orange, .white]
var start: CGPoint = .zero
var direction: CGVector = CGVector(angle: angle)
for i in 0...4 {
guard let result = rayCast(start: start, direction: direction) else { return }
let vector = CGVector(from: start, to: result.destination)
// draw
drawVector(point: start, vector: vector, color: colors[i])
// prepare for next iteration
start = result.destination
direction = vector.normalized().bounced(withNormal: result.normal.normalized()).normalized()
}
}
private func rayCast(start: CGPoint, direction: CGVector) -> (destination:CGPoint, normal: CGVector)? {
let endVector = CGVector(
dx: start.x + direction.normalized().dx * 4000,
dy: start.y + direction.normalized().dy * 4000
)
let endPoint = CGPoint(x: endVector.dx, y: endVector.dy)
var closestPoint: CGPoint?
var normal: CGVector?
physicsWorld.enumerateBodies(alongRayStart: start, end: endPoint) {
(physicsBody:SKPhysicsBody,
point:CGPoint,
normalVector:CGVector,
stop:UnsafeMutablePointer<ObjCBool>) in
guard start.distanceTo(point) > 1 else {
return
}
guard let newClosestPoint = closestPoint else {
closestPoint = point
normal = normalVector
return
}
guard start.distanceTo(point) < start.distanceTo(newClosestPoint) else {
return
}
normal = normalVector
}
guard let p = closestPoint, let n = normal else { return nil }
return (p, n)
}
private func drawVector(point: CGPoint, vector: CGVector, color: SKColor) {
let start = point
let destX = (start.x + vector.dx)
let destY = (start.y + vector.dy)
let to = CGPoint(x: destX, y: destY)
let path = CGMutablePath()
path.move(to: start)
path.addLine(to: to)
path.closeSubpath()
let line = SKShapeNode(path: path)
line.strokeColor = color
line.lineWidth = 6
addChild(line)
}
}
extension CGVector {
init(angle: CGFloat) {
self.init(dx: cos(angle), dy: sin(angle))
}
func normalized() -> CGVector {
let len = length()
return len>0 ? self / len : CGVector.zero
}
func length() -> CGFloat {
return sqrt(dx*dx + dy*dy)
}
static func / (vector: CGVector, scalar: CGFloat) -> CGVector {
return CGVector(dx: vector.dx / scalar, dy: vector.dy / scalar)
}
func bounced(withNormal normal: CGVector) -> CGVector {
let dotProduct = self.normalized() * normal.normalized()
let dx = self.dx - 2 * (dotProduct) * normal.dx
let dy = self.dy - 2 * (dotProduct) * normal.dy
return CGVector(dx: dx, dy: dy)
}
init(from:CGPoint, to:CGPoint) {
self = CGVector(dx: to.x - from.x, dy: to.y - from.y)
}
static func * (left: CGVector, right: CGVector) -> CGFloat {
return (left.dx * right.dx) + (left.dy * right.dy)
}
}
extension CGPoint {
func length() -> CGFloat {
return sqrt(x*x + y*y)
}
func distanceTo(_ point: CGPoint) -> CGFloat {
return (self - point).length()
}
static func - (left: CGPoint, right: CGPoint) -> CGPoint {
return CGPoint(x: left.x - right.x, y: left.y - right.y)
}
}
2. 它是如何工作的?
让我们看看这段代码做了什么。我们将从底部开始。
3.CGPoint
和CGVector
扩展
这些只是简单的扩展(主要取自Ray Wenderlich 在 GitHub 上的存储库),以简化我们将要执行的几何操作。
4.drawVector(point:vector:color)
vector
这是一种从给定color
开始绘制给定的简单方法point
。
这里没有什么花哨的。
private func drawVector(point: CGPoint, vector: CGVector, color: SKColor) {
let start = point
let destX = (start.x + vector.dx)
let destY = (start.y + vector.dy)
let to = CGPoint(x: destX, y: destY)
let path = CGMutablePath()
path.move(to: start)
path.addLine(to: to)
path.closeSubpath()
let line = SKShapeNode(path: path)
line.strokeColor = color
line.lineWidth = 6
addChild(line)
}
5.rayCast(start:direction) -> (destination:CGPoint, normal: CGVector)?
此方法执行光线投射并返回光线与物理体碰撞时进入的最近点。
private func rayCast(start: CGPoint, direction: CGVector) -> (destination:CGPoint, normal: CGVector)? {
let endVector = CGVector(
dx: start.x + direction.normalized().dx * 4000,
dy: start.y + direction.normalized().dy * 4000
)
let endPoint = CGPoint(x: endVector.dx, y: endVector.dy)
var closestPoint: CGPoint?
var normal: CGVector?
physicsWorld.enumerateBodies(alongRayStart: start, end: endPoint) {
(physicsBody:SKPhysicsBody,
point:CGPoint,
normalVector:CGVector,
stop:UnsafeMutablePointer<ObjCBool>) in
guard start.distanceTo(point) > 1 else {
return
}
guard let newClosestPoint = closestPoint else {
closestPoint = point
normal = normalVector
return
}
guard start.distanceTo(point) < start.distanceTo(newClosestPoint) else {
return
}
normal = normalVector
}
guard let p = closestPoint, let n = normal else { return nil }
return (p, n)
}
几乎是壁橱是什么意思?
这意味着目标点必须距离起点至少 1 点
guard start.distanceTo(point) > 1 else {
return
}
好的,但是为什么?
因为如果没有这条规则,光线就会卡在一个物理体中,并且永远无法离开它。
6.drawRayCasting(angle)
这种方法基本上使局部变量保持最新以正确生成 5 个段。
private func drawRayCasting(angle: CGFloat) {
let colors: [UIColor] = [.red, .green, .blue, .orange, .white]
var start: CGPoint = .zero
var direction: CGVector = CGVector(angle: angle)
for i in 0...4 {
guard let result = rayCast(start: start, direction: direction) else { return }
let vector = CGVector(from: start, to: result.destination)
// draw
drawVector(point: start, vector: vector, color: colors[i])
// prepare next direction
start = result.destination
direction = vector.normalized().bounced(withNormal: result.normal.normalized()).normalized()
}
}
第一段的起点为零,方向与角度参数相隔。
段 2 到 5 使用上一段的终点和“镜像方向”。
更新(_ currentTime: TimeInterval)
在这里,我只是调用 drawRayCasting 每一帧传递当前角度值和增加 0.001 的角度。
var angle: CGFloat = 0
override func update(_ currentTime: TimeInterval) {
removeAllChildren()
drawRayCasting(angle: angle)
angle += 0.001
}
6.didMove(to view: SKView)
最后在这里,我在场景周围创建了一个物理体,以使光线在边界上反弹。
override func didMove(to view: SKView) {
self.physicsBody = SKPhysicsBody(edgeLoopFrom: frame)
}
7. 总结
我希望解释清楚。如果您有任何疑问,请告诉我。
更新
弹回功能中存在错误。它妨碍了对反射光线的正确计算。现在已修复。
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