# SwiftUI 如何绘制多边形和星星？

``````struct Star: Shape {
// 储存恒星有多少个角，以及它有多光滑/尖锐
let corners: Int
let smoothness: CGFloat

func path(in rect: CGRect) -> Path {
// 确保我们至少有两个角，否则请发送空路径
guard corners >= 2 else { return Path() }

// 从矩形的中心绘制
let center = CGPoint(x: rect.width / 2, y: rect.height / 2)

// start from directly upwards (as opposed to down or to the right)
var currentAngle = -CGFloat.pi / 2

// calculate how much we need to move with each star corner
let angleAdjustment = .pi * 2 / CGFloat(corners * 2)

// figure out how much we need to move X/Y for the inner points of the star
let innerX = center.x * smoothness
let innerY = center.y * smoothness

var path = Path()

// move to our initial position
path.move(to: CGPoint(x: center.x * cos(currentAngle), y: center.y * sin(currentAngle)))

// track the lowest point we draw to, so we can center later
var bottomEdge: CGFloat = 0

// loop over all our points/inner points
for corner in 0..<corners * 2  {
// figure out the location of this point
let sinAngle = sin(currentAngle)
let cosAngle = cos(currentAngle)
let bottom: CGFloat

// if we're a multiple of 2 we are drawing the outer edge of the star
if corner.isMultiple(of: 2) {
// store this Y position
bottom = center.y * sinAngle

// …and add a line to there
path.addLine(to: CGPoint(x: center.x * cosAngle, y: bottom))
} else {
// we're not a multiple of 2, which means we're drawing an inner point

// store this Y position
bottom = innerY * sinAngle

// …and add a line to there
path.addLine(to: CGPoint(x: innerX * cosAngle, y: bottom))
}

// if this new bottom point is our lowest, stash it away for later
if bottom > bottomEdge {
bottomEdge = bottom
}

// move on to the next corner
}

// figure out how much unused space we have at the bottom of our drawing rectangle
let unusedSpace = (rect.height / 2 - bottomEdge) / 2

// create and apply a transform that moves our path down by that amount, centering the shape vertically
let transform = CGAffineTransform(translationX: center.x, y: center.y + unusedSpace)
return path.applying(transform)
}
}

struct ContentView: View {
var body: some View {
Star(corners: 5, smoothness: 0.45)
.fill(Color.red)
.frame(width: 200, height: 200)
.background(Color.green)

}
}``````